Exercise and Fluid Replacement

Influence of sustained mild dehydration on thermoregulatory and cognitive functions during prolonged moderate exercise

PURPOSE

The current study investigated whether sustained mild dehydration affects thermoregulatory function and cognitive performance during prolonged exercise.

METHODS

Twelve young adults performed a test consisting of three sets of 20-min exercise with 2-min intervals under euhydrated (control, CON) and mildly dehydrated conditions (MDEH) at an ambient temperature of 30 °C and 60% relative humidity. MDEH was established by restricting water intake for 24 h, resulting in urine specific gravity of ≥ 1.020. Heart rate (HR), mean arterial blood pressure (MAP), skin blood flow (SkBF), sweat rate (SR) on the chest and forearm, and ear canal and mean skin surface temperatures (Tear and mean Tskin, respectively) were continuously recorded. For each exercise set, thermal and humid sensations and thermal discomfort were assessed using visual analog scales (VAS), and the rating of perceived exertion (RPE) was estimated. Cognitive performance on the Go/No-Go (easy) and incongruent Stroop (difficult) tasks was assessed before and after the test.

RESULTS

No differences were observed in HR, MAP, SkBF, SR, Tear, and mean Tskin between the CON and MDEH. Thermal and humidity sensations, thermal discomfort, and RPE were higher in MDEH than in CON. Moreover, response time to the Stroop task was prolonged in MDEH.

CONCLUSION

These findings suggest that sustained mild dehydration does not affect autonomic thermoregulation during exercise. Augmented thermal perception and perceived exertion, which are necessary for behavioral thermoregulation, were noted; however, cognitive function may be attenuated under MDEH.

A Review on In Vivo Research Dehydration Models and Application of Rehydration Strategies

Background: Dehydration, a common condition where the amount water lost from the body exceeds intake, disrupts metabolic processes and negatively impacts health and performance. Rehydration, the process of restoring body fluids and electrolytes to normal levels, is crucial for maintaining physiological health. In vivo dehydration models are experimental systems used to study the effects of dehydration on living organisms. However, a comprehensive summary of in vivo models and the application of human rehydration strategies is lacking. Methods: This review provides a comprehensive overview of various in vivo models and rehydration strategies. Results: In vivo models, stimulated by fluid restriction, exercise, thermal exposure, and chemicals, have been used to study dehydration. Importantly, the principles, characteristics, and limitations of the in vivo models are also discussed, along with rehydration administration methods, including oral, intestinal, intravenous, subcutaneous, and intraperitoneal routes. Additionally, rehydration strategies and the application for managing different dehydration conditions both in daily life and clinical settings have been summarized. Conclusions: Overall, this review aims to enhance the understanding of the conditions in which in vivo dehydration models and rehydration strategies are applicable, thereby advancing research into the physiological and pathological mechanisms of dehydration and supporting the development of effective rehydration therapies.

Plasma and serum volume remain unchanged following a 12-h fast from food and drink despite changes in blood and urinary hydration markers

BACKGROUND/OBJECTIVES

The effect of mild dehydration on plasma and serum volume has not been well established. Furthermore, the ability of urinary and blood biomarkers to monitor small hydration changes have not been solidified. There were two objectives of this research: 1. Determine if mild dehydration affects plasma and serum volume; 2. Determine if mild dehydration can be detected better by urinary or blood biomarkers.

SUBJECTS/METHODS

47 subjects were recruited; 10 subjects were removed from the study and 37 subjects (27% male) completed the study. This was a crossover study design such that each subject underwent all protocols in a counterbalanced order. Protocols consisted of 12-h dehydration, 12-h hydration, and control.

RESULTS

Neither plasma volume (p = 0.914), plasma volume status (p = 0.649), nor serum volume (p = 0.273) were different among protocols. Body mass (p < 0.001) was lower following the dehydration protocol. Urine color (p < 0.001), urine osmolality (p < 0.001), urine specific gravity (p < 0.001), serum osmolality (p < 0.001), and plasma osmolality (p < 0.001) were all lower following the hydration protocol. Hematocrit (p = 0.842) and hemoglobin concentration (p = 0.558) were not different among protocols.

CONCLUSIONS

Dehydration did not affect plasma or serum volume. Therefore, a 12-h fast from food and water as done in this study will not likely affect laboratory test results of biomarker concentration. All 3 urinary measures were able to detect changes in hydration status, whereas only 2 blood measures were able to detect changes in hydration status. This may indicate that urinary measures are best at detecting small changes in hydration status.

Training, environmental and nutritional practices in indoor cycling: an explorative cross-sectional questionnaire analysis

Introduction

Indoor cycling at home has grown rapidly in recent years facilitated by advances in technology and gamification. However, there is limited data on individual's training practices when cycling indoors.

Methods

Using a single-time point, cross-sectional questionnaire, we gathered information on equipment, environmental considerations, training practices and nutrition during indoor cycling.

Results

Following 492 responses, external variables (weather; 88.4%, lack of daylight; 56.3%), time efficiency (81.9%) and general fitness (70.9%) were most frequently cited as reasons to engage in indoor cycling. "Smart" turbo trainers linked to a mixed-reality cycling software were most frequently reported in equipment set-up. 78% of participants attempted to control temperature with 96% of these participants using at least 1 fan to control airflow. The volume of indoor training differed between seasons (winter: 6h10 ± 3 h 30, summer 2h52 ± 2h57, p < 0.001), and structured (61.9%) and unstructured work-outs (64.7%) were completed more than once a week with fewer participants engaging in competitive/racing events (20.9%). 98% percent of participants consumed fluids with an average fluid intake of 0.74 ± 0.28 L/h. Dependent on type of work-out, participants reported less planning of carbohydrate and protein intake during short-duration work-outs (∼40%-60%) relative to longer-duration work-outs (∼56%-80%). Caffeine use was the most frequently reported ergogenic aid.

Conclusion

Together we report indoor cycling practices with respect to training equipment, considerations of environmental and nutritional strategies and training habits. Our findings could be used to support the development of future research and indoor training guidelines.

Impact of a simulated multiday heatwave on nocturnal physiology, behavior, and sleep: a 10-day confinement study

This study investigated the impact of a multiday heatwave on nocturnal physiology, behavior, and sleep under controlled conditions with comprehensive monitoring of environmental factors and participant activities. Seven young healthy males were confined for 10 days in controlled conditions that ranged between hot-to-warm (day: 35.4 °C, night: 26.3 °C) during nights 4-6 and temperate (day: 25.4 °C, night: 22.3 °C) before (nights 1-3) and after (nights 7-10) the heatwave. Measurements included core and skin temperatures, heart rate, sympathovagal balance, vasomotion indicators, urine samples, blanket coverage, subjective sleep assessments, and partial polysomnography. The average nocturnal core temperature was 0.2 °C higher during and after the heatwave compared to the pre-heatwave period, with this difference being more pronounced (+0.3 °C) in the first 2 h of sleep (p < 0.001). For every 0.1 °C rise in overnight core temperature, the total sleep time decreased by 14 min (pseudo-R2 = 0.26, p = 0.01). The elevated core temperatures occurred despite the participants exhibiting evident thermoregulatory behavior, as they covered 30% less body surface during the heatwave compared to pre- and post-heatwave periods (p < 0.001). During the heatwave, mean skin temperature at bedtime was 1.3 °C higher than pre-heatwave and 0.8 °C higher than post-heatwave periods (p < 0.001). No differences in other responses, including heart rate and vasomotion indicators, were observed. The paper details a 20-min sleepwalking episode that was coupled with marked changes in sleepwalker's thermophysiological responses. In conclusion, the simulated heatwave resulted in higher overnight core temperature which was associated with reduced total sleep time. Behavioral thermoregulation during sleep may serve as a defense against these effects, though more research is needed.

Cognitive, Psychophysiological, and Perceptual Responses to a Repeated Military-Specific Load Carriage Treadmill Simulation

BACKGROUND

Dismounted military operations require soldiers to complete cognitive tasks whilst undertaking demanding and repeated physical taskings.

OBJECTIVE

To assess the effects of repeated fast load carriage bouts on cognitive performance, perceptual responses, and psychophysiological markers.

METHODS

Twelve civilian males (age, 28 ± 8 y; stature, 186 ± 6 cm; body mass 84.3 ± 11.1 kg; V̇O2max, 51.5 ± 6.4 mL·kg-1·min-1) completed three ∼65-min bouts of a Fast Load Carriage Protocol (FLCP), each interspersed with a 65-min recovery period, carrying a representative combat load of 25 kg. During each FLCP, cognitive function was assessed using a Shoot/Don't-Shoot Task (SDST) and a Military-Specific Auditory N-Back Task (MSANT), along with subjective ratings. Additional psychophysiological markers (heart rate variability, salivary cortisol, and dehydroepiandrosterone-sulfate concentrations) were also measured.

RESULTS

A main effect of bout on MSANT combined score metric (p < .001, Kendall's W = 69.084) and for time on the accuracy-speed trade-off parameter of the SDST (p = .025, Ѡ2 = .024) was evident. These likely changes in cognitive performance were coupled with subjective data indicating that participants perceived that they increased their mental effort to maintain cognitive performance (bout: p < .001, Ѡ2 = .045; time: p < .001, Ѡ2 = .232). Changes in HRV and salivary markers were also evident, likely tracking increased stress.

CONCLUSION

Despite the increase in physiological and psychological stress, cognitive performance was largely maintained; purportedly a result of increased mental effort.

APPLICATION

Given the likely increase in dual-task interference in the field environment compared with the laboratory, military commanders should seek approaches to manage cognitive load where possible, to maintain soldier performance.

