Percent Body Mass Loss Research Articles

Females Maintain Fluid Balance across Consecutive Workdays in Heat When Fluids are Readily Accessible

Workers should aim to fully replace fluid losses during work in the heat to maintain work productivity and minimize risk of heat illnesses, however, fluid balance of females working during consecutive days in the heat is unknown. The purpose of this study was to test the hypothesis that females would maintain fluid balance during work across two consecutive workdays. Eight healthy females (age: 29±5, body mass: 75.3±20.1, body fat: 23±8%) completed two consecutive days (Day 1, Day 2) of heavy intensity work in a hot environment (35.9±1.2°C, 24±6% relative humidity). Work consisted of repeated 45/15 work/rest cycles of treadmill walking or cycling at 398±7 W of metabolic heat production and seated rest for 4 h. Every 20 min, participants were provided 237 mL of a sport drink to consume ad libitum. Urine flow rate (UFR) was measured before work. Urine specific gravity (USG) and nude body mass were measured before and after work. Fluid volume consumed and thirst (9-point Likert scale, 1=not thirsty at all, 9=very, very thirsty) were measured during work. Two-way repeated measures analysis of variance and paired samples t-tests were used to compare differences. Significance was set at p≤0.05. Percent body mass loss was not different between Day 1 (0.69±0.82%) and Day 2 (0.96±2.25%, p=0.935). Similarly, sweat rate was not different between Day 1 (0.57±0.12 L/h) and Day 2 (0.65±0.21 L/h, p=0.312). Participants consumed less fluid on Day 1 (64±21%, 25±10 mL/kg) compared to Day 2 (74±20%, p=0.026; 29±10 mL/kg, p=0.025). Participants consumed 68±19% and 77±20% (p=0.040) of fluid offered during work and 55±27% and 66±22% (p=0.173) of fluid offered during rest on Day 1 and Day 2, respectively. Resting thirst (Day 1: 2.1±1.1, Day 2: 1.6±0.5, p=0.096), change in thirst (Day 1: -0.5±0.9, Day 2: +0.3±1.3, p=0.111) and maximum thirst (Day 1: 3.6±1.1, Day 2: 3.6±1.4, p=1.000) were not different between days. USG was not different (p=0.839) across days before (Day 1: 1.009±0.010, Day 2: 1.009±0.010) or after (Day 1: 1.012±1.010, Day 2: 1.012±0.010) work, respectively. UFR was not different between days (Day 1: 2.2±1.4 mL/min, Day 2: 2.0±1.2 mL/min, p=0.836). Females completing heavy intensity work in heat maintained fluid balance across two consecutive days when fluids were readily accessible. Ad libitum fluid consumption may be suffcient to adequately replace fluid losses in females across consecutive days of work in heat. This project was funded by the National Institute for Occupational Safety and Health (1K01OH012016-01A1). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Repeatability of Ad Libitum Water Intake during Repeated 1 h Walking/Jogging Exercise Sessions Conducted under Hot Ambient Conditions.

A drinking strategy aiming to replace a given percentage of the sweat losses incurred during exercise should result in reproducible fluid intake volume and, hence, fluid balance from one exercise session to the other performed under similar scenarios. Whether this may also be the case with ad libitum drinking during exercise is unclear. We characterized the repeatability of ad libitum water intake during repeated 1 h exercise sessions and examined its effect over time on fluid balance and selected physiological functions and perceptual sensations. Twelve (3 women) healthy individuals participated in this study. At weekly intervals, they completed four 2 × 30 min walking/jogging exercise bouts (55% V˙O2max, 40 °C, 20-30% relative humidity) interspersed by a 3 min recovery period. During exercise, participants consumed water (20 °C) ad libitum. There were no significant differences among the four exercise sessions for absolute water intake volume (~1000 mL·h-1), percent body mass loss (~0.4%), sweat rate (~1300 mL·h-1) and percent of sweat loss replaced by water intake (~80%). Heart rate, rectal temperature, and perceived thirst and heat stress did not differ significantly between the first and fourth exercise sessions. Perceived exertion was significantly lower during the fourth vs. the first exercise session, but the difference was trivial (<1 arbitrary unit). In conclusion, ad libitum water intake during four successive identical 1 h walking/jogging sessions conducted in the heat will result in similar water intake volumes and perturbations in fluid balance, heart rate, rectal temperature, and perceived thirst, heat stress and exertion.

Relationship Between Pre- and Post-exercise Body Mass Changes and Pre-exercise Urine Color in Female Athletes.

