Whole-body cooling effectiveness of cold intravenous saline following exercise hyperthermia: a randomized trial.

INTRODUCTION: In some athletic, occupational, military and emergency settings, cold intravenous (IV) fluids are used to facilitate whole-body cooling in an effort to treat heat illness. This treatment has anecdotal support, but currently lacks evidence supporting it as a whole-body cooling modality. Other modalities may offer superior cooling rates, and thus, patient outcomes following treatment. We sought to evaluate cooling rates of cold-IV normal saline immediately following exercise-induced hyperthermia. METHODS: Eight healthy participants (3 females; 25 ± 2y; 72.9 ± 10.9 kg) completed 2 trials in random order. Prior to exercise, participants provided a small urine sample to confirm hydration status via urine specific gravity. Wet bulb globe temperature (WBGT) was assessed throughout trials. In both trials, participants exercised outdoors until rectal temperature (Tre) reached ∼38.9 °C, or volitional exhaustion, and then were cooled. In cooling, participants received either cold-IV (∼5 °C 0.9% NaCl fluids) or no treatment (sat in the shade; passive). Throughout exercise and treatment, Tre and heart rate (HR) were monitored. During exercise and every 10 min throughout cooling, participants were asked to assess thermal sensation. RESULTS: Hydration status (P = .847) was not significantly different prior to exercise between trials. WBGT throughout was not different between trials (P = .426). Maximum Tre reached was not different between cold-IV (38.88 ± 0.30 °C) and passive cooling (38.76 ± 0.28 °C) trials (P = .184). Mean cooling rate for cold-IV (0.039 ± 0.005 °C·min-1) was significantly greater than for passive cooling (0.028 ± 0.005 °C·min-1; P = .002). Tre throughout cooling was not different between trials (P = .707), but did decrease throughout (P = .008), regardless of trial. HR was decreased over time (P < .001), but cold-IV and passive cooling were not different throughout HR recovery (P = .141). Thermal sensation decreased throughout cooling (P < .001), but was not different between trials (p = .278). CONCLUSION: Emergency medical personnel should adopt treatment protocols that employ documented effective treatments for exertional heat stroke. In isolation, our data casts significant doubt for the use of cold-IV saline infusion for whole-body cooling of hyperthermic individuals.

Examining the links between hydration knowledge, attitudes and behavior.

PURPOSE: This study aimed to examine the psychological factors (knowledge, barriers and facilitators) that can contribute to hydration-related behaviors (i.e., fluid intake) in the general population and how these relate to physical health. METHODS: A structured survey was developed to examine the links between hydration knowledge (29 items), attitudes about hydration (80 items), and fluid intake behavior (8 items) among US adults. Survey data from Phase 1 (n =301, US adults) psychometrically evaluated the items via item analysis (knowledge and fluid behavior) and factor analysis (attitudes). Phase 2 survey data (n =389, US adults and college students) refined and validated the new 16-item hydration knowledge measure, 4-item fluid intake behavior index, and 18-item attitude measure (barriers and facilitators of hydration-related behaviors) alongside indices of physical health (BMI and exercise behaviors). RESULTS: Participants had a moderate level of hydration knowledge (Phase 1: 10.91 ± 3.10; Phase 2: 10.87 ± 2.47). A five-factor measure of attitudes which assessed both facilitators (social pressure and attention to monitoring) and barriers (lack of effort, physical barriers and lack of a fluid container) to hydration demonstrated strong internal consistency (αs from 0.75 to 0.90). Attitudes about hydration-most notably barriers to hydration-were associated with indicators of health and with fluid intake behaviors, whereas hydration knowledge was not. CONCLUSIONS: Increasing hydration knowledge may be necessary for people who hold inaccurate information about hydration, but attitudes about hydration are likely to have a larger impact on fluid intake behaviors and health-related outcomes.

Sweat Characteristics of Cramp-Prone and Cramp-Resistant Athletes.