Whole body sweat rate prediction: indoor treadmill and cycle ergometer exercise

This article describes the development and validation of accurate whole body sweat rate prediction equations for individuals performing indoor cycle ergometer and treadmill exercise, where power output can be measured or derived from simple inputs. For cycle ergometry, 112 trials (67 participants) were used for model development and another 56 trials (42 participants) for model validation. For treadmill exercise, 171 trials (67 participants) were used for model development and another 95 trials (63 participants) for model validation. Trials were conducted over a range of dry-bulb temperature (20°C to 40°C), relative humidity (14% to 60%), and exercise intensity (∼40% to 85% of peak aerobic power) conditions, which were matched between model development and model validation. Whole body sweat rates were measured, and proprietary prediction models were developed (accounting for all relevant biophysical factors) and then validated. For model validation, mean absolute error for predicted sweating rate was 0.01 and 0.02 L·h-1 for cycle and treadmill trials, respectively. The 95% confidence intervals were modest for cycle ergometer (+0.25 and -0.22 L·h-1) and treadmill exercise (+0.33 and -0.29 L·h-1). The accounted for variance between predicted and measured values was 92% and 78% for cycle and treadmill exercise, respectively. Bland-Altman analysis indicated that zero and one predicted value exceeded the a priori acceptable level of agreement (equivalent to ±2% of total body mass in 3 h) for cycle and treadmill exercise, respectively. There were fewer trials with female subjects, but their values did not differ from those expected for males. This is the foremost study to develop and validate whole body sweat rate prediction equations for indoor treadmill and cycle ergometer exercise of moderate to high intensity. These prediction equations are publicly available for use (https://sweatratecalculator.com).NEW & NOTEWORTHY This study presents the development of new proprietary whole body sweat rate prediction models for people exercising indoors on a cycle ergometer or treadmill using simple input parameters and delivered through a publicly available online calculator: https://sweatratecalculator.com. In an independent validation group, the predictive models for both indoor cycling and treadmill exercise were accurate across moderate to high exercise intensities in temperate to hot conditions. These equations will enable individualized hydration management during physical training and exercise physiology experiments.

Associations between urine specific gravity and race/ethnicity at the population level: Implications for hydration status categorization

OBJECTIVE

We aimed to evaluate how urine specific gravity (USG) and rates of supposed hypohydration vary by race/ethnicity, and to examine how adjustment for several important factors impacts estimated USG.

METHODS

Using the National Health and Nutrition Examination Survey, this cross-sectional study evaluated a total of 4195 (2098 female, 2097 male) Americans and categorized them as supposedly hypohydrated (USG≥1.020) or not using spot urine samples. USG and prevalence of supposed hypohydration were compared across racial/ethnic groups, separately by gender. The analyses considered the impact of urine creatinine, body composition, age, dietary nutrients, and physical activity.

RESULTS

Differences in supposed hypohydration prevalence were observed by race/ethnicity in men (p = .030) and women (p < .001). In unadjusted models, Black women's USG (1.0189) was higher (p < .05) than all the other race/ethnicity groups' USG (1.0142-1.0171). In men, Blacks' USG (1.0197) was higher (p < .05) than the USG of Whites (1.0177) and other/multi-racial (1.0176) but not Mexican Americans (1.0196) or other Hispanics (1.0192). Adjustments for age, arm circumference, nutrients (protein, sodium, potassium, and moisture), and physical activity minimally influenced USG estimates. Further adjustment for urine creatinine lowered USG for Black women and men by 0.003 and 0.0023, respectively, with no notable lowering of USG in the other races/ethnicities. Supplemental analyses matching Whites and Blacks on age, moisture intake, and poverty-to-income ratio confirmed racial differences in urine creatinine and USG, though the effects were most pronounced in women.

CONCLUSIONS

Using a USG≥1.020 to identify hypohydration in all races/ethnicities may be inappropriate due to, among other factors, differences in urinary creatinine.

Nutrition and Golf Performance: A Systematic Scoping Review

BACKGROUND

Golf is played both recreationally and professionally by approximately 66.6 million people worldwide. Despite the potential for nutrition to influence golf performance, research in this area is somewhat limited.

OBJECTIVE

To identify the existing literature regarding nutrition and golf and where the current research gaps lie.

DESIGN

Scoping review. Online databases were used to retrieve data from 2003 to the present day.

DATA SOURCES

A three-step search strategy identified relevant primary and secondary articles as well as grey literature. Published and unpublished articles in the English language, identified by searching electronic databases (ProQuest Central, Web of Science, Scopus, SPORTDiscus and PubMed) and reference searching.

REVIEW METHODS

Relevant identified studies were screened for final inclusion. Data were extracted using a standardised tool to create a descriptive analysis and a thematic summary. In summary, studies were included if they focused on nutrition, hydration, energy requirements, supplements, or body composition in relation to golf.

RESULTS AND DISCUSSION

Our initial search found 3616 relevant articles. Eighty-two of these articles were included for the scoping review. Nutrition has the potential to impact golf performance in areas including the maintenance of energy levels, cognitive function, and body composition. Currently, there is limited research available discussing the effects of nutrition interventions related specifically to golf performance.

CONCLUSION

This scoping review highlights that more work is needed to provide golfers and practitioners with golf-specific nutrition research. The key areas for future golf-specific nutrition research include nutrition on cognitive performance, body composition, energy requirements, supplementation, and the potential role of nutrition for the travelling golfer. Systematic reviews could also be used to identify future priorities for nutrition and golf research.

Gastrointestinal symptoms and nutritional intake among participants in a non-professional cycling event

PURPOSE

To determine the occurrence of gastrointestinal (GI) symptoms in different settings among cyclists participating in a non-professional cycling event. The nutritional intake during the event and the association between GI symptoms and both nutritional and non-nutritional factors were also analyzed.

METHODS

A descriptive correlational study was performed among participants in the 2023 'Mallorca 312-Milestone Series' cycling event. A pre-race questionnaire was completed by 247 participants (37 women) while a post-race questionnaire was completed by 138 participants (24 women).

RESULTS

The prevalence of GI symptoms in training sessions and in previous cycling events were 22-26%. GI complaints during the race were reported by 38.4% of participants. GI symptoms during training (p = 0.003), in previous cycling events (p = 0.012) and in the Mallorca 312 event (during: p = 0.010; after p = 0.014) were associated with rest GI symptoms. Furthermore, GI symptoms during the Mallorca 312 event were associated with an immediately previous more nervous feeling (p = 0.016). Participants with shorter previous experience in similar events reported a more nervous feeling (p = 0.023). On average, participants in the Mallorca 312 achieved the recommended carbohydrate intake (59.2 g/h; recommended 30-60 g/h) and the fluid intake (500 ml; recommended 400-800 ml/h) rates. No association was found between GI symptoms and nutritional parameters or food intake.

CONCLUSION

GI symptoms at rest could be considered the main factor associated with GI symptoms in cyclists. GI symptoms during the event were also associated with a more nervous feeling, which could be explained, at least in part, by shorter previous experience.

Chasing Gold: Heat Acclimation in Elite Handcyclists with Spinal Cord Injury

Thermoregulation is impaired in individuals with a spinal cord lesion (SCI), affecting sweat capacity, heat loss, and core temperature. This can be particularly problematic for athletes with SCI who exercise in hot and humid conditions, like those during the Tokyo 2020 Paralympic Games. Heat acclimation can support optimal preparation for exercise in such challenging environments, but evidence is limited in endurance athletes with SCI. We evaluated whether seven consecutive days of exercise in the heat would result in heat acclimation. Five elite para-cycling athletes with SCI participated (two females, three males, median (Q1-Q3) 35 (31-51) years, four with paraplegia and one with tetraplegia). All tests and training sessions were performed in a heat chamber (30°C and 75% relative humidity). A time-to-exhaustion test was performed on day 1 (pretest) and day 7 (posttest). On days 2-6, athletes trained daily for one hour at 50-60% of individual peak power (PPeak). Comparing pretest and posttest, all athletes increased their body mass loss (p=0.04), sweat rate (p=0.04), and time to exhaustion (p=0.04). Effects varied between athletes for core temperature and heart rate. All athletes appeared to benefit from our heat acclimation protocol, helping to optimize their preparation for the Tokyo 2020 Paralympic Games.

What About Water? Implications for Body Composition Assessment in Military Personnel

ABSTRACT

Sergi, TE, Roberts, BM, and Heileson, JL. What About Water? Implications for Body Composition Assessment in Military Personnel. J Strength Cond Res 38(9): e534-e540, 2024-Body composition standards ensure service members maintain physical fitness, wellness, and support mission readiness. Anthropometric techniques (i.e., height/mass, circumference-based "tape test") have been the primary screening and percent body fat (%BF) assessment method in military personnel for about 4 decades. Recently, the Army and Marine Corps have implemented more advanced body composition assessment methods, such as air displacement plethysmography (ADP), multifrequency bioelectrical impedance analysis (MF-BIA), and dual-energy x-ray absorptiometry (DXA), to serve as supplemental %BF assessment after failing the tape test. Although supplemental assessments are intended to improve on the accuracy and precision of the tape test, preassessment standardization, specifically regarding acute water ingestion (AWI), is lacking. Thus, the purpose of this narrative review was to (a) summarize the available literature regarding the influence of AWI on body composition estimates derived from ADP, MF-BIA, and DXA and (b) provide evidence-based recommendations for researchers and practitioners. Studies indicate that AWI increases %BF estimates with ADP (4 of 6 [4/6] observations) and MF-BIA (6/7), whereas AWI increases muscle mass (6/6) and likely decreases %BF (2/3) when obtained by DXA. In conclusion, ADP, MF-BIA, and DXA are susceptible to confounding from AWI, leading to inaccurate body composition estimates that may negatively affect the careers of military personnel. Based on the findings from this narrative review, military practitioners and researchers should (a) follow manufacturer guidelines for calorie intake [food and fluid] and exercise avoidance, (b) conduct urine-specific gravity testing [if possible], and (c) limit AWI to <250 ml before assessment.

Nourishing Physical Productivity and Performance On a Warming Planet - Challenges and Nutritional Strategies to Mitigate Exertional Heat Stress

PURPOSE OF REVIEW: Climate change is predicted to increase the frequency and severity of exposure to hot environments. This can impair health, physical performance, and productivity for active individuals in occupational and athletic settings. This review summarizes current knowledge and recent advancements in nutritional strategies to minimize the impact of exertional-heat stress (EHS). RECENT FINDINGS: Hydration strategies limiting body mass loss to < 3% during EHS are performance-beneficial in weight-supported activities, although evidence regarding smaller fluid deficits (< 2% body mass loss) and weight-dependent activities is less clear due to a lack of well-designed studies with adequate blinding. Sodium replacement requirements during EHS depends on both sweat losses and the extent of fluid replacement, with quantified sodium replacement only necessary once fluid replacement > 60-80% of losses. Ice ingestion lowers core temperature and may improve thermal comfort and performance outcomes when consumed before, but less so during activity. Prevention and management of gastrointestinal disturbances during EHS should focus on high carbohydrate but low FODMAP availability before and during exercise, frequent provision of carbohydrate and/or protein during exercise, adequate hydration, and body temperature regulation. Evidence for these approaches is lacking in occupational settings. Acute kidney injury is a potential concern resulting from inadequate fluid replacement during and post-EHS, and emerging evidence suggests that repeated exposures may increase the risk of developing chronic kidney disease. Nutritional strategies can help regulate hydration, body temperature, and gastrointestinal status during EHS. Doing so minimizes the impact of EHS on health and safety and optimizes productivity and performance outcomes on a warming planet.