Although studies use body mass changes or urine color to measure hydration status, the purpose of this study was to examine the relationship between pre-practice urine color and exercise body mass changes in female tackle football players. Twenty-six female American football players (Age: 29.9 ± 7.3 years; Height: 165.2 ± 2.6 cm; Weight: 83.8 ± 24.4 kg) volunteered. Fluid consumptions (FC) was measured during tackle football practices, while urine color (Ucol), and percent body mass loss (%BML) were taken before and after practices. Subjects were grouped by %BML: lost mass (LM), gained mass (GM), or no change (NC). A one-way ANOVA compared groups on Ucol and FC. There were differences across groups for pre-practice Ucol (P < 0.01) and FC (P < 0.01). GM had a higher pre-practice Ucol than LM (P < 0.01) and NC (P < 0.05) and consumed more fluid than LM (P < 0.01) and NC (P < 0.05). A stepwise linear regression examined the extent that Ucol and FC were related to %BML. When predicting BML, FC accounted for 45% of variance (P < 0.01). The addition of pre-practice Ucol increased predicted variance explained (R2 change= 2.5%, P = 0032). Subjects who gained mass during practice arrived with elevated urine color (Ucol 5 ± 2), while those who lost mass arrived with pale urine color (Ucol 3 ± 2). Findings indicate those who arrived with an elevated urine color attempted to improve hydration status by consuming more fluid and gaining body mass during exercise.

Heat tolerance during uncompensable heat stress in men and women wearing firefighter personal protective equipment

Firefighters run a risk of heat strain during occupational tasks. The number of female firefighters has been increasing, but research relevant to this group is still scarce. We aimed to investigate whether there are any sex differences in heat tolerance or physiological responses during uncompensable heat stress while wearing firefighter personal protective equipment. Twelve female (28 ± 7 years, 66 ± 5 kg, 51.7 ± 4.7 mL kg−1 min−1) and 12 male (27 ± 7 years, 83 ± 8 kg, 58.8 ± 7.5 mL kg−1 min−1) participants performed walking (maximum of 60 min) at 6W·kg−1, 40 °C, and 14% relative humidity. No differences were observed between groups in heat tolerance, rectal temperature, heart rate, percent body mass loss, thermal sensation, and rate of perceived exertion. Thus, when personnel are selected using gender-neutral physical employment standards, sex is not an independent factor influencing heat tolerance when wearing firefighter personal protective equipment during uncompensable heat stress.

Inadequate Fluid Intake In Free Living Fluid Consumption College Students

PURPOSE: The prevalence of hypohydrated children has been reported as 54.5%, with males more hypohydrated. Hydration status and fluid drinking habits of college-aged students are unclear. Also, it is uncertain if sex differences continue into young adulthood. Therefore, the purpose of this project is to analyze hydration status in college-aged students and to identify sex differences. METHODS: First morning body mass, urine and thirst levels were collected in 21 males (age = 21 ± 1 y, body mass = 78.7 ± 14.6 kg) and 22 females (age = 20 ± 1 y, body mass = 65.4 ± 12.6 kg) over 10 days. Subjects were euhydrated (urine specific gravity [USG]: <1.020) for the first 3 days, followed by free-living fluid consumption the remaining 7. First morning percent body mass Loss (%BML), thirst, USG, urine osmolality (Uosmo) and urine color (Ucolor) were analyzed between the 3 day baseline average and 7 day free-living average. 2 x 2 (sex x time) repeated measures ANOVA with post-hoc paired t-tests were used, with alpha set at 0.05. A Venn diagram introduced by Cheuvront et al determined daily hydration status during free-living condition. Dehydration parameters were defined as %BML >1%, Ucolor > 5 and thirst >4. Two markers present indicated fluid intake was considered “likely inadequate,” and three markers indicated “very likely inadequate.” RESULTS: Time difference (Baseline to Free-Living Mean ± SD, p-value) between the euhydrated baseline and free-living days for USG (1.013 ± 0.005 to 1.018 ± 0.004, 0.001), Uosmo (405 ± 114 to 660 ± 179, 0.001) and Ucolor (3 ± 1 to 5 ± 1, 0.001) was found, but not for %BML (-0.07 ± 0.18 to -0.33 ± 0.81, 0.108) or thirst (5 ± 1 to 5.5 ± 1-0.2, 0.55). No sex differences for any hydration measure were found. Based on the Venn criteria, regardless of sex, fluid intake was likely inadequate 38.9%, and very likely inadequate 6.1% of the time. CONCLUSIONS: For this sample, regardless of sex, there were differences for all hydration markers except %BML and thirst when comparing the euhydrated baseline to 7 days of free-living. However, there were no differences in hydration markers based on sex. Finally, fluid needs were considered likely inadequate 38.9%, and very likely inadequate 6.1% of the time. This is important to consider as inadequate hydration state may negatively impact overall health and mental acuity, regardless of sex.

Sex differences in the physiological responses to exercise-induced dehydration: consequences and mechanisms.

Physiological strain during exercise is increased by mild dehydration (∼1%-3% body mass loss). This response may be sex-dependent, but there are no direct comparative data in this regard. This review aimed to develop a framework for future research by exploring the potential impact of sex on thermoregulatory and cardiac strain associated with exercise-induced dehydration. Sex-based comparisons were achieved by comparing trends from studies that implemented similar experimental protocols but recruited males and females separately. This revealed a higher core temperature (Tc) in response to exercise-induced dehydration in both sexes; however, it seemingly occurred at a lower percent body mass loss in females. Although less clear, similar trends existed for cardiac strain. The average female may have a lower body water volume per body mass compared with males, and therefore the same percent body mass loss between the sexes may represent a larger portion of total body water in females potentially posing a greater physiological strain. In addition, the rate at which Tc increases at exercise onset might be faster in females and induce a greater thermoregulatory challenge earlier into exercise. The Tc response at exercise onset is associated with lower sweating rates in females, which is commonly attributed to sex differences in metabolic heat production. However, a reduced sweat gland sensitivity to stimuli, lower fluid output per sweat gland, and sex hormones promoting fluid retention in females may also contribute. In conclusion, the limited evidence suggests that sex-based differences exist in thermoregulatory and cardiac strain associated with exercise-induced dehydration, and this warrants future investigations.