Exercise-associated muscle cramps (EAMCs) are thought to be caused by dehydration and/or electrolyte losses. In this multicenter, cross-sectional study, the authors determined whether sweat rates (SRs), sweat electrolyte concentrations, or sweat electrolyte content differed in athletes with (i.e., crampers) and without (i.e., noncrampers) a history of EAMCs and whether these variables could predict EAMC-prone athletes. Male and female collegiate athletes (N = 350) from 11 sports with (n = 245) and without (n = 105) a self-reported history of EAMCs completed a typical exercise or conditioning session. SRs, calculated from body mass, and posterior forearm sweat were analyzed for sweat sodium concentration ([Na+]sw), sweat potassium concentration ([K+]sw), and sweat chloride concentration ([Cl-]sw). The authors used SRs and sweat electrolyte concentrations to calculate sweat electrolyte content lost. Within each gender, no differences in SRs (204 males, p = .92; 146 females, p = .24); [Na+]sw (191 males, p = .55; 126 females, p = .55); Na+sw content (191 males, p = .59; 126 females, p = .20); [K+]sw (192 males, p = .57; 126 females, p = .87); K+sw content (192 males, p = .49; 126 females, p = .03); [Cl-]sw (192 males, p = .94; 77 females, p = .57); and Cl-sw content (192 males, p = .55; 77 females, p = .34) occurred between crampers and noncrampers. Receiver operating characteristic curve analysis revealed that sweat electrolyte content and SRs were predictive of EAMC-prone athletes in American football (area under curve = 0.65-0.72, p ≤ .005), but not in any other sport. EAMCs may not be solely caused by fluid or electrolyte losses in most athletes. Fluid and electrolyte replacement may help American footballers. Clinicians should individualize fluid and electrolyte replacement and understand different etiologies for EAMCs.

Mild hypohydration impairs cycle ergometry performance in the heat: A blinded study.

The aim of the present study was to observe the effect of mild hypohydration on exercise performance with subjects blinded to their hydration status. Eleven male cyclists (weight 75.8 ± 6.4 kg, VO2peak : 64.9 ± 5.6 mL/kg/min, body fat: 12.0 ± 5.8%, Powermax : 409 ± 40 W) performed three sets of criterium-like cycling, consisting of 20-minute steady-state cycling (50% peak power output), each followed by a 5-km time trial at 3% grade. Following a familiarization trial, subjects completed the experimental trials, in counter-balanced fashion, on two separate occasions in dry heat (30°C, 30% rh) either hypohydrated (HYP) or euhydrated (EUH). In both trials, subjects ingested 25 mL of water every 5 minutes during the steady-state and every 1 km of the 5-km time trials. In the EUH trial, sweat losses were fully replaced via intravenous infusion of isotonic saline, while in the HYP trial, a sham IV was instrumented. Following the exercise protocol, the subjects' bodyweight was changed by -0.1 ± 0.1% and -1.8 ± 0.2% for the EUH and HYP trial, respectively (P < 0.05). During the second and third time trials, subjects averaged higher power output (309 ± 5 and 306 ± 5 W) and faster cycling speed (27.5 ± 3.0 and 27.2 ± 3.1 km/h) in the EUH trial compared to the HYP trial (Power: 287 ± 4 and 276 ± 5 W, Speed: 26.2 ± 2.9 and 25.5 ± 3.3 km/h, all P < 0.05). Core temperature (Tre ) was higher in the HYP trial throughout the third steady-state and 5-km time trial (P < 0.05). These data suggest that mild hypohydration, even when subjects were unaware of their hydration state, impaired cycle ergometry performance in the heat probably due to greater thermoregulatory strain.

Postsynaptic cutaneous vasodilation and sweating: influence of adiposity and hydration status.

INTRODUCTION: Obesity and hypohydration independently affect postsynaptic endothelial function, but it is unknown if hypohydration affects lean and obese individuals differently. PURPOSE: To examine the effect of hypohydration on postsynaptic cutaneous vasodilation and sweating in men with high and low adiposity (HI- and LO-BF, respectively). METHODS: Ten males with LO-BF and ten with HI-BF were instrumented for forearm microdialysis when euhydrated and hypohydrated. Changes in cutaneous vascular conductance (CVC) with intradermal infusion of sodium nitroprusside (SNP) and methacholine chloride (MCh) were assessed. Local sweat rate (LSR) was simultaneously assessed at the MCh site. At the end of the last dose, maximal CVC was elicited by delivering a maximal dose of SNP for 30 min to both sites with simultaneous local heating at the SNP site. The concentration of drug needed to elicit 50% of the maximal response (EC50) was compared between groups and hydration conditions. RESULTS: When euhydrated, EC50 of MCh-induced CVC was not different between LO- vs. HI-BF [- 3.04 ± 0.12 vs. - 2.98 ± 0.19 log (MCh) M, P = 0.841]. EC50 of SNP-induced CVC was higher in euhydrated HI- vs. LO-BF (- 1.74 ± 0.17 vs. - 2.13 ± 0.06 log (SNP) M, P = 0.034). Within each group, hydration status did not change MCh- or SNP-induced CVC (P > 0.05). LSR was not different between groups or hydration condition (P > 0.05). CONCLUSIONS: These data suggest reduced sensitivity of endothelium-independent vasodilation in individuals with high adiposity when euhydrated. However, hypohydration does not affect cutaneous vasodilation or local sweat rate differently between individuals with low or high adiposity.

