Normative data for sweating rate, sweat sodium concentration, and sweat sodium loss in athletes: An update and analysis by sport.

The purpose of this study was to expand our previously published sweat normative data/analysis (n = 506) to establish sport-specific normative data for whole-body sweating rate (WBSR), sweat [Na+], and rate of sweat Na+ loss (RSSL). Data from 1303 athletes were compiled from observational testing (2000-2017) using a standardized absorbent sweat patch technique to determine local sweat [Na+] and normalized to whole-body sweat [Na+]. WBSR was determined from change in exercise body mass, corrected for food/fluid intake and urine/stool loss. RSSL was the product of sweat [Na+] and WBSR. There were significant differences between sports for WBSR, with highest losses in American football (1.51 ± 0.70 L/h), then endurance (1.28 ± 0.57 L/h), followed by basketball (0.95 ± 0.42 L/h), soccer (0.94 ± 0.38 L/h) and baseball (0.83 ± 0.34 L/h). For RSSL, American football (55.9 ± 36.8 mmol/h) and endurance (51.7 ± 27.8 mmol/h) were greater than soccer (34.6 ± 19.2 mmol/h), basketball (34.5 ± 21.2 mmol/h), and baseball (27.2 ± 14.7 mmol/h). After ANCOVA, significant between-sport differences in adjusted means for WBSR and RSSL remained. In summary, due to the significant sport-specific variation in WBSR and RSSL, American football and endurance have the greatest need for deliberate hydration strategies. Abbreviations: WBSR: whole body sweating rate; SR: sweating rate; Na+: sodium; RSSL: rate of sweat sodium loss.

Body map of regional vs. whole body sweating rate and sweat electrolyte concentrations in men and women during moderate exercise-heat stress.

This study determined the relations between regional (REG) and whole body (WB) sweating rate (RSR and WBSR, respectively) as well as REG and WB sweat Na+ concentration ([Na+]) during exercise. Twenty-six recreational athletes (17 men, 9 women) cycled for 90 min while WB sweat [Na+] was measured using the washdown technique. RSR and REG sweat [Na+] were measured from nine regions using absorbent patches. RSR and REG sweat [Na+] from all regions were significantly ( P < 0.05) correlated with WBSR ( r = 0.58-0.83) and WB sweat [Na+] ( r = 0.74-0.88), respectively. However, the slope and y-intercept of the regression lines for most models were significantly different than 1 and 0, respectively. The coefficients of determination ( r2) were 0.44-0.69 for RSR predicting WBSR [best predictors: dorsal forearm ( r2 = 0.62) and triceps ( r2 = 0.69)] and 0.55-0.77 for REG predicting WB sweat [Na+] [best predictors: ventral forearm ( r2 = 0.73) and thigh ( r2 = 0.77)]. There was a significant ( P < 0.05) effect of day-to-day variability on the regression model predicting WBSR from RSR at most regions but no effect on predictions of WB sweat [Na+] from REG. Results suggest that REG cannot be used as a direct surrogate for WB sweating responses. Nonetheless, the use of regression equations to predict WB sweat [Na+] from REG can provide an estimation of WB sweat [Na+] with an acceptable level of accuracy, especially using the forearm or thigh. However, the best practice for measuring WBSR remains conventional WB mass balance calculations since prediction of WBSR from RSR using absorbent patches does not meet the accuracy or reliability required to inform fluid intake recommendations. NEW & NOTEWORTHY This study developed a body map of regional sweating rate and regional (REG) sweat electrolyte concentrations and determined the effect of within-subject (bilateral and day-to-day) and between-subject (sex) factors on the relations between REG and the whole body (WB). Regression equations can be used to predict WB sweat Na+ concentration from REG, especially using the forearm or thigh. However, prediction of WB sweating rate from REG sweating rate using absorbent patches does not reach the accuracy or reliability required to inform fluid intake recommendations.

Trapped sweat in basketball uniforms and the effect on sweat loss estimates.