Collegiate Marching Band Artists Experience High Core Body Temperatures during Rehearsals and Performances.

No research has investigated thermoregulatory responses and exertional heat illness (EHI) risk factors in marching band (MB) artists performing physical activity in high environmental temperatures. Examine core temperature (Tc) and EHI risk factors in MB artists. Descriptive epidemiology study. Three rehearsals and 2 football games for 2 NCAA Division I MBs. Nineteen volunteers completed the study (female = 13, males = 6; age = 20.5 ± 0.9 years; weight = 75.0 ± 19.1 kg; height = 165.1 ± 7.1 cm). We measured Tc pre-, post-, and every 15 minutes during activity and recorded wet-bulb globe temperature (WBGT) and relative humidity (RH) every 15 minutes. Other variables included activity time and intensity, ground surface, hydration characteristics (fluid volume, sweat rate, urine specific gravity, percent body mass loss [%BM]), and medical history (eg, previous EHI, medications). Statistical analysis included descriptives (mean ± standard deviation), comparative analyses determined differences within and between days, and linear regression identified variables that significantly explained Tc. Mean rehearsal time = 102.8 ± 19.8 minutes and game time = 260.5 ± 47.7 minutes. Max game Tc (39.1 ± 1.1°C) was significantly higher than rehearsal (38.4 ± 0.7°C, P = .003). The highest max game Tc = 41.2°C. Participants consumed significantly more fluid than their sweat rates (P < .003), which minimized %BM loss, particularly during rehearsals (-0.4 ± 0.6%). Mean game %BM loss = -0.9 ± 2.0%; however, 63.6% of the time, participants reported hypohydrated to game day. Max Tc was significantly predicted by max WBGT, max RH, ground surface, using mental health medications, and hours of sleep (adjusted R2 = 0.542, P < .001). Marching band artists experience high Tc during activity and should have access to athletic trainers who can implement EHI prevention and management strategies.

Body Mass And Urinary Hydration Measures During Preseason High School Football Practices In The Heat

Hydration assessment is an important measure to help reduce the risk of exertional heat illness. Maintaining adequate hydration can be problematic for football players practicing in the heat on consecutive days. PURPOSE: To examine day to day differences and the relationships between urinary markers of urine color (Ucol) and urine specific gravity (USG), and percent body mass loss (%BML) during football practices in the heat. METHODS: Thirty-one male high school football players (16 ± 1 years; 181.2 ± 12.0 cm; 68.1 ± 5.4 kg; BMI: 20.8 ± 1.8 km/m2) volunteered to participate in this study. Before and after each practice, players were weighed (in shorts) and provided a urine sample. Urine was assessed for Ucol and USG and was assessed by the same person. Correlations assessed relationships, while t-tests assessed differences between both pre-post differences and subsequent days. P value was significant at P<.05. RESULTS: Mean wet-bulb globe temperature across 8 practices was 30.6 ± 2.5oC. There were significant correlations between pre-Ucol and pre-USG (r = 0.73, p=0.00, n = 209) and post-Ucol and post-USG (r = 0.66, p = 0.00, n = 209). Post-Ucol (5 ± 1) was significantly greater than pre-Ucol (4 ± 2; p = 0.00). Post-USG (1.022 ± 0.008) was significantly greater than pre-USG (1.020 ± 0.008; p = 0.00). Post body mass measures were significantly lower than pre-body mass resulting in 0.9 ± 1.1%BML. Post-practice body mass and USG were not significantly different from the next day’s pre-practice measures (p > 0.05); however, post-Ucol was significantly higher (5 ± 2) compared to the next day’s pre-practice Ucol (4 ± 1; p = 0.000). CONCLUSION: Although the football players’ body mass measures were similar on subsequent days, their Ucol was lighter before the next day’s practice. We also found a strong relationship between Ucol and USG, suggesting Ucol is an acceptable hydration measure where USG is not feasible in field settings. Due to individual variability in these hydration measures, clinicians should provide individualized recommendations to ensure adequate hydration during practices in the heat as well as from one day to the next. This study was fully funded by the National Athletic Trainers’ Association Research & Education Foundation.

Do The National Institute Of Occupational Safety And Health Recommendations Prevent Hyperthermia And Dehydration?

