Fluid Balance in Team Sport Athletes and the Effect of Hypohydration on Cognitive, Technical, and Physical Performance

The Effect of Fluid Restriction and Intake Conditions on the Shooting Performance of Competitive Adolescent Handball Players

(1) Background: This study aimed to investigate the effects of fluid restriction and intake (water vs. sports drink) on shooting accuracy and speed in adolescent handball players, a population with high sensitivity to hydration levels yet understudied in this context. (2) Methods: A total of 47 adolescent competitive handball players (15.04 ± 1.5 years) were included in this study, and the participants were divided into low, average, and high performance according to their shooting performance in the familiarization session. All participants were exposed to fluid restriction and intake conditions during handball training on different days. Before and after the training sessions, changes in shooting accuracy and speed were evaluated. (3) Results: The training protocol resulted in body mass loss in the Average Performer group (p = 0.001). Compared to fluid restriction, fluid intake (water intake and sports drink intake) post-training had a positive main effect on shooting accuracy, F(2, 88) = 34.32, p < 0.001, ηp2 = 0.44, and shooting speed, F(1, 61) = 4.05, p = 0.35, ηp2 = 0.84. (4) Conclusions: Hydration level plays an important role in shooting accuracy and speed performance in adolescent handball players. Therefore, fluid intake integrated into training or match sessions may contribute to the maintenance and improvement of shooting performance.

Prospective heat stress risk assessment for professional soccer players in the context of the 2026 FIFA World Cup

This study investigates the risk of severe heat stress and associated potential water losses in professional soccer players, considering as well the oxygen content of the inhaled air in the context of the 2026 FIFA World Cup. For the 16 stadiums, hourly values of biometeorological indices (adjusted Universal Thermal Climate Index - UTCI, Water loss - SW and Oxygen volume - Ov) were calculated. UTCI adjustments included modifications to activity levels, movement speeds and clothing configurations to better reflect the level of thermal stress on soccer player during a match. Ten out of the sixteen sites of the 2026 FIFA World Cup are at very high risk of experiencing extreme heat stress conditions. The highest risk of uncompensable thermal stress due to very high average hourly UTCI values above 49.5 °C and excessive water loss (> 1.5 kg/h) occur in the afternoon in stadiums located in Arlington, Houston (USA) and in Monterrey (Mexico). The results of this study will enable optimization of match schedules at individual venues, taking into account the health risks associated with extreme heat stress, but also the physiological reactions to heat potentially affecting the performance of players on the pitch.

Bioimpedance Vector Analysis-Derived Body Composition Influences Strength and Power in Alpine Skiers

Purpose: Alpine ski racing is a complex sport where no single factor can exclusively account for performance. We assessed body composition, using bioelectrical impedance vector analysis (BIVA), and our purpose was to study its influence on the strength and power profile of young alpine skiers. Methods: Anthropometric measurements and advanced BIVA parameters were recorded on eighteen alpine ski racers (6 females/12 males; 17.0 ± 1.3 years; 172.2 ± 9.3 cm; 68.5 ± 9.8 kg). Dynamic force and power were assessed using countermovement jumps (CMJ), while maximal isometric strength was evaluated for hip flexion-extension and abduction-adduction movements. Stepwise regression models examined the relationship between BIVA-derived parameters and strength/power variables. Results: Body cellular mass (BCM) positively related to jump height (p = .021, R2 = 74%), jump momentum (p < .001, R2 = 89%), reactive strength index modified (p = .026, R2 = 75%) and peak concentric power (p < .001, R2 = 82%), while intracellular water (ICW) related to peak eccentric (p < .001, R2 = 76%) and concentric force (p < .001, R2 = 77%) as well as to concentric rate of force development together with the phase angle (PhA) (p = .008, R2 = 79% and R2 = 0.015). Regarding isometric assessment, ICW was a significant predictor for all four movement directions, and PhA contributed to hip adduction strength. Conclusions: Body composition, particularly BCM and ICW, significantly predict force- and power-related factors in young alpine skiers.

Randomized Trial to Assess the Safety and Tolerability of Daily Intake of an Allulose Amino Acid-Based Hydration Beverage in Men and Women

BACKGROUND

Maintaining adequate hydration is critical to optimal health, well-being, and performance. Those who are physically active in stressful environments, such as warm and/or humid scenarios, may be at particular risk for dehydration with ensuing loss of electrolytes, leading to sluggishness and impaired physical performance.

METHODS

We evaluated an electrolyte and amino acid product containing L-alanine and L-glutamine, as well as select vitamins [B3 (niacin), B5 (pantothenic acid), B6 (pyridoxine), B12 (cobalamin), and vitamin C (ascorbic acid)]. Subjects (n = 40; four groups, n = 10) were randomized to consume either a placebo packet or one, two, or three packets daily of the test product for 4 weeks with site visits at 0, 2, and 4 weeks. We tested safety and tolerability by analyzing hematological parameters (complete blood counts), metabolic parameters (hepatic, renal, acid-base balance), urinalysis end products, thyroid status [T3 (triiodothyronine), T4 (thyroxine), TSH (thyroid-stimulating hormone)], tolerability (via questionnaire), vital signs, and dietary intake.

RESULTS

Statistical analyses displayed ten significant main effects (p < 0.05) with white blood cells, lymphocytes, neutrophils, urinary pH, thyroxine, urination frequency, calcium, calories, fat, and cholesterol. Interactions for time and group (p < 0.05) were observed for MCV, eGFR, potassium, overall tolerability, bloating, and cramping-demonstrating mild GA disturbances. Little to no change of physiological relevance was noted for any outcome variable, regardless of dosing level.

CONCLUSIONS

Our results indicate the product was well-tolerated at all dosing levels and no significant adverse changes occurred in any of the test parameters compared to the placebo group, indicating relative safety of ingestion over a 4-week treatment period, at the volumes used, and outside the context of physical stress.

The Effects of Acute Deep Seawater Supplementation on Muscle Function after Triathlon

(1) Background: Trainers and athletes have always sought to reduce the failure of muscle function during long endurance events. However, nowadays, it is a topic that is generating much debate in the scientific field. Currently, deep-sea water (DSW) intake seems to be a suitable hydration alternative for this type of endurance event. Therefore, the aim of this study was to determine whether DSW consumption during a triathlon event could preserve muscle function after exercise. (2) Methods: Nineteen trained male triathletes (age = 39.0 ± 4.25 years; BMI = 23.67 ± 1.81 kg/m2) randomly performed three triathlons, one of them consuming DSW (Totum SPORT 30 AB, Laboratories Quinton International, S.L., Spain), the other consuming isotonic placebo and the last with tap water-hydration. A vertical jump test with countermovement and an isometric muscle strength test were conducted before and after the triathlon test. (3) Results: There was a significant difference between treatment × time during the isometric muscle strength test. Based on the Tukey post hoc analysis, the peak net force decreased statistically in the placebo (p = 0.045) and control conditions (p = 0.026), but not in the experimental condition (p = 0.121). In addition, all of the conditions studied obtained similar results in the countermovement vertical jump after exercise. (4) Conclusions: As a result, consumption of DSW seems to delay the failure of muscle function specifically in isometric exercises but does not improve performance in sports. Thus, DSW does not alter muscle capacity in a negative way; therefore, its consumption may be recommended.

Sweat Characteristics and Fluid Balance Responses During Two Heat Training Camps in Elite Female Field Hockey Players

We examined the sweat characteristics and fluid balance of elite female field hockey players during two heat training camps. Fourteen elite female field hockey players from the Australian national squad participated in two heat training camps held ∼6 months apart, following winter- (Camp 1) and summer-based training (Camp 2). Daily waking body mass (BM) and urine specific gravity (USG) were collected, along with several markers of sweat and fluid balance across two matches per camp. There was a 19% mean reduction in estimated whole-body sweat sodium concentration from Camp 1 (45.8 ± 6.5 mmol/L) to Camp 2 (37.0 ± 5.0 mmol/L; p < .001). Waking urine specific gravity ≥ 1.020 was observed in 31% of samples, with no significant differences in mean urine specific gravity or BM between camps (p > .05), but with substantial interindividual variation. Intramatch sweat rates were high (1.2-1.8 L/hr), with greater BM losses in Camp 1 (p = .030), resulting in fewer players losing ≥2% BM in Camp 2 (0%-8%), as compared with Camp 1 (36%-43%; p = .017). Our field data suggest that elite female field hockey players experience substantial sweat losses during competition in the heat regardless of the season. In agreement with previous findings, we observed substantial interindividual variation in sweat and hydration indices, supporting the use of individualized athlete hydration strategies.