Skimmed, Lactose-Free Milk Ingestion Postexercise: Rehydration Effectiveness and Gastrointestinal Disturbances Versus Water and a Sports Drink in Physically Active People

Postexercise hydration is fundamental to replace fluid loss from sweat. This study evaluated rehydration and gastrointestinal (GI) symptoms for each of three beverages: water (W), sports drink (SD), and skimmed, lactose-free milk (SLM) after moderate-intensity cycling in the heat. Sixteen college students completed three exercise sessions each to lose ≈2% of their body mass. They drank 150% of body mass loss of the drink assigned in randomized order; net fluid balance, diuresis, and GI symptoms were measured and followed up for 3 hr after completion of fluid intake. SLM showed higher fluid retention (∼69%) versus W (∼40%; p < .001); SD (∼56%) was not different from SLM or W (p > .05). Net fluid balance was higher for SLM (-0.26 kg) and SD (-0.42 kg) than W (-0.67 kg) after 3 hr (p < .001), resulting from a significantly lower diuresis with SLM. Reported GI disturbances were mild and showed no difference among drinks (p > .05) despite ingestion of W (1,992 ± 425 ml), SD (1,999 ± 429 ml), and SLM (1,993 ± 426 ml) in 90 min. In conclusion, SLM was more effective than W for postexercise rehydration, showing greater fluid retention for the 3-hr follow-up and presenting with low-intensity GI symptoms similar to those with W and SD. These results confirm that SLM is an effective option for hydration after exercise in the heat.

Compromised heat loss leads to a delayed ice slurry induced reduction in heat storage

Compromised heat loss due to limited convection and evaporation can increase thermal strain. We aimed to determine the effectiveness of ice slurry ingestion to reduce thermal strain following hyperthermia in a state of compromised heat loss. Twelve healthy males (age: 25 ± 4y) underwent hot water immersion to elevate rectal temperature (Trec) by 1.82 ± 0.08°C on four occasions. In the subsequent 60-min of seated recovery, participants ingested either 6.8 g·kg-1 of ice slurry (-0.6°C) or control drink (37°C) in ambient conditions (21 ± 1°C, 39 ± 10% relative humidity), wearing either t-shirt and shorts (2 trials: ICE and CON) or a whole-body sweat suit (2 trials: ICE-SS and CON-SS). Trec and mean skin temperature (Tsk) were recorded and a two-compartment thermometry model of heat storage was calculated. Heat storage was lower in ICE compared with CON at 20-40min (p ≤ 0.044, d ≥ 0.88) and for ICE-SS compared with CON-SS at 40-60 min (p ≤ 0.012, d ≥ 0.93). Trec was lower in ICE compared with CON from 30-60min (p ≤ 0.034, d ≥ 0.65), with a trend for a reduced Trec in ICE-SS compared with CON-SS at 40min (p = 0.079, d = 0.60). A greater Tsk was found in ICE-SS and CON-SS compared with ICE and CON (p < 0.001, d ≥ 3.37). A trend for a lower Tsk for ICE compared with CON was found at 20-40min (p ≤ 0.099, d ≥ 0.53), no differences were found for ICE-SS vs CON-SS (p ≥ 0.554, d ≤ 0.43). Ice slurry ingestion can effectively reduce heat storage when heat loss through convection and evaporation is compromised, relevant to those wearing personal protective equipment or those with compromised sweat loss. Compromised heat loss delays the reduction in heat storage, possibly related to ice slurry ingestion not lowering Tsk.

Metabolic, cardiovascular, neuromuscular and perceptual responses to repeated military-specific load carriage treadmill simulations

Bouts of military load carriage are rarely completed in isolation; however, limited research has investigated the physiological responses to repeated load carriage tasks. Twelve civilian men (age, 28 ± 8 years; stature, 185.6 ± 5.8 cm; body mass 84.3 ± 11.1 kg and maximal oxygen uptake, 51.5 ± 6.4 mL·kg-1 min-1) attended the laboratory on two occasions to undertake a familiarisation and an experimental session. Following their familiarisation session, participants completed three bouts of a fast load carriage protocol (FLCP; ∼65 min), carrying 25 kg, interspersed with a 65-min recovery period. Physiological strain (oxygen uptake [V̇O2] and heart rate [HR]) was assessed during the FLCP bouts, and physical performance assessments (weighted counter-movement jump [wCMJ], maximal isometric voluntary contraction of the quadriceps [MIVC] and seated medicine ball throw [SMBT]) was measured pre and post each FLCP bout. A main effect for bout and measurement time was evident for V̇O2 and HR (both p < 0.001 and Ѡ2 = 0.103-0.816). There was no likely change in SMBT distance (p = 0.201 and Ѡ2 = 0.004), but MIVC peak force reduced by approximately 25% across measurement points (p < 0.001 and Ѡ2 = 0.133). A mean percentage change of approximately -12% from initial values was also evident for peak wCMJ height (p = 0.001 and Ѡ2 = 0.028). Collectively, these data demonstrate that repeated FLCP bouts result in an elevated physiological strain for each successive bout, along with a substantial reduction in lower body power (wCMJ and MIVC). Therefore, future research should investigate possible mitigation strategies to maintain role-related capability.

Nicotine exacerbates exertional heat strain in trained men: a randomized, placebo-controlled, double-blind study

To determine whether using nicotine exacerbates exertional heat strain through an increased metabolic heat production (Hprod) or decreased skin blood flow (SkBF), 10 nicotine-naïve trained males [37 ± 12 yr; peak oxygen consumption (V̇o2peak): 66 ± 10 mL·min-1·kg-1] completed four trials at 20°C and 30°C following overnight transdermal nicotine (7 mg·24 h-1) and placebo use in a crossover, double-blind design. They cycled for 60 min (55% V̇o2peak) followed by a time trial (∼75% V̇o2peak) during which measures of gastrointestinal (Tgi) and mean weighted skin ([Formula: see text]sk) temperatures, SkBF, Hprod, and mean arterial pressure (MAP) were made. The difference in ΔTgi between nicotine and placebo trials was greater during 30°C (0.4 ± 0.5°C) than 20°C (0.1 ± 0.7°C), with [Formula: see text]sk higher during nicotine than placebo trials (0.5 ± 0.5°C, P = 0.02). SkBF became progressively lower during nicotine than placebo trials (P = 0.01) and progressively higher during 30°C than 20°C trials (P < 0.01); MAP increased from baseline (P < 0.01) and remained elevated in all trials. The difference in Hprod between 30°C and 20°C trials was lower during nicotine than placebo (P = 0.01) and became progressively higher during 30°C than 20°C trials with exercise duration (P = 0.03). Mean power output during the time trial was lower during 30°C than 20°C trials (24 ± 25 W, P = 0.02), and although no effect of nicotine was observed (P > 0.59), two participants (20%) were unable to complete their 30°C nicotine trials as one reached the ethical limit for Tgi (40.0°C), whereas the other withdrew due to "nausea and chills" (Tgi = 39.7°C). These results demonstrate that nicotine use increases thermal strain and risk of exertional heat exhaustion by reducing SkBF.NEW & NOTEWORTHY In naïve participants, acute nicotine use exerts a hyperthermic effect that increases the risk of heat exhaustion during exertional heat strain, which is driven by a blunted skin blood flow response. This has implications for 1) populations that face exertional heat strain and demonstrate high nicotine use (e.g., athletes and military, 25%-50%) and 2) study design whereby screening and exclusion for nicotine use or standardization of prior use (e.g., overnight abstinence) is encouraged.

New Zealand blackcurrant extract modulates the heat shock response in men during exercise in hot ambient conditions

PURPOSE

To determine if 7d of New Zealand blackcurrant (NZBC) extract alters the heat shock, inflammatory and apoptotic response during prolonged exertional-heat stress.

METHODS

Ten men (Age: 29 ± 2 years, Stature: 1.82 ± 0.02 m, Mass: 80.3 ± 2.7 kg, V̇O2max: 56 ± 2 mL·kg-1·min-1) ingested two capsules of CurraNZ™ (NZBC extract: 210 mg anthocyanins·day-1) or PLACEBO for 7d prior to 1 h treadmill run (65% V̇O2max) in hot ambient conditions (34 °C/40% RH). Blood samples were collected before (Pre), immediately after (Post), 1 h after (1-Post), and 4 h after (4-Post) exercise. Heat shock proteins (HSP90, HSP70, HSP32) were measured in plasma. HSP and protein markers of inflammatory capacity (TLR4, NF-κB) and apoptosis (BAX/BCL-2, Caspase 9) were measured in peripheral blood mononuclear cells (PBMC).

RESULTS

eHSP32 was elevated at baseline in NZBC(+ 31%; p < 0.001). In PLACEBO HSP32 content in PBMC was elevated at 4-Post(+ 98%; p = 0.002), whereas in NZBC it fell at Post(- 45%; p = 0.030) and 1-Post(- 48%; p = 0.026). eHSP70 was increased at Post in PLACEBO(+ 55.6%, p = 0.001) and NZBC (+ 50.7%, p = 0.010). eHSP90 was increased at Post(+ 77.9%, p < 0.001) and 1-Post(+ 73.2%, p < 0.001) in PLACEBO, with similar increases being shown in NZBC (+ 49.0%, p = 0.006 and + 66.2%, p = 0.001; respectively). TLR4 and NF-κB were both elevated in NZBC at PRE(+ 54%, p = 0.003 and + 57%, p = 0.004; respectively). Main effects of study condition were also shown for BAX/BCL-2(p = 0.025) and Caspase 9 (p = 0.043); both were higher in NZBC.

CONCLUSION

7d of NZBC extract supplementation increased eHSP32 and PBMC HSP32 content. It also increased inflammatory and apoptotic markers in PBMC, suggesting that NZBC supports the putative inflammatory response that accompanies exertional-heat stress.

Role of nutrition in human performance in military populations

The role of nutrition and performance is well established. Service members' physical and cognitive performance, sleep and mood are impacted by nutritional choices. Although many eating patterns have emerged, consensus among experts recommend a dietary pattern focused on predominantly whole plant-based foods. Adequate intakes of fruits, vegetables, whole grains, beans, legumes, nuts and seeds should be prioritised. Implementation of strategic and intentional fuelling strategies around times of activity maintain adequate energy stores, enhance recovery and protect against training injuries. Carbohydrates are prioritised before, during and after activity or a mission, although the type and amount will vary based on duration and intensity of activity. Protein is generally the focus after activity or a mission and may be included before activity depending on individual tolerance. There are no specific recommendations for fat consumption before, during and after exercise that will improve performance. That said, Service members generally tolerate low-fat meals/snacks prior to exercise, limit fat intake during exercise, may include fat as part of the post exercise meal/snack, and generally consume most fat during the maintenance and growth phase. Careful consideration and planning for food and fluid requirements should be made when Service members are exposed to heat, cold and/or altitude. Operational rations are formulated to meet the nutritional needs of all Service members across a variety of diverse climates, environments and altitudes. Service members may use dietary supplements to improve their performance and need to be aware of available resources to help them make informed decisions.