The National Institute of Occupational Safety and Health (NIOSH) recommendations for work in the heat suggest consuming 237 mL of water every 15-20 min and rest intervals are not necessary for work if conditions are not extreme. The efficacy of these recommendations to protect against hyperthermia (rise in core temperature) and dehydration (percent body mass loss) has not been tested. PURPOSE: To test the effectiveness of the NIOSH guidelines to prevent body temperature from exceeding 38.0°C and dehydration greater than 2% of body mass. METHODS: Seven men walked for 2 hours at 6.4 kph in the highest thermal stress NIOSH allows before recommending work-to-rest ratios (34°C, 30% relative humidity). Participants drank 237 mL of water every 20 minutes while rectal temperature (Tre) monitored. Body mass and urine specific gravity (USG) were measured before and after exertion. Tre was extrapolated out to four- and eight-hour workdays based on the rate of Tre rise in the last hour of exertion. Percent dehydration was extrapolated out to four- and eight-hour workdays based on body mass lost and planned hydration during exertion. RESULTS: Tre rose from baseline (36.8±0.3°C) to the completion of exertion (38.1±0.6°C, p<0.001), with two subjects reaching the 38°C threshold. Four- and eight-hour predicted Tre were 38.6±1.1°C and 39.6±2.1°C, respectively, with 5 subjects predicted to exceed Tre threshold at 4hr and 6 subjects at 8hr. Subjects began work euhydrated (USG: 1.013±0.005) and dehydrated 0.03±0.48% during the work protocol, with no subjects reaching 2% dehydration. Four- and eight-hour predicted percent dehydration were 0.05±0.95% and 0.10±1.90%, respectively. CONCLUSIONS: Adherence to the NIOSH recommendations may be insufficient to prevent workers from reaching the hyperthermia threshold but would protect against dehydration during heavy intensity work in the heat. Adjustments to NIOSH work-to-rest ratio recommendations should be explored to maintain worker safety.

The Effect Of Hydration Status And Ice Water Dousing On Heart Rate Variability Prior To And During Intermittent Exercise In The Heat

PURPOSE: Determine the effect of hydration status and ice water dousing on heart rate variability (HRV) prior to and during intermittent exercise in the heat. METHODS: Ten team sport athletes (mean [M]± standard deviation [SD]; age, 21±1; body mass, 69.8±7.7kg; height, 175.0±7.3cm; VO2max, 54.5±6.8ml·kg-1·min-1) performed a soccer simulated intermittent exercise treadmill protocol in the heat (ambient temperature, 33°C; relative humidity, 50%) with four conditions: Euhydrated without dousing (EuND), Dehydrated without dousing (DeND), Euhydrated with dousing (EuD), and Dehydrated with dousing (DeD). Resting HRV (LnRMSSD) was measured prior to (PRE) and between intermittent exercise (MID) for 5 min. Repeated measures ANOVA was used to examine the differences of HRV in each condition followed by post-hoc with LSD. 95% confidence intervals (95%CI) were calculated. Significance was set a-priori p<0.05. RESULTS: Percent body mass loss for each condition at MID was MID-EuND (-0.9±1.8%), MID-DeND (-3.3±1.7%), MID-EuD (-0.8±1.1%), and MID-DeD (-2.4±2.2%). There were no differences between PRE-EuND (M±SD, 1.7±0.5 ln ms), PRE-DeND (M±SD, 1.8±0.9 ln ms), PRE-EuD (M±SD, 2.0±0.6 ln ms), and PRE-DeD (M±SD, 19.7±0.2 ln ms) (p>0.05). However, MID-EuND (M±SD, 1.9±0.8 ln ms) was significantly lower than MID-EuD (M±SD, 2.8±0.6 ln ms, 95%CI=-1.7- -0.2, p=0.021) and MID-DeND (M±SD, 1.6±0.5 ln ms) was significantly lower than MID-DeD (M±SD, 2.8±0.7 ln ms, 95%CI=-1.8 - -0.6, p=0.002). Furthermore, MID-DeND was significantly lower than MID-EuD (95%CI=-1.8 - -0.7, p=0.001) and MID-EuND was significantly lower than MID-DeD (95%CI=-1.9 - -0.1, p=0.037). CONCLUSIONS: There were no differences in HRV between euhydration and dehydration prior to exercise. However, ice water dousing increased HRV regardless of hydration status at the middle of intermittent exercise. Thus, ice water dousing, which is practical and time efficient, might lead to improved recovery at the middle of intermittent exercise in the heat.

Thermoregulation and Hydration in Female American Football Players During Practices.

Lopez, RM, Ashley, CD, Zinder, SM, and Tritsch, AJ. Thermoregulation and hydration in female American football players during practices. J Strength Cond Res 35(9): 2552-2557, 2021-Little is known about hydration practices and thermoregulation in female tackle football players. The purpose of the study was to examine the thermoregulatory and hydration responses of female professional American football players. Fifteen females from the same tackle football team volunteered for this observational field study. Each subject was observed for 4 practices for the following measures: gastrointestinal temperature (TGI), maximum TGI, heart rate (HR), maximum HR (HRmax), fluid consumption, sweat rate, percent body mass loss (%BML), urine specific gravity (USG), urine color (Ucol), perceptual measures of thirst, thermal sensations, and rating of perceived exertion (RPE). Descriptive data (mean ± SD) were calculated for all measures. Main measures were analyzed using a repeated-measures analysis of variance. Trials took place during evening practices. Average TGI during practices was 38.0 ± 0.3° C while maximum TGI was 38.4 ± 0.3° C (n = 14). Average practice HR was 118 ± 11 b·min-1, while HRmax was 148 ± 13 b·min-1. Subjects arrived at practices with Ucol of 3 ± 1 and USG of 1.018 ± 0.007. Postpractice USG (1.022 ± 0.007) was significantly higher than prepractice across all days (p < 0.001). The average sweat rate across 4 practices was 0.6 ml·h-1. Average %BML was 0.3 ± 0.4%. Thirst and thermal sensations were moderate (4 ± 1 and 5 ± 1, respectively), while RPE was 11 ± 1. Female football players tended to have similar physiological responses to males. Although subjects seemed to adequately match their sweat losses with fluid consumed during practice, there was considerable variability in hydration indices and hydration habits, with some subjects experiencing hypohydration and others overestimating their fluid needs. Those working with this population should emphasize the need for hydration education and establish individualized hydration regimens.