A Comparison of Normalization Techniques for Individual Baseline-Free Estimation of Absolute Hypovolemic Status Using a Porcine Model

Hypovolemic shock is one of the leading causes of death in the military. The current methods of assessing hypovolemia in field settings rely on a clinician assessment of vital signs, which is an unreliable assessment of hypovolemia severity. These methods often detect hypovolemia when interventional methods are ineffective. Therefore, there is a need to develop real-time sensing methods for the early detection of hypovolemia. Previously, our group developed a random-forest model that successfully estimated absolute blood-volume status (ABVS) from noninvasive wearable sensor data for a porcine model (n = 6). However, this model required normalizing ABVS data using individual baseline data, which may not be present in crisis situations where a wearable sensor might be placed on a patient by the attending clinician. We address this barrier by examining seven individual baseline-free normalization techniques. Using a feature-specific global mean from the ABVS and an external dataset for normalization demonstrated similar performance metrics compared to no normalization (normalization: R2 = 0.82 ± 0.025|0.80 ± 0.032, AUC = 0.86 ± 5.5 × 10-3|0.86 ± 0.013, RMSE = 28.30 ± 0.63%|27.68 ± 0.80%; no normalization: R2 = 0.81 ± 0.045, AUC = 0.86 ± 8.9 × 10-3, RMSE = 28.89 ± 0.84%). This demonstrates that normalization may not be required and develops a foundation for individual baseline-free ABVS prediction.

Fluid and water balance: a scoping review for the Nordic Nutrition Recommendations 2023

Water, being an essential nutrient, is crucial for all life. Adequate maintenance of body water compartments is required for optimal fluid balance, which is a prerequisite for cellular homeostasis and blood pressure regulation. Water balance is the result of dietary intake of both fluids and foods as well as metabolically produced water, excretion from the kidneys and losses from other sources (e.g. sweat and feces). The water content in food items varies considerably and ranges from about 5% in nuts to 90% in many fruits and vegetables. Intake of drinking water and beverages also provides varying amounts of water. In everyday life assessment of water balance (i.e. hydration status) is challenging as clinical observations are inaccurate. There is no data regarding drinking water intake in the Nordic or Baltic countries.

Accuracy of a smart bottle in measuring fluid intake by American football players during pre-season training

Rehydration is important for athlete performance and recovery. However, it can be challenging to follow appropriate fluid replacement practices due in part to difficulties in tracking fluid intake in real time. The purpose of this study was to determine the accuracy of a smart bottle in measuring fluid intake during exercise. Thirty male American football athletes drank from bottles equipped with a smart cap during outdoor pre-season practices (110 ± 30 min; 29.3 ± 3.0 °C; 75 ± 11% rh). The cap technology included optical sensors, microprocessors, batteries, and wireless connectivity that transmitted fluid volume data to a smartphone application in real-time. Reference measurements of fluid intake from the smart bottle were determined by gravimetry followed by conversion to volume using the density of the fluid consumed. There was no significant mean difference in fluid intake between the smart bottle and reference method (1220 ± 371 ml vs. 1236 ± 389 ml, p = 0.39 paired t test). Bland-Altman 95% limits of agreement between methods was - 212 to 180 ml. The smart bottle provided accurate measurements of fluid intake during exercise in real-world field conditions on a group level and within limits of agreement of - 212 to 180 ml (or approximately ± 15% of overall fluid intake) on an individual level.

Athletes with different habitual fluid intakes differ in hydration status but not in body water compartments

Physiological differences have been reported between individuals who have habitual low (LOW) and high (HIGH) water intake (WI). The aims of this study were to explore body water compartments, hydration status, and fat-free mass (FFM) hydration of elite athletes exposed to different habitual WI. A total of 68 athletes (20.6 ± 5.3 years, 23 females) participated in this observational cross-sectional study. Total WI was assessed by seven-day food diaries and through WI, athletes were categorized as HIGH (n = 28, WI≥40.0 mL/kg/d) and LOW (n = 40, WI≤35.0 mL/kg/d). Total body water (TBW) and extracellular water (ECW) were determined by dilution techniques and intracellular water (ICW) as TBW-ECW. Hydration status was assessed by urine-specific gravity (USG) using a refractometer. Fat (FM) and FFM were assessed by dual-energy X-ray absorptiometry (DXA). The FFM hydration was calculated by TBW/FFM. The USG was statistically different between groups for females (LOW: 1.024 ± 0.003; HIGH: 1.015 ± 0.006; p = 0.005) and males (LOW: 1.024 ± 0.002; HIGH: 1.018 ± 0.005; p < 0.001). No differences between groups were detected in body water compartments and FFM hydration in both sexes (p > 0.05). Multiple regression showed that WI remains a predictor of USG regardless of FFM, age, and sex (β = -0.0004, p < 0.01). We concluded that LOW athletes were classified as dehydrated through USG although their water compartments were not different from HIGH athletes. These results suggest that LOW athletes may expectedly maintain the body water compartments' homeostasis through endocrine mechanisms. Interventions should be taken to encourage athletes to have sufficient WI to maintain optimal hydration.

Young Artistic Gymnasts Drink Ad Libitum Only Half of Their Fluid Lost during Training, but More Fluid Intake Does Not Influence Performance

To examine the effect of the fluid balance on and performance in young artistic gymnasts during training under ad libitum and prescribed fluid intake conditions, eleven males (12.3 ± 2.6 years, mean ± SD) performed two 3 h identical training sessions. Participants ingested, in a random order, water equivalent to either 50% (LV) or 150% (HV) of their fluid loss. After the 3 h training, the gymnasts performed program routines on three apparatuses. The pre-exercise urine specific gravity (USG) was similar between conditions (LV: 1.018 ± 0.007 vs. HV: 1.015 ± 0.007; p = 0.09), while the post-exercise USG was lower in the HV condition (LV: 1.017 ± 0.006 vs. HV: 1.002 ± 0.003; p < 0.001). Fluid loss corresponding to percentage of body mass was higher in the LV condition (1.2 ± 0.5%) compared to the HV condition (0.4 ± 0.8%) (p = 0.02); however, the sums of the score performances were not different (LV: 26.17 ± 2.04 vs. HV: 26.05 ± 2.00; p = 0.57). Ingesting fluid equivalent to about 50% of the fluid lost, which was the amount that was drunk ad libitum during training, maintained short-term hydration levels and avoided excessive dehydration in artistic preadolescent and adolescent gymnasts. A higher amount of fluid, equivalent to about 1.5 times the fluid loss, did not provide an additional performance benefit.

Exercise-induced hypohydration impairs 3 km treadmill-running performance in temperate conditions

Research assessing exercise-induced hypohydration on running performance in a temperate environment is scarce. Given the weight-bearing nature of running, the negative effects of hypohydration might be offset by the weight-loss associated with a negative fluid balance. Therefore, this study investigated the effect of exercise-induced hypohydration on running performance in temperate conditions. Seventeen intermittent games players (age 22 ± 1 y; VO2peak 52.5 ± 4.1 mL∙kg-1∙min-1) completed preliminary and familiarisation trials, and two experimental trials consisting of 12 blocks of 6 min of running (65% VO2peak; preload) with 1 min passive rest in-between, followed by a 3 km time trial (TT). During the preload, subjects consumed minimal fluid (60 mL) to induce hypohydration (HYP) or water to replace 95% sweat losses (1622 ± 343 mL; EUH). Body mass loss (EUH -0.5 ± 0.3%; HYP -2.2 ± 0.4%; P < 0.001), and other changes indicative of hypohydration, including increased serum osmolality, heart rate, thirst sensation, and decreased plasma volume (P ≤ 0.022), were apparent in HYP by the end of the preload. TT performance was ~6% slower in HYP (EUH 900 ± 87 s; HYP 955 ± 110 s; P < 0.001). Exercise-induced hypohydration of ~2% body mass impaired 3 km running TT performance in a temperate environment.