Parade safety and planning: A heat balance case study of marching band artists

Marching band (MB) artists are subject to exertional heat illnesses (EHIs) similar to other active groups like laborers and athletes. Yet, they are an understudied population with no evidence-based heat safety guidelines. Presented here is a case study of the 233rd annual Bristol, RI Independence Day Parade in 2018 that resulted in over 50 EHIs, including 25 from the Saint Anthony Village marching band (MB) from suburban Minneapolis, MN. This research aims to identify the contributing factors that led to the large number of EHIs, as well as guide ensuring the safety of MB artists in future events. A human heat balance model in conjunction with local weather data was used to simulate heat stress on MB artists. Three modeling scenarios were used to isolate the roles of clothing (band uniform vs. t-shirt and shorts), weather (July 4, 2018 vs. 30-year climatology), and metabolic rate (slow, moderate, and brisk marching pacing) on heat stress. The results identify several key factors that increased heat stress. The meteorological conditions were unusually hot, humid, and sunny for Bristol, resulting in reduced cooling from evaporation and convection, and increased radiant heating. Behavioral factors also affect heat stress. The full marching band uniforms reduced evaporative cooling by 50% and the activity levels of marching 4 km over several hours without breaks resulted in conditions that were uncompensable. Finally, it is speculated that a lack of acclimatization for participants from cooler regions may have exacerbated heat-related impacts. These findings highlight several recommendations for MB directors and race organizers, including the use of summer uniforms for anticipated hot conditions, and advance parade planning that includes providing shade/hydration before and after the parade for participants, considering cooler routes that reduce radiant heating and preparing for anticipated heat-related health impacts appropriate for anticipated hot conditions.

Reliability and validity of the MX3 portable sweat sodium analyser during exercise in warm conditions

PURPOSE

Accurately measuring sweat sodium concentration ([Na+]) in the field is advantageous for coaches, scientists, and dieticians looking to tailor hydration strategies. The MX3 hydration testing system is a new portable analyser that uses pre-calibrated biosensors to measure sweat [Na+]. This study aimed to assess the validity and reliability of the MX3 hydration testing system.

METHODS

Thirty-one (11 females) recreationally active participants completed one experimental trial. During this trial, participants exercised at a self-selected pace for 45 min in a warm environment (31.5 ± 0.8 °C, 63.2 ± 1.3% relative humidity). Sweat samples were collected from three measurement sites using absorbent patches. The samples were then analysed for sweat [Na+] using both the MX3 hydration testing system and the Horiba LAQUAtwin-NA-11. The reliability of the MX3 hydration testing system was determined following two measurements of the same sweat sample.

RESULTS

The mean difference between measurements was 0.1 mmoL·L-1 (95% limits of agreement (LoA): - 9.2, 9.4). The analyser demonstrated a coefficient of variation (CV) of 5.6% and the standard error of measurement was 3.3 mmoL·L-1. When compared to the Horiba LAQUAtwin-NA-11, there was a mean difference of - 1.7 mmoL·L-1 (95% LoA: - 0.25 X ¯ , 0.25 X ¯ ) and the CV was 9.8%.

CONCLUSION

The MX3 hydration testing system demonstrated very good single-trial reliability, moderate agreement and a very good CV relative to the Horiba LAQUAtwin-Na-11. To further validate its performance, the MX3 hydration testing system should be compared with analytical techniques known for superior reliability and validity.

Trehalose Improved 20-min Cycling Time-Trial Performance After 100-min Cycling in Amateur Cyclists

Carbohydrate (CHO) supplementation during endurance exercise can improve performance. However, it is unclear whether low glycemic index (GI) CHO leads to differential ergogenic and metabolic effects compared with a standard high GI CHO. This study investigated the ergogenic and metabolic effects of CHO supplementation with distinct GIs, namely, (a) trehalose (30 g/hr), (b) isomaltulose (30 g/hr), (c) maltodextrin (60 g/hr), and (d) placebo (water). In this double-blind, crossover, counterbalanced, placebo-controlled study, 13 male cyclists cycled a total of 100 min at varied exercise intensity (i.e., 10-min stages at 1.5, 2.0, and 2.5 W/kg; repeated three times plus two 5-min stages at 1.0 W/kg before and after the protocol), followed by a 20-min time trial on four separated occasions. Blood glucose and lactate (every 20 min), heart rate, and ratings of perceived exertion were collected throughout, and muscle biopsies were taken before and immediately after exercise. The results showed that trehalose improved time-trial performance compared with placebo (total work done 302 ± 39 vs. 287 ± 48 kJ; p = .01), with no other differences between sessions (all p ≥ .07). Throughout the 100-min protocol, blood glucose was higher with maltodextrin compared with the other supplements at all time points (all p < .05). Heart rate, ratings of perceived exertion, muscle glycogen content, blood glucose, and lactate were not different between conditions when considering the 20-min time trial (all p > .05). Trehalose supplementation throughout endurance exercise improved cycling performance and appears to be an appropriate CHO source for exercise tasks up to 2 hr. No ergogenic superiority between the different types of CHO was established.

Health Claims for Sports Drinks-Analytical Assessmentaccording to European Food Safety Authority's Scientific Opinion

In Europe, sports food supplements (SSFs) are subject to specific laws and regulations. Up to 70% of athletes are highly influenced by the information on the label or the advertisement of the SSF, which often does not correspond to the scientific evidence, such as health claims. The aim is to analyze such claims relating to sports drinks (SDs) in commercial messages. To this end, an observational and cross-sectional study was conducted based on the analysis of the content and degree of adequacy of the health claims indicated on the labelling or technical data sheet of the SDs with those established by the European legislation in force according to the European Food Safety Authority (EFSA). The SSFs were searched for via Amazon and Google Shopping. A total of 114 health claims were evaluated. No claim fully conformed with the recommendations. A total of 14 claims (n = 13 products) almost conformed to the recommendations; they were "Maintain endurance level in exercises requiring prolonged endurance", "Improve water absorption during physical exercise", and "Improved physical performance during high intensity, high duration physical exercise in trained adults", representing 12.3% of the total (n = 114). The vast majority of the claims identified indicated an unproven cause-effect and should be modified or eliminated, which amounts to food fraud towards the consumer.

Whole body sweat rate prediction: outdoor running and cycling exercise

Our aim was to develop and validate separate whole body sweat rate prediction equations for moderate to high-intensity outdoor cycling and running, using simple measured or estimated activity and environmental inputs. Across two collection sites in Australia, 182 outdoor running trials and 158 outdoor cycling trials were completed at a wet-bulb globe temperature ranging from ∼15°C to ∼29°C, with ∼60-min whole body sweat rates measured in each trial. Data were randomly separated into model development (running: 120; cycling: 100 trials) and validation groups (running: 62; cycling: 58 trials), enabling proprietary prediction models to be developed and then validated. Running and cycling models were also developed and tested when locally measured environmental conditions were substituted with participants' subjective ratings for black globe temperature, wind speed, and humidity. The mean absolute error for predicted sweating rate was 0.03 and 0.02 L·h-1 for running and cycling models, respectively. The 95% confidence intervals for running (+0.44 and -0.38 L·h-1) and cycling (+0.45 and -0.42 L·h-1) were within acceptable limits for an equivalent change in total body mass over 3 h of ±2%. The individual variance in observed sweating described by the predictive models was 77% and 60% for running and cycling, respectively. Substituting measured environmental variables with subjective assessments of climatic characteristics reduced the variation in observed sweating described by the running model by up to ∼25%, but only by ∼2% for the cycling model. These prediction models are publicly accessible (https://sweatratecalculator.com) and can guide individualized hydration management in advance of outdoor running and cycling.NEW & NOTEWORTHY We report the development and validation of new proprietary whole body sweat rate prediction models for outdoor running and outdoor cycling using simple activity and environmental inputs. Separate sweat rate models were also developed and tested for situations where all four environmental parameters are not available, and some must be subsequently estimated by the user via a simple rating scale. All models are freely accessible through an online calculator: https://sweatratecalculator.com. These models, via the online calculator, will enable individualized hydration management for training or recreational cycling or running in an outdoor environment.

Recommendations for management of diabetes and its complications during Hajj (Muslim Pilgrimage) - 2024 update

Hajj is an obligatory duty for all healthy adult Muslims once in the lifetime subjected to the ability. Considering the 10.5 % global prevalence of diabetes coupled with the numbers of Muslims performing the Hajj, ∼ 1.8 million in 2023, it is estimated that Muslims with diabetes performing Hajj may exceed 340,000 this year. During Hajj the pattern and amount of their meal, fluid intake and physical activity are markedly altered. Many people with diabetes insist on doing the Hajj duty, thereby creating a medical challenge for themselves and their health care providers. It is therefore important that medical professionals be aware of the potential risks that may be associated with Hajj. People with diabetes may face many health hazards during Hajj including but not limited to the killer triad which might occur during Hajj: Hypoglycemia, Foot injury and Infections. Many precautions should be taken to prevent and treat these potentially serious complications. Risk stratification, medication adjustments, proper clinical assessment, and education before doing Hajj are crucial.

External auricle temperature enhances ear-based wearable accuracy during physiological strain monitoring in the heat

Body core temperature (Tc) monitoring is crucial for minimizing heat injury risk. However, validated strategies are invasive and expensive. Although promising, aural canal temperature (Tac) is susceptible to environmental influences. This study investigated whether incorporation of external auricle temperature (Tea) into an ear-based Tc algorithm enhances its accuracy during multiple heat stress conditions. Twenty males (mean ± SD; age = 25 ± 3 years, BMI = 21.7 ± 1.8, body fat = 12 ± 3%, maximal aerobic capacity (VO2max) = 64 ± 7 ml/kg/min) donned an ear-based wearable and performed a passive heating (PAH), running (RUN) and brisk walking trial (WALK). PAH comprised of immersion in hot water (42.0 ± 0.3 °C). RUN (70 ± 3%VO2max) and WALK (50 ± 10%VO2max) were conducted in an environmental chamber (Tdb = 30.0 ± 0.2 °C, RH = 71 ± 2%). Several Tc models, developed using Tac, Tea and heart rate, were validated against gastrointestinal temperature. Inclusion of Tea as a model input improved the accuracy of the ear-based Tc algorithm. Our best performing model (Trf3) displayed good group prediction errors (mean bias error = - 0.02 ± 0.26 °C) but exhibited individual prediction errors (percentage target attainment ± 0.40 °C = 88%) that marginally exceeded our validity criterion. Therefore, Trf3 demonstrates potential utility for group-based Tc monitoring, with additional refinement needed to extend its applicability to personalized heat strain monitoring.

