Evan C. Johnson

The American Football Uniform: Uncompensable Heat Stress and Hyperthermic Exhaustion

CONTEXT In hot environments, the American football uniform predisposes athletes to exertional heat exhaustion or exercise-induced hyperthermia at the threshold for heat stroke (rectal temperature [T(re)] > 39 degrees C). OBJECTIVE To evaluate the differential effects of 2 American football uniform configurations on exercise, thermal, cardiovascular, hematologic, and perceptual responses in a hot, humid environment. DESIGN Randomized controlled trial. SETTING Human Performance Laboratory. PATIENTS OR OTHER PARTICIPANTS Ten men with more than 3 years of competitive experience as football linemen (age = 23.8 +/- 4.3 years, height = 183.9 +/- 6.3 cm, mass = 117.41 +/- 12.59 kg, body fat = 30.1% +/- 5.5%). INTERVENTION(S) Participants completed 3 controlled exercise protocols consisting of repetitive box lifting (lifting, carrying, and depositing a 20.4-kg box at a rate of 10 lifts per minute for 10 minutes), seated recovery (10 minutes), and up to 60 minutes of treadmill walking. They wore one of the following: a partial uniform (PART) that included the National Football League (NFL) uniform without a helmet and shoulder pads; a full uniform (FULL) that included the full NFL uniform; or control clothing (CON) that included socks, sneakers, and shorts. Exercise, meals, and hydration status were controlled. MAIN OUTCOME MEASURE(S) We assessed sweat rate, T(re), heart rate, blood pressure, treadmill exercise time, perceptual measurements, plasma volume, plasma lactate, plasma glucose, plasma osmolality, body mass, and fat mass. RESULTS During 19 of 30 experiments, participants halted exercise as a result of volitional exhaustion. Mean sweat rate, T(re), heart rate, and treadmill exercise time during the CON condition were different from those measures during the PART (P range, .04-.001; d range, 0.42-0.92) and FULL (P range, .04-.003; d range, 1.04-1.17) conditions; no differences were detected for perceptual measurements, plasma volume, plasma lactate, plasma glucose, or plasma osmolality. Exhaustion occurred during the FULL and PART conditions at the same T(re) (39.2 degrees C). Systolic and diastolic blood pressures (n = 9) indicated that hypotension developed throughout exercise (all treatments). Compared with the PART condition, the FULL condition resulted in a faster rate of T(re) increase (P < .001, d = 0.79), decreased treadmill exercise time (P = .005, d = 0.48), and fewer completed exercise bouts. Interestingly, T(re) increase was correlated with lean body mass during the FULL condition (R(2) = 0.71, P = .005), and treadmill exercise time was correlated with total fat mass during the CON (R(2) = 0.90, P < .001) and PART (R(2) = 0.69, P = .005) conditions. CONCLUSIONS The FULL and PART conditions resulted in greater physiologic strain than the CON condition. These findings indicated that critical internal temperature and hypotension were concurrent with exhaustion during uncompensable (FULL) or nearly uncompensable (PART) heat stress and that anthropomorphic characteristics influenced heat storage and exercise time to exhaustion.

Effect of quercetin supplementation on maximal oxygen uptake in men and women

Abstract Quercetin is a naturally occurring flavonoid with anti-oxidant and anti-inflammatory properties. The effect of quercetin supplementation on maximal oxygen uptake ([Vdot]O2max) is unknown. The purpose of this investigation was to test the effects of quercetin supplementation on [Vdot]O2max in untrained, sedentary individuals. After baseline treadmill [Vdot]O2max testing, 11 participants (5 males, 6 females) ingested either placebo or quercetin-supplemented (1000 mg · day−1) food bars in a randomized, double-blind, counterbalanced, crossover research design. The participants ingested food bars for six consecutive mornings (5 days). On the sixth morning, participants underwent repeat [Vdot]O2max testing. After a 22 day wash-out, the participants repeated baseline [Vdot]O2max testing, daily consumption of the opposite food bars, and post-supplementation [Vdot]O2max testing. The condition × time interaction for [Vdot]O2max was non-significant when expressed in absolute (litres · min−1; P = 0.929) and relative (ml · kg−1 · min−1; P = 0.778) terms. These findings were similar when taking sex into account (P > 0.05). The mean difference in [Vdot]O2max change from pre to post between groups (quercetin vs. placebo) was 0.139 ml · kg−1 · min−1 (P = 0.780). Other physiological measures also were similar between conditions (P > 0.05). In conclusion, 5 days of quercetin supplementation did not influence [Vdot]O2max or related variables in sedentary men and women.

