Influence of body mass loss on changes in heart rate during exercise in the heat: a systematic review

The Effect of Pre-Exercise Hyperhydration on Exercise Performance, Physiological Outcomes and Gastrointestinal Symptoms: A Systematic Review

BACKGROUND

Fluid loss during prolonged exercise in hot conditions poses thermoregulatory and cardiovascular challenges for athletes that can lead to impaired performance. Pre-exercise hyperhydration using nutritional aids is a strategy that may prevent or delay the adverse effects of dehydration and attenuate the impact of heat stress on exercise performance.

OBJECTIVES

The aim of this systematic review was to examine the current literature to determine the effect of pre-exercise hyperhydration on performance, key physiological responses and gastrointestinal symptoms.

METHODS

English language, full-text articles that compared the intervention with a baseline or placebo condition were included. An electronic search of Medline Complete, SPORTDiscus and Embase were used to identify articles with the final search conducted on 11 October 2022. Studies were assessed using the American Dietetic Association Quality Criteria Checklist.

RESULTS

Thirty-eight studies involving 403 participants (n = 361 males) were included in this review (n = 22 assessed exercise performance or capacity). Two studies reported an improvement in time-trial performance (range 5.7-11.4%), three studies reported an improvement in total work completed (kJ) (range 4-5%) and five studies reported an increase in exercise capacity (range 14.3-26.2%). During constant work rate exercise, nine studies observed a reduced mean heart rate (range 3-11 beats min-1), and eight studies reported a reduced mean core temperature (range 0.1-0.8 °C). Ten studies reported an increase in plasma volume (range 3.5-12.6%) compared with a control. Gastrointestinal symptoms were reported in 26 studies, with differences in severity potentially associated with factors within the ingestion protocol of each study (e.g. treatment, dose, ingestion rate).

CONCLUSIONS

Pre-exercise hyperhydration may improve exercise capacity during constant work rate exercise due to a reduced heart rate and core temperature, stemming from an acute increase in plasma volume. The combination of different osmotic aids (e.g. glycerol and sodium) may enhance fluid retention and this area should continue to be explored. Future research should utilise valid and reliable methods of assessing gastrointestinal symptoms. Furthermore, studies should investigate the effect of hyperhydration on different exercise modalities whilst implementing a strong level of blinding. Finally, females are vastly underrepresented, and this remains a key area of interest in this area.

Impact of Preparticipating Hypohydration on Cardiopulmonary Exercise Capacity in Ambitious Recreational Athletes

BACKGROUND

Heat induces a thermoregulatory strain that impairs cardiopulmonary exercise capacity. The aim of the current study is to elucidate the effect of isolated dehydration on cardiopulmonary exercise capacity in a model of preparticipating hypohydration.

METHODS

Healthy recreational athletes underwent a standardised fluid deprivation test. Hypohydration was assessed by bioelectrical impedance analysis (BIA) and laboratory testing of electrolytes and retention parameters in the blood and urine. The participants underwent cardiopulmonary exercise testing (CPET) with a cycle ramp protocol. Each participant served as their own control undergoing CPET in a hypohydrated [HYH] and euhydrated [EUH] state.

RESULTS

Fluid deprivation caused a mild (2%) but significant reduction of body water (38.6 [36.6; 40.7] vs. 39.4 [37.4; 41.5] %; p < 0.01) and an increase of urine osmolality (767 [694; 839] vs. 537 [445; 629] mosm/kg; p < 0.01). Hypohydration was without alterations of electrolytes, serum osmolality or hematocrit. The oxygen uptake was significantly lower after hypohydration (-4.8%; p = 0.02 at ventilatory threshold1; -2.0%; p < 0.01 at maximum power), with a corresponding decrease of minute ventilation (-4% at ventilatory threshold1; p = 0.01, -3.3% at maximum power; p < 0.01). The power output was lower in hypohydration (-6.8%; p < 0.01 at ventilatory threshold1; -2.2%; p = 0.01 at maximum power).

CONCLUSION

Isolated hypohydration causes impairment of workload as well as peak oxygen uptake in recreational athletes. Our findings might indicate an important role of hypohydration in the heat-induced reduction of exercise capacity.

Impact of dehydration on perceived exertion during endurance exercise: A systematic review with meta-analysis

Background

Understanding the impact of stressors on the rating of perceived exertion (RPE) is relevant from a performance and exercise adherence/participation standpoint. Athletes and recreationally active individuals dehydrate during exercise. No attempt has been made to systematically determine the impact of exercise-induced dehydration (EID) on RPE.

Objective

The present meta-analysis aimed to determine the effect of EID on RPE during endurance exercise and examine the moderating effect of potential confounders.

Data analyses

Performed on raw RPE values using random-effects models weighted mean effect summaries and meta-regressions with robust standard errors, and with a practical meaningful effect set at 1 point difference between euhydration (EUH) and EID. Only controlled crossover studies measuring RPE with a Borg scale in healthy adults performing ≥30 min of continuous endurance exercise while dehydrating or drinking to maintain EUH were included.