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

ObjectivesTo investigate the roles that training load and environmental conditions have on fluid balance during a collegiate men’s soccer preseason. DesignObservational study. MethodsTwenty-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%; VO2max, 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 (TAMB) 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. ResultsTotal distance covered predicted %BML during all preseason activities (r2=0.253, p<0.001), with TAMB 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 UCOL was above 4 on 13/15days, indicating a state of hypohydration. ConclusionsTotal 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.

Examining the Influence of Exercise Intensity and Hydration on Gastrointestinal Temperature in Collegiate Football Players.

DeMartini-Nolan, JK, Martschinske, JL, Casa, DJ, Lopez, RM, Stearns, RL, Ganio, MS, and Coris, E. Examining the influence of exercise intensity and hydration on gastrointestinal temperature in collegiate football players. J Strength Cond Res 32(10): 2888-2896, 2018-Debate exists regarding the influence of intensity and hydration on body temperature during American football. The purpose of this study was to observe body core temperature responses with changes in intensity and hydration. Twenty-nine male football players (age = 21 ± 1 year, height = 187 ± 9 cm, mass = 110.1 ± 23.5 kg, body mass index [BMI] = 31.3 ± 5.0, and body surface area [BSA] = 2.34 ± 0.27 m) participated in 8 days of practice in a warm environment (wet bulb globe temperature: 29.6 ± 1.6° C). Participants were identified as starters (S; n = 12) or nonstarters (n = 17) and linemen (L; n = 14) or nonlinemen (NL; n = 15). Variables of interest included core body temperature (T), hydration status, and physical performance characteristics as measured by a global positioning system. Intensity measures of average heart rate (138 ± 9 bpm), low-velocity movement (4.2 ± 1.7%), high-velocity movement (0.6 ± 0.6%), and average velocity (0.36 ± 0.10 m·s) accounted for 42% of the variability observed in T (38.32 ± 0.34° C, r = 0.65, p = 0.01). Hydration measures (percent body mass loss = -1.56 ± 0.80%, urine specific gravity [Usg] = 1.025 ± 0.006, and urine color [Ucol] = 6 ± 1) did not add to the prediction of T (p = 0.83). Metrics of exercise intensity accounted for 39% of the variability observed in maximum T (38.83 ± 0.42° C, r = 0.62, p = 0.02). Hydration measures did not add to this prediction (p = 0.40). Low-velocity movement, high-velocity movement, average velocity, BMI, and BSA were significantly different (p = 0.002, p < 0.001, p = 0.02, p < 0.001, p < 0.001, respectively) between L vs. NL. Heart rate and T were not different between L and NL (p > 0.05). Exercise intensity primarily accounted for the rise in core body temperature. Although L spent less time at higher velocities, T was similar to NL, suggesting that differences in BMI and BSA added to thermoregulatory strain.