Ad-libitum fluid intake was insufficient to achieve euhydration 20 h after intermittent running in male team sports athletes

This study documented 20 h rehydration from intermittent running while concealing the primary outcome of rehydration from subjects. Twenty-eight male team sports athletes (age 25 ± 3 y; predicted V̇O_2max 54 ± 3 mL∙kg^-1∙min^-1) were pair-matched to exercise (EX) or rest (REST) groups. To determine hydration status, body mass, urine and blood samples were collected at 08:00, pre-intervention (09:30), post-intervention (12:00), 3 h post-intervention and 08:00 the following morning (20 h). The intervention was 110 min intermittent running (EX) or seated rest (REST), with ad-libitum fluid provided in both. Subjects completed a weighed diet record and collected all urine for the 24 h. Changes typical of hypohydration were apparent in EX following the intervention period (body mass: EX -2.0 ± 0.5%; REST -0.2 ± 0.3%; serum osmolality: EX 293 ± 4 mOsm∙kgH₂O^-1; REST 287 ± 6 mOsm∙kgH₂O^-1; P≤0.022). Fluid intake during the intervention period (EX 704 ± 286 mL, REST 343 ± 230 mL) and fluid intake within the first 3 h post-intervention (EX 1081 ± 460 mL, REST 662 ± 230 mL) were greater (P≤0.004), and 24 h urine volume lower (EX 1697 ± 824 mL, REST 2370 ± 842 mL; P=0.039) in EX. Compared to baseline, body mass remained lower (-0.6 ± 0.5%; P=0.030) and urine osmolality elevated (20 h: 844 ± 197 mOsm∙kgH₂O^-1, 08:00: 698 ± 200 mOsm∙kgH₂O^-1; P=0.004) at 20 h in EX. When games players drank fluid ad-libitum during exercise and post-exercise in free-living conditions, a small degree of hypohydration remained 20 h post-exercise.

Body surface profile in ambient and hot temperatures during a rectangular test in race walker champions of the World Cup in Oman 2022

There is current interest in infrared thermography as a method to assess changes in body surface temperature to determine thermoregulatory mechanisms, especially in endurance sports. The aim of this study was to evaluate the effect of two environmental temperatures (17 and 28°C) on body surface temperature in different anterior and posterior aspects of the body during a rectangular test in international walkers of the Spanish National Team. Three international walkers performed a rectangular test, where body temperature was measured at rest, and after the 5th, 10th and 15th run using an infrared thermographic camera in room temperatures at 17 and 28°C. In addition, oxygen consumption was measured simultaneously. ANOVA detected a group × time interaction in the chest and abdomen (right and left), left back and right calf (p = < 0.05), with a trend in the right hamstring (p = 0.053) when comparing 17°C and 28°C. ANOVA detected no significant group × time interaction (p = 0.853) but there was a significant group effect (p = 0.022). The eleven degrees increase in ambient temperature (17 to 28°C) produces changes in almost all anatomical zones, but not homogeneously in international walkers during a rectangular test. This indicates that metabolic and blood flow changes are different depending on the anatomical zone measured.

Fluid Balance, Sodium Losses and Hydration Practices of Elite Squash Players during Training

Elite squash players are reported to train indoors at high volumes and intensities throughout a microcycle. This may increase hydration demands, with hypohydration potentially impairing many key performance indicators which characterise elite squash performance. Consequently, the main aim of this study was to quantify the sweat rates and sweat [Na+] of elite squash players throughout a training session, alongside their hydration practices. Fourteen (males = seven; females = seven) elite or world class squash player’s fluid balance, sweat [Na+] and hydration practices were calculated throughout a training session in moderate environmental conditions (20 ± 0.4 °C; 40.6 ± 1% RH). Rehydration practices were also quantified post-session until the players’ next training session, with some training the same day and some training the following day. Players had a mean fluid balance of −1.22 ± 1.22% throughout the session. Players had a mean sweat rate of 1.11 ± 0.56 L·h−1, with there being a significant difference between male and female players (p < 0.05), and a mean sweat (Na+) of 46 ± 12 mmol·L−1. Players training the following day were able to replace fluid and sodium losses, whereas players training again on the same day were not. These data suggest the variability in players hydration demands and highlight the need to individualise hydration strategies, as well as training prescription, to ensure players with high hydration demands have ample time to optimally rehydrate.

A Study of the Fluid Intake, Hydration Status, and Health Effects among Pregnant Women in Their Second Trimester in China: A Cross-Sectional Study

The fluid intake and hydration status during pregnancy may influence the health outcomes of both the mother and the fetus. However, there are few studies related to this. The aim of the present study was to investigate fluid intake behaviors among pregnant women in their second trimester, to evaluate their hydration status and pregnancy complications, and to further explore the association of fluid intake and the amniotic fluid index (AFI). Participants’ total fluid intake (TFI) levels were determined using a 7-day 24 h fluid intake questionnaire. The levels of water intake from food were not recorded or measured. Morning urine samples were collected, and both urine osmolality levels and urine specific gravity (USG) were tested to evaluate their hydration status. Fasting blood samples were also collected and measured for osmolality and complete blood count (CBC). A total of 324 participants completed the study. They were divided into four groups based on quartiles of TFI, including participants with lower (LFI1 and LFI2) and higher (HFI1 and HFI2) fluid intake levels. The median TFI was 1485 mL, and the median values of the four groups with different TFI levels were 1348, 1449, 1530, and 1609 mL, respectively. Only 3.4% of the participants attained the recommended value following an adequate water intake (1.7 L) level for pregnant women in China. Plain water was the main TFI resource (78.8~100.00%), and differences in the plain water intake levels among the four groups were evident (χ2 = 222.027, p < 0.05). The urine osmolality decreased sequentially with increasing TFI values from the LFI1 to HFI2 group, and significant differences in the urine osmolality levels among the four groups were evident (p < 0.05). Meanwhile, the percentage of dehydrated participants decreased from 26.8% in the LFI1 group to 0.0% in the HFI2 group (χ2 = 131.241, p < 0.05). Participants with higher TFI values had higher AFI values (χ2 = 58.386, all p < 0.05), and moderate-intensity correlations were found between TFI and urine osmolality, hydration status, and AFI (all p < 0.05). A large proportion of the participants had insufficient TFIs during the second trimester of pregnancy, and a proportion of the participants were dehydrated. The preliminary analysis showed that the AFI was correlated with the TFI during the second trimester of pregnancy. A sufficient TFI is necessary for pregnant women to improve their hydration status and may have effects on their health. The results can provide appropriate scientific references for the development of beneficial recommendations concerning adequate water intake levels for pregnant women in China.

Fluid intake is a strong predictor of outdoor team sport pre-season training performance

Our aim was to characterize fluid intake during outdoor team sport training and use generalized additive models to quantify interactions with the environment and performance. Fluid intake, body mass (BM) and internal/external training load data were recorded for male rugby union (n = 19) and soccer (n = 19) athletes before/after field training sessions throughout an 11-week preseason (357 observations). Running performance (GPS) and environmental conditions were recorded each session and generalized additive models were applied in the analysis of data. Mean body mass loss throughout all training sessions was -1.11 ± 0.63 kg (~1.3%) compared with a mean fluid intake at each session of 958 ± 476 mL during the experimental period. For sessions >110 min, when fluid intake reached ~10-19 mL·kg^-1 BM the total distance increased (7.47 to 8.06 km, 7.6%; P = 0.049). Fluid intake above ~10 mL·kg^-1 BM was associated with a 4.1% increase in high-speed running distance (P < 0.0001). Most outdoor team sport athletes fail to match fluid loss during training, and fluid intake is a strong predictor of running performance. Improved hydration practices during training should be beneficial and we provide a practical ingestion range to promote improved exercise capacity in outdoor team sport training sessions.