Results

Sixteen studies were included, representing 147 individuals. Mean body mass loss with EUH was 0.5 ± 0.4%, compared to 2.3 ± 0.5% with EID (range 1.7-3.1%). Within an EID of 0.5-3% body mass, a maximum difference in RPE of 0.81 points (95% CI: 0.36-1.27) was observed between conditions. A meta-regression revealed that RPE increases by 0.21 points for each 1% increase in EID (95% CI: 0.12-0.31). Humidity, ambient temperature and aerobic capacity did not alter the relationship between EID and RPE.

Conclusion

Therefore, the effect of EID on RPE is unlikely to be practically meaningful until a body mass loss of at least 3%.

Palatable Flavoured Fluids without Carbohydrates and Electrolytes Do Not Enhance Voluntary Fluid Consumption in Male Collegiate Basketball Players in the Heat

Using palatable fluids to enhance drinking in athletes who display insufficient compensatory hydration behaviour may mitigate the risks of hypohydration and performance deficits. However, it is unclear whether flavour can independently enhance fluid consumption. This study examined the effects of a colourless, artificially sweetened flavoured water (FW), without carbohydrates and with negligible amounts of sodium, compared to plain water (W) on fluid consumption in male collegiate basketball players in a practical game setting. Eighteen male basketball players (age 23.1 ± 1.3 years) played a 3v3 basketball small-sided game. The players were randomly assigned to consume either FW or W. Pre-game urine-specific gravity, fluid consumption, body mass, and hedonic taste perceptions were assessed. Basketball performance was analysed through notational analysis. Ratings of perceived exertion and thirst were recorded at pre-, post-game, and at each rest period. Heart rate was recorded throughout the gameplay. Despite significantly higher hedonic ratings for FW than W (6.78 ± 0.83 vs. 5.56 ± 1.33, p = 0.033, d = 1.36), there were no significant differences in fluid consumption (1083 ± 32 mL vs. 1421 ± 403 mL, p = 0.068, d = 0.92). Our result highlighted that using palatable fluids as a strategy to increase fluid consumption during high-intensity gameplay in the heat may not be effective if used without carbohydrates and electrolytes. Practitioners could consider both fluid palatability and composition in establishing a hydration plan for athletes.

Hydration Status and Fluid Replacement Strategies of High-Performance Adolescent Athletes: An Application of Machine Learning to Distinguish Hydration Characteristics

There are limited data on the fluid balance characteristics and fluid replenishment behaviors of high-performance adolescent athletes. The heterogeneity of hydration status and practices of adolescent athletes warrant efficient approaches to individualizing hydration strategies. This study aimed to evaluate and characterize the hydration status and fluid balance characteristics of high-performance adolescent athletes and examine the differences in fluid consumption behaviors during training. In total, 105 high-performance adolescent athletes (male: 66, female: 39; age 14.1 ± 1.0 y) across 11 sports had their hydration status assessed on three separate occasions—upon rising and before a low and a high-intensity training session (pre-training). The results showed that 20–44% of athletes were identified as hypohydrated, with 21–44% and 15–34% of athletes commencing low- and high-intensity training in a hypohydrated state, respectively. Linear mixed model (LMM) analyses revealed that athletes who were hypohydrated consumed more fluid (F (1.183.85)) = 5.91, (p = 0.016). Additional K-means cluster analyses performed highlighted three clusters: “Heavy sweaters with sufficient compensatory hydration habits,” “Heavy sweaters with insufficient compensatory hydration habits” and “Light sweaters with sufficient compensatory hydration habits”. Our results highlight that high-performance adolescent athletes with ad libitum drinking have compensatory mechanisms to replenish fluids lost from training. The approach to distinguish athletes by hydration characteristics could assist practitioners in prioritizing future hydration intervention protocols.

The Impact of Environmental Conditions on Player Loads During Preseason Training Sessions in Women's Soccer Athletes

ABSTRACT

Austin, AB, Collins, SM, Huggins, RA, Smith, BA, and Bowman, TG. The impact of environmental conditions on player loads during preseason training sessions in women's soccer athletes. J Strength Cond Res 35(10): 2775-2782, 2021-Our objective was to determine the impact of environmental conditions on player loads during preseason training sessions in women's soccer athletes. Eleven women's NCAA Division III soccer players (age = 20 ± 1 year, height = 167.28 ± 8.65 cm, body mass = 60.18 ± 5.42 kg, V̇o2max = 43.70 ± 3.95 ml·kg-1·min-1) volunteered to wear Global Positioning System (GPS) devices (Sports Performance Tracking, Melbourne, Australia) that provided measures of training session external intensity throughout all preseason practices (n = 15). We recorded wet-bulb globe temperature (WBGT), session Rating of Perceived Exertion-Training Load (sRPE-TL), and ΔBM during each preseason training session and set α ≤ 0.05. The combination of WBGT, sRPE-TL, and ΔBM explained 34% of the variance in GPS-based intensity score (proprietary measure) (F3,153 = 26.25, p < 0.001). Wet-bulb globe temperature (t156 = -2.58, p = 0.01), sRPE (t156 = 8.24, p < 0.001), and ΔBM (t156 = 2.39, p = 0.02) were significantly associated with intensity. The ΔBM from prepractice (60.00 ± 5.21 kg) to postpractice (59.61 ± 5.10 kg) was statistically significant (p < 0.001); however, ΔBM from the beginning of preseason (59.87 ± 5.31 kg) to the end of preseason (59.91 ± 5.58 kg) was not significant (p = 0.89). Despite relatively low to moderate environmental conditions, increases in WBGT were associated with reductions in GPS intensity and elevated internal load via sRPE-TL. Our findings support the association between exercise intensity and WBGT, internal load, and hydration status; thus, coaches and exercise scientists should take these factors into account when monitoring or interpreting intensity metrics. Furthermore, these findings support the continued use of environmental monitoring and hydration best-practice policies to limit exercise intensity in the heat so as to mitigate excessive heat stress.