The effect of pre-exercise oral hyperhydration on endurance exercise performance, heart rate, and thermoregulation: a meta-analytical review

This study aimed to determine the effect of pre-exercise hyperhydration on endurance performance (primary outcome), heart rate, thermoregulation, and perceptual responses (secondary outcomes). Six academic databases were searched to February 2023. Only studies reporting differences in hydration between intervention and placebo/control were included. Meta-analysis determined overall effect size (Hedges' g), and meta-regression the influence of independent moderators (ambient temperature, hyperhydration agent, exercise mode, extent of hyperhydration). Overall, 10 publications generating 19 effect estimates for primary outcomes, and 11 publications reporting 48 effect estimates for secondary outcomes, were included. A small-to-moderate improvement in time-to-exhaustion (TTE) (Hedges' g = 0.31, 95% CI: 0.13-0.50, p = 0.001) and time trial (TT) (g = 0.25, 95% CI: 0.002-0.51, p = 0.049) but not total work (TW) tasks (p = 0.120) was found following hyperhydration. No moderating effects were observed. No effect of hyperhydration was found for heart rate following steady state (SS) exercise (p = 0.069) or the performance task (p = 0.072), nor for body temperature post-SS (p = 0.132) or post-performance task (p = 0.349), but meta-regression of sodium versus glycerol showed lower body temperature post-performance task with sodium (g = 0.80, t (5) = 2.65, p = 0.046). No effects were found for perceived exertion or thermal comfort. Study heterogeneity was low, lacking representation of elite and female athletes, and weight-bearing (i.e., running) exercise modalities. These results suggest pre-exercise hyperhydration provides a small-to-moderate benefit to endurance performance in TTE and TT, but not TW performance tasks. While no moderating effects were observed, lack of heterogeneity makes it difficult to generalise these findings.

Influence of acute dietary nitrate supplementation timing on nitrate metabolism, central and peripheral blood pressure and exercise tolerance in young men

PURPOSE

Dietary nitrate (NO3-) supplementation can lower systolic blood pressure (SBP) and improve exercise performance. Salivary flow rate (SFR) and pH are key determinants of oral NO3- reduction and purported to peak in the afternoon. We tested the hypotheses that NO3--rich beetroot juice (BR) would increase plasma [nitrite] ([NO2-]), lower SBP and improve exercise performance to a greater extent in the afternoon (AFT) compared to the morning (MORN) and evening (EVE).

METHOD

Twelve males completed six experimental visits in a repeated-measures, crossover design. NO3--depleted beetroot juice (PL) or BR (~ 13 mmol NO3-) were ingested in the MORN, AFT and EVE. SFR and pH, salivary and plasma [NO3-] and [NO2-], brachial SBP and central SBP were measured pre and post supplementation. A severe-intensity exercise tolerance test was completed to determine cycling time to exhaustion (TTE).

RESULTS

There were no between-condition differences in mean SFR or salivary pH. The elevation in plasma [NO2-] after BR ingestion was not different between BR-MORN, BR-AFT and BR-EVE. Brachial SBP was unchanged following BR supplementation in all conditions. Central SBP was reduced in BR-MORN (- 3 ± 4 mmHg), BR-AFT (- 4 ± 3 mmHg), and BR-EVE (- 2 ± 3 mmHg), with no differences between timepoints. TTE was not different between BR and PL at any timepoint.

CONCLUSION

Acute BR supplementation was ineffective at improving TTE and brachial SBP and similarly effective at increasing plasma [NO2-] and lowering central SBP across the day, which may have implications for informing NO3- supplementation strategies.

Case example of a female solo sailor competing in the Vendée Globe reveals extraordinary biological demands

The Vendée Globe is a non-stop, unassisted, single-handed round the world sailing race. It is regarded as the toughest sailing race, requiring high cognitive functioning and constant alertness. Little is known about the amount of sleep restriction and nutritional deficit experienced at sea and effects that fatigue have on sailors' performance. This report aimed to investigate these aspects by monitoring one of the female participants of the latest Vendée Globe. Sleep, food intake and stress were self-reported daily using specific app. Cognitive assessments were digitally completed. Heart rate and activity intensity were measured using a wrist-worn wearable device. Mean self-report sleep duration per 24 h was 3 hours 40 minutes. By the end of the 95 race days, the sailor reached a caloric deficit of 27,900 kcal. On average, the sailor spent 50 minutes per day in moderate-to-vigorous activity. Cognitive assessments did not show any effect of fatigue or stress on completion time or performance. Recent technological and communication advancement for offshore sailors, enabled continuous data to be monitored in near real time, even from the Southern Ocean. Moving forward this will enable greater understanding of when sailors will be at risk of poor decision making, illness or injury.

Effects of ingesting beverages containing glycerol and sodium with isomaltulose or sucrose on fluid retention in young adults: a single-blind, randomized crossover trial

We evaluated changes in hyperhydration and beverage hydration index (BHI, a composite measure of fluid balance after consuming a test beverage relative to water) during resting, induced by the consumption of beverages containing glycerol and sodium supplemented with fast-absorbing sucrose or slow-absorbing isomaltulose. In a randomized crossover, single-blinded protocol (clinical trials registry: UMIN000042644), 14 young physically active adults (three women) consumed 1 L of beverage containing either 7% glycerol + 0.5% sodium (Gly + Na), Gly + Na plus 7% sucrose (Gly + Na + Suc), Gly + Na plus 7% isomaltulose (Gly + Na + Iso), or water (CON) over a 40 min period. We assessed the change in plasma volume (ΔPV), BHI (calculated from cumulative urine output following consumption of water relative to that of the beverage), and blood glucose and sodium for 180 min after initiating ingestion. Total urine volume was reduced in all beverages containing glycerol and sodium compared to CON (all P ≤ 0.002). The addition of isomaltulose increased BHI by ∼45% (3.43 ± 1.0 vs. 2.50 ± 0.7 for Gly + Na, P = 0.011) whereas sucrose did not (2.6 ± 0.6, P = 0.826). The PV expansion was earliest for Gly + Na (30 min), slower for Gly + Na + Suc (90 min), and slowest for Gly + Na + Iso (120 min) with a concomitant lag in the increase of blood glucose and sodium concentrations. Supplementation of beverages containing glycerol and sodium with isomaltulose but not sucrose enhances BHI from those of glycerol and sodium only under a resting state, likely due to the slow absorption of isomaltulose-derived monosaccharides (i.e., glucose and fructose).

A Systematic review of the factors that affect soccer players' short-passing ability-based on the Loughborough Soccer Passing Test

OBJECTIVE

This study synthesizes evidence from the Loughborough Passing Test to evaluate the short-passing ability of soccer players and summarizes the reported variables that affect this ability to provide support for the development and improvement of short-passing abilities in soccer players.

METHODS

In this systematic review using the PRISMA guidelines, a comprehensive search was conducted in Web of Science, PubMed, and EBSCOhost from inception to July 2023 to identify relevant articles from the accessible literature. Only studies that used the Loughborough test to assess athletes' short-passing ability were included. The quality of the included studies was independently assessed by two reviewers using the PEDro scale, and two authors independently completed the data extraction.

RESULTS

Based on the type of intervention or influencing factor, ten studies investigated training, nine studies investigated fatigue, nine studies investigated supplement intake, and five studies investigated other factors.

CONCLUSION

Evidence indicates that fitness training, small-sided games training, and warm-up training have positive effects on athletes' short-passing ability, high-intensity special-position training and water intake have no discernible impact, mental and muscular exhaustion have a significantly negative effect, and the effect of nutritional ergogenic aid intake is not yet clear. Future research should examine more elements that can affect soccer players' short-passing ability.

TRIAL REGISTRATION

https://inplasy.com/ ., identifier: INPLASY20237.

Investigating the Effects of Ultraendurance Running on Athletes' Heart Rate and Blood Pressure

Background While the effects of exercise on the cardiovascular system are well documented, ultra-endurance sports involve distances beyond the scope of traditional marathons and have grown in popularity at a staggering pace in recent years. While short-term high-intensity exercise stimulates sympathetic rises in heart rate (HR) and blood pressure (BP), the depletion of fluid and electrolyte reserves characteristic of ultra-endurance sports may contribute to decreases in overall BP after the race. If decompensation of the autonomic safety net occurs, orthostatic hypotension as a result of fluid loss during an event may cause fatigue, dizziness, syncope, or collapse. Methodology Subjects were recruited by emails sent to race participants and at pre-race meetings, and no participants were excluded from the study. We observed BP and HR changes in subjects before and after ultramarathon activity in both supine and standing positions over multiple races of variant length and terrain from 50 to 240 km from 2013 to 2018. Participants entered races in Florida, with a mean age of 43.8 and an average body mass index (BMI) of 21.2. In addition to pre-race and post-race measurements, positional post-race BPs and HRs were analyzed for orthostatic trends. Results Of those who participated, 140 completed the events and post-race HR and BP measurements were recorded. The mean systolic blood pressure (SBP) increase from pre-race to post-race standing was 21 mmHg, while the mean diastolic blood pressure (DBP) rise was 13 mmHg. While in a supine position, there was a 15 mmHg increase in SBP from pre-race to post-race, along with a 7 mmHg rise in diastolic pressure. Post-race supine to standing average BP change was insignificant. In the supine position, the mean HR increased by 20 beats per minute (bpm) after the race and by 27 bpm while standing. After the race, the average increase in HR supine to standing was 15 bpm. Conclusions The SBP changed much more notably than diastolic pressures likely due to the increase in stroke volume associated with the sympathetic response during exercise. HR values also climbed as a result of exercise stress in the setting of catecholamine release, and the combined influence contributed to increased cardiac output despite water and electrolyte loss during the event. Post-race, no trends of orthostatic hypotension were noted either with HR or BP when rising from a supine position. The significance of the contribution of fluid intake during the race to compensatory mechanisms under neural control requires further study.