Hydration biomarkers and dietary fluid consumption of women.

Normative values and confidence intervals for the hydration indices of women do not exist. Also, few publications have precisely described the fluid types and volumes that women consume. This investigation computed seven numerical reference categories for widely used hydration biomarkers (eg, serum and urine osmolality) and the dietary fluid preferences of self-reported healthy, active women. Participants (n=32; age 20±1 years; body mass 59.6±8.5 kg; body mass index [calculated as kg/m(2)] 21.1±2.4) were counseled in the methods to record daily food and fluid intake on 2 consecutive days. To reduce day-to-day body water fluctuations, participants were tested only during the placebo phase of the oral contraceptive pill pack. Euhydration was represented by the following ranges: serum osmolality=293 to 294 mOsm/kg; mean 24-hour total fluid intake=2,109 to 2,506 mL/24 hours; mean 24-hour total beverage intake=1,300 to 1,831 mL/24 hours; urine volume=951 to 1,239 mL/24 hours; urine specific gravity=1.016 to 1.020; urine osmolality=549 to 705 mOsm/kg; and urine color=5. However, only 3% of women experienced a urine specific gravity <1.005, and only 6% exhibited a urine color of 1 or 2. Water (representing 45.3% and 47.9% of 24-hour total fluid intake), tea, milk, coffee, and fruit juice were consumed in largest volumes. In conclusion, these data provide objective normative values for hyperhydration, euhydration, and dehydration that can be used by registered dietitians and clinicians to counsel women about their hydration status.

Assessment of hydration biomarkers including salivary osmolality during passive and active dehydration

BACKGROUND/OBJECTIVES:Hydration state can be assessed via body mass change (BMΔ), serum and urine osmolality (Sosm, Uosm), urine-specific gravity (Usg) and urine volume (Uvol). As no hydration index has been shown to be valid in all circumstances, value exists in exploring novel biomarkers such as salivary osmolality (Vosm). Utilizing acute BMΔ as the reference standard, this research examined the efficacy of Sosm, Vosm, Uosm, Uvol and Usg, during passive (PAS) and active (ACT) heat exposure.SUBJECTS/METHODS:Twenty-three healthy men (age, 22±3 years; mass, 77.3±12.8 kg; height, 179.9±8.8cm; body fat, 10.6±4.5%) completed two randomized 5-h dehydration trials (36±1 °C). During PAS, subjects sat quietly, and during ACT, participants cycled at 68±6% maximal heart rate. Investigators measured all biomarkers at each 1% BMΔ.RESULTS:Average mass loss during PAS was 1.4±0.3%, and 4.1±0.7% during ACT. Significant between-treatment differences at −1% BMΔ were observed for Sosm (PAS, 296±4; ACT, 301±4 mOsm/kg) and Uosm (PAS, 895±207; ACT, 661±192 mOsm/kg). During PAS, only Uosm, Uvol and Usg increased significantly (−1 and −2% BMΔ versus baseline). During ACT, Vosm most effectively diagnosed dehydration ⩾2% (sensitivity=86%; specificity=91%), followed by Sosm (sensitivity=83%; specificity=83%). Reference change values were validated for Sosm, Usg and BMΔ.CONCLUSIONS:The efficacy of indices to detect dehydration ⩾2% differed across treatments. At rest (PAS), only urinary indices increased in concert with body water loss. During exercise (ACT), Sosm and Vosm exhibited the highest sensitivity and specificity. Sosm, Usg and BMΔ exhibited validity in serial measurements. These findings indicate hydration biomarkers should be selected by considering daily activities.