Effects of Face Mask Use on Objective and Subjective Measures of Thermoregulation During Exercise in the Heat

BACKGROUND

While increased face mask use has helped reduce COVID-19 transmission, there have been concerns about its influence on thermoregulation during exercise in the heat, but consistent, evidence-based recommendations are lacking.

HYPOTHESIS

No physiological differences would exist during low-to-moderate exercise intensity in the heat between trials with and without face masks, but perceptual sensations could vary.

STUDY DESIGN

Crossover study.

LEVEL OF EVIDENCE

Level 2.

METHODS

Twelve physically active participants (8 male, 4 female; age = 24 ± 3 years) completed 4 face mask trials and 1 control trial (no mask) in the heat (32.3°C ± 0.04°C; 54.4% ± 0.7% relative humidity [RH]). The protocol was 60 minutes of walking and jogging between 35% and 60% of relative VO2max. Rectal temperature (Trec), heart rate (HR), temperature and humidity inside and outside of the face mask (Tmicro_in, Tmicro_out, RHmicro_in, RHmicro_out) and perceptual variables (rating of perceived exertion (RPE), thermal sensation, thirst sensation, fatigue level, and overall breathing discomfort) were monitored throughout all trials.

RESULTS

Mean Trec and HR increased at 30- and 60-minute time points compared with 0-minute time points, but no difference existed between face mask trials and control trials (P > 0.05). Mean Tmicro_in, RHmicro_in, and humidity difference inside and outside of the face mask (ΔRHmicro) were significantly different between face mask trials (P < 0.05). There was no significant difference in perceptual variables between face mask trials and control trials (P > 0.05), except overall breathing discomfort (P < 0.01). Higher RHmicro_in, RPE, and thermal sensation significantly predicted higher overall breathing discomfort (r2 = 0.418; P < 0.01).

CONCLUSION

Face mask use during 60 minutes of low-to-moderate exercise intensity in the heat did not significantly affect Trec or HR. Although face mask use may affect overall breathing discomfort due to the changes in the face mask microenvironment, face mask use itself did not cause an increase in whole body thermal stress.

CLINICAL RELEVANCE

Face mask use is feasible and safe during exercise in the heat, at low-to-moderate exercise intensities, for physically active, healthy individuals.

Estimated Sweat Loss, Fluid and Carbohydrate Intake, and Sodium Balance of Male Major Junior, AHL, and NHL Players During On-Ice Practices

Several previous studies have reported performance decrements in team sport athletes who dehydrated approximately 1.5-2% of their body mass (BM) through sweating. This study measured on-ice sweat loss, fluid intake, sodium balance, and carbohydrate (CHO) intake of 77 major junior (JR; 19 ± 1 years), 60 American Hockey League (AHL; 24 ± 4 years), and 77 National Hockey League (NHL; 27 ± 5 years) players. Sweat loss was calculated from pre- to post-exercise BM plus fluid intake minus urine loss. AHL (2.03 ± 0.62 L/hr) and NHL (2.02 ± 0.74 L/hr) players had higher sweat rates (p < .05) than JR players (1.63 ± 0.58 L/hr). AHL (1.23 ± 0.69%; p = .006) and NHL (1.29% ± 0.63%; p < .001) players had ∼30% greater BM losses than JR players (0.89% ± 0.57%). There was no difference in fluid intake between groups (p > .05). Sodium deficits (sodium loss - intake) were greater (p < .05) in AHL (1.68 ± 0.74 g/hr) and NHL (1.56 ± 0.84 g/hr) players compared with JR players (1.01 ± 0.50 g/hr). CHO intake was similar between groups (14-20 g CHO/hr), with 29%, 32%, and 40% of JR, AHL, and NHL players consuming no CHO, respectively. In summary, sweat rates were high in all players, but the majority of players (74/77, 54/60, and 68/77 of JR, AHL, and NHL, respectively) avoided mild dehydration (>2% BM) during 60 min of practice. However, ∼15%, 41%, and 48% of the JR, AHL, and NHL players, respectively, may have reached mild dehydration and increased risk of performance decrements in a 90-min practice.

European Resuscitation Council Guidelines 2021: First aid

The European Resuscitation Council has produced these first aid guidelines, which are based on the 2020 International Consensus on Cardiopulmonary Resuscitation Science with Treatment Recommendations. The topics include the first aid management of emergency medicine and trauma. For medical emergencies the following content is covered: recovery position, optimal positioning for shock, bronchodilator administration for asthma, recognition of stroke, early aspirin for chest pain, second dose of adrenaline for anaphylaxis, management of hypoglycaemia, oral rehydration solutions for treating exertion-related dehydration, management of heat stroke by cooling, supplemental oxygen in acute stroke, and presyncope. For trauma related emergencies the following topics are covered: control of life-threatening bleeding, management of open chest wounds, cervical spine motion restriction and stabilisation, recognition of concussion, cooling of thermal burns, dental avulsion, compression wrap for closed extremity joint injuries, straightening an angulated fracture, and eye injury from chemical exposure.

