Estimated Sweat Loss Research Articles

Collegiate soccer players consistently underestimate practice sweat losses regardless of practice sweat loss volume

Soccer play in hot environments can result in major fluid deficit. If competitors are unsure of their sweat losses, accurate fluid intake needs during and between training bouts cannot be established. This study evaluated sweat loss estimation accuracy among collegiate male soccer players (n = 17) following three, 90-minute practice ses- sions in the heat. Data were collected during the last week of pre-season training during a morning (P1; wet bulb globe temperature (WBGT) = 31.2 °C) and same day afternoon (P2; WBGT = 26.9 °C) practice. The third estimation took place after a regular season morning practice (P3; WBGT = 31.5 °C) the following week. Change in nude body mass, with adjustment for fluid intake and urine output, from pre- to post-practice was assessed to determine sweat loss volume. After each practice participants estimated their sweat loss volume by filling cups with a vol- ume of water equivalent to the volume of sweat they believed they lost during the practice session. Sweat losses differed (p < 0.05) among all 3 practices (P1 2.181 ± 0.693; P2 1.706 ± 0.474; P 3.360 ± 0.956 L). Estimated sweat loss volume was less (p < 0.001) than actual sweat losses for P1 (0.804 ± 0.329 L; 40.2 ± 21.5%), P2 (0.672 ± 0.324 L; 40.1 ± 19.9%) and P3 (1.076 ± 0.489 L; 31.8 ± 11.6%), but there were no differences in percentage accuracy. Players estimations of sweat loss trended up and downward with actual sweat losses, but players greatly and consistently underestimated sweat losses. Visual depiction of sweat loss volume could potentially increase awareness of be- tween training bout fluid intake needs of soccer players training in hot conditions.

Sex difference in initial thermoregulatory response to dehydrated exercise in the heat.

Although it is well established that dehydration has a negative impact on thermoregulation during exercise in the heat, it is unclear whether this effect of dehydration is different between men and women, or across the phases of the menstrual cycle (MC). Twelve men and seven women (men: 20 ± 2 years, 70.13 ± 10.5 kg, 173.4 ± 6.0 cm, 54.2 ± 8.6 ml kg−1 min−1; women: 20 ± 2 years, 57.21 ± 7.58 kg, 161 ± 5 cm, 40.39 ± 3.26 ml kg−1 min−1) completed trials either euhydrated (urine specific gravity, USG ≤ 1.020, Euhy) or dehydrated (USG > 1.020, Dehy). Trial order was randomized and counterbalanced; men completed two trials (MEuhy and MDehy) and women completed four over two MC phases (late follicular: days 10–13, FDehy, FEuhy; midluteal: days 18–22, LDehy, LEuhy). Each trial consisted of 1.5 h, split into two 30 min blocks of exercise (B1 and B2, 15 min at 11 W/kg & 15 min at 7 W/kg) separated by 15 min rest in between and after. Rectal temperature (T re) was measured continuously and estimated sweat loss was calculated from the body mass measured before and after each block of exercise. When dehydrated, the rate of rise in T re was greater in women in the first block of exercise compared to men, independently of the MC phase (MDehy: 0.03 ± 0.03°C/min, FDehy: 0.06 ± 0.02, LDehy: 0.06 ± 0.02, p = 0.03). Estimated sweat loss was lower in all groups in B1 compared to B2 when dehydrated (p < 0.05), with no difference between sexes for either hydration condition. These data suggest that women may be more sensitive to the negative thermoregulatory effects of dehydration during the early stages of exercise in the heat.

Salt and water balance after sweat loss: A study of Bikram yoga.

Bikram yoga is practiced in a room heated to 105°F with 40% humidity for 90 min. During the class a large volume of water and electrolytes are lost in the sweat, specifically, sodium is lost, the main cation of the extracellular fluid. There is little known about the volume of sweat and the amount of sodium lost in sweat during Bikram yoga or the optimum quantity of fluid required to replace these losses. The participants who took part in this small feasibility study were five females with a mean age of 47.4 ± 4.7 years and 2.6 ± 1.6 years of experience at Bikram yoga. The total body weight, water consumed, serum sodium concentration, serum osmolality, and serum aldosterone levels were all measured before and after a Bikram yoga practice. Sweat sodium chloride concentration and osmolality were measured at the end of the practice. The mean estimated sweat loss was 1.54 ± 0.65 L, while the amount of water consumed during Bikram yoga was 0.38 ± 0.22 L. Even though only 25% of the sweat loss was replenished with water intake during the Bikram yoga class, we did not observe a change in serum sodium levels or serum osmolality. The sweat contained 82 ± 16 mmol/L of sodium chloride for an estimated total of 6.8 ± 2.1 g of sodium chloride lost in the sweat. The serum aldosterone increased 3.5‐fold from before to after Bikram yoga. There was a decrease in the extracellular body fluid compartment of 9.7%. Sweat loss in Bikram yoga predominately produced a volume depletion rather than the dehydration of body fluids. The sweating‐stimulated rise in serum aldosterone levels will lead to increased sodium reabsorption from the kidney tubules and restore the extracellular fluid volume over the next 24 hr.

Post-Exercise Sweat Loss Estimation Accuracy of Athletes and Physically Active Adults: A Review.