Personality Determinants of Exercise-Related Nutritional Behaviours among Polish Team Sport Athletes

A proper diet increases the effectiveness of training and accelerates post-workout regeneration. One of the factors determining eating behaviour are personality traits, including those included in the Big Five model, i.e., neuroticism, extraversion, openness, agreeableness, and conscientiousness. The aim of this study was to analyse the personality determinants of peri-exercise nutritional behaviours among an elite group of Polish athletes practicing team sports. The study was conducted in a group of 213 athletes, using the author's validated questionnaire of exercise-related nutrition behaviours and the NEO-PI-R (Neuroticism Extraversion Openness-Personality Inventory-Revised). A statistical analysis was performed using Pearson's linear correlation and Spearman's rank correlation coefficients as well as a multiple regression analysis, assuming a significance level of α = 0.05. It has been shown that the level of the overall index regarding normal peri-exercise eating behaviours decreased with increasing neuroticism (r = -0.18) and agreeableness (r = -0.18). An analysis of the relationship between the personality traits (sub-scales) of the Big Five model demonstrated that the overall index of proper peri-exercise nutrition decreased with the intensification of three neuroticism traits, i.e., hostility/anger (R = -0.20), impulsiveness/immoderation (R = -0.18), and vulnerability to stress/learned helplessness (R = -0.19), and four traits of agreeableness, i.e., straightforwardness/morality (R = -0.17), compliance/cooperation (R = -0.19), modesty (R = -0.14), and tendermindedness/sympathy (R = -0.15) (p < 0.05). A multiple regression analysis exhibited that the full model consisting of all the analysed personality traits explained 99% of the variance concerning the level of the proper peri-exercise nutrition index. In conclusion, the index of proper nutrition under conditions of physical effort decreases along with the intensification of neuroticism and agreeableness among Polish athletes professionally practicing team sports.

Full-Cut Manufacture of Skin-Interfaced Microfluidic Patch with Copper Electrode for In Situ Admittance Sensing of Sweat Rate

Sweat-rate measurement has received more and more attention, especially for specific groups, such as athletes, soldiers and manual workers, due to their excessive sweat loss under prolonged intense heat stress, which increases the risk of dehydration and electrolyte imbalance. The highly effective manufacture of a sweat-sensing device is essential to its wide range of applications in perspiration-related physiological information detection. In this work, we propose a simple and cost-effective strategy for the manufacture of a microfluidic sweat-rate-sensing patch via laser cutting and transfer printing technology. A copper foil tape is used as the electrode for in situ admittance based sweat-rate-sensing. The detection circuits and measurement conditions are optimized to prevent the negative effect of an electrochemical reaction between a copper electrode and sweat for precise admittance measurement. In vitro and on-body experiments demonstrate that the copper electrode is applicable for admittance-based sweat sensing and is capable of achieving equivalent sensing accuracy as a gold electrode and that the proposed sensor structure can perform consecutive and accurate sweat-rate-sensing and facilitates a significant increase in manufacturing efficiency.

Exercise-related hemoconcentration and hemodilution in hydrated and dehydrated athletes: An observational study of the Hungarian canoeists

Hemoconcentration during exercise is a well-known phenomenon, however, the extent to which dehydration is involved is unclear. In our study, the effect of dehydration on exercise-induced hemoconcentration was examined in 12 elite Hungarian kayak-canoe athletes. The changes of blood markers were examined during acute maximal workload in hydrated and dehydrated states. Dehydration was achieved by exercise, during a 120-minute extensive-aerobic preload. Our research is one of the first studies in which the changes in blood components were examined with a higher time resolution and a wider range of the measured parameters. Hydration status had no effect on the dynamics of hemoconcentration during both the hydrated (HS) and dehydrated (DHS) load, although lower maximal power output were measured after the 120-minute preload [HS Hemoglobin(Hgb)Max median 17.4 (q1 17.03; q3 17.9) g/dl vs. DHS HgbMax median 16.9 (q1 16.43; q3 17.6) g/dl (n.s); HS Hematocrit(Hct)Max 53.50 (q1 52.28; q3 54.8) % vs. DHS HctMax 51.90 (q1 50.35; q3 53.93) % (n.s)]. Thirty minutes after the maximal loading, complete hemodilution was confirmed in both exercises. Dehydration had no effect on hemoconcentration or hemodilution in the recovery period [HS HgbR30' 15.7 (q1 15.15; q3 16.05) g/dl (n.s.) vs. DHS HgbR30' 15.75 (q1 15.48; q3 16.13) g/dl (n.s.), HS HctR30' 48.15 (q1 46.5; q3 49.2) % vs. DHS HctR30' 48.25 (q1 47.48; q3 49.45) % (n.s.)], however, plasma osmolality did not follow a corresponding decrease in hemoglobin and hematocrit in the dehydrated group. Based on our data, metabolic products (glucose, lactate, sodium, potassium, chloride, bicarbonate ion, blood urea nitrogen) induced osmolality may not play a major role in the regulation of hemoconcentration and post-exercise hemodilution. From our results, we can conclude that hemoconcentration depends mainly on the intensity of the exercise.

Dehydration, Wellness, and Training Demands of Professional Soccer Players during Preseason

Purpose

Our study is aimed at analyzing the relationships between water loss and a professional soccer team's internal and external training load throughout the first three months of a season, covering all the preseason and the first two months of the competitive season.

Methods

This study followed an observational analytic design. Twenty-seven athletes (age: 25.5 ± 4.1 years, height: 180.7 ± 8.2 cm, and body mass: 78.4 ± 8.7 kg) were included in the study, conducted over the first three months of the season. Players were weighed at the beginning and end of all training sessions to estimate fluid losses. They were asked to complete a wellness questionnaire and indicate the color of the first urine of the day upon their arrival at the practice session. Additionally, all sessions were monitored for locomotor demands.

Results

We found a positive correlation between urine color and sprint distance (r = 0.46, p = 0.01) and a positive correlation between dehydration and rating of perceived exertion (r = 0.44, p = 0.015), whereas a negative correlation between dehydration and number of acceleration (r = −0.39, p = 0.034).

Conclusions

Dehydration increased perceived physical exertion. Regularly monitoring training load and changes in body mass, as well as raising awareness about hydration, can contribute to cognitive and physical performance.

Behaviors of Water Intake, Hydration Status, and Related Hydration Biomarkers among Physically Active Male Young Adults in Beijing, China: A Cross-Sectional Study

Studies on the water intake of athletes in daily life are insufficient. The objective was to determine the water intake and hydration status among physically active male young adults. In this cross-sectional studies study, 111 physically active male young adults were recruited. The amount of daily total drinking fluid intake (TDF) among participants was recorded and evaluated in real time over 7 days using the "7-day 24-hour fluid intake questionnaire" (liq. In 7). The daily water intake from food (WFF) was calculated using the weighing, duplicate portion, and direct-drying method over 3 days. All urine samples over 3 days were collected, and urine biomarkers were determined. According to 24 h urine osmolality, the participants were divided into three groups with euhydration status, middle hydration, and hypo hydration statuses. Finally, 109 participants completed the study. The median daily total water intake (TWI), TDF, and WFF were 2701, ik1789, and 955 mL, respectively. Among participants, 17 participants (16%) were in euhydration status, 47 participants (43%) were in hypohydration, and 45 participants (41%) were in middle hydration. There were statistical significances in the 24 h urine volume, osmolality, urine specific gravity, and concentrations of K, Na, and Cl in different hydration statuses (χ 2  = 28.212, P < 0.01; χ 2  = 91.341, P < 0.01; χ 2  = 47.721, P < 0.01; χ 2  = 41.548, P < 0.01; χ 2  = 46.863, P < 0.01; and χ 2  = 40.839, P < 0.01). Moderate-intensity correlations were found between the TDF and 24 h urine volume, 24 h urine osmolality, 24 h urine Na concentration, morning urine osmolality, and morning urine Na concentration (r = 0.408, P < 0.01; r = -0.378, P < 0.01; r = -0.325, P < 0.01; r = -0.344, P < 0.01; and r = -0.329, P < 0.01). There were also moderate-intensity correlations between the TDF and 24 h urine osmolality, morning urine osmolality, and morning urine Na concentration (r = -0.365, P < 0.01; r = -0.371, P < 0.01; and r = -0.322, P = 0.01). Increased and higher moderate-intensity correlations were found between plain water and 24 h urine volume, 24 h urine osmolality, 24 h urine K and Na concentration, morning urine osmolality, and morning urine Na concentration (r = 0.374, P < 0.01; r = -0.520, P < 0.01; r = -0.312,P < 0.01; r = -0.355, P < 0.01; r = -0.446, P < 0.01; and r = -0.378, P < 0.01). Insufficient water intake and hypohydration were common among physically active male young adults. The amount and type of water intake were correlated with hydration status and urine biomarkers. The results could provide scientific and accurate references for the development of recommendations on water intake for athletes.