Positional Differences in Pre-Season Scrimmage Performance of Division I Collegiate Football Players

This study aimed to describe the physical demands of American football players using novel performance analysis techniques. Heart rate (HR) and accelerometer-based activity levels were observed across two pre-season scrimmages in 23 Division I collegiate football players (age: 19 ± 1 y, height: 1.90 ± 0.06 m, weight: 116.2 ± 19.4 kg). Data were analyzed using a MATLAB program and inter-rater reproducibility assessed using inter-class correlations (ICC). Players were analyzed by side (offense/defense) and position (skill/non-skill). Performance variables assessed in bursts of activity included burst duration, HR_mean and HR_max (bpm), and mean activity (vector magnitude units [vmu]). Exercise intensity was categorized as time spent in % HRmax in 5% increments. The burst duration (8.1±3.9 min, ICC = 0.72), HR_mean (157 ± 12 bpm, ICC = 0.96) and mean activity (0.30 ± 0.05 vmu, ICC = 0.86) were reproducible. HR_mean (p = 0.05) and HR_max (p = 0.001) were greater on defense. Offense spent more time at 65-70% HR_max (p = 0.01), 70-75% HR_max (p = 0.02) while defense spent more time 90-95% HR_max and ≥95% HR_max (p = 0.03). HR_mean (p = 0.70) and HR_peak (p = 0.80) were not different between positions across both sides. Skilled players demonstrated greater mean activity (p = 0.02). The sport-specific analysis described HR and activity level in a reproducible manner. Automated methods of assessing HR may be useful in training and game time performance but ultimately provides support to coaching decision making.

Practices of Athletic Trainers Using Weight Charts to Determine Hydration Status and Fluid-Intervention Strategies

CONTEXT

Determining an athlete's hydration status allows hydration-related concerns to be identified before significant medical or performance concerns arise. Weight charts are an accurate measure of hydration status changes, yet their clinical use by athletic trainers (ATs) is unknown.

OBJECTIVE

To investigate ATs' use of weight charts in athletic settings and describe their subsequent clinical decisions.

DESIGN

Cross-sectional survey.

SETTING

High schools and National Collegiate Athletic Association Divisions I, II, III and National Association Intercollegiate Athletics colleges.

PATIENTS OR OTHER PARTICIPANTS

A total of 354 ATs (men = 162, women = 175; 17 respondents did not answer the demographic questions) responded across athletic settings (Division I [45.7%]; Division II, Division III, National Association Intercollegiate Athletics combined [n = 19.9%]; and high school [34.4%]).

MAIN OUTCOME MEASURE(S)

The 26-question online survey was developed by content experts and pilot tested before data collection. Participants answered questions focused on weight-chart use (implementation, timing, and calculations) and clinical decision processes (policies, interventions, and referral). Frequency statistics were calculated.

RESULTS

The majority of ATs (57.2%) did not use weight charts. Of those who did, most (76.0%) used charts with football, soccer (28%), and wrestling (6%) athletes. They calculated changes as either an absolute (42.2%) or percentage (36.7%) change from prepractice to postpractice; only 11.7% used a baseline weight for calculations. Of those who used the percentage change in body mass, 66.0% selected a threshold of -3% to -4% for an intervention. Most ATs (97.0%) intervened with verbal education, whereas only one-third (37.0%) provided specific fluid amounts based on body mass changes.

CONCLUSIONS

Typically, ATs in athletic settings did not use weight charts. They considered a body mass change of -3% the indication for intervention but did not specify rehydration amounts for hypohydrated athletes. Educational workshops or technology applications could be developed to encourage ATs to use weight charts and calculate appropriate individual fluid interventions for their athletes.

Sustainable solutions to mitigate occupational heat strain - an umbrella review of physiological effects and global health perspectives

BACKGROUND

Climate change is set to exacerbate occupational heat strain, the combined effect of environmental and internal heat stress on the body, threatening human health and wellbeing. Therefore, identifying effective, affordable, feasible and sustainable solutions to mitigate the negative effects on worker health and productivity, is an increasingly urgent need.

OBJECTIVES

To systematically identify and evaluate methods that mitigate occupational heat strain in order to provide scientific-based guidance for practitioners.

METHODS

An umbrella review was conducted in biomedical databases employing the following eligibility criteria: 1) ambient temperatures > 28 °C or hypohydrated participants, 2) healthy adults, 3) reported psychophysiological (thermal comfort, heart rate or core temperature) and/or performance (physical or cognitive) outcomes, 4) written in English, and 5) published before November 6, 2019. A second search for original research articles was performed to identify interventions of relevance but lacking systematic reviews. All identified interventions were independently evaluated by all co-authors on four point scales for effectiveness, cost, feasibility and environmental impact.