Observation of Women Soccer Players' Physiology During a Single Season.

Paulsen, KM, Butts, CL, and McDermott, BP. Observation of women soccer players' physiology during a single season. J Strength Cond Res 32(6): 1702-1707, 2018-The purpose of this study was to observe heart rate (HR) responses in match settings over the course of a conference season in National Collegiate Athletic Association Division I women's soccer. Twenty-one female collegiate soccer players were provided a HR monitor and instructed to wear it for the duration of match play. Player positions included 6 defenders (DEF), 6 midfielders (MID), and 9 forwards (FWD). Defenders were further identified as either center defenders (CD) or outside defenders (OD). A 1-way analysis of variance was used to determine if mean HR varied between FWD, MID, and DEF. An independent t-test was used to determine if there was a difference between CD and OD HRs. The FWD, MID, and DEF did have significantly different mean HR (p ≤ 0.05), but post-hoc analysis revealed no significant differences (p ≥ 0.05). However, CD demonstrated significantly lower HRs than OD (p = 0.009). Player position, specifically in the CD and OD role, impact the intensity of exercise in match settings and may be used to specify training and conditioning sessions.

Effect of a Cooling Kit on Physiology and Performance Following Exercise in the Heat.

CONTEXT: Exercising in the heat leads to an increase in body temperature that can increase the risk of heat illness or cause detriments in exercise performance. OBJECTIVE: To examine a phase change heat emergency kit (HEK) on thermoregulatory and perceptual responses and subsequent exercise performance following exercise in the heat. DESIGN: Two randomized crossover trials that consisted of 30 minutes of exercise, 15 minutes of treatment (T1), performance testing (5-10-5 pro-agility test and 1500-m run), and another 15 minutes of treatment (T2) identical to T1. SETTING: Outdoors in the heat (wet-bulb globe temperature: 31.5°C [1.8°C] and relative humidity: 59.0% [5.6%]). PARTICIPANTS: Twenty-six (13 men and 13 women) individuals (aged 20-27 y). INTERVENTIONS: Treatment was performed with HEK and without HEK (control, CON) modality. MAIN OUTCOME MEASURES: Gastrointestinal temperature, mean skin temperature, thirst sensation, and muscle pain. RESULTS: Maximum gastrointestinal temperature following exercise and performance was not different between trials (P > .05). Cooling rate was faster during T1 CON (0.053°C/min [0.049°C/min]) compared with HEK (0.043°C/min [0.032°C/min]; P = .01). Mean skin temperature was lower in HEK during T1 (P < .001) and T2 (P = .05). T2 thirst was lower in CON (P = .02). Muscle pain was lower in HEK in T2 (P = .03). Performance was not altered (P > .05). CONCLUSIONS: HEK improved perception but did not enhance cooling or performance following exercise in the heat. HEK is therefore not recommended to facilitate recovery, treat hyperthermia, or improve performance.

Effect of passive heat stress and exercise in the heat on arterial stiffness.