Perceptual Responses While Wearing an American Football Uniform in the Heat

CONTEXT The protective equipment worn during American football has been shown to increase thermal strain; however, the perception of this increased heat has not been examined. OBJECTIVE To evaluate perceptual responses of American football players while wearing different uniforms during exercise in the heat and to evaluate how these responses may be used to monitor athlete safety. DESIGN Randomized controlled trial. SETTING Human Performance Laboratory. PATIENTS OR OTHER PARTICIPANTS Ten men with more than 3 years of competitive experience as football linemen (age = 23.8 +/- 1.3 years, height = 183.9 +/- 1.8 cm, mass = 117.4 +/- 3.5 kg, body fat = 30.1% +/- 1.7%) participated. INTERVENTION(S) On 3 occasions in hot, humid (33 degrees C, 48%-49% relative humidity) environmental conditions, participants completed 10 minutes of strenuous repetitive box lifting (RBL), 10 minutes of seated rest, and up to 60 minutes of treadmill walking. At each trial, they wore a different uniform condition: control (CON) clothing comprising shorts, socks, and sneakers; partial (PART) National Football League (NFL) uniform comprising the uniform without helmet or shoulder pads; or full (FULL) NFL uniform. Exercise, meals, and hydration status were controlled. MAIN OUTCOME MEASURE(S) Rectal temperature (T(re)), skin temperature (T(sk)), rating of perceived exertion (RPE), thermal perception (THM), perception of thirst (TST), and perception of muscle pain (MPN) were obtained for time points matched across trials. RESULTS Nineteen of the 30 trials ended before 60 minutes of treadmill walking as a result of participant exhaustion. Mean treadmill time was longer for the CON condition (51.7 +/- 13.4 minutes) than for the PART (43.1 +/- 15.6 minutes; t(9) = 3.092, P = .01) or the FULL (36.2 +/- 13.2 minutes; t(9) = 4.393, P = .002) conditions. Neck and forearm T(sk) increased between the initial time point and the end of exercise in the PART (33.6 +/- 0.9 degrees C and 35.0 +/- 0.6 degrees C, respectively; F(2,18) = 9.034, P < .001) and the FULL (33.4 +/- 0.9 degrees C and 35.2 +/- 0.6 degrees C, respectively; F(2,18) = 21.011, P = .002) conditions. Rate of T(re) rise was greater in the FULL (0.042 +/- 0.010 degrees C/min) than in the PART (0.034 +/- 0.006 degrees C/min) condition (F(2,27) = 10.69, P = .04). We found a relationship at the post-RBL and final time points between RPE and THM (r = 0.75, P < .001 and r = 0.59, P < .001, respectively), RPE and TST (r = 0.76, P < .001 and r = 0.61, P < .001, respectively), and RPE and MPN (r = 0.63, P < .001 and r = 0.64, P < .001, respectively). The RPE was greater at the end of exercise in the PART (17 +/- 2) and FULL (18 +/- 1) conditions than in the CON (15 +/- 3) condition (F(2,18) = 7.403, P = .005). CONCLUSIONS Although no differences in perceptual scales existed between the PART and FULL conditions, the T(sk) and rate of T(re) increase differed, indicating that football athletes find it difficult to perceptually rate exercise conditions as potentially dangerous hyperthermia develops. In addition, correlations between the perceptual scales further defined perceptual responses during exercise in the heat.

Interpreting common hydration biomarkers on the basis of solute and water excretion

Background/Objectives:This investigation evaluated 12 hydration biomarkers, to determine which represent 24-h whole-body water balance (that is, measured as water retention or clearance (WR-C) by the kidneys).Subjects/Methods:Healthy males (n=59; body mass, 75.1±7.9 kg; height, 178±6 cm; age, 22±3 years; body mass index, 23.9±2.4 kg/m2) met with a registered dietitian each morning (days 1–11) to optimize completeness and accuracy of food and fluid records, then went about ordinary daily activities. These men visited the laboratory for blood samples and collected all urine produced on days 1, 3, 6, 9 and 12. The reference standard (WR-C) was calculated using 24-h urine volume, 24-h urine osmolality, and serum osmolality (single morning venous sample).Results:Statistical regression analyses indicated that, among the 12 hydration biomarkers, only 24-h urine osmolality (r2=0.60, P<0.0001) and 24-h urine specific gravity (r2=0.52, P<0.0001) strongly predicted WR-C. The 24-h fluid intake, 24-h body mass change, 24-h urine color and 24-h urine volume were weak (P>0.05) predictors of WR-C, similar to serum osmolality and other single measurements (range of r2 values, 0.19–0.0001).Conclusions:These observations of healthy, active young men demonstrate that WR-C is strongly related to the 24-h concentration of urine, which in turn reflects the excretion of total solids in the diet. Although morning urine assessments provided information about a single time point, 24-h urine osmolality and 24-h urine specific gravity were the best predictors of 24-h body water balance.

Specific Exercise Heat Stress Protocol for a Triathlete's Return from Exertional Heat Stroke

A triathlete collapsed with exertional heatstroke (EHS) during 2 races over 3 months. The American College of Sports Medicine recommends a heat tolerance test (HTT) following EHS if there is a concern with return to play. The classical walking HTT may not be the best test to evaluate elite triathletes’ heat tolerance due to race intensity, nor is it suited to evaluate acclimation ability, which may play a role in risk of heat illness. Is the athlete capable of returning to racing or should he retire from sport due to heat intolerance? Up to 90 min of cycling (70% of V˙O2max; 36°C, 50% relative humidity) was followed by 9 d of exercise heat acclimation and a final identical exercise heat stress test. After acclimation, exercise duration before reaching a gastrointestinal temperature (Tgi) of 39.5°C increased 25 min, sweat rate increased 0.5 L·h−1, initial Tgi decreased 0.85°C, and rate of Tgi rise decreased 0.6°C·h−1. Adaptations were deemed acceptable, and the athlete was allowed to return to competition. The athlete has since raced in hot environments without incident.