RESULTS

Following screening, 36 systematic reviews fulfilled the inclusion criteria. The most effective solutions at mitigating occupational heat strain were wearing specialized cooling garments, (physiological) heat acclimation, improving aerobic fitness, cold water immersion, and applying ventilation. Although air-conditioning and cooling garments in ideal settings provide best scores for effectiveness, the limited applicability in certain industrial settings, high economic cost and high environmental impact are drawbacks for these solutions. However, (physiological) acclimatization, planned breaks, shading and optimized clothing properties are attractive alternative solutions when economic and ecological sustainability aspects are included in the overall evaluation.

DISCUSSION

Choosing the most effective solution or combinations of methods to mitigate occupational heat strain will be scenario-specific. However, this paper provides a framework for integrating effectiveness, cost, feasibility (indoors and outdoor) and ecologic sustainability to provide occupational health and safety professionals with evidence-based guidelines.

Gender-Based Vegetarian and Nonvegetarian Dietary Impact on Cardiac Autonomic Function of Heart Rate Variability

Objective: Cardiovascular disease is one among the major mortality threats throughout the world. Autonomic activity of the nervous system can be examined by heart rate variability (HRV) analysis. Association of sympathetic and parasympathetic activities is directly related to HRV modulation. The aim of the study is to determine variations in HRV parameters among adult/adolescent male and female subjects due to vegetarian and nonvegetarian diet.Method: Ninety undergraduate students in each male and female group (N = 180) volunteered for the study. Based upon food habits, male and female subjects were categorized into four groups. Short-term (5-minute) heart rate recordings were measured from the subjects in a seated position before breakfast with minimum of 12 hours' fasting. Two-way analysis of variance was performed among the time and frequency domain variables.Results: Time domain variables are observed as significant (p < 0.05) between vegetarian males and females and also (p < 0.05) between male vegetarian and female nonvegetarians for standard deviation of NN intervals. Frequency domain HRV indices such as low frequency (LF; p = 0.01), high frequency (HF; p = 0.0001), and LF/HF (p < 0.001) resulted between male and female vegetarians. Significance of LF (p = 0.02), HF (p < 0.0001), and LF/HF (p < 0.01) was measured between male vegetarians and female nonvegetarians. LF (p = 0.02), HF (p = 0.04), and LF/HF (p = 0.002) resulted between nonvegetarian males and females. HF (p = 0.05) was enumerated between male vegetarians and nonvegetarians.Conclusions: Significant predominance of sympathetic cardiac activity was observed among male nonvegetarian consumers more than female vegetarians. Analysis demonstrates that the gender-based influence of vegetarian and nonvegetarian diet has significant correlation under HRV measurements.

Novel Acclimatization and Acclimation Strategies for Hot Climates

Exercising in hot, humid temperatures increases the risk for heat-related illnesses, ranging from mild heat edema to severe heat stroke. With increasing globalization in the world of sports, athletes are sometimes expected to compete in unforgiving conditions that expose them to these risks. In an effort to improve exercise capacity and reduce the risk of serious heat injury, many athletes are recommended to undergo heat acclimatization program prior to competing in climates with elevated average temperature. This article will look at current recommendations as well as studies on differing techniques for acclimatization and acclimation, with hopes to provide guidance for the modern-day clinician and athletes.

Autonomic adaptations mediate the effect of hydration on brain functioning and mood: Evidence from two randomized controlled trials

Dehydration (water loss >2.0% of body weight) has significant negative effects on physical and mental performance. In two studies the effects of minor hypo-hydration (water loss <1.0% of body weight) on CNS function, mood and cardiovascular functioning were measured. Study 1: On two mornings twelve male participants were exposed to a temperature of 30 °C for four hours and either did or did not drink two 150 ml glasses of water during that time. Study 2: Fifty-six (25 M) individuals were exposed to the same 30 °C environment and randomly allocated to either drink (2 × 150 ml) or not drink. When not given water 0.59% (Study 1) and 0.55% (Study 2) bodyweight was lost. Participant’s heart rate variability (HRV) was measured, and they rated their thirst and mood. In study 1, participants participated in an fMRI protocol during which they completed a modified version of the Paced Auditory Serial Addition Test (PASAT), at the end of which they rated its difficulty. Decreases in fMRI BOLD activity in the orbito-frontal cortex, ventral cingulate gyrus, dorsal cingulate cortex, hypothalamus, amygdala, right striatum, post-central gyrus and superior parietal cortex were observed when participants were hypo-hydrated. These deactivations were associated with reduced HRV, greater perceived effort, and more anxiety. In study 2 declines in HRV were found to mediate the effect of hypo-hydration on ratings of anxiety. These data are discussed in relation to a model that describes how autonomic regulatory and interoceptive processes may contribute to the affective consequences of minor hypo-hydration.

Hydration Status and Cardiovascular Function

Hypohydration, defined as a state of low body water, increases thirst sensations, arginine vasopressin release, and elicits renin–angiotensin–aldosterone system activation to replenish intra- and extra-cellular fluid stores. Hypohydration impairs mental and physical performance, but new evidence suggests hypohydration may also have deleterious effects on cardiovascular health. This is alarming because cardiovascular disease is the leading cause of death in the United States. Observational studies have linked habitual low water intake with increased future risk for adverse cardiovascular events. While it is currently unclear how chronic reductions in water intake may predispose individuals to greater future risk for adverse cardiovascular events, there is evidence that acute hypohydration impairs vascular function and blood pressure (BP) regulation. Specifically, acute hypohydration may reduce endothelial function, increase sympathetic nervous system activity, and worsen orthostatic tolerance. Therefore, the purpose of this review is to present the currently available evidence linking acute hypohydration with altered vascular function and BP regulation.