PURPOSE: Prior evidence indicates that acute heat stress and aerobic exercise independently reduce arterial stiffness. The combined effects of exercise and heat stress on PWV are unknown. The purpose of this study was to determine the effects of heat stress with passive heating and exercise in the heat on arterial stiffness. METHODS: Nine participants (n = 3 females, 47 ± 11 years old; 24.1 ± 2.8 kg/m2) completed four trials. In a control trial, participants rested supine (CON). In a passive heating trial (PH), participants were heated with a water-perfusion suit. In two other trials, participants cycled at ~50% of [Formula: see text] in a hot (~40 °C; HC trial) or cool (~15 °C; CC trial) environment. Arterial stiffness, measured by PWV, was obtained at baseline and after each intervention (immediately, 15, 30, 45, and 60 min post). Central PWV (C PWV) was assessed between the carotid/femoral artery sites. Upper and lower peripheral PWV was assessed using the radial/carotid (U PWV) and dorsalis pedis/femoral (L PWV) artery sites. The mean body temperature (T B) was calculated from the skin and rectal temperatures. RESULTS: No significant changes in T B were observed during the CON and CC trials. As expected, the PH and HC trials elevated T B 2.69 ± 0.23 °C and 1.67 ± 0.27 °C, respectively (p < 0.01). PWV did not change in CON, CC, or HC (p > 0.05). However, in the PH trial, U PWV was reduced immediately (-107 ± 81 cm/s) and 15 min (-93 ± 82 cm/s) post-heating (p < 0.05). CONCLUSIONS: Heat stress via exercise in the heat does not acutely change arterial stiffness. However, passive heating reduces U PWV, indicating that heat stress has an independent effect on PWV.

Exertional Hyponatremia and Serum Sodium Change During Ultraendurance Cycling.

INTRODUCTION: Exertional hyponatremia (EH) during prolonged exercise involves all avenues of fluid-electrolyte gain and loss. Although previous research implicates retention of excess fluid, EH may involve either loss, gain, or no change of body mass. Thus, the etiology, predisposing factors, and recommendations for prevention are vague-except for advice to avoid excessive drinking. PURPOSE: This retrospective field study presents case reports of two unacquainted recreational cyclists (LC, 31y and AM, 39 years) who began exercise with normal serum electrolytes but finished a summer 164-km ride (ambient, 34±5°C) with a serum [Na+] of 130 mmol/L. METHODS: To clarify the etiology of EH, their pre- and post-exercise measurements were compared to a control group (CON) of 31 normonatremic cyclists (mean ± SD; 37±6 years; 141±3 mmol Na+/L). RESULTS: Anthropomorphic characteristics, exercise time, and post-exercise ratings of thermal sensation, perceived exertion and muscle cramp were similar for LC, AM and CON. These two hyponatremic cyclists consumed a large and similar volume of fluid (191 and 189 ml/kg), experienced an 11 mmol/L decrease of serum [Na+], reported low thirst sensations; however, LC gained 3.1 kg (+4.3% of body mass) during 8.9 hr of exercise and AM maintained body mass (+0.1kg, +0.1%, 10.6h). In the entire cohort (n = 33), post-event serum [Na+] was strongly correlated with total fluid intake (R2 = 0.45, p < .0001), and correlated moderately with dietary sodium intake (R2=0.28, p = .004) and body mass change (R2 = 0.22, p = .02). Linear regression analyses predicted the threshold of EH onset (<135 mmol Na+/L) as 168 ml fluid/kg. CONCLUSIONS: The wide range of serum [Na+] changes (+6 to -11 mmol/L) led us to recommend an individualized rehydration plan to athletes because the interactions of factors were complex and idiosyncratic.

Effect of Caffeine on Perceived Soreness and Functionality Following an Endurance Cycling Event.

Caldwell, AR, Tucker, MA, Butts, CL, McDermott, BP, Vingren, JL, Kunces, LJ, Lee, EC, Munoz, CX, Williamson, KH, Armstrong, LE, and Ganio, MS. Effect of caffeine on perceived soreness and functionality following an endurance cycling event. J Strength Cond Res 31(3): 638-643, 2017-Caffeine can reduce muscle pain during exercise; however, the efficacy of caffeine in improving muscle soreness and recovery from a demanding long-duration exercise bout has not been established. The purpose of this study was to investigate the effects of caffeine intake on ratings of perceived muscle soreness (RPMS) and perceived lower extremity functionality (LEF) following the completion of a 164-km endurance cycling event. Before and after cycling RPMS (1-to-6; 6 = severe soreness) and LEF (0-to-80; 80 = full functionality) were assessed by questionnaires. Subjects ingested 3 mg/kg body mass of caffeine or placebo pills in a randomized, double-blind fashion immediately after the ride and for the next 4 mornings (i.e., ∼800 hours) and 3 afternoons (i.e., ∼1200 hours). Before each ingestion, RPMS and LEF were assessed. Afternoon ratings of LEF were greater with caffeine ingestion the first day postride (65.0 ± 6.1 vs. 72.3 ± 6.7; for placebo and caffeine, respectively; p = 0.04), but at no other time points (p > 0.05). The caffeine group tended to have lower overall RPMS in the afternoon versus placebo (i.e., main effect of group; 1.1 ± 0.2 vs. 0.5 ± 0.2; p = 0.09). Afternoon RPMS for the legs was significantly lower in the caffeine group (main effect of caffeine; 1.3 ± 0.2 vs. 0.5 ± 0.3; p = 0.05). In conclusion, ingesting caffeine improved RPMS for the legs, but not LEF in the days following an endurance cycling event. Athletes may benefit from ingesting caffeine in the days following an arduous exercise bout to relieve feelings of soreness and reduced functionality.