The aims of this study were to determine: (1) trapped sweat (TS) in basketball uniforms and the effect on sweat loss (SL) estimates during a laboratory-based basketball simulation protocol; (2) the impact of exercise intensity, body mass, age, and SL on TS; and (3) TS during on-court training to assess the ecological validity of the laboratory-based results. Twenty-four recreational/competitive male basketball players (23 ± 10 years, 77.0 ± 16.7 kg) completed three randomized laboratory-based trials (Low, Moderate, and High intensity) consisting of 150-min intermittent exercise. Eighteen elite male players (23 ± 4 years, 92.0 ± 20.6 kg) were observed during coach-led, on-court training. Nude and clothed body mass were measured pre and postexercise to determine TS. Data are mean ± SD. There was a significant effect of intensity on SL and TS (P < 0.001, Low

Effect of Different Osmolalities, CHO Types, and [CHO] on Gastric Emptying in Humans.

PURPOSE: This study investigated the effect of beverage osmolalities, carbohydrate (CHO) type, and CHO concentration on gastric emptying in euhydrated subjects at rest. METHODS: The gastric emptying of water (W), four glucose beverages (2%, 4%, 6%, and 8% glucose: 2G, 4G, 6G, and 8G), and four sucrose beverages (2%, 4%, 6%, and 8% sucrose: 2S, 4S, 6S, and 8S) were determined in eight healthy subjects using the modified George double-sampling technique. Subjects ingested a beverage (7 mL·kg body weight) containing 25 ppm phenol red as quickly as possible (≤1.0 min), and subsequent gastric and blood samples were collected every 10 min for 40 min. A linear regression and a repeated-measures ANOVA were used for statistical analysis. RESULTS: The gastric secretion volume was not significantly different among beverages across time. Gastric residual beverage volume (GRBV) at each sampling time point was not different among 2S, 4S, 6S, 8S, and water (P > 0.05). The 8G resulted in a significantly greater GRBV compared with other beverages at 20, 30, and 40 min (P < 0.05). GRBV from 6G was significantly higher than 2G at 30 min, but no other statistical differences were found among W, 2G, 4G, and 6G. The 8S had a greater GRBV compared with W at 40 min (P < 0.05). Mean gastric osmolality positively correlated to mean GRBV (r = 0.93). Gastric emptying rate was negatively correlated to the calories emptied (r = 0.84) with a greater effect from glucose beverages compared with sucrose beverages. CONCLUSIONS: These data suggest that glucose exerts a stronger inhibitory stimulus compared with sucrose on gastric emptying and that a physiological threshold exists for the combined influence of glucose concentration and beverage osmolality to trigger the feedback inhibition of gastric emptying.

Normative data for regional sweat sodium concentration and whole-body sweating rate in athletes.

The purpose of this study was to establish normative data for regional sweat sodium concentration ([Na+]) and whole-body sweating rate in athletes. Data from 506 athletes (367 adults, 139 youth; 404 male, 102 female) were compiled from observational athlete testing for a retrospective analysis. The participants were skill/team-sport (including American football, baseball, basketball, soccer and tennis) and endurance (including cycling, running and triathlon) athletes exercising in cool to hot environmental conditions (15-50 °C) during training or competition in the laboratory or field. A standardised regional absorbent patch technique was used to determine sweat [Na+] on the dorsal mid-forearm. Whole-body sweat [Na+] was predicted using a published regression equation (y = 0.57x+11.05). Whole-body sweating rate was calculated from pre- to post-exercise change in body mass, corrected for fluid/food intake (ad libitum) and urine output. Data are expressed as mean ± SD (range). Forearm sweat [Na+] and predicted whole-body sweat [Na+] were 43.6 ± 18.2 (12.6-104.8) mmol · L(-1) and 35.9 ± 10.4 (18.2-70.8) mmol · L(-1), respectively. Absolute and relative whole-body sweating rates were 1.21 ± 0.68 (0.26-5.73) L · h(-1) and 15.3 ± 6.8 (3.3-69.7) ml · kg(-1) · h(-1), respectively. This retrospective analysis provides normative data for athletes' forearm and predicted whole-body sweat [Na+] as well as absolute and relative whole-body sweating rate across a range of sports and environmental conditions.