Practical Hydration Solutions for Sports

Personalized hydration strategies play a key role in optimizing the performance and safety of athletes during sporting activities. Clinicians should be aware of the many physiological, behavioral, logistical and psychological issues that determine both the athlete’s fluid needs during sport and his/her opportunity to address them; these are often specific to the environment, the event and the individual athlete. In this paper we address the major considerations for assessing hydration status in athletes and practical solutions to overcome obstacles of a given sport. Based on these solutions, practitioners can better advise athletes to develop practices that optimize hydration for their sports.

Heart-rate variability: a biomarker to study the influence of nutrition on physiological and psychological health?

As the influence of diet on health may take place over a period of decades, there is a need for biomarkers that help to identify those aspects of nutrition that have either a positive or a negative influence. The evidence is considered that heart-rate variability (HRV) (the time differences between one beat and the next) can be used to indicate the potential health benefits of food items. Reduced HRV is associated with the development of numerous conditions for example, diabetes, cardiovascular disease, inflammation, obesity and psychiatric disorders. Although more systematic research is required, various aspects of diet have been shown to benefit HRV acutely and in the longer term. Examples include a Mediterranean diet, omega-3 fatty acids, B-vitamins, probiotics, polyphenols and weight loss. Aspects of diet that are viewed as undesirable, for example high intakes of saturated or trans-fat and high glycaemic carbohydrates, have been found to reduce HRV. It is argued that the consistent relationship between HRV, health and morbidity supports the view that HRV has the potential to become a widely used biomarker when considering the influence of diet on mental and physical health.

Factors influencing hydration status during a National Collegiate Athletics Association division 1 soccer preseason

OBJECTIVES

To investigate the roles that training load and environmental conditions have on fluid balance during a collegiate men's soccer preseason.

DESIGN

Observational study.

METHODS

Twenty-eight male collegiate soccer players (mean±SD; age, 20±1.7y; body mass (BM), 79.9±7.3kg; height, 180.9±6.8cm; body fat, 12.7±3.1%; VO_2max, 50.7±4.3ml·kg^-1·min^-1) participated in this study. Prior to (PRE) and following (POST) each team session, BM, percent BM loss (%BML) and hydration status was measured. Participants donned a heart rate and GPS enabled monitor to measure training load. For all team activities, ambient temperature (T_AMB) and relative humidity (RH) were obtained from the nearest local weather station. Participants consumed 500mL of water as part of the team-based hydration strategy before and after training session. Stepwise linear regression was used to identify the variables that predicted %BML. Significance was set a-priori p<0.05.

RESULTS

Total distance covered predicted %BML during all preseason activities (r²=0.253, p<0.001), with T_AMB and RH further adding to the model (r²=0.302, p<0.001). %BML never exceeded 2% of BM during any one session and daily variation in BM was <1% from baseline measures. Urine specific gravity was greater than 1.020 on 12/15days and U_COL was above 4 on 13/15days, indicating a state of hypohydration.

CONCLUSIONS

Total distance covered was the best predictor for the extent of body water losses during a collegiate preseason. While the team-based hydration strategy during preseason was successful in minimizing fluid losses during activity, participants arrived hypohydrated 80% of the time, necessitating a greater focus on daily fluid needs.

Exploring how a traditional diluted yoghurt drink may mitigate heat strain during medium-intensity intermittent work: a multidisciplinary study of occupational heat strain

It is common practice in India to consume the dairy drink buttermilk as a way of mitigating occupational heat strain. This paper explores the thermoregulatory and hydration benefits of drinking buttermilk but also the impacts of work in a hot environment on the gut microbiota, renal and cognitive function. Twelve healthy participants were subjected to a 3-h period of medium load physical intermittent work in a climatic chamber (34°C, 60% RH). The subjects were given water, buttermilk (700 ml) or no rehydration at random. Mean body temperatures when no rehydration was given were significantly higher (p≤0.001). When subjects drank water or buttermilk they had a lower sweat rate than with no rehydration (p≤0.05) and the perception of feeling hot, uncomfortable, thirsty and physically exerted was significantly reduced (p≤0.05). A hormonal stress response at the end of the exposure was seen when not drinking (p≤0.05). No differences in cognitive abilities and gut microbiota were found. The exposure lowered the renal blood flow suggesting an acute impact of short term heat exposure. It was also found that buttermilk has a protective effect on this impact. Our results demonstrated that keeping hydrated by water/buttermilk consumption mitigates heat strain in well-nourished subjects.

National Athletic Trainers' Association Position Statement: Fluid Replacement for the Physically Active

OBJECTIVE

  To present evidence-based recommendations that promote optimized fluid-maintenance practices for physically active individuals.

BACKGROUND

  Both a lack of adequate fluid replacement (hypohydration) and excessive intake (hyperhydration) can compromise athletic performance and increase health risks. Athletes need access to water to prevent hypohydration during physical activity but must be aware of the risks of overdrinking and hyponatremia. Drinking behavior can be modified by education, accessibility, experience, and palatability. This statement updates practical recommendations regarding fluid-replacement strategies for physically active individuals.