Effects of mild hypohydration on cooling during cold-water immersion following exertional hyperthermia.

PURPOSE: We investigated the effects of mild hypohydration compared to euhydration on the cooling efficacy of cold-water immersion (CWI). METHODS: Fourteen participants (eight male, six female; age 26 ± 5 years; ht 1.77 ± 0.08 m; wt 72.2 ± 8.8 kg; 20.6 ± 7.4 % body fat) completed one euhydrated (EU) trial followed by one hypohydrated trial (HY; via 24 h fluid restriction) in an environmental chamber (33.6 ± 0.9 °C, 55.8 ± 1.7 % RH). Volitional exercise was performed in a manner that matched end-exercise rectal temperature (T re) through repeating exercise mode and intensity. Participants were then immersed in ice water (2.0 ± 0.8 °C) until T re reached 38.1 °C or for a maximum of 15 min. T re, heart rate (HR), skin blood flux (SBF) and mean skin temperature (T sk) were monitored continuously during cooling. RESULTS: Pre-cooling body mass was decreased in the HY trial (-2.66 ± 1.23 % body mass) and maintained in the EU trial (-0.66 ± 0.44 %) compared to baseline mass (P < 0.001). Cooling rates were faster when EU (0.14 ± 0.05 °C/min) compared to HY (0.11 ± 0.05 °C/min, P = 0.046). HR, SBF, and T sk were not different between EU and HY trials (P > 0.05), however, all variables significantly decreased with immersion independent of hydration status (P < 0.001). CONCLUSION: The primary finding was that hypohydration modestly attenuates the rate of cooling in exertionally hyperthermic individuals. Regardless of hydration status, the cooling efficacy of CWI was preserved and should continue to be utilized in the treatment of exertional hyperthermia.

Pro- and anti-inflammatory cytokine responses to a 164-km road cycle ride in a hot environment.

PURPOSE: The purpose of this study was to examine the circulating cytokine response to a recreational 164-km road cycling event in a high ambient temperature and to determine if this response was affected by self-paced exercise time to completion. METHODS: Thirty-five men and five women were divided into tertiles based on time to complete the cycling event: slowest (SLOW), moderate (MOD), and fastest (FAST) finishers. Plasma samples were obtained 1-2 h before (PRE) and immediately after (IP) the event. A high-sensitivity multiplex assay kit was used to determine the concentration of plasma anti-inflammatory cytokines (IL-4, IL-5, IL-10, IL-13) and pro-inflammatory cytokines (IL-1ß, IL-2, IL-6, IL-7, IL-8, IL-12, GM-CSF, IFN-γ, and TNF-α). RESULTS: The concentration of plasma IL-10 increased significantly (p < 0.05) in FAST and MOD groups and had no change in the SLOW group in response to a 164-km cycling event in the hot environment. Other cytokine responses were not influenced by the Time to completion. Pro-inflammatory cytokines IL-1ß, IL-2, GM-CSF, and TNF-α decreased; whereas, IL-6 and IL-8 increased from PRE to IP. Additionally, anti-inflammatory cytokines IL-4 and IL-13 decreased. CONCLUSIONS: Completion of a 164-km cycling event induced substantial changes in circulating pro- and anti-inflammatory cytokine concentrations. Time to completion appears to have a greater influence on the systemic IL-10 response than the environmental condition; however, it is possible that a threshold for absolute intensity must be reached for environmental conditions to affect the IL-10 response to exercise. Thus, cyclists from the FAST/MOD groups appear more likely to experience an acute transient immune suppression than cyclists from the SLOW group.