Validity and reliability of a field technique for sweat Na+ and K+ analysis during exercise in a hot-humid environment.

Abstract This study compared a field versus reference laboratory technique for extracting (syringe vs. centrifuge) and analyzing sweat [Na(+)] and [K(+)] (compact Horiba B-722 and B-731, HORIBA vs. ion chromatography, HPLC) collected with regional absorbent patches during exercise in a hot-humid environment. Sweat samples were collected from seven anatomical sites on 30 athletes during 1-h cycling in a heat chamber (33°C, 67% rh). Ten minutes into exercise, skin was cleaned/dried and two sweat patches were applied per anatomical site. After removal, one patch per site was centrifuged and sweat was analyzed with HORIBA in the heat chamber (CENTRIFUGE HORIBA) versus HPLC (CENTRIFUGE HPLC). Sweat from the second patch per site was extracted using a 5-mL syringe and analyzed with HORIBA in the heat chamber (SYRINGE HORIBA) versus HPLC (SYRINGE HPLC). CENTRIFUGE HORIBA, SYRINGE HPLC, and SYRINGE HORIBA were highly related to CENTRIFUGE HPLC ([Na(+)]: ICC = 0.96, 0.94, and 0.93, respectively; [K(+)]: ICC = 0.87, 0.92, and 0.84, respectively), while mean differences from CENTRIFUGE HPLC were small but usually significant ([Na(+)]: 4.7 ± 7.9 mEql/L, -2.5 ± 9.3 mEq/L, 4.0 ± 10.9 mEq/L (all P < 0.001), respectively; [K(+)]: 0.44 ± 0.52 mEq/L (P < 0.001), 0.01 ± 0.49 mEq/L (P = 0.77), 0.50 ± 0.48 mEq/L (P < 0.001), respectively). On the basis of typical error of the measurement results, sweat [Na(+)] and [K(+)] obtained with SYRINGE HORIBA falls within ±15.4 mEq/L and ±0.68 mEq/L, respectively, of CENTRIFUGE HPLC 95% of the time. The field (SYRINGE HORIBA) method of extracting and analyzing sweat from regional absorbent patches may be useful in obtaining sweat [Na(+)] when rapid estimates in a hot-humid field setting are needed.

Exercise-induced trace mineral element concentration in regional versus whole-body wash-down sweat.

Simultaneous whole-body wash-down (WBW) and regional skin surface sweat collections were completed to compare regional patch and WBW sweat calcium (Ca), magnesium (Mg), copper (Cu), manganese (Mn), iron (Fe), and zinc (Zn) concentrations. Athletes (4 men, 4 women) cycled in a plastic open-air chamber for 90 min in the heat. Before exercise, the subjects and cycle ergometer (covered in plastic) were washed with deionized water. After the onset of sweating, sterile patches were attached to the forearm, back, chest, forehead, and thigh and removed on saturation. After exercise, the subjects and cycle ergometer were washed with 5 L of 15-mM ammonium sulfate solution to collect all sweat minerals and determine the volume of unevaporated sweat. Control trials were performed to measure mineral contamination in regional and WBW methods. Because background contamination in the collection system was high for WBW Mn, Fe, and Zn, method comparisons were not made for these minerals. After correction for minimal background contamination, WBW sweat [Ca], [Mg], and [Cu] were 44.6 ± 20.0, 9.8 ± 4.8, and 0.125 ± 0.069 mg/L, respectively, and 5-site regional (weighted for local sweat rate and body surface area) sweat [Ca], [Mg], and [Cu] were 59.0 ± 15.9, 14.5 ± 4.8, and 0.166 ± 0.031 mg/L, respectively. Five-site regional [Ca], [Mg], and [Cu] overestimated WBW by 32%, 48%, and 33%, respectively. No individual regional patch site or 5-site regional was significantly correlated with WBW sweat [Ca] (r = -.21, p = .65), [Mg] (r = .49, p = .33), or [Cu] (r = .17, p = .74). In conclusion, regional sweat [Ca], [Mg], and [Cu] are not accurate surrogates for or significantly correlated with WBW sweat composition.