Fluid Balance and Carbohydrate Intake of Elite Female Soccer Players during Training and Competition

This study examined sweat rate, sweat sodium concentration [Na⁺], and ad-libitum carbohydrate and fluid intakes in elite female soccer players during training (n = 19) and a match (n = 8); eight completed both for comparisons. Body mass (kg) was obtained before and after exercise to calculate sweat rate. The sweat [Na⁺] was determined from absorbent patches on the thigh or back. Sweat rate, percentage body mass change, and sweat [Na⁺] for 19 players during training were 0.47 ± 0.19 L·h⁻¹, +0.19 ± 0.65%, and 28 ± 10 mmol·L⁻¹, respectively. Sweat rate was higher during a match (0.98 ± 0.34 L·h⁻¹) versus training (0.49 ± 0.26 L·h⁻¹, p = 0.007). Body mass losses were greater post-match (−1.12 ± 0.86%) than training (+0.29 ± 0.34%, p = 0.003). Sweat [Na⁺] was similar for training (29 ± 9 mmol·L⁻¹) and a match (35 ± 9 mmol·L⁻¹) (p = 0.215). There were no differences in match versus training carbohydrate intakes (2.0 ± 2.3 g·h⁻¹, 0.9 ± 1.5 g·h⁻¹, respectively, p = 0.219) or fluid intakes (0.71 ± 0.30 L·h⁻¹, 0.53 ± 0.21 L·h⁻¹, respectively, p = 0.114). In conclusion, female soccer players’ sweat rates were higher during a match than during training, and carbohydrate intakes were below recommendations for matches and training.

Fluid Balance and Thermoregulatory Responses during Wheelchair Basketball Games in Hot vs. Temperate Conditions

The impaired vaso- and sudomotor functions limit sweat capacity in individuals with a spinal cord injury (SCI) and might increase the risk for heat-related illness and decreased performance, especially in hot conditions (HOT). This study investigated the differences in fluid balance and thermal responses between wheelchair basketball (WCB) games in HOT and temperate conditions (TMP). Eleven male WCB athletes (39.8 y, 82.8 kg) with SCI (lesion level C5-L4) participated, five in HOT (31 °C) and eight in TMP games (21 °C). Fluid balance, sweat rate, body core temperature, distance, velocity and thermal sensation were assessed. The relative change in body mass was higher in the HOT group (median: −0.35%, interquartile-range: 0.15%, p = 0.02) compared to TMP (+0.11%, 0.35%) group. The sweat rate was significantly higher in the HOT group (0.93 L/h, 0.58 L/h, p = 0.02) compared to the TMP groups (0.48 L/h, 0.19 L/h). Body core temperature increased significantly higher in the TMP group (1.05 °C, 0.15 °C, p = 0.01) compared to the HOT group (0.8 °C, 0.4 °C). The mean velocity (HOT: 1.12 m/s, 0.11 m/s, TMP: 1.07 m/s, 0.08 m/s, p = 0.54) did not differ between the games. The WCB game in HOT leads to significantly higher sweat rate and loss in body mass compared to TMP. Even relative body mass loss was less than 2%. Athletes thus have to be supported with enough fluid, especially during games in HOT.

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%.

Modelling sodium requirements of athletes across a variety of exercise scenarios - identifying when to test and target, or season to taste

AbstractEvidence suggests the focus for sodium replacement during exercise should be maintenance of plasma sodium concentration ([Na⁺]_plasma) for any given total body water (TBW) volume. The sodium intake to achieve stable [Na⁺]_plasma given known fluid and electrolyte intakes and losses can be mathematically estimated. Therefore the aim of this investigation was to model sodium requirements of athletes during exercise, observing the influence of sweat rate, exercise duration, body mass, baseline [Na⁺]_plasma and sweat potassium [K⁺]_sweat, and relevance to competition (soccer, elite marathon, and 160 km ultramarathon running). Models were constructed across a range of sweat sodium concentrations ([Na⁺]_sweat) (20-80 mmol·L^-1), sweat rates (0.5-2.5 L·h^-1) and fluid replacement (10-90% of losses). In the competition-specific scenarios, fluid replacement was calculated to achieve 2% TBW losses. Sodium requirements were driven by fluid replacement (% of losses) and [Na⁺]_sweat, with minimal or no influence of other variables. Replacing sodium was unnecessary in all realistic scenarios modelled for a soccer match and elite marathon. In contrast, the 160 km ultramarathon required ≥47% sodium replacement when [Na⁺]_sweat was ≥40 mmol·L^-1 and >80% of fluid losses were replaced. In conclusion, sodium requirements to maintain stable [Na⁺]_plasma during exercise depend on both the proportion of fluid losses replaced, and [Na⁺]_sweat. Only when prolonged exercise is coupled with aggressive fluid replacement (>80%) and whole body [Na⁺]_sweat ≥40 mmol·L^-1 does sweat composition testing and significant, targeted sodium replacement appear necessary.

Sweating Rate and Sweat Chloride Concentration of Elite Male Basketball Players Measured With a Wearable Microfluidic Device Versus the Standard Absorbent Patch Method

The purpose of this study was to compare a wearable microfluidic device and standard absorbent patch in measuring local sweating rate (LSR) and sweat chloride concentration ([Cl-]) in elite basketball players. Participants were 53 male basketball players (25 ± 3 years, 92.2 ± 10.4 kg) in the National Basketball Association's development league. Players were tested during a moderate-intensity, coach-led practice (98 ± 30 min, 21.0 ± 1.2 °C). From the right ventral forearm, sweat was collected using an absorbent patch (3M Tegaderm™ + Pad). Subsequently, LSR and local sweat [Cl-] were determined via gravimetry and ion chromatography. From the left ventral forearm, LSR and local sweat [Cl-] were measured using a wearable microfluidic device and associated smartphone application-based algorithms. Whole-body sweating rate (WBSR) was determined from pre- to postexercise change in body mass corrected for fluid/food intake (ad libitum), urine loss, and estimated respiratory water and metabolic mass loss. The WBSR values predicted by the algorithms in the smartphone application were also recorded. There were no differences between the absorbent patch and microfluidic patch for LSR (1.25 ± 0.91 mg·cm-2·min-1 vs. 1.14 ±0.78 mg·cm-2·min-1, p = .34) or local sweat [Cl-] (30.6 ± 17.3 mmol/L vs. 29.6 ± 19.4 mmol/L, p = .55). There was no difference between measured and predicted WBSR (0.97 ± 0.41 L/hr vs. 0.89 ± 0.35 L/hr, p = .22; 95% limits of agreement = 0.61 L/hr). The wearable microfluidic device provides similar LSR, local sweat [Cl-], and WBSR results compared with standard field-based methods in elite male basketball players during moderate-intensity practices.

Prevalence of Dehydration and the Relationship with Fluid Intake and Self‐Assessment of Hydration Status in Czech First League Soccer Players

The objective of this cross-sectional study was to evaluate the hydration status of Czech First League soccer players, and to compare the reported fluid intake, perceived fluid intake and thirst sensation of euhydrated (EU) and dehydrated (DE) players. The study involved 124 Czech male professional soccer players (age 25.2±5.0 years) participating in annual winter, pre-season laboratory testing. Hydration status was assessed based on urine specific gravity (USG), euhydration was set at USG≤1.020. Fluid intake and thirst perception were evaluated by a questionnaire. The sample mean for USG was 1.021±0.008, 56% of players were dehydrated. Reported daily fluid intake was significantly (p<0.001, d=0.95, large effect) higher in EU compared to DE players. Daily fluid intake negatively correlated with USG (rS=-0.46, p<0.001, medium effect). The fluid intake perception score was significantly (p=0.005, d=0.54, medium effect) better in EU compared to DE players. Reported intake perception scores negatively correlated with USG (rS=-0.32, p<0.001, medium effect). However, there was no correlation (rS=-0.09, p=0.34, trivial effect) between thirst perception scores and USG. Thirst perception scores were not significantly different between EU and DE players (p=0.35, d=0.18, trivial effect). Our results indicated that self-assessment of both daily fluid intake and perceived fluid intake matched with objective hydration status, while self-assessment of thirst perception was not an appropriate indicator of hydration status in elite soccer players.