Fluid Balance of Adolescent Swimmers During Training.

Swimming, either competitively or leisurely, is a unique activity that involves prolonged exercise while immersed in stable water temperatures. This environment could have an influence on the hydration status of swimmers independently of fluid balance. Forty-six healthy adolescent swimmers (26 males and 20 females; 12.8 ± 2.3 years; 50.6 ± 13.4 kg) were studied during a typical training session in an indoor swimming pool. First morning, prepractice and postpractice urine samples were tested for osmolality and specific gravity, whereas all athletes consumed fluids ad libitum. Sixty-seven percent of the athletes were hypohydrated (urine osmolality [Uosm] ≥700 mmol·kg(-1)) based on their first morning urine sample, which increased to 78% immediately before training. During the 2-hour swimming practice, the minimal sweat loss (0.39 ± 0.27 L) combined with ad libitum fluid availability resulted in unchanged body weight (0.1 ± 0.3 kg). Additionally, thirst was similar (before practice: 46 ± 26, after practice: 55 ± 33 mm on a 100-mm visual analog scale) at pretraining and posttraining time points (p > 0.05). Interestingly, postpractice Uosm was reduced significantly compared with the prepractice value (630 vs. 828 mmol·kg(-1); p = 0.001), without any significant change in body weight (0.1 ± 0.3 kg; p > 0.05). In conclusion, the present data indicated that more than two-thirds of the young swimmers appeared in their practice suboptimally hydrated. Although no changes in body mass were observed during the swimming practice, the decrease in urine hydration markers after swimming might less accurately reflect hydration state.

Hydration status affects mood state and pain sensation during ultra-endurance cycling.

Laboratory-based studies indicate mild dehydration adversely affects mood. Although ultra-endurance events often result in mild to moderate dehydration, little research has evaluated whether the relationship between hydration status and mood state also exists in these arduous events. Therefore, the purpose of this study was to evaluate how hydration status affected mood state and perceptual measures during a 161 km ultra-endurance cycling event. One hundred and nineteen cyclists (103 males, 16 females; age = 46 ± 9 years; height = 175.4 ± 17.9 cm; mass = 82.8 ± 16.3 kg) from the 2011 and 2013 Hotter'N Hell events participated. Perceived exertion, Thermal, Thirst, and Pain sensations, Brunel Profile of Mood States, and urine specific gravity (USG) were measured pre- (~1 h before), mid- (~97 km), and post-ride. Participants were classified at each time point as dehydrated (USG ≥ 1.022) or euhydrated (USG ≤ 1.018). Independent of time point, dehydrated participants (USG = 1.027 ± 0.004) had decreased Vigour and increased Fatigue, Pain, Thirst, and Thermal sensations compared to euhydrated participants (USG = 1.012 ± 0.004; all P < 0.01). USG significantly correlated with Fatigue (r = 0.36), Vigour (r = -0.27), Thirst (r = 0.15), and Pain (r = 0.22; all P < 0.05). In conclusion, dehydrated participants had greater Fatigue and Pain than euhydrated participants. These findings indicate dehydration may adversely affect mood state and perceptual ratings during ultra-endurance cycling.

Effect of air-filled vest on exercise-heat strain when wearing ballistic protection.