Core temperature and sweat responses in professional women's tennis players during tournament play in the heat.

CONTEXT: Tennis is often played in hot, humid environments, intensifying the thermoregulatory strain placed on the athletes. As a safety measure, some tennis organizations allow for a 10-minute break in play between the second and third sets when environmental conditions are extreme. However, the actual effect of these breaks in reducing core temperature is unknown. OBJECTIVE: To determine change in core temperature after a 10-minute break in play and assess fluid balance in professional female tennis players during tournament matches in the heat. DESIGN: Cross-sectional study. SETTING: A Women's Tennis Association Tour-sanctioned outdoor tournament on hard courts under hot conditions (30.3°C ± 2.3°C). PATIENTS OR OTHER PARTICIPANTS: Seven professional tennis players. MAIN OUTCOME MEASURE(S): Change in core temperature after a 10-minute break in tournament play, fluid intake, and sweat losses during match play. RESULTS: Core temperature was reduced from 38.92°C to 38.67°C (change of -0.25°C ± 0.20°C) when a break was taken (P  =  .02). Mean sweat rate during match play was 2.0 ± 0.5 L/h. During that time, mean fluid intake was 1.5 ± 0.5 L/h, resulting in a 1.2% ± 1.0% reduction in body mass. CONCLUSIONS: Female professional tennis players are subjected to high heat loads during match play in hot environments. However, a 10-minute break in play decreased core temperature in 6 of 7 players by an average of 0.25°C, indicating that the break provides practical benefits in the field. Furthermore, although mean sweat rate in this group of female tennis players was high, most athletes were still able to minimize mass loss to less than 2% of their prematch weight.

Serum sodium concentration changes are related to fluid balance and sweat sodium loss.

PURPOSE: This study determined if changes in serum sodium concentration are related to fluid balance as well as sweat sodium losses in triathletes competing in the Hawaii Ironman triathlon. METHODS: Endurance trained athletes (N = 46, age = 24-67 yr) were studied during 30 min of stationary cycling at 70%-75% of HRmax in a warm outdoor laboratory (26.4 degrees C +/- 1.7 degrees C wet bulb globe temperature [WBGT], 28.3 degrees C +/- 1.2 degrees C dry bulb [DB]) 3-7 d before race day. Sweat sodium concentration was measured from absorbent patches on the forearm and scapula, and sweating rate was derived from changes in body mass. Before and after the race, serum sodium concentration, body mass, and nutritional intake during the race were also measured (N = 46). Sweating and race day comparisons and changes in serum sodium concentration were analyzed via Student's t-test, correlation, and multiple regression. RESULTS: In men, the change in serum sodium concentration during the race was correlated with relative sweating rate (mL.kg.h; r = -0.49, P = 0.012), rate of sweat sodium loss (mEq.kg.h; r = -0.44, P = 0.023), and body mass change (kg; r = -0.54, P = 0.005). Together, the rate of sweat sodium loss and body mass change accounted for 46% of the change in serum sodium concentration in men (R = 0.46). In women, body mass change alone was significantly correlated with the change in serum sodium concentration (r = 0.31). The rate of sodium intake (mEq.kg.h) was related to the rate of sweat sodium loss in women (mEq.kg.h; r = 0.64, P = 0.035) but not in men (r = 0.27, P = 0.486). CONCLUSION: Changes in serum sodium concentration during an ultraendurance triathlon are significantly related to interactions of fluid balance, sweat sodium loss, and sodium ingestion.

Comparison of regional patch collection vs. whole body washdown for measuring sweat sodium and potassium loss during exercise.