Hypohydration induced by prolonged cycling in the heat increases biomarkers of renal injury in males

PURPOSE

Recent studies have shown that hypohydration can increase renal injury. However, the contribution of hypohydration to the extent of renal injury is often confounded by exercise induced muscle damage. Therefore, the aim of the present study was to investigate the effect of manipulating hydration status during moderate-intensity cycling in the heat on biomarkers of renal injury.

METHODS

Following familiarisation, fourteen active males (age: 21 [20-22] y; BMI: 22.1 ± 1.9 kg/m2; V ˙ O2peak: 55 ± 9 mL/kg/min) completed two experimental trials, in a randomised cross-over design. Experimental trials consisted of up to 120 min of intermittent cycling (~ 50% Wpeak) in the heat (~ 35 °C, ~ 50% relative humidity). During exercise, subjects consumed either a water volume equal to 100% body mass losses (EU) or minimal water (HYP; 75-100 mL) to induce ~ 3% body mass loss. Blood and urine samples were collected at baseline, 30 min post-exercise and 24 h post-baseline, with an additional urine sample collected immediately post-exercise.

RESULTS

Thirty minutes post-exercise, body mass and plasma volume were lower in HYP than EU (P < 0.001), whereas serum and urine osmolality (P < 0.001), osmolality-corrected urinary kidney injury molecule-1 concentrations (HYP: 2.74 [1.87-5.44] ng/mOsm, EU: 1.15 [0.84-2.37] ng/mOsm; P = 0.024), and percentage change in osmolality-corrected urinary neutrophil gelatinase-associated lipocalin concentrations (HYP: 61 [17-141] %, EU: 7.1 [- 4 to 24] %; P = 0.033) were greater in HYP than EU.

CONCLUSION

Hypohydration produced by cycling in the heat increased renal tubular injury, compared to maintaining euhydration with water ingestion.

Perceived dehydration impairs endurance cycling performance in the heat in active males

Dehydration of >3 % body mass impairs endurance performance irrespective of the individual's knowledge of their hydration status, but whether knowledge of hydration status influences performance at lower levels of dehydration is unknown. This study examined whether perception of hydration status influenced endurance performance. After familiarisation, nine active males (age 25 ± 2 y, V̇O2peak 52.5 ± 9.1 mL kg min-1) completed two randomised trials at 34 °C. Trials involved an intermittent exercise preload (8 × 10 min cycling/5 min rest), followed by a 15 min all-out cycling performance test. During the preload in both trials, water was ingested orally every 10 min (0.3 mL kg body mass-1), with additional water infused into the stomach via gastric feeding tube to produce dehydration of ∼1.5 % body mass pre-performance test. Participants were told intra-gastric infusion was manipulated to produce euhydration (0 % dehydration; Perceived-EUH) or dehydration (2 % dehydration; Perceived-DEH) pre-performance test, which was told to them pre-preload and confirmed after body mass measurement pre-performance test. Body mass loss during the preload (Perceived-EUH 1.6 ± 0.2 %, Perceived-DEH 1.7 ± 0.2 %; P = 0.459), heart rate, gastrointestinal temperature and RPE (P ≥ 0.110) were not different between trials. Thirst was greater at the end of the preload and performance test in Perceived-DEH (P ≤ 0.040). Work completed during the performance test was 5.6 ± 6.1 % lower in Perceived-DEH (187.4 ± 37.0 kJ vs. 176.9 ± 36.0 kJ; P = 0.038). These results suggest that at lower levels of dehydration (<2 % body mass), an individual's perception of their hydration status could impair their performance, as well as their thirst perception.

Long-Chain Omega-3 Fatty Acid Supplementation and Exercise-Induced Muscle Damage: EPA or DHA?

PURPOSE

Long-chain omega-3 polyunsaturated fatty acids, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) may enhance recovery from exercise-induced muscle damage (EIMD). However, it is unclear if the effects are due to EPA, DHA, or both. The purpose of this investigation was to examine the effect of EPA + DHA, EPA, and DHA compared with placebo (PL) on muscular recovery.

METHODS

Thirty males were randomized to 4 g·d -1 EPA + DHA ( n = 8), EPA ( n = 8), DHA ( n = 7), or PL ( n = 7). After 7-wk supplementation, a downhill running (20 min, 70% V̇O 2max , -16% gradient) plus jumping lunges (5 × 20 reps, 2-min rest intervals) muscle damage protocol was performed. Indices of muscle damage, soreness, muscle function, and inflammation were measured at baseline and throughout recovery. The omega-3 index (O3i; %EPA + %DHA in erythrocytes) was used to track tissue EPA and DHA status.

RESULTS

After supplementation, the O3i was significantly higher than PL in all experimental groups ( P < 0.001). Leg press performance was lower in the PL group at 24 h compared with EPA ( P = 0 .019) and at 72 h for EPA ( P = 0.004) and DHA ( P = 0 .046). Compared with PL, muscle soreness was lower in the DHA ( P = 0.015) and EPA ( P = 0.027) groups at 48 h. Albeit nonsignificant, EPA + DHA tended to attenuate muscle soreness ( d = 1.37) and leg strength decrements ( d = 0.75) compared with PL. Jump performance and power metrics improved more rapidly in the EPA and DHA groups (time effects: P < 0.001). Measures of inflammation, range of motion, and muscle swelling were similar between groups ( P > 0.05).

CONCLUSIONS

Compared with PL, 4 g·d -1 of EPA or DHA for 52 d improves certain aspects of recovery from EIMD. EPA + DHA did not clearly enhance recovery. Equivalent dosing of EPA + DHA may blunt the performance effects observed in EPA or DHA alone.

Investigating Nutrition and Hydration Knowledge and Practice among a Cohort of Age-Grade Rugby Union Players

Optimal athletic performance relies on meeting specific nutritional requirements, encompassing adequate calorie intake, macronutrient intake, and hydration. Misinformation or misconceptions about these necessities are prevalent among young athletes. This study investigated nutrition and hydration knowledge and practices among 28 male rugby union players aged 16 to 17, participating in Munster Rugby's 2023 Summer Age-Grade Development Programme, specifically the U18's Schools Squad. The Nutrition for Sport Knowledge Questionnaire assessed nutrition knowledge, while the Hydration Assessment Questionnaire evaluated hydration knowledge. Urinalysis for hydration status utilised urine specific gravity measurements pre-exercise on five separate days (1.018 ± 0.008 Usg). Dietary intake was recorded using a 3-day estimated food intake record on the Libro App, analysed with Nutritics software(Version 9.50). Suboptimal nutrition knowledge (49.6 ± 8.2%) and dietary practices were observed, with incongruent nutrient intakes compared to recommendations for adolescent athletes. While superior hydration knowledge (79.0 (77.3, 83.6) %) was evident, pre-exercise urine specific gravity readings indicated significant variation (p < 0.001) and signs of dehydration (USG > 1.020 Usg). No statistically significant correlations were found between knowledge and practices. The study highlights suboptimal nutrition and hydration knowledge and practices in youth athletes, suggesting the need for tailored support and educational interventions to enhance their overall health and performance. Further investigation into barriers and facilitators to dietary adherence is recommended for more effective interventions.

Effect of Various Hydration Strategies on Work Intensity and Selected Physiological Indices in Young Male Athletes during Prolonged Physical Exercise at High Ambient Temperatures

Background: In high temperatures, adequate hydration is vital for sustained physical exercise. This study explores the effect of three hydration strategies on physiological indices and work intensity. Methods: The research involved 12 healthy males who engaged in three test series, each separated by a one-week interval. During the trials, participants underwent a 120 min cycling session in a thermal climate chamber (temperature: 31 ± 2 °C, humidity: 60 ± 3%, air movement: <1 m/s). Measurements of rectal temperature (Tre) and heart rate (HR), and assessment of subjective workload perception, and thermal comfort were made both before and during the exercise. The computation of the physical strain index (PSI) relied on Tre and HR values. Three hydration strategies (isotonic drink, water, and no hydration) were administered before, during, and after the exercise. Results: Regardless of the hydration strategy, the participants' mean body mass decreased as a result of the exercise. Statistically significant differences in HR were observed between the no-hydration and water groups (p < 0.036). The mean PSI values significantly varied between hydration strategies, with the no hydration group exhibiting a higher PSI compared to the isotonic drink or water groups (p < 0.001). Conclusions: All hydration strategies contribute to thermoregulatory processes and mitigate the rise in internal body temperature during sustained physical exercise in elevated ambient temperatures.

Effect of a cajuína hydroelectrolytic drink on the physical performance and hydration status of recreational runners

Cajuína is a processed drink derived from cashew and is widely consumed in the northeast region of Brazil. This study evaluated the effect of a cajuína-based hydroelectrolytic drink on the aerobic performance and hydration status of recreational runners. Seventeen males (31.9 ± 1.6 years, 51.0 ± 1.4 ml/kg/min) performed three time-to-exhaustion running sessions on a treadmill at 70% VO2max, ingesting cajuína hydroelectrolytic drink (CJ), high carbohydrate commercial hydroelectrolytic drink (CH) and mineral water (W) every 15 min during the running test. The participants ran 80.3 ± 8.4 min in CJ, 70.3 ± 6.8 min in CH and 71.8 ± 6.9 min in W, with no statistical difference between procedures. Nevertheless, an effect size of η2 = 0.10 (moderate) was observed. No statistical difference was observed in the concentrations of sodium, potassium, and osmolality in both serum and urine between the three conditions. However, the effect size was moderate (urine sodium) and high (serum sodium, potassium, and osmolality). Urine specific gravity, sweating rate and heart rate were not significantly different between drinks. The cajuína-based hydroelectrolytic drink promotes similar effects compared to commercial hydroelectrolytic drink and water, considering specific urine gravity, heart rate, sweating, and time to exhaustion in recreational runners.

Validity of combined hydration self-assessment measurements to estimate a low vs. high urine concentration in a small sample of (tactical) athletes

PURPOSE

Relationships between body weight, urine color (Uc), and thirst level (WUT) have been proposed as a simple and inexpensive self-assessment method to predict dehydration. This study aimed to determine if this method also allowed us to accurately identify a low vs. high urine concentration in (tactical) athletes.

METHODS

A total of n = 19 Army Reserve Officer Training Corps cadets and club sports athletes (22.7 ± 3.8 years old, of which 13 male) were included in the analysis, providing morning body weight, thirst sensation, and Uc for five consecutive days. Each item received a score 0 or 1, resulting in a WUT score ranging from 0 (likely hydrated) to 3 (very likely dehydrated). WUT model and individual item outcomes were then compared with a ≥ 1.020 urine specific gravity (USG) cut-off indicating a high urine concentration, using descriptive comparisons, generalized linear mixed models, and logistic regression (to calculate the area under the curve (AUC)).