RECOMMENDATIONS

  Educate physically active people regarding the benefits of fluid replacement to promote performance and safety and the potential risks of both hypohydration and hyperhydration on health and physical performance. Quantify sweat rates for physically active individuals during exercise in various environments. Work with individuals to develop fluid-replacement practices that promote sufficient but not excessive hydration before, during, and after physical activity.

Heat Exposure and Hypohydration Exacerbate Physiological Strain During Load Carrying

Adams, EL, Casa, DJ, Huggins, RA, DeMartini-Nolan, JK, Stearns, RL, Kennedy, RM, Bosworth, MM, DiStefano, LJ, Armstrong, LE, and Maresh, CM. Heat exposure and hypohydration exacerbate physiological strain during load carrying. J Strength Cond Res 33(3): 727-735, 2019-Heat exposure and hypohydration induce physiological and psychological strain during exercise; however, it is unknown if the separate effects of heat exposure and hypohydration are synergistic when co-occurring during loaded exercise. This study compared separate and combined effects of heat exposure and hypohydration on physiological strain, mood state, and visual vigilance during loaded exercise. Twelve men (mean ± SD; age, 20 ± 2 years; body mass, 74.0 ± 8.2 kg; maximal oxygen uptake, 57.0 ± 6.0 ml·kg·min) completed 4 trials under the following conditions: euhydrated temperate (EUT), hypohydrated temperate (HYT), euhydrated hot (EUH), and hypohydrated hot (HYH). Exercise was 90 minutes of treadmill walking (∼50% V[Combining Dot Above]O2max, 5% grade) while carrying a 45-lb rucksack. Profile of Mood States and the Scanning Visual Vigilance Test were completed before and after exercise. The separate effects of heat exposure (EUH) and hypohydration (HYT) on post-exercise rectal temperature (Tre) were similar (38.25 ± 0.63°C vs. 38.22 ± 0.29°C, respectively, p > 0.05), whereas in combination (HYH), post-exercise Tre was far greater (39.32 ± 0.43°C). Increase in Tre per 1% body mass loss (BML) for HYH (vs. EUH) was greater than HYT (vs. EUT) (0.32 vs. 0.04°C, respectively, p = 0.02); heart rate increase per 1% BML for HYH (vs. EUH) was 7 b·min compared with HYT (vs. EUT) at 3 b·min (p = 0.30). Hypohydrated hot induced greater mood disturbance (post-exercise - pre-exercise) (35 ± 21 units) compared with other conditions (EUT = 3 ± 9 units; HYT = 3 ± 16 units; EUH = 16 ± 26 units; p < 0.001). No differences occurred in visual vigilance (p > 0.05). Independently, heat exposure and hypohydration induced similar physiological strain during loaded exercise; when combined, heat exposure with hypohydration, synergistically exacerbated physiological strain and mood disturbance.

Deviation from goal pace, body temperature and body mass loss as predictors of road race performance

OBJECTIVES

The purpose of this study was to examine the relationship between pacing, gastrointestinal temperature (T_GI), and percent body mass loss (%BML) on relative race performance during a warm weather 11.3km road race.

DESIGN

Observational study of a sample of active runners competing in the 2014 Falmouth Road Race.

METHODS

Participants ingested a T_GI pill and donned a GPS enabled watch with heart rate monitoring capabilities prior to the start of the race. Percent off predicted pace (%_OFF) was calculated for seven segments of the race. Separate linear regression analyses were used to assess the relationship between pace, T_​GI, and %BML on relative race performance. One-way ANOVA was used to analyse post race T_GI (≥40°C vs <40°C) on pace and %_OFF.

RESULTS

Larger %BML was associated with faster finish times (R²=0.19, p=0.018), faster average pace (R²=0.29, p=0.012), and a greater %_OFF (R²=0.15, p=0.033). %_OFF during the first mile (1.61km) significantly predicted overall finish time (R²=0.64, p<0.001) while %_OFF during the second mile (3.22km) (R² change=0.18, p<0.001) further added to the model (R²=0.82, p<0.001). Body temperature (pre race T_GI and post race T_GI) was not predictive of overall finish time (p>0.05). There was a trend in a slower pace (p=0.055) and greater %_OFF (p=0.056) in runners finishing the race with a T_GI>40°C.

CONCLUSIONS

Overall, finish time was influenced by greater variations in pace during the first two miles of the race. In addition, runners who minimized fluid losses and had lower T_GI were associated with meeting self-predicted goals.

National Athletic Trainers' Association Position Statement: Exertional Heat Illnesses

OBJECTIVE

To present best-practice recommendations for the prevention, recognition, and treatment of exertional heat illnesses (EHIs) and to describe the relevant physiology of thermoregulation.

BACKGROUND

Certified athletic trainers recognize and treat athletes with EHIs, often in high-risk environments. Although the proper recognition and successful treatment strategies are well documented, EHIs continue to plague athletes, and exertional heat stroke remains one of the leading causes of sudden death during sport. The recommendations presented in this document provide athletic trainers and allied health providers with an integrated scientific and clinically applicable approach to the prevention, recognition, treatment of, and return-to-activity guidelines for EHIs. These recommendations are given so that proper recognition and treatment can be accomplished in order to maximize the safety and performance of athletes.