Caffeine lowers muscle pain during exercise in hot but not cool environments

Caffeine (CAF) ingestion may enhance endurance exercise by lowering perceived exertion (RPE) and muscle pain. However, exercise in the heat may be detrimental to performance by increasing RPE and pain. The purpose of this study was to examine if caffeine affects pain and related perceptual responses differently in cool and hot ambient conditions. Eleven male cyclists (mean ± SD; age, 25 ± 6 years; mass, 72.6 ± 8.1 kg; VO(2max), 58.7 ± 2.9 ml kg(-1) min(-1)) completed four trials in a randomized, double blind design. While remaining euhydrated, subjects cycled for 90 min at 65 ± 7% VO(2max) followed by a 15-min performance trial. Subjects ingested 3 mg kg(-1) of encapsulated caffeine (CAF) or placebo (PLA) 60 min before and 45 after beginning exercise in 12°C and 33°C (i.e., 12-CAF, 33-CAF, 12-PLA, and 33-PLA trials). Central, local, and overall perceived exertion (C-, L-, and O-RPE) and pain were measured throughout exercise. Throughout submaximal exercise C-, L-, and O-RPE were significantly greater in 33°C (P<0.05) but were not affected by CAF (P>0.05). Using area-under-the-curve analysis, pain in 33-PLA was increased by 74% vs 12-PLA (P<0.05). CAF did not reduce pain in 12°C (P=0.542), but in 33°C, CAF reduced pain by 27% (P=0.032). Despite this apparent advantage, CAF improved performance independent of ambient temperature (i.e., non-significant interaction; P=0.662). This study found that, although caffeine improves exercise capacity, its effect on leg muscle pain is dependent on ambient temperature. Although exercise in the heat increases muscle pain compared to a cooler environment, caffeine reduces this pain.

Validation Testing Demonstrates Efficacy of a 7-Day Fluid Record to Estimate Daily Water Intake in Adult Men and Women When Compared with Total Body Water Turnover Measurement

Background: Mean daily water intake from fluids (WATER-FL) has proven to be difficult to measure because of a range of nonvalidated data collection techniques. Few questionnaires have been validated to estimate WATER-FL against self-reported diaries or urinary hydration markers, which may limit their objectivity.Objectives: The goals of this investigation were 1) to assess the validity of a 7-d fluid record (7dFLR) to measure WATER-FL (WATER-FL-7dFLR) through comparison with WATER-FL as calculated by measuring deuterium oxide (D2O) disappearance (WATER-FL-D2O), and 2) to evaluate the reliability of the 7dFLR in measuring WATER-FL.Methods: Participants [n = 96; 51% female; mean ± SD age: 41 ± 14 y; mean ± SD body mass index (in kg/m2): 26.2 ± 5.1] completed body water turnover analysis over 3 consecutive weeks. They completed the 7dFLR and food diaries during weeks 2 and 4 of the observation. The records were entered into nutritional software to determine the water content of all foods and fluids consumed. WATER-FL-D2O was calculated from water turnover (via the D2O dilution method), minus water from food and metabolic water. The agreement between the 2 methods of determining WATER-FL were compared according to a Bland-Altman plot at week 2. The test-retest reliability of 7dFLR between weeks 2 and 4 was assessed via intraclass correlation (ICC).Results: The mean ± SD difference between WATER-FL-7dFLR and WATER-FL-D2O was -131 ± 845 mL/d. In addition, no bias was observed (F[1,94] = 0.484; R2 = 0.006; P = 0.488). When comparing WATER-FL-7dFLR from weeks 2 and 4, no significant difference (mean ± SD difference: 71 ± 75 mL/d; t[79] = 0.954; P = 0.343) and an ICC of 0.85 (95% CI: 0.77, 0.90) was observed.Conclusions: The main findings of this study were that the use of the 7dFLR is an effective and reliable method to estimate WATER-FL in adults. This style of questionnaire may be extremely helpful for collecting water intake data for large-scale epidemiologic studies.

COUNTERVIEW: Is Drinking to Thirst Adequate to Appropriately Maintain Hydration Status During Prolonged Endurance Exercise? No

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