RESULTS

WUT score was not significantly predictive of urine concentration, z = 1.59, p = 0.11. The AUC ranged from 0.54 to 0.77 for test days, suggesting a fair AUC on most days. Only Uc was significantly related to urine concentration, z = 2.49, p = 0.01. The accuracy of the WUT model for correctly classifying urine samples with a high concentration was 68% vs. 51% of samples with a low concentration, resulting in an average accuracy of 61%.

CONCLUSION

This study shows that WUT scores were not predictive of urine concentration, and the method did not substantially outperform the accuracy of Uc scoring alone.

Are the Dietary-Nutritional Recommendations Met? Analysis of Intake in Endurance Competitions

BACKGROUND

In recent decades the number of endurance events has increased, as well as the number of athletes participating in them. Adequate nutritional and water planning is essential to maintain optimal sports performance and to reduce the incidence of gastrointestinal problems. The main objective of this study is to determine the dietary intake and compliance with nutritional recommendations of athletes in two endurance competitions, as well as to assess the incidence of gastrointestinal complaints.

METHODS

An observational and cross-sectional study was carried out on the consumption of liquids, food, and supplements in 42 triathletes and mountain runners (MRs) participating in a Vi-Half-Gasteiz triathlon and the Ultra Sierra de Cazorla trail run. At the completion of the trials, participants completed a validated questionnaire (NIQEC).

RESULTS

The mean caloric intake during the test of the participants in this study was 192.17 kcal/h, while the mean carbohydrate intake was 43.67 g/h, the mean sodium intake was 267.43 mg/h, and the mean caffeine intake was 15.53 mg/h, with no significant differences between the two sports. The amount of liquids consumed by the participants was 421.21 mL/h, with no significant differences between the triathletes and MRs. As for gastrointestinal problems, it was observed that the participants presented gastrointestinal discomfort in 61.9% of the cases.

CONCLUSIONS

The intakes of energy, carbohydrates, water, sodium, and caffeine were lower than the current recommendations. There were no differences in the energy, carbohydrate, water, sodium, and caffeine intakes between the triathletes and mountain runners. Gastrointestinal problems showed a high prevalence in these athletes.

Divergent mechanisms regulate TLR4 expression on peripheral blood mononuclear cells following workload-matched exercise in normoxic and hypoxic environments

Exercise in hypoxia increases immune responses compared with normoxic exercise, and while Toll-like receptor 4 (TLR4) is implicated in these responses, its regulation remains undefined. The purpose of this study was to 1) investigate TLR4 regulation during workload-matched endurance exercise in normoxic and hypoxic conditions in vivo and 2) determine the independent effects of hypoxia and muscle contractions on TLR4 expression in vitro. Eight recreationally active men cycled for 1 h at 65% of their V̇o2max in normoxia (630 mmHg) and in hypobaric hypoxia (440 mmHg). Exercise in normoxia decreased TLR4 expressed on peripheral blood mononuclear cells (PBMCs), had no effect on the expression of inhibitor of κBα (IκBα), and increased the concentration of soluble TLR4 (sTLR4) in circulation. In contrast, exercise in hypoxia decreased the expression of TLR4 and IκBα in PBMCs, and sTLR4 in circulation. Markers of physiological stress were higher during exercise in hypoxia, correlating with markers of intestinal barrier damage, circulating lipopolysaccharides (LPS), and a concurrent decrease in circulating sTLR4, suggesting heightened TLR4 activation, internalization, and degradation in response to escalating physiological strain. In vitro, both hypoxia and myotube contractions independently, and in combination, reduced TLR4 expressed on C2C12 myotubes, and these effects were dependent on hypoxia-inducible factor 1 (HIF-1). In summary, the regulation of TLR4 varies depending on the physiological stress during exercise. To our knowledge, our study provides the first evidence of exercise-induced effects on sTLR4 in vivo and highlights the essential role of HIF-1 in the reduction of TLR4 during contraction and hypoxia in vitro.NEW & NOTEWORTHY We provide the first evidence of exercise affecting soluble Toll-like receptor 4 (sTLR4), a TLR4 ligand decoy receptor. We found that the degree of exercise-induced physiological stress influences TLR4 regulation on peripheral blood mononuclear cells (PBMCs). Moderate-intensity exercise reduces PBMC TLR4 and increases circulating sTLR4. Conversely, workload-matched exercise in hypoxia induces greater physiological stress, intestinal barrier damage, circulating lipopolysaccharides, and reduces both TLR4 and sTLR4, suggesting heightened TLR4 activation, internalization, and degradation under increased strain.

Effect of sportswear on performance and physiological heat strain during prolonged running in moderately hot conditions

INTRODUCTION

This study examined the impact of different upper-torso sportswear technologies on the performance and physiological heat strain of well-trained and national-level athletes during prolonged running in moderately hot conditions.

METHODS

A randomized crossover design was employed in which 20 well-trained (n = 16) and national-level (n = 4) athletes completed four experimental trials in moderately hot conditions (35°C, 30% relative humidity). In each trial, participants ran at 70% of their peak oxygen uptake (70% V̇O2peak ) for 60 min, while wearing a different upper-body garment: cotton t-shirt, t-shirt with sweat-wicking fabric, compression t-shirt, and t-shirt with aluminum dots lining the inside of the upper back of the garment. Running speed was adjusted to elicit the predetermined oxygen consumption associated with 70% V̇O2peak . Physiological (core and skin temperatures, total body water loss, and urine specific gravity) and perceptual (thermal comfort and sensation, ratings of perceived exertion, and garment cooling functionality) parameters along with running speed at 70% V̇O2peak were continuously recorded.

RESULTS

No significant differences were observed between the four garments for running speed at 70% V̇O2peak , physiological heat strain, and perceptual responses (all p > 0.05). The tested athletes reported larger areas of perceived suboptimal cooling functionality in the cotton t-shirt and the t-shirt with aluminum dots relative to the sweat-wicking and compression t-shirts (d: 0.43-0.52).

CONCLUSION

There were not differences among the tested garments regarding running speed at 70% V̇O2peak , physiological heat strain, and perceptual responses in well-trained and national-level endurance athletes exercising in moderate heat.

Football Practices in Hot Environments Impact Subsequent Days' Hydration

ABSTRACT

Ashley, CD, Lopez, RM, and Tritsch, AJ. Football practices in hot environments impact subsequent days' hydration. J Strength Cond Res 38(1): 90-96, 2024-The impact of proper hydration to prevent exertional heat illness in American football has not been evaluated during high school preseason football practices in a hot environment (wet-bulb globe temperature = 31.3 ± 1.8° C). The purposes of this study were to examine the accuracy of urinary hydration measures to assess body mass (BM) changes and to examine carryover effects of consecutive practices by comparing postpractice with the next prepractice values. Before and after each of 7 outdoor practices, 31 male high school football players (age = 16 ± 1 years, height = 181.2 ± 12.0 cm, BM = 85.7 ± 19.1 kg, body mass index = 20.8 ± 1.8) provided a urine sample and were weighed to assess hydration. Sensitivity and specificity of urine color (Ucol) and urine-specific gravity (USG) to determine BM changes were determined using receiver operating characteristic (ROC) analysis. Paired samples t -tests assessed carryover effects between practices. Repeated-measures analysis of variance assessed carryover effects across practices. Significance was set at p < 0.05. Sensitivity and specificity for using Ucol or USG to determine BM changes was not significant. For Ucol, there was a carryover effect from practice numbers 2 to 3, 6 to 7 am , 7 am to 7 pm ( p < 0.001 for all), and 10 to 11 ( p = 0.004); most with less than 24 hours between practices. The %BM loss (%BML) was significantly greater ( p = 0.001 to 0.024) after 2-a-day practices. Effects of previous days' exercise in the heat, as evidenced by higher Ucol and %BL, are greater after 2-a-day practices, which occurred on later practice days. Athletes must replenish fluids during and between practices to remain euhydrated.

A century of exercise physiology: concepts that ignited the study of human thermoregulation. Part 3: Heat and cold tolerance during exercise

In this third installment of our four-part historical series, we evaluate contributions that shaped our understanding of heat and cold stress during occupational and athletic pursuits. Our first topic concerns how we tolerate, and sometimes fail to tolerate, exercise-heat stress. By 1900, physical activity with clothing- and climate-induced evaporative impediments led to an extraordinarily high incidence of heat stroke within the military. Fortunately, deep-body temperatures > 40 °C were not always fatal. Thirty years later, water immersion and patient treatments mimicking sweat evaporation were found to be effective, with the adage of cool first, transport later being adopted. We gradually acquired an understanding of thermoeffector function during heat storage, and learned about challenges to other regulatory mechanisms. In our second topic, we explore cold tolerance and intolerance. By the 1930s, hypothermia was known to reduce cutaneous circulation, particularly at the extremities, conserving body heat. Cold-induced vasodilatation hindered heat conservation, but it was protective. Increased metabolic heat production followed, driven by shivering and non-shivering thermogenesis, even during exercise and work. Physical endurance and shivering could both be compromised by hypoglycaemia. Later, treatments for hypothermia and cold injuries were refined, and the thermal after-drop was explained. In our final topic, we critique the numerous indices developed in attempts to numerically rate hot and cold stresses. The criteria for an effective thermal stress index were established by the 1930s. However, few indices satisfied those requirements, either then or now, and the surviving indices, including the unvalidated Wet-Bulb Globe-Thermometer index, do not fully predict thermal strain.

The physiology of ice hockey performance: An update

Ice hockey is an intense team sport characterized by repeated bursts of fast-paced skating, rapid changes in speed and direction and frequent physical encounters. These are performed in on-ice shifts of ~30-80 s interspersed with longer sequences of passive recovery, resulting in about 15-25 min on-ice time per player. Nearly 50% of the distance is covered at high-intensity skating speeds and with an accentuated intense activity pattern in forwards compared to defensemen. During ice hockey match-play, both aerobic and anaerobic energy systems are significantly challenged, with the heart rate increasing toward maximum levels during each shift, and with great reliance on both glycolytic and phosphagen ATP provision. The high-intensity activity pattern favors muscle glycogen as fuel, leading to pronounced reductions despite the relatively brief playing time, including severe depletion of a substantial proportion of individual fast- and slow-twitch fibers. Player-tracking suggests that the ability to perform high-intensity skating is compromised in the final stages of a game, which is supported by post-game reductions in repeated-sprint ability. Muscle glycogen degradation, in particular in individual fibers, as well as potential dehydration and hyperthermia, may be prime candidates implicated in exacerbated fatigue during the final stages of a game, whereas multiple factors likely interact to impair exercise tolerance during each shift. This includes pronounced PCr degradation, with potential inadequate resynthesis in a proportion of fast-twitch fibers in situations of repeated intense actions. Finally, the recovery pattern is inadequately described, but seems less long-lasting than in other team sports.