RECOMMENDATIONS

Athletic trainers and other allied health care professionals should use these recommendations to establish onsite emergency action plans for their venues and athletes. The primary goal of athlete safety is addressed through the appropriate prevention strategies, proper recognition tactics, and effective treatment plans for EHIs. Athletic trainers and other allied health care professionals must be properly educated and prepared to respond in an expedient manner to alleviate symptoms and minimize the morbidity and mortality associated with these illnesses.

Reduction in body temperature using hand cooling versus passive rest after exercise in the heat

OBJECTIVES

To examine the effects of hydration and hand cooling on lowering body temperature after exercise in the heat.

DESIGN

Randomized cross-over design.

METHODS

Nine recreationally active male participants (mean±SD; age, 24±4; height, 177.3±9.9cm; body mass, 76.7±11.6kg; body fat, 14.7±5.8%) completed a bout of treadmill exercise in a hot environment. After completion of exercise, participants were assigned to the following trials for post-exercise cooling: (1) hydrated with passive rest (HY), (2) hydrated with hand cooling on both hands (HY+2HC), (3) dehydrated with passive rest (DY), and (4) dehydrated with hand cooling on both hands (DY+2HC). Within subject differences were assessed using a three-way (Hydration×Condition×Time) repeated measures ANOVA with Tukey's post hoc analysis if significant interactions were found.

RESULTS

Irrespective of hydration status, hand cooling on both hands resulted in significantly greater reductions in T_REC than passive cooling at minute 20 (0.27°C [0.05, 0.49], ES=2.08, p=0.017) (Fig. 1). The reduction in T_REC at minute 18 trended towards statistical significance (0.21°C [.003, .42], ES=1.59, p=0.053). Hydration status alone and when differentiated among modes of cooling showed no differences on changes of T_REC or heart rate across all conditions during post exercise recovery (p>0.05).

CONCLUSIONS

Hand cooling on both hands reduced T_REC more than passive cooling, however, the cooling rates observed render hand cooling a poor option for cooling. Greater reductions in T_REC after exercise or between bouts of exercise may enhance recovery and subsequent performance.

National Athletic Trainers' Association Position Statement: Exertional Heat Illnesses

OBJECTIVE

To present best-practice recommendations for the prevention, recognition, and treatment of exertional heat illnesses (EHIs) and to describe the relevant physiology of thermoregulation.

BACKGROUND

Certified athletic trainers recognize and treat athletes with EHIs, often in high-risk environments. Although the proper recognition and successful treatment strategies are well documented, EHIs continue to plague athletes, and exertional heat stroke remains one of the leading causes of sudden death during sport. The recommendations presented in this document provide athletic trainers and allied health providers with an integrated scientific and clinically applicable approach to the prevention, recognition, treatment of, and return-to-activity guidelines for EHIs. These recommendations are given so that proper recognition and treatment can be accomplished in order to maximize the safety and performance of athletes.

RECOMMENDATIONS

Athletic trainers and other allied health care professionals should use these recommendations to establish onsite emergency action plans for their venues and athletes. The primary goal of athlete safety is addressed through the appropriate prevention strategies, proper recognition tactics, and effective treatment plans for EHIs. Athletic trainers and other allied health care professionals must be properly educated and prepared to respond in an expedient manner to alleviate symptoms and minimize the morbidity and mortality associated with these illnesses.

The influence of hydration status during prolonged endurance exercise on salivary antimicrobial proteins

PURPOSE

Antimicrobial proteins (AMPs) in saliva including secretory immunoglobulin A (SIgA), lactoferrin (SLac) and lysozyme (SLys) are important in host defence against oral and respiratory infections. This study investigated the effects of hydration status on saliva AMP responses to endurance exercise.

METHODS

Using a randomized design, 10 healthy male participants (age 23 ± 4 years, [Formula: see text] 56.8 ± 6.5 ml/kg/min) completed 2 h cycling at 60 % [Formula: see text] in states of euhydration (EH) or dehydration (DH) induced by 24 h fluid restriction. Unstimulated saliva samples were collected before, during, immediately post-exercise and each hour for 3 h recovery.

RESULTS

Fluid restriction resulted in a 1.5 ± 0.5 % loss of body mass from baseline and a 4.3 ± 0.7 % loss immediately post-exercise. Pre-exercise urine osmolality was higher in DH than EH and overall, saliva flow rate was reduced in DH compared with EH (p < 0.05). Baseline SIgA secretion rates were not different between conditions; however, exercise induced a significant increase in SIgA concentration in DH (161 ± 134 to 309 ± 271 mg/L) which remained elevated throughout 3 h recovery. SLac secretion rates increased from pre- to post-exercise in both conditions which remained elevated in DH only. Overall, SLac concentrations were higher in DH than EH. Pre-exercise SLys concentrations were lower in DH compared with EH (1.6 ± 2.0 vs. 5.5 ± 6.7 mg/L). Post-exercise SLys concentrations remained elevated in DH but returned to pre-exercise levels by 1 h post-exercise in EH.

CONCLUSIONS

Exercise in DH caused a reduction in saliva flow rate yet induced greater secretion rates of SLac and higher concentrations of SIgA and SLys. Thus, DH does not impair saliva AMP responses to endurance exercise.