Evidence‐Based Recovery in Soccer – Low‐Effort Approaches for Practitioners

Strategies to improve recovery are widely used among soccer players at both amateur and professional levels. Sometimes, however, recovery strategies are ineffective, improperly timed or even harmful to players. This highlights the need to educate practitioners and athletes about the scientific evidence of recovery strategies as well as to provide practical approaches to address this issue. Therefore, recent surveys among soccer athletes and practitioners were reviewed to identify the recovery modalities currently in use. Each strategy was then outlined with its rationale, its physiological mechanisms and the scientific evidence followed by practical approaches to implement the modality. For each intervention, practical and particularly low-effort strategies are provided to ensure that practitioners at all levels are able to implement them. We identified numerous interventions regularly used in soccer, i.e., sleep, rehydration, nutrition, psychological recovery, active recovery, foam-rolling/massage, stretching, cold-water immersion, and compression garments. Nutrition and rehydration were classified with the best evidence, while cold-water immersion, compression garments, foam-rolling/massage and sleep were rated with moderate evidence to enhance recovery. The remaining strategies (active recovery, psychological recovery, stretching) should be applied on an individual basis due to weak evidence observed. Finally, a guide is provided, helping practitioners to decide which intervention to implement. Here, practitioners should rely on the evidence, but also on their own experience and preference of the players.

Regional Bioelectrical Phase Angle Is More Informative than Whole-Body Phase Angle for Monitoring Neuromuscular Performance: A Pilot Study in Elite Young Soccer Players

Background: The objective of this study was to investigate the association between regional and total phase angle (PhA) with lower-body neuromuscular performance in young elite soccer players. Methods: Sixteen elite male soccer players (14.3 ± 1.0 years) participated in this study. Lower (LPhA)- and upper (UPhA)-hemisome PhA together with whole-body PhA (WBPhA) were measured by a bioelectrical-impedance analysis (BIA), while appendicular arm and leg lean soft tissue (ALST and LLST, respectively) were estimated. Urine osmolarity (UOsm) and urine-specific gravity (USG) were also considered. Sprints over 10 m and 20 m and countermovement jump (CMJ) tests were employed to evaluate neuromuscular performance. Results: LPhA (p = 0.003) and UOsm (p = 0.012) explained 62% of the variance in the 10 m sprint. UOsm (p = 0.001) and both LPhA (p < 0.001) and WBPhA (p = 0.024) explained 81% of the total variance in the 20 m sprint. The CMJ height was affected by LPhA (p < 0.001) and UOsm (p = 0.024), which overall explained 68% of its variance (p < 0.05), while 93% of the CMJ power variance was explained by LPhA (p < 0.001), ALST (p < 0.001), and WBPhA (p = 0.011). Conclusions: Regional PhA is a relevant and non-invasive tool to monitor lower-body neuromuscular performance in elite youth soccer. Specifically, LPhA may be favored over WBPhA as more informative.

Changes in the skin characteristics associated with dehydration and rehydration

AbstractThe present study aimed to test the hypothesis that changes in the dermal tissue dielectric constant (TDC) and biomechanical properties of the skin would be correlated with the indicators related to dehydration. Ten healthy adult men were enrolled in three trials: no fluid intake (DEH), ad libitum fluid intake (AL-HYD), and programmed fluid intake (P-HYD) after exercise in a randomized crossover design. The participants performed a pedaling exercise at 60% heart rate reserve until 2% body mass loss. At 120 min after exercise, an incremental exercise test was carried out. Aerobic capacity, body composition, TDC, biomechanical properties of the skin (pliability, viscoelasticity, and total recovery), and indicators related to dehydration in the serum and urine were measured before and 120 min after exercise. Higher values of the pliability and viscoelasticity, and lower value of the total recovery on the hand were demonstrated in the P-HYD trial compared to the DEH trial (all P < 0.05). Changes in the TDC were significantly correlated with changes in body mass (P < 0.05), total body water (P < 0.05), serum osmolarity (P < 0.05), and hematocrit (P < 0.01). Changes in the biomechanical properties of the hand were significantly correlated with changes in body mass, hematocrit, and urine specific gravity (all P < 0.05). The present study showed that the changes in skin characteristics correlated with the body water and dehydration-associated indicators in the serum and urine, thus suggesting that skin characteristics may be useful in the assessment of dehydration.

Reference Percentiles for Bioelectrical Phase Angle in Athletes

Simple Summary

The bioelectrical phase angle is a raw parameter that can be utilized as an indicator of performance, muscle quantity and hydration status of cells. However, sex- and sport-specific phase angle reference percentiles are lacking for the athletic population. For the first time, this study provides 5th, 15th, 50th, 85th, and 95th reference percentiles for phase angle in male and female athletes practicing different sports. These reference values can be used to track body composition and performance related-outcomes in sports practice, while leveraging the portability of bioelectric impedance analysis.

Abstract

The present study aimed to develop reference values for bioelectrical phase angle in male and female athletes from different sports. Overall, 2224 subjects participated in this study [1658 males (age 26.2 ± 8.9 y) and 566 females (age 26.9 ± 6.6 y)]. Participants were categorized by their sport discipline and sorted into three different sport modalities: endurance, velocity/power, and team sports. Phase angle was directly measured using a foot-to-hand bioimpedance technology at a 50 kHz frequency during the in-season period. Reference percentiles (5th, 15th, 50th, 85th, and 95th) were calculated and stratified by sex, sport discipline and modality using an empirical Bayesian analysis. This method allows for the sharing of information between different groups, creating reference percentiles, even for sports disciplines with few observations. Phase angle differed (men: p < 0.001; women: p = 0.003) among the three sport modalities, where endurance athletes showed a lower value than the other groups (men: vs. velocity/power: p = 0.010, 95% CI = −0.43 to −0.04; vs. team sports: p < 0.001, 95% CI = −0.48 to −0.02; women: vs. velocity/power: p = 0.002, 95% CI = −0.59 to −0.10; vs. team sports: p = 0.015, 95% CI = −0.52 to −0.04). Male athletes showed a higher phase angle than female athletes within each sport modality (endurance: p < 0.01, 95% CI = 0.63 to 1.14; velocity/power: p < 0.01, 95% CI = 0.68 to 1.07; team sports: p < 0.01, 95% CI = 0.98 to 1.23). We derived phase angle reference percentiles for endurance, velocity/power, and team sports athletes. Additionally, we calculated sex-specific references for a total of 22 and 19 sport disciplines for male and female athletes, respectively. This study provides sex- and sport-specific percentiles for phase angle that can track body composition and performance-related parameters in athletes.

Risk of Dehydration Due to Sweating While Wearing Personal 2 Protective Equipment in COVID-19 Clinical Care: A Pilot Study

Objective: The objectives of this study were (a) to determine the physical impact of the personal protective equipment (PPE) used in COVID-19 care, specifically the impact on the hydration state of the temperature and the comfort of the healthcare workers who use it, and (b) to show the high-fidelity simulated environment as an appropriate place to test the experimental designs to be developed in real environments for COVID-19. Background: All healthcare staff use full PPE in the care of COVID-19 patients. There are problems, such as excessive sweating, which have not been quantified thus far. Methods: A descriptive pilot design was used in a simulated high-fidelity setting. There was paired activity, with mild–moderate physical activity, between 45 and 60 min continuously, with the COVID-19 PPE. Sixteen intensive care nurses were selected. The before–after differential of weight, thirst, weight use of the PPE, body temperature, thermal body image, general and facial warmth sensation, and perspiration sensation were measured. Results: All subjects lost weight in the form of sweat with both PPEs during the simulation scenario, with a mean of 200 g (0.28% of initial weight), and increased thirst sensation. Body thermal image increased by 0.54 °C in people using the full COVID-19 PPE. Conclusions: The use of PPE in the management of critically ill COVID-19 patients generates weight loss related to excessive sweating. The weight loss shown in this pilot test is far from the clinical limits of dehydration. The use of ventilated PPE, such as PAPR, reduce the body temperature and heat sensation experienced by the users of it; at the same time, it improves the comfort of those who wear it. The simulated environment is a suitable place to develop the piloting of applicable research methodologies in future studies in a real environment.