This study compared simultaneous whole body washdown (WBW) and regional skin surface (REG) sweat collections to generate regression equations to predict WBW sweat Na(+) concentration ([Na(+)]) and K(+) concentration ([K(+)]) from single- and five-site REG sweat patch collections. Athletes (10 men, 10 women) cycled in a plastic chamber for 90 min in the heat. Before exercise, the subject and bike were washed with deionized water. After the onset of sweating, sterile patches were attached to the forearm, back, chest, forehead, and thigh and removed on saturation. After exercise, the subject and bike were washed with ammonium sulfate solution to collect all sweat electrolyte loss and determine the volume of unevaporated sweat. All individual patch sites and five-site REG (weighted for local sweat rate and body surface area) were significantly (P = 0.000) correlated with WBW sweat [Na(+)]. The equation for predicting WBW sweat [Na(+)] from five-site REG was y = 0.68x + 0.44 [r = 0.97, intraclass correlation coefficient (ICC) = 0.70] and did not differ between sexes. There were sex differences in the regression results between five-site REG and WBW sweat [K(+)] (men: y = 0.74x + 0.30, r = 0.89, ICC = 0.73; women: y = 0.04x + 3.18, r = 0.03, ICC = 0.00). Five-site REG sweat [Na(+)] and [K(+)] significantly overestimated that of WBW sweat (59 +/- 27 vs. 41 +/- 19 meq/l, P = 0.000 and 4.4 +/- 0.7 vs. 3.6 +/- 0.7 meq/l, P = 0.000, respectively). For both sexes, the best sites for predicting WBW sweat [Na(+)] and [K(+)] were the thigh (1 +/- 8 meq/l < WBW, P = 1.000, y = 0.75x + 11.37, r = 0.96, ICC = 0.93) and chest (0.2 +/- 0.3 meq/l > WBW, P = 1.000, y = 0.76x + 0.55, r = 0.89, ICC = 0.87), respectively. In conclusion, regression equations can be used to accurately and reliably predict WBW sweat [Na(+)] and [K(+)] from REG sweat collections when study conditions and techniques are similar to that of the present protocol.

Core temperature and metabolic responses after carbohydrate intake during exercise at 30 degrees C.

CONTEXT: Carbohydrate ingestion has recently been associated with elevated core temperature during exercise in the heat when testing for ergogenic effects. Whether the association holds when metabolic rate is controlled is unclear. Such an effect would have undesirable consequences for the safety of the athlete. OBJECTIVE: To examine whether ingesting fluids containing carbohydrate contributed to an accelerated rise in core temperature and greater overall body heat production during 1 hour of exercise at 30 degrees C when the effort was maintained at steady state. DESIGN: Crossover design (repeated measures) in randomized order of treatments of drinking fluids with carbohydrate and electrolytes (CHO) or flavored-water placebo with electrolytes (PLA). The beverages were identical except for the carbohydrate content: CHO = 93.7 +/- 11.2 g, PLA = 0 g. SETTING: Research laboratory. PATIENTS OR OTHER PARTICIPANTS: Nine physically fit, endurance-trained adult males. INTERVENTION(S): Using rectal temperature sensors, we measured core temperature during 30 minutes of rest and 60 minutes of exercise at 65% of maximal oxygen uptake (Vo(2) max) in the heat (30.6 degrees C, 51.8% relative humidity). Participants drank equal volumes (1.6 L) of 2 beverages in aliquots 30 minutes before and every 15 minutes during exercise. Volumes were fixed to approximate sweat rates and minimize dehydration. MAIN OUTCOME MEASURE(S): Rectal temperature and metabolic response (Vo(2), heart rate). RESULTS: Peak temperature, rate of temperature increase, and metabolic responses did not differ between beverage treatments. Initial hydration status, sweat rate, and fluid replacement were also not different between trials, as planned. CONCLUSIONS: Ingestion of carbohydrate in fluid volumes that minimized dehydration during 1 hour of steady-state exercise at 30 degrees C did not elicit an increase in metabolic rate or core temperature.