Impact of Exercise‐Induced Dehydration on Perceived Sleep Quality

ObjectiveTo examine the effect of exercise‐induced dehydration on perceived sleep quality.MethodsTwenty‐three recreationally active males (mean±SD; age, 21±2 y; height, 179.8±6.4 cm; body mass, 75.18±8.09 kg; VO2max, 51.7±5.5 ml•kg−1•min−1; body fat, 14.4±4.6%) completed three randomized exercise trials: euhydrated + fluid replacement during exercise (EUR), euhydrated + no fluid replacement during exercise (EUD), and hypohydrated arrival via fluid restriction + no fluid replacement during exercise (HYPO) in hot conditions (ambient temperature, 35.3±0.6°C; relative humidity, 31.3±2.0%). Twenty‐four hours prior to (PRE24) and following (POST24) the exercise trial, a nude body mass (NBM) was recorded, and participants collected all urine in a sealed container to assess 24 h hydration status via urine osmolality (UOSMO) and percent body mass loss (%BML). Prior to exercise (PREEX) and following exercise (POSTEX), NBM was measured to calculate %BML. At PREEX and POST24 participants completed the Karolinska Sleep Diary (KSD) to obtain measures of overall perceived sleep quality (KSDTOT) from the previous night's sleep. Time spent sleeping (SLTM), sleep efficiency (SLEFF), overall sleep quality (SLQUAL), and total number of awakenings (AWTOT) was were also reported. Trial x time repeated measures ANOVAs with a Tukey post hoc test were used to evaluate differences in continuous dependent variables with significance set a priori p&lt;0.05.ResultsAt PRE24, UOSMO was significantly different (p&lt;0.05) in HYPO (605±212 mOsm•kg−1) versus EUD (441±176 mOsm•kg−1), and EUR (411±207 mOsm•kg−1). %BML was significantly greater (p&lt;0.001) in HYPO at PREEX (1.3±1.2%) and POSTEX (5.0±0.9%) versus EUD (−0.9±1.0%, 3.4±1.0%) and EUR (−0.8±1.0%, 0.2±1.0%). %BML in EUD was significantly greater than EUR at POSTEX, p&lt;0.001. At POST24, UOSMO was significantly higher (p=0.002) in HYPO (714±292 mOsm•kg−1) versus EUR (443±158 mOsm•kg−1); however, no significant differences (p&gt;0.05) were observed in %BML (HYPO, 0.3± 1.3%; EUD, −0.3± 0.9%; EUR, −0.0±1.1%). Hypohydration achieved prior to (PREEX) and following (POSTEX) exercise did not influence KSDTOT, SLTM, SLEFF, SLQUAL, KSDTOT, or AWTOT (p&gt;0.05). Independent of trial, SLTM (MD [95%CI], 34.6 min [7.7, 61.5], p=0.012) and SLEFF (1.4% [0.6, 2.78], p=0.041) were significantly greater at POST24 versus PREEX.ConclusionsFollowing exercise in hot conditions, participants reported an increased length and more efficient bout of sleep. The ability of participants to return to within ±1% of baseline body mass within 24 h may have negated any adverse effects of hydration state on perceived sleep quality, however future research is needed to investigate the effects of sustained hypohydration on sleep quality.Support or Funding InformationThis study was funded in part by Halo Wearables, LLC and General Electric.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Influence of cold-water immersion on recovery of elite triathletes following the ironman world championship

ObjectivesCold water immersion (CWI) has been widely used for enhancing athlete recovery though its use following an Ironman triathlon has never been examined. The purpose of this paper is to determine the influence of CWI immediately following an Ironman triathlon on markers of muscle damage, inflammation and muscle soreness. DesignProspective cohort study. MethodsThirty three (22 male, 11 female), triathletes participating in the Ironman World Championships volunteered to participate (mean±SD: age=40±11years; height=174.5±9.1cm; body mass=70±11.8kg; percent body fat=11.4±4.1%, finish time=11:03.00±01:25.08). Post race, participants were randomly assigned to a 10-min bout of 10°C CWI or no-intervention control group. Data collection occurred pre-intervention (PRE), post-intervention (POST), 16h (16POST) and 40h (40POST) following the race. Linear mixed model ANOVA with Bonferroni corrections were performed to examine group by time differences for delayed onset muscle soreness (DOMS), hydration indices, myoglobin, creatine kinase (CK), cortisol, C-reactive protein (CRP), IL-6 and percent body mass loss (%BML). Pearson’s bivariate correlations were used for comparisons with finishing time. Alpha level was set a priori at 0.05. ResultsNo significant group by time interactions occurred. Significant differences occurred for POST BML (−1.7±0.9kg) vs. 16POST, and 40POST BML (0.9±1.4, −0.1±1.2kg, respectively; p<0.001). Compared to PRE, myoglobin, CRP and CK remained significantly elevated at 40POST. Cortisol returned to PRE values by 16POST and IL-6 returned to PRE values by 40POST. ConclusionA single bout of CWI did not provide any physiological benefit during recovery from a triathlon within 40h post race. Effect of CWI beyond this time is unknown.

Outcomes from a Modified Heat Tolerance Test to Track Thermal Strain

Heat tolerance testing has been utilized within military settings to assess one’s readiness to return to duty after sustaining an exertional heat stroke (EHS). The military protocol (2-h walk at 5km·h-1 with a 2% grade in 40°C ambient temperature [TA] and 40% relative humidity [RH]) has also been applied in athletic settings to assist clinicians when returning athletes to play after EHS. However, the efficacy of the military protocol has been questioned for use in athletic settings due to its relatively low intensity compared to the physical demands of most sports. PURPOSE: To examine the physiological responses from a modified heat tolerance test (mHTT) and identify potential measures to assess individual heat tolerance from mHTT. METHODS: Thirty participants completed a VO2max test (TA, 22.9±1.1°C; RH, 39±3.9%) and a mHTT (TA, 40°C; RH, 40%) on a motorized treadmill set at 2% incline. mHTT consisted of sustained treadmill running at 60% of the velocity achieved at VO2max for up to thirty minutes. Heart rate (HR) and rectal temperature (TREC) were measured throughout the mHTT. Nude body mass (BM) was measured pre and post mHTT. Body surface area (BSA) was calculated using the equation by DuBois (1989). Adjusted physical strain index (PSIA) was calculated using the formula developed by Moran et al. (1998) with an adjustment based on the maximal HR observed during the VO2max test as the upper HR threshold for each participant. RESULTS: Average VO2max was 42.4±7.2ml·kg-1·min-1. Percent body mass loss from mHTT was 1.3±0.3%, and average end TREC was 38.87±0.38°C. The mean rate of TREC rise in the last 15 minutes of mHTT was 0.05°C ·min-1 (range, 0.02-0.09°C ·min-1). Standard linear regression analysis showed BM (R2 change, 0.23; β, -0.93; p=0.009), BSA (R2 change, 0.12; β, 0.56; p=0.053), and VO2max (R2 change, 0.12; β, 0.46; p=0.047) explained 48% of the variance observed in the TREC gain at the end of mHTT (R2=0.48, p=0.064). Mean end mHTT PSIA was 7.89 (range, 5.95-9.95; Shapiro-Wilk test, df, 31, p=0.629). There was no correlation between PSIA and BM, BSA, and VO2max (p>0.05). CONCLUSION: While TREC response in mHTT was influenced by BM, BSA, and VO2max, PSIA was able to track thermal strain independent from these variables and with normal distribution, suggesting further exploration of the utility of PSIA during the mHTT.