Bioelectrical Impedance Vector and Creatine Phosphokinase Changes Induced by a High-Intensity Training Session in Rink Hockey Players

This study aimed to analyze anthropometric and whole-body/muscle-localized bioelectrical impedance vector analysis (BIVA) adaptations and their relation to creatine kinase (CK) as a biomarker of muscle damage in a group of seven male players in the maximum category of professional rink hockey. There were three checkpoint assessments in relation to a high-intensity training session: pre-session (PRE), post-session (POST), and 24 h-post-session (POST24H). The resistance, reactance, and impedance module were adjusted by height (R/h, Xc/h, and Z/h, respectively). The Wilcoxon signed-rank test was used to compare the data at baseline and follow-up, while Spearman correlation was used to explore the relationship between CK and the rest of the parameters. The results registered a decrease in body mass at POST (p = 0.03) and a reestablishment at POST24H (p = 0.02). Whole-body BIVA registered a significant increase in R/h between PRE–to–POST (p = 0.02) and returned to baseline values at POST24H (p = 0.02), which was expected since this parameter is related to hydration processes. Muscle-localized BIVA in the rectus femoris muscle showed an increase in both Xc/h and phase angle in POST (p = 0.04 and p = 0.03, respectively) and a decrease in Xc/h at POST24H (p = 0.02). CK correlated with R/h in the rectus femoris at all the checkpoints (PRE–to–POST: r = 0.75, p = 0.05; PRE–to–POST24H: r = 0.81, p = 0.03; POST–to–POST24H: r = 0.82, p = 0.02). Our results indicate that BIVA is a sensitive methodology to assess general and muscle-localized hydration induced by a high-intensity training session in rink hockey players. A correlation between BIVA and CK was also reported.

Improving hydration in elite male footballers during a national team training camp – an observational case study

[Purpose] The purpose of this study was to (i) assess hydration levels in elite male football players during a national team training camp before and during qualifying matches, (ii) evaluate the effect of coaching strategies for hydration based on feedback from hydration monitoring, and (iii) assess possible relationships between hydration status and training load or wellness markers.[Methods] Thirty-one male players (age 27±4 yrs; height 185±6 cm; weight 82.9±6.7 kg; body fat 10.4±2.3%) representing a national team from the Union of European Football Associations (UEFA) participated. The players were studied during three different national team training camps related to the UEFA Nations League tournament. Urine specific gravity (USG) was measured to assess hydration status. During all camps, the players were actively coached on improving strategies for hydration and given individual feedback on their test results. The training load was measured using GPS technology, and wellness questionnaires were completed.[Results] USG decreased progressively and significantly (p<0.005) during camp 1 and hydration status improved over the three camps, with fewer dehydrated and more well-hydrated players identified during the last part of camp 3. Significantly (p<0.05) higher USG values were observed 2 days prior to a match (MD-2) than on match day (MD); consequently, 52% of the players were dehydrated on MD-2 and only 6% on MD. No correlations were observed between hydration status and training load or wellness markers.[Conclusion] Dehydration is a challenge in elite male football, but continuous monitoring of hydration status and coaching on hydration strategies can lead to major improvements and reduce the degree of dehydration.

Fluid Restriction Negatively Influences Perceived Morning Alertness and Visuomotor Ability

The purpose of this study was to assess the effect of two fluid intake protocols on alertness and reaction time before and after fluid intake. Healthy college-age males (n = 12) followed two fluid intake protocols on separate occasions: (1) prescribed fluid (PF) and fluid restricted (FR). In PF, participants were instructed to consume 500 mL of fluid the night prior to and the morning of data collection. In FR, participants were instructed to refrain from the consumption of fluid for 12 h. To assess hydration status, urine specific gravity and urine color were measured. Participants perceived level of thirst and alertness were also recorded. Participants then completed visuomotor reaction time tests using the Dynavision LED board, using both a central visuomotor test and a peripheral visuomotor test (PVRT) prior to (1) and following (2) the ingestion of 100 mL of water. Participants displayed significantly improved PVRT in PF state as compared to FR (PF1 = 1.13 ± 0.16, PF2 = 1.04 ± 0.14; FR1 = 1.27 ± 0.27, FR2 = 1.18 ± 0.20; p = 0.038, η_p² = 0.363). Both CVRT and PVRT improved over time, following the ingestion of 100 mL of fluid. Participants in the PF state were also significantly more alert than participants in the FR state (PF = 4 ± 2, FR = 5 ± 2; p = 0.019, ES = 0.839). Collectively, perceived alertness and PVRT were negatively impacted by FR.

In-Season Nutrition Strategies and Recovery Modalities to Enhance Recovery for Basketball Players: A Narrative Review

Basketball players face multiple challenges to in-season recovery. The purpose of this article is to review the literature on recovery modalities and nutritional strategies for basketball players and practical applications that can be incorporated throughout the season at various levels of competition. Sleep, protein, carbohydrate, and fluids should be the foundational components emphasized throughout the season for home and away games to promote recovery. Travel, whether by air or bus, poses nutritional and sleep challenges, therefore teams should be strategic about packing snacks and fluid options while on the road. Practitioners should also plan for meals at hotels and during air travel for their players. Basketball players should aim for a minimum of 8 h of sleep per night and be encouraged to get extra sleep during congested schedules since back-to back games, high workloads, and travel may negatively influence night-time sleep. Regular sleep monitoring, education, and feedback may aid in optimizing sleep in basketball players. In addition, incorporating consistent training times may be beneficial to reduce bed and wake time variability. Hydrotherapy, compression garments, and massage may also provide an effective recovery modality to incorporate post-competition. Future research, however, is warranted to understand the influence these modalities have on enhancing recovery in basketball players. Overall, a strategic well-rounded approach, encompassing both nutrition and recovery modality strategies, should be carefully considered and implemented with teams to support basketball players' recovery for training and competition throughout the season.

Nutritional optimization for female elite football players-topical review

Women's football is an intermittent sport characterized by frequent intense actions throughout the match. The high number of matches with limited recovery time played across a long competitive season underlines the importance of nutritional strategies to meet these large physical demands. In order to maximize sport performance and maintain good health, energy intake must be optimal. However, a considerable proportion of female elite football players does not have sufficient energy intake to match the energy expenditure, resulting in low energy availability that might have detrimental physiologic consequences and impair performance. Carbohydrates appear to be the primary fuel covering the total energy supply during match-play, and female elite football players should aim to consume sufficient carbohydrates to meet the requirements of their training program and to optimize the replenishment of muscle glycogen stores between training bouts and matches. However, several macro- and micronutrients are important for ensuring sufficient energy and nutrients for performance optimization and for overall health status in female elite football players. The inadequacy of macro-and micronutrients in the diet of these athletes may impair performance and training adaptations, and increase the risk of health disorders, compromising the player's professional career. In this topical review, we present knowledge and relevant nutritional recommendations for elite female football players for the benefit of sports nutritionists, dietitians, sports scientists, healthcare specialists, and applied researchers. We focus on dietary intake and cover the most pertinent topics in sports nutrition for the relevant physical demands in female elite football players as follows: energy intake, macronutrient and micronutrient requirements and optimal composition of the everyday diet, nutritional and hydration strategies to optimize performance and recovery, potential ergogenic effects of authorized relevant supplements, and future research considerations.

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.

Nutritional approaches to counter performance constraints in high-level sports competition

New Findings

What is the topic of this review?

The nutritional strategies that athletes use during competition events to optimize performance and the reasons they use them.

What advances does it highlight?

A range of nutritional strategies can be used by competitive athletes, alone or in combination, to address various event‐specific factors that constrain event performance. Evidence for such practices is constantly evolving but must be combined with understanding of the complexities of real‐life sport for optimal implementation.

Abstract

High‐performance athletes share a common goal despite the unique nature of their sport: to pace or manage their performance to achieve the highest sustainable outputs over the duration of the event. Periodic or sustained decline in the optimal performance of event tasks, involves an interplay between central and peripheral phenomena that can often be reduced or delayed in onset by nutritional strategies. Contemporary nutrition practices undertaken before, during or between events include strategies to ensure the availability of limited muscle fuel stores. This includes creatine supplementation to increase muscle phosphocreatine content and consideration of the type, amount and timing of dietary carbohydrate intake to optimize muscle and liver glycogen stores or to provide additional exogenous substrate. Although there is interest in ketogenic low‐carbohydrate high‐fat diets and exogenous ketone supplements to provide alternative fuels to spare muscle carbohydrate use, present evidence suggests a limited utility of these strategies. Mouth sensing of a range of food tastants (e.g., carbohydrate, quinine, menthol, caffeine, fluid, acetic acid) may provide a central nervous system derived boost to sports performance. Finally, despite decades of research on hypohydration and exercise capacity, there is still contention around their effect on sports performance and the best guidance around hydration for sporting events. A unifying model proposes that some scenarios require personalized fluid plans while others might be managed by an ad hoc approach (ad libitum or thirst‐driven drinking) to fluid intake.