Daily fluid turnover during preseason training in U.S. college football.

The authors measured 24-h fluid-turnover (FTO) rate during 6 d of preseason training in U.S. college football players. Players, training (T, n = 9, full gear and contact drills) and reference (R, n = 4, conditioning without gear or contact), ingested a deuterium oxide (D(2)O) dose and provided urine samples every 24 h for analysis of D(2)O. During one approximately 2.3-h practice (wet-bulb globe temperature 24.6 degrees C), body-mass change, urine production, and voluntary fluid intake were measured to calculate gross sweat loss (GSL). Average FTO was 10.3 +/- 2.2 L/d for T and 7.0 +/- 1.0 L/d for R. GSL was 3.4 +/- 1.5 L for T and 1.7 +/- 1.3 for R (P > 0.05). By Day 6, body mass decreased significantly in T (-2.4 +/- 1.3 kg, P < 0.05) but not in R (0.38 +/- 0.95 kg). With preseason training under moderate environmental stress, football players had high FTO and sweat rates, which might have contributed to a loss of body mass during preseason football training.

Sweat and sodium losses in NCAA football players: a precursor to heat cramps?

This observational study was designed to determine whether football players with a history of heat cramps have elevated fluid and sodium losses during training. During a "two-a-day" training camp, five Division I collegiate football players (20.2 +/- 1.6 y, 113 +/- 20 kg) with history of heat cramps (C) were matched (weight, age, race and position) with a cohort of teammates (19.6 +/- 0.6 y, 110 +/- 20 kg) who had never cramped (NC). Change in body weight (adjusted by fluid intake) determined gross sweat loss. Sweat samples (forearm patch) were analyzed for sodium and potassium concentrations. Ad libitum fluid intake was measured by recording pre- and post-practice bottle weights. Average sweat sodium loss for a 2.5-h practice was projected at 5.1 +/- 2.3 g (C) vs. 2.2 +/- 1.7 g (NC). When averaged across two practices within the day, fluid intake was similar between groups (C: 2.6 +/- 0.8 L vs. NC: 2.8 +/- 0.7 L), as was gross sweat loss (C: 4.0 +/- 1.1 L vs. NC: 3.5 +/- 1.6 L). There was wide variability in the fluid deficit incurred for both C and NC (1.3 +/- 0.9 vs. 0.7 +/- 1.2%) due to fluid intake. Sweat potassium was similar between groups, but sweat sodium was two times higher in C versus NC (54.6 +/- 16.2 vs. 25.3 +/- 10.0 mmol/L). These data indicate that sweat sodium losses were comparatively larger in cramp-prone football players than in NC. Although both groups consumed sodium-containing fluids (on-field) and food (off-field), both appeared to experience an acute sodium deficit at the end of practices based on sweat sodium losses. Large acute sodium and fluid losses (in sweat) may be characteristic of football players with a history of heat cramping.

Gastrointestinal discomfort during intermittent high-intensity exercise: effect of carbohydrate-electrolyte beverage.

This study investigated whether different beverage carbohydrate concentration and osmolality would provoke gastrointestinal (GI) discomfort during intermittent, high-intensity exercise. Thirty-six adult and adolescent athletes were tested on separate days in a double-blind, randomized trial of 6 % and 8 % carbohydrate-electrolytes (CHO-E) beverages during four 12-min quarters (Q) of circuit training that included intermittent sprints, lateral hops, shuttle runs, and vertical jumps. GI discomfort and fatigue surveys were completed before the first Q and immediately after each Q. All ratings of GI discomfort were modest throughout the study. The cumulative index for GI discomfort, however, was greater for the 8 % CHO-E beverage than for the 6 % CHO-E beverage at Q3 and Q4 (P < 0.05). Averaging across all 4 quarters, the 8 % CHO-E treatment produced significantly higher mean ratings of stomach upset and side ache. In conclusion, higher CHO concentration and osmolality in an ingested beverage provokes stomach upset and side ache.