Self-monitoring As A Predictor For Weight Loss In A Family-based Pediatric Obesity Treatment Program

Family-based pediatric obesity treatment programs for children in the 95th-99th BMI percentile are suggested to be comprehensive and multidisciplinary to change behaviors and decrease weight. Self-monitoring (SM) has shown to be an effective strategy in child weight loss. PURPOSE: To determine if child and parent SM of weekly nutrition (NUTR), physical activity (PA), and body mass (BM) predict weight loss during a 12-week pediatric obesity treatment program. METHODS: 51 children (age: 9.8 ± 2.3 years, BMI percentile: 98.0 ± 1.3), 45 mothers (age: 41.5 ± 6.2 years), and 37 fathers (age: 41.5 ± 6.2 years) participated in 12 weekly healthy living education sessions. SM scores were determined as the number of weeks participants logged energy intake (SM-NUTR), monitored steps per day (SM-PA), and weighed-in (SM-BM) over the 12 weeks. A sum score (SM-SUM) of the three SM components was created. Stepwise multiple regression models were used to predict parent and child weight loss from SM scores. RESULTS: In 12 weeks, children lost 5.1 ± 4.4% of BM, mothers lost 5.3 ± 8.0% of BM, and fathers lost 8.2 ± 4.7% of BM. SM-SUM was 79% for fathers, 81% for children, and 88% for mothers. Table 1 represents Pearson correlation coefficients between percent body mass loss and self-monitoring scores.Table: No title available.Stepwise multiple regression models suggested that Child’s SM-SUM accounted for 19% of the variance in Child’s % BM loss after 12 weeks (R2=0.19, p<0.05). Mother’s SM-NUTR score (R2=0.47, p<0.05) and Child’s SM-SUM score (R2=0.08, p<0.05) accounted for 55% of the variance in Mother’s % BM loss (p<0.05). Father’s SM-NUTR score accounted for 29% of the variance (R2=0.29, p<0.05) in Father’s % BM loss. CONCLUSION: SM-NUTR, SM-PA, and SM-BM all appear to play a role with family weight loss, with SM-NUTR being most influential. Continuance of self-monitoring post-intervention and its influence on weight loss should be examined.

Efficacy of a Personalized Hydration Plan on Repeated Countermovement Jump Performance after Exercise-Heat Stress

Exercise-induced hyperthermia, dehydration, and fatigue independently impair anaerobic power production, but any synergistic effect on anaerobic power is less known. Further, the efficacy of a personalized hydration plan in maintaining anaerobic power after exercise-heat stress is unclear. PURPOSE: To evaluate the effect of exercise-induced hyperthermia, dehydration, and fatigue on anaerobic power during a 20-second repeated countermovement jump (CMJ). Secondly, to assess the efficacy of a personalized hydration plan in maintaining anaerobic power during CMJ after exercise-heat stress. METHODS: Five males (age: 25.4±5.7 y; height: 175.4±8.2 cm; weight: 78.7±16.8 kg; VO2max: 60.1±6.1 mL·kg-1·min-1) completed 50-90 min of exercise in warm conditions (wet bulb globe temperature: 27.0±2.24°C) with (EXP) and without (CON) fluid replacement equal to sweat rate in a counterbalanced, randomized, cross-over fashion. Gastrointestinal temperature (Tgi) and fatigue (scale of 0-10) were measured throughout exercise. Dehydration was determined by percent body mass loss (BML). Peak power (PP), mean peak power (MPP), and heart rate (HR) were measured during CMJ pre- and post-exercise using dual force plates and a HR strap. Dependent t-tests evaluated post-exercise Tgi, fatigue, and BML between groups. Separate two-way repeated measures ANOVA evaluated differences in PP, MPP, and HR with α=0.05. RESULTS: Subjects achieved 2.59±0.52% BML in CON and 0.92±0.41% in EXP (p<0.001). Post-exercise Tgi (39.29±0.31, 39.03±0.61 °C, p=0.425) and fatigue (9±1, 9±2; p=0.424) were similar between CON and EXP, respectively. HR response during post-exercise CMJ was greater in CON than EXP (174±7, 161±11, p=0.040). No differences (p>0.05) were seen in PP or MPP pre-exercise (PP: 53.80±10.78, 55.80±11.63; MPP: 45.20±8.26, 45.80±8.14) to post-exercise (PP: 52.80±12.05, 52.20±8.17; MPP: 46.40±7.83; 44.20±7.29) for EXP and CON, respectively. CONCLUSION: Exercise-induced hyperthermia, dehydration, and fatigue to the levels achieved in this study did not affect anaerobic power. Fluid replacement reduced cardiovascular strain but did not affect anaerobic power during CMJ, likely due to the mild hyperthermia and <3% dehydration in CON. Supported by CSU Fresno Grad. Student Research and Creative Activities Support Award