Effects of Heat Acclimatization, Heat Acclimation, and Intermittent Exercise Heat Training on Time-Trial Performance

BACKGROUND

The purpose of this study was to investigate effects of heat acclimatization (HAz) followed by heat acclimation (HA), and intermittent heat training (IHT) on time-trial performance.

HYPOTHESIS

Time-trial performance will improve after HA and will further improve with twice a week of IHT.

STUDY DESIGN

Interventional study.

LEVEL OF EVIDENCE

Level 3.

METHODS

A total of 26 male athletes (mean ± SD; age, 35 ± 12 years; body mass, 72.8 ± 8.9 kg; peak oxygen consumption [VO_2peak], 57.3 ± 6.7 mL·kg^-1·min^-1) completed five 4-km time trials (baseline, post-HAz, post-HA, post-IHT4, post-IHT8) in the heat (ambient temperature, 35.4°C ± 0.3°C; relative humidity, 46.7% ± 1.2%) on a motorized treadmill. After baseline time trial, participants performed HAz (109 ± 10 days) followed by post-HAz time trial. Then, participants completed 5 days of HA, which involved exercising to induce hyperthermia (38.50°C-39.75°C) for 60 minutes. Participants were then divided into 3 groups and completed IHT either twice per week (IHT_MAX), once per week (IHT_MIN), or not at all (IHT_CON) over an 8-week period. The exercise used for the IHT matched the HA. Four-kilometer time trials were performed after 4 weeks (post-IHT4) and 8 weeks of IHT (post-IHT8).

RESULTS

Time trial was faster in post-HA (17.98 ± 2.51 minutes) compared with baseline (18.61 ± 3.06 minutes; P = 0.037) and post-HAz (18.66 ± 3.12 minutes; P = 0.023). Percentage change in time trial was faster in IHT_MAX (-3.9% ± 5.2%) compared with IHT_CON (11.5% ± 16.9%) (P = 0.020) and approached statistical significance with large effect (effect size = 0.96) compared with IHT_MIN (1.6% ± 6.2%; P = 0.059) at post-IHT8. Additionally, IHT_MAX (-2.2% ± 4.2%) was faster than IHT_CON (3.6% ± 6.9%) (P = 0.05) at post-IHT4.

CONCLUSION

These results indicate that HA after HAz induces additional improvement in time-trial performance. IHT twice per week shows improvement after 8 weeks, while once per week maintains performance for 8 weeks. No IHT results in a loss of adaptations after 4 weeks and even greater losses after 8 weeks.

CLINICAL RELEVANCE

HA after HAz improves time-trial performance, twice a week of IHT improves performance further, and once a week of IHT maintains performance for at least 8 weeks.

Awareness of dehydration state and fluid intake practice among adults population in the Jazan Region of Saudi Arabia, 2019

Despite the hot climate and high humidity in the Jazan Region of Saudi Arabia, which increases risk for dehydration, no previous studies have assessed awareness of dehydration and fluid intake practice among adults in this region. Therefore, the aim of this cross-sectional study was to determine awareness of the dehydration state and fluid intake practices among 440 adults in the Jazan Region of Saudi Arabia. Out of the total, 51⋅8 % were male and 48⋅2 % were females. Good knowledge of dehydration definition and prevention and recommended minimum water intake was observed in 98, 95 and 75 % of the participants, respectively. Fifty-nine percent of the participants met the minimum daily requirement of 3 l or more per day. The age (95 % CI 1⋅003, 1⋅017, P value = 0⋅006), diabetes (95 % CI 1⋅028, 1⋅459, P value = 0⋅023) and prior hospitalisation due to dehydration (95 % CI 1⋅010, 1⋅378, P value = 0⋅037) were associated with higher water intake. Additional glasses of coffee (95 % CI 1⋅02, 1⋅115, P value = 0⋅004) and juice (95 % CI 1⋅039, 1⋅098, P value < 0⋅001) were associated with more water intake. The participants exhibited good knowledge of dehydration definition, symptoms and consequences. Intake of fluids such as 'juice and coffee' enhances more water intake. Although two-thirds of the participants met the recommended daily water intake, still one-third of them did not meet this level. Innovative approaches to enhance healthy drinking are warranted and may include partnering with patients to take an active role in hydration monitoring and increasing communication with the different healthcare providers.

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.

Hypohydration produced by high-intensity intermittent running increases biomarkers of renal injury in males

Purpose

Whilst there is evidence to suggest that hypohydration caused by physical work in the heat increases renal injury, whether this is the case during exercise in temperate conditions remains unknown. This study investigated the effect of manipulating hydration status during high-intensity intermittent running on biomarkers of renal injury.

Methods

After familiarisation, 14 males (age: 33 ± 7 years; V̇O_2peak: 57.1 ± 8.6 ml/kg/min; mean ± SD) completed 2 trials in a randomised cross-over design, each involving 6, 15 min blocks of shuttle running (modified Loughborough Intermittent Shuttle Test protocol) in temperate conditions (22.3 ± 1.0 °C; 47.9 ± 12.9% relative humidity). During exercise, subjects consumed either a volume of water equal to 90% of sweat losses (EU) or 75 mL water (HYP). Body mass, blood and urine samples were taken pre-exercise (baseline/pre), 30 min post-exercise (post) and 24 h post-baseline (24 h).

Results

Post-exercise, body mass loss, serum osmolality and urine osmolality were greater in HYP than EU (P ≤ 0.024). Osmolality-corrected urinary kidney injury molecule-1 (uKIM-1) concentrations were increased post-exercise (P ≤ 0.048), with greater concentrations in HYP than EU (HYP: 2.76 [1.72–4.65] ng/mOsm; EU: 1.94 [1.1–2.54] ng/mOsm; P = 0.003; median [interquartile range]). Osmolality-corrected urinary neutrophil gelatinase-associated lipocalin (uNGAL) concentrations were increased post-exercise (P < 0.001), but there was no trial by time interaction effect (P = 0.073).

Conclusion

These results suggest that hypohydration produced by high-intensity intermittent running increases renal injury, compared to when euhydration is maintained, and that the site of this increased renal injury is at the proximal tubules.

Portuguese Football Federation consensus statement 2020: nutrition and performance in football

Nutrition is an undeniable part of promoting health and performance among football (soccer) players. Nevertheless, nutritional strategies adopted in elite football can vary significantly depending on culture, habit and practical constraints and might not always be supported by scientific evidence. Therefore, a group of 28 Portuguese experts on sports nutrition, sports science and sports medicine sought to discuss current practices in the elite football landscape and review the existing evidence on nutritional strategies to be applied when supporting football players. Starting from understanding football's physical and physiological demands, five different moments were identified: preparing to play, match-day, recovery after matches, between matches and during injury or rehabilitation periods. When applicable, specificities of nutritional support to young athletes and female players were also addressed. The result is a set of practical recommendations that gathered consensus among involved experts, highlighting carbohydrates periodisation, hydration and conscious use of dietary supplements.

The influence of thermal stress on the physical and technical activities of soccer players: lessons from the 2018 FIFA World Cup in Russia

The present study attempts to assess changes in soccer players' physical and technical activity profiles due to thermal stress, measured with the Universal Thermal Climate Index (UTCI), in training centres and during matches of the 2018 FIFA World Cup in Russia. The study also verifies the theoretical models of soccer players' physiological parameters. The study sample consisted of 945 observations of 340 players of national teams taking part in the World Cup in Russia. The measured variables included physical activities: total distance covered, distances covered with an intensity of 20-25 km/h, number of sprints; technical activities: number of shots, number of passes, pass accuracy and physiological indicators: evaporative water loss and heart rate. In addition, the final ranking places of each national team were also used in the study. The UTCI was calculated based on meteorological data recorded at training centres and during matches. The UTCI records were then classified into two ranges: NTS-no thermal stress (UTCI 9-26 °C) and TS-thermal stress (UTCI > 26 °C). Climatic conditions at soccer training centres assessed as involving "no thermal stress" are found to be more beneficial for increasing the total distance covered and the number of sprints performed by players during a match. The theoretical models for determining soccer players' physiological parameters used in the study reduce the players' heart rate effort and evaporative water loss, which is in line with findings in studies by other authors. The climatic conditions at soccer training centres and during tournament matches should be taken into account in planning preparations for future World Cup tournaments, especially those in hotter countries.