OBJECTIVES: The purpose was to determine if an air-filled vest worn under ballistic protection reduces physiological strain during exercise in the heat either while wearing a tactical military (TM) protective vest or a law enforcement (LE) concealable vest. METHODS: Sixteen men (24.5±3.9 years; 179.5±5.6 cm; 84.6±12.3kg) performed either two or four trials of treadmill walking (1.34 m s(-1); 2% grade) over 120 min in a hot, dry environment (37°C, 30% relative humidity, wind speed 3.5 m s(-1)). Participants completed trials wearing a TM or LE, with either the air-filled vest (TMa; LEa) or no vest (TMc; LEc) in random order. During trials, participants wore Army Combat Uniform pants. Physiological variables measured every 5min included gastrointestinal temperature (T GI), mean skin temperature (T sk), and heart rate (HR). Sweat rate (SR) was calculated based on fluid intake and body mass measures. RESULTS: In the tactical trial (TMa versus TMc), no differences in final T GI (38.2±0.4 versus 38.3±0.4°C), T sk (35.0±0.9 versus 35.0±1.0°C), HR (142±19 versus 143±23 bpm) existed (P>0.05). In the LE trials (LEa versus LEc), no differences in final T GI (38.0±0.4 versus 38.1±0.3°C), T sk (35.3±1.1 versus 35.6±0.9°C), HR (132±20 versus 135±20 bpm) existed (P>0.05). Despite slightly higher SR, there was no statistical difference in TM (1.15±1.13 versus 1.54±0.46 l h(-1); P=0.10) or in LE (1.39±0.52 versus 1.37±0.18 l h(-1); P=0.35) during trials. CONCLUSION: When participants exercised with a TM or LE while wearing the air-filled vest, there were no thermoregulatory and physiological differences compared to control trials. In our testing conditions, the air-filled device had little effect on physiological responses during prolonged mild exercise in the heat.

Association of Knowledge and Health Habits with Physiological Hydration Status.

The association of hydration knowledge and health habits with hydration status and fluid intake is rarely examined. We sought to determine whether knowledge or physical health behaviors predict physiological hydration status and fluid intake. Ninety-six participants (59 female; 27 ± 10 year) completed the previously validated hydration survey. Participants then recorded total fluids consumed (TFC), collected urine, and tracked void frequency for 24 h. Hydration status was assessed via 24 h urine specific gravity (USG) and osmolality (Uosm). Health behaviors included self-reported physical activity, BMI, smoking, alcoholic drinking, and sleep status. TFC was significantly correlated with 24 h USG (r = -0.390; p < 0.001), Uosm (r = -0.486; p < 0.001), total urine volume (r = 0.675; p < 0.001), and void frequency (r = 0.518; p < 0.001). Hydration knowledge was not correlated with 24 h USG (r = 0.085; p = 0.420), Uosm (r = 0.087; p = 0.419), urine total volume (r = 0.019; p = 0.857), void frequency (r = 0.030; p = 0.771), or TFC (r = 0.027; p = 0.813). Hydration knowledge did not predict 24 h USG (LR+ = 1.10; LR- = 0.90), Uosm (LR+ = 0.81; LR- = 1.35), or TFC (LR+ = 1.00; LR- = 1.00). Health habits did not predict 24 h USG, Uosm, or TFC. In conclusion, self-reported 24 h diet and fluid log recording is comparable to hydration status verification via 24 h urine collection. Hydration knowledge and health habits are not related to, or predictive of, hydration status.

Sports drinks do not increase acute kidney injury risk in males during industrial work in the heat when euhydration is maintained, a randomized crossover trial.

Industrial workers regularly perform physical labor under high heat stress, which may place them at risk for dehydration and acute kidney injury. Current guidelines recommend that workers should consume sports drinks to maintain euhydration during work shifts. However, the impact of fructose sweetened sports drinks on acute kidney injury risk is unknown. The purpose of this study was to investigate the effects of sports drink consumption on markers of acute kidney injury following simulated industrial work in the heat. Twenty males completed two matched 2 h simulated industrial work trial visits in a warm and humid environment (30 °C and 55% relative humidity). During and following the bout of simulated work, participants consumed either a commercially available sports drink or a noncaloric placebo. Urine and blood samples, collected pre-, post-, and 16 h post-work were assayed for markers of hydration (plasma/urine osmolality, and urine specific gravity) and acute kidney injury (KIM-1 and NGAL). There were no differences in physiological or perceptual responses to the bout of work (interaction p > 0.05 for all indices), and markers of hydration were similar between trials (interaction p > 0.05 for all indices). KIM-1 (Placebo: Δ Ln 1.18 ± 1.64; Sports drink: Δ Ln 1.49 ± 1.10 pg/mL; groupwide d = 0.89, p < 0.001) and NGAL (Placebo: Δ Ln 0.44 ± 1.11; Sports drink: Δ Ln 0.67 ± 1.22 pg/mL; groupwide d = 0.39, p = 0.03) were elevated pre- to post-work, but there were no differences between trials (interaction p > 0.05). These data provide no evidence that consumption of fructose sweetened sports drinks increases the risk of acute kidney injury during physical work in the heat.