Carbohydrate Mouth Rinse Does Not Affect 60-min Running Performance In Females

Mouth rinsing with carbohydrate may improve 60-min endurance cycling or running performance in males. However, no data exist regarding the effect of mouth rinsing on endurance performance in females. PURPOSE: To examine the effect of mouth rinsing with a carbohydrate solution on endurance running performance in females. METHODS: Fifteen female recreational endurance runners (30-57 years) ran 2 races of 1-hour duration on an indoor track after an 8 h post-prandial period with a 7 days interval between races. This time period corresponded to the 3rd-10th day of each runner’s menstrual cycle, for the eumenorrhoeic premenopausal runners, or any time for the runners who were at menopause. Following a double-blind process and random order, participants rinsed their mouth, before the initiation of exercise and at 15, 30 and 45 min of exercise with 25 ml of either a 6.4% carbohydrate (RCHO) or a placebo solution (0% carbohydrate) (RP). Pre-race euhydration was insured by ingestion of 6 ml·kg-1 water. No fluids were ingested during exercise. Races started at 18:00 hours. RESULTS: There was no difference between treatments in runners hormonal status prior to each race for serum 17β-Estradiol [median (inter-quartile range)], RCHO: 50.2(5; 74.1) pg[BULLET OPERATOR]ml-1 vs RP: 26.0(5; 61.1) pg[BULLET OPERATOR]ml-1, z= -0.533, (p= 0.59) and Progesterone (RCHO: 0.75(0.61; 1.64) ng[BULLET OPERATOR]ml-1 vs RP: 0.74(0.64; 0.9) ng[BULLET OPERATOR]ml-1, z= -0.938, (p= 0.35). Percent body mass loss due to exercise was similar between treatments (mean ± SE, RCHO: 1.9% ± 0.1% and RP: 1.9% ± 0.1%). There was no difference in 1-hour running performance, neither by treatment (RCHO: 10621.88 ± 205.98 m vs. RP: 10454.00 ± 206.64 m; t= 1.784, p= 0.096), nor by race order (1st race: 10549.13 ± 213.67 m vs. 2nd race 10526.75 ± 201.16 m; t= 0.215, p= 0.833) (mean ± SE). Furthermore, the mean percentage effect (±99%CI) of RCHO relative to RP, 1.67%(-1.1% to 4.4%), and Cohen’s effect size (d = 0.21) support a trivial outcome effect of RCHO for total distance covered. In addition, there was no difference between treatments in the rate of perceived exertion (p= 0.14) and heart rate (p= 0.06). CONCLUSION: Carbohydrate mouth rinsing did not improve 1-h running performance in female recreational runners competing in a low ovarian hormone condition, following an 8 h fast and when no fluid was ingested during exercise.

Effect of hypohydration on postsynaptic cutaneous vasodilation and sweating in healthy men.

Hypohydration decreases cutaneous vasodilation and sweating during heat stress, but it is unknown if these decrements are from postsynaptic (i.e., sweat gland/blood vessel) alterations. The purpose of this study was to determine if hypohydration affects postsynaptic cutaneous vasodilation and sweating responses. Twelve healthy men participated in euhydrated (EU) and hypohydrated (HY) trials, with hypohydration induced via fluid restriction and passive heat stress. Changes in cutaneous vascular conductance (CVC; %max) in response to incremental intradermal infusion of the endothelium-independent vasodilator sodium nitroprusside (SNP) and the endothelium-dependent vasodilator methacholine chloride (MCh) were assessed by laser Doppler flowmetry. Local sweat rate (LSR) was simultaneously assessed at the MCh site via ventilated capsule. At the end of the last dose, maximal CVC was elicited by delivering a maximal dose of SNP (5 × 10-2 M) for 30 min to both sites with simultaneous local heating (~44°C) at the SNP site. The concentration of drug needed to elicit 50% of the maximal response (log EC50) was compared between hydration conditions. The percent body mass loss was greater with HY vs. EU (-2.2 ± 0.7 vs. -0.1 ± 0.7%, P < 0.001). Log EC50 of endothelium-dependent CVC was lower with EU (-3.62 ± 0.22) vs. HY (-2.93 ± 0.08; P = 0.044). Hypohydration did not significantly alter endothelium-independent CVC or LSR (both P > 0.05). In conclusion, hypohydration attenuated endothelium-dependent CVC but did not affect endothelium-independent CVC or LSR responses. These data suggest that reductions in skin blood flow accompanying hypohydration can be partially attributed to altered postsynaptic function.