Body fluids and muscle changes in trail runners of various distances

Background

This study aims to investigate body fluids and muscle changes evoked by different trail races using anthropometric, bioelectrical, and creatine kinase (CK) measurements.

Methods

A total of 92 subjects (55 men, 37 women) participating in three different races of 14, 35, and 52 km were evaluated before (PRE) and after (POST) the races. Classic bioelectrical impedance vector analysis was applied at the whole-body level (WB-BIVA). Additionally, muscle-localized bioelectrical assessments (ML-BIVA) were performed in a subgroup of 11 men (in the quadriceps, hamstrings, and calves). PRE-POST differences and correlations between bioelectrical values and CK, running time and race distance were tested.

Results

Changes in whole-body vectors and phase angles disclosed an inclination towards dehydration among men in the 14, 35, and 52 km groups (p < 0.001), as well as among women in the 35 and 52 km groups (p < 0.001). PRE Z/H was negatively correlated with running time in the 35 km men group and 14 km women group (r = -0.377, p = 0.048; r = -0.751, p = 0.001; respectively). POST Z/H was negatively correlated with running time in the 14 km women group (r = -0.593, p = 0.02). CK was positively correlated with distance in men and women (p < 0.001) and negatively correlated with reactance and vector length in the 14 km men group (p < 0.05). ML-BIVA echoed the same tendency as the WB-BIVA in the 35 and 52 km runners, with the most notable changes occurring in the calves (p < 0.001).

Conclusions

WB-BIVA and CK measurements underscored a conspicuous trend towards post-race dehydration and muscle damage, displaying a weak association with performance. Notably, ML-BIVA detected substantial alterations primarily in the calves. The study underscores the utility of BIVA as a technique to assess athlete's body composition changes.

Effect of acute heat exposure on the determination of critical power and W' in women and men

The goal of this study was to investigate to what extent acute heat exposure would affect the parameters of the power-duration relationship, i.e. CP and W', using multiple constant workload tests to task failure, in women and men. Twenty four young physically active participants (12 men, 12 women) performed 3-5 constant load tests to determine CP and W', both in temperate (TEMP; 18°C) and hot (HOT; 36°C) environmental conditions. A repeated-measures ANOVA was executed to find differences between TEMP and HOT, and between women and men. In HOT, CP was reduced by 6.5% (227 ± 50 vs. 212 ± 47 W), while W' increased 12.4% (16.4 ± 4.4 vs. 18.5 ± 5.6 kJ). No significant two-way sex × temperature interactions were observed, indicating that the environmental conditions did not have a different effect in men compared with women. The intersection of the average curvatures in TEMP and HOT occurred at 137 s and 280 W in women, and 153 s and 397 W in men. Acute heat exposure had an impact on the parameters CP and W', i.e. CP decreased whereas W' increased. The increase in W' might be a consequence of the mathematical modelling for the used test methodology, rather than a physiological accurate value of W' in HOT. No differences induced by heat exposure were observed between women and men.

Effect of fluid replacement with green tea on body fluid balance and renal responses under mild thermal hypohydration: a randomized crossover study

PURPOSE

Maintaining an appropriate hydration level by ingesting fluid in a hot environment is a measure to prevent heat-related illness. Caffeine-containing beverages, including green tea (GT), have been avoided as inappropriate rehydration beverages to prevent heat-related illness because caffeine has been assumed to exert diuretic/natriuretic action. However, the influence of caffeine intake on urine output in dehydrated individuals is not well documented. The aim of the present study was to examine the effect of fluid replacement with GT on body fluid balance and renal water and electrolyte handling in mildly dehydrated individuals.

METHODS

Subjects were dehydrated by performing three bouts of stepping exercise for 20 min separated by 10 min of rest. They were asked to ingest an amount of water (H2O), GT, or caffeinated H2O (20 mg/100 ml; Caf-H2O) that was equal to the volume of fluid loss during the dehydration protocol; fluid balance was measured for 2 h after fluid ingestion.

RESULTS

The dehydration protocol induced hypohydration by ~ 10 g/kg body weight (~ 1% of body weight). Fluid balance 2 h after fluid ingestion was significantly less negative in all trials, and the fluid retention ratio was 52.2 ± 4.2% with H2O, 51.0 ± 5.0% with GT, and 47.9 ± 6.2% with Caf-H2O; those values did not differ among the trials. After rehydration, urine output, urine osmolality, and urinary excretions of osmotically active substances, sodium, potassium and chloride were not different among the trials.

CONCLUSION

The data indicate that ingestion of GT or an equivalent caffeine amount does not worsen the hydration level 2 h after ingestion and can be effective in reducing the negative fluid balance for acute recovery from mild hypohydration.

TRIAL REGISTRATION

ISRCTN53057185; retrospectively registered.

International society of sports nutrition position stand: energy drinks and energy shots

Position Statement: The International Society of Sports Nutrition (ISSN) bases the following position stand on a critical analysis of the literature regarding the effects of energy drink (ED) or energy shot (ES) consumption on acute exercise performance, metabolism, and cognition, along with synergistic exercise-related performance outcomes and training adaptations. The following 13 points constitute the consensus of the Society and have been approved by the Research Committee of the Society: Energy drinks (ED) commonly contain caffeine, taurine, ginseng, guarana, carnitine, choline, B vitamins (vitamins B1, B2, B3, B5, B6, B9, and B12), vitamin C, vitamin A (beta carotene), vitamin D, electrolytes (sodium, potassium, magnesium, and calcium), sugars (nutritive and non-nutritive sweeteners), tyrosine, and L-theanine, with prevalence for each ingredient ranging from 1.3 to 100%. Energy drinks can enhance acute aerobic exercise performance, largely influenced by the amount of caffeine (> 200 mg or >3 mg∙kg bodyweight [BW-1]) in the beverage. Although ED and ES contain several nutrients that are purported to affect mental and/or physical performance, the primary ergogenic nutrients in most ED and ES based on scientific evidence appear to be caffeine and/or the carbohydrate provision. The ergogenic value of caffeine on mental and physical performance has been well-established, but the potential additive benefits of other nutrients contained in ED and ES remains to be determined. Consuming ED and ES 10-60 minutes before exercise can improve mental focus, alertness, anaerobic performance, and/or endurance performance with doses >3 mg∙kg BW-1. Consuming ED and ES containing at least 3 mg∙kg BW-1 caffeine is most likely to benefit maximal lower-body power production. Consuming ED and ES can improve endurance, repeat sprint performance, and sport-specific tasks in the context of team sports. Many ED and ES contain numerous ingredients that either have not been studied or evaluated in combination with other nutrients contained in the ED or ES. For this reason, these products need to be studied to demonstrate efficacy of single- and multi-nutrient formulations for physical and cognitive performance as well as for safety. Limited evidence is available to suggest that consumption of low-calorie ED and ES during training and/or weight loss trials may provide ergogenic benefit and/or promote additional weight control, potentially through enhanced training capacity. However, ingestion of higher calorie ED may promote weight gain if the energy intake from consumption of ED is not carefully considered as part of the total daily energy intake. Individuals should consider the impact of regular coingestion of high glycemic index carbohydrates from ED and ES on metabolic health, blood glucose, and insulin levels. Adolescents (aged 12 through 18) should exercise caution and seek parental guidance when considering the consumption of ED and ES, particularly in excessive amounts (e.g. > 400 mg), as limited evidence is available regarding the safety of these products among this population. Additionally, ED and ES are not recommended for children (aged 2-12), those who are pregnant, trying to become pregnant, or breastfeeding and those who are sensitive to caffeine. Diabetics and individuals with preexisting cardiovascular, metabolic, hepatorenal, and/or neurologic disease who are taking medications that may be affected by high glycemic load foods, caffeine, and/or other stimulants should exercise caution and consult with their physician prior to consuming ED. The decision to consume ED or ES should be based upon the beverage's content of carbohydrate, caffeine, and other nutrients and a thorough understanding of the potential side effects. Indiscriminate use of ED or ES, especially if multiple servings per day are consumed or when consumed with other caffeinated beverages and/or foods, may lead to adverse effects. The purpose of this review is to provide an update to the position stand of the International Society of Sports Nutrition (ISSN) integrating current literature on ED and ES in exercise, sport, and medicine. The effects of consuming these beverages on acute exercise performance, metabolism, markers of clinical health, and cognition are addressed, as well as more chronic effects when evaluating ED/ES use with exercise-related training adaptions.

Salivary concentrations of secretory leukocyte protease inhibitor and matrix metallopeptidase-9 following a single bout of exercise are associated with intensity and hydration status

AIM

To investigate the effects of exercise on salivary concentrations of inflammatory markers by analyzing a panel of 25 inflammatory markers in subjects who had participated in bicycle ergometer tests varying in workload and hydration status.

METHODS

Fifteen healthy young men (20-35 years) had performed 4 different exercise protocols of 1 hour duration in a randomly assigned cross-over design, preceded by a rest protocol. Individual workloads depended on participant's pre-assessed individual maximum workload (Wmax): rest (protocol 1), 70% Wmax in hydrated (protocol 2) and dehydrated (protocol 3) state, 50% Wmax (protocol 4) and intermittent 85%/55% Wmax in 2 min blocks (protocol 5). Saliva samples were collected before (T0) and immediately after exercise (T1), and at several time points after exercise (2 hours (T3), 3 hours (T4), 6 hours (T5) and 24 hours (T6)). Secretory Leukocyte Protease Inhibitor (SLPI), Matrix Metallopeptidase-9 (MMP-9) and lactoferrin was analyzed using a commercial ELISA kit, a panel of 22 cytokines and chemokines were analyzed using a commercial multiplex immunoassay. Data was analyzed using a multilevel mixed linear model, with multiple test correction.

RESULTS

Among a panel of 25 inflammatory markers, SLPI concentrations were significantly elevated immediately after exercise in all protocols compared to rest and higher concentrations reflected the intensity of exercise and hydration status. MMP-9 showed a significant increase in the 70% Wmax dehydrated, 50% Wmax and intermittent protocols.

CONCLUSIONS

Salivary concentrations of SLPI and MMP-9 seem associated with exercise intensity and hydration status and may offer non-invasive biomarkers to study (local) inflammatory responses to different exercise intensities in human studies.