The main purposes of this review were to provide a qualitative description of nine investigations in which sweat losses were estimated by participants following exercise and to perform a quantitative analysis of the collective data. Unique estimations (n = 297) were made by 127 men and 116 women after a variety of exercise modalities in moderate to hot environmental conditions. Actual sweat loss exceeded estimated sweat loss (p < 0.001) for women (1.072 ± 0.473 vs. 0.481 ± 0.372 L), men (1.778 ± 0.907 vs. 0.908 ± 0.666 L) and when all data were combined (1.428 ± 0.806 vs. 0.697 ± 0.581 L), respectively. However, estimation accuracy did not differ between women (55.2 ± 51.5%) and men (62.4 ± 54.5%). Underestimation of 50% or more of sweat losses were exhibited in 168 (54%) of estimation scenarios with heavier sweaters displaying a higher prevalence and trend of greater underestimations in general. Most modern guidelines for fluid intake during and between training bouts are based on approximate sweat loss estimation knowledge. These guidelines will likely have minimal efficacy if greater awareness of how to determine sweat losses and accurate recognition of sweat losses is not increased by coaches and athletes.

Thermoregulatory responses to ice slurry ingestion during low and moderate intensity exercises with restrictive heat loss

ObjectivesWe investigated the thermoregulatory responses to ice slurry ingestion during low- and moderate-intensity exercises with restrictive heat loss. DesignRandomised, counterbalanced, cross-over design. MethodsFollowing a familiarisation trial, ten physically active males exercised on a motorised treadmill at low-intensity (L; 40% VO2max) or moderate-intensity (M; 70% VO2max) for 75-min, in four randomised, counterbalanced trials. Throughout the exercise bout, participants donned a raincoat to restrict heat loss. Participants ingested 2gkg−1 body mass of ambient water (L+AMB and M+AMB trials) or ice slurry (L+ICE and M+ICE trials) at 15-min intervals during exercise in environmental conditions of Tdb, 25.1±0.6°C and RH, 63±5%. Heart rate (HR), gastrointestinal temperature (Tgi), mean weighted skin temperature (Tsk), estimated sweat loss, ratings of perceived exertion (RPE) and thermal sensation (RTS) were recorded. ResultsCompared to L+AMB, participants completed L+ICE trials with lower ΔTgi (0.8±0.3°C vs 0.6±0.2°C; p=0.03), mean RPE (10±1 vs 9±1; p=0.03) and estimated sweat loss (0.91±0.2L vs 0.78±0.27L; p=0.04). Contrastingly, Tgi (p=0.22), Tsk (p=0.37), HR (p=0.31), RPE (p=0.38) and sweat loss (p=0.17) were similar between M+AMB and M+ICE trials. RTS was similar during both low-intensity (4.9±0.5 vs 4.7±0.3; p=0.10) and moderate-intensity exercise (5.3±0.47 vs 5.0±0.4; p=0.09). ConclusionsPer-cooling using ice slurry ingestion marginally reduced thermal strain during low-intensity but not during moderate-intensity exercise. Ice slurry may be an effective and practical heat mitigation strategy during low-intensity exercise such as in occupational and military settings, but a greater volume should be considered to ensure its efficacy.

Calcium loss in sweat does not stimulate PTH release: A study of Bikram hot yoga

It has been hypothesized that sweat loss during exercise causes a disruption in calcium homeostasis that activates bone resorption and over time leads to low bone mineral density. The purpose of this small pilot study was to determine whether dermal calcium loss from a bout of excessive sweating during light intensity physical activity triggers an increase in biomarkers of bone resorption. Biochemical markers related to bone homeostasis were measured before and after a 90 min Bikram hot yoga practice performed in a room heated to 105 °F with 40 % humidity. Participants were five females with a mean age of 47.4 ± 4.7 years. Nude body weight, serum total calcium (Ca2+), free ionized calcium, albumin, parathyroid hormone (PTH) and CTX-I were measured before and after a Bikram hot yoga practice. Mean estimated sweat loss was 1.54 ± 0.65 L, which elicited a 1.9 ± 0.9 % decrease in participant’s body weight. Mean Ca2+ concentration in sweat was 2.9 ± 1.7 mg/dl and the estimated mean total calcium lost was 41.3 ± 16.4 mg. Serum ionized Ca2+ increased from 4.76 ± 0.29 mg/dl to 5.35 ± 0.36 mg/dl after the Bikram hot yoga practice (p = 0.0118). Serum PTH decreased from pre- 33.9 ± 3.3 pg/ml to post- 29.9 ± 2.1 pg/ml yoga practice (p = 0.0015) when adjusted for hemoconcentration (PTHADJ), implying a decrease in PTH secretion. We conclude that calcium loss in sweat during 90 min of Bikram hot yoga did not trigger an increase in PTH secretion and did not initiate bone resorption.

PL - 029 Responses of Urine and Blood Biochemical Markers to Exercise-induced Body Fluid Losses in Elite Chinese Road Cyclists

Objective To examine biochemistry parameters regarding exercise induced fatigue, e.g. Sweat Loss (SL), Creatine Kinase (CK), Lactate Dehydrogenase (LDH), Blood Urinary Nitrogen (BUN), etc.&#x0D; Methods This study examined Sweat Loss and blood biochemistry biomarkers regarding fatigue and muscle injury among elite cyclists under a training mode of 120 min moderate workload at 50 - 70% VO2max, then, 10 min relaxation, and then, followed up with a 20 min of spinning session over 85% VO2max. 12 healthy elite Chinese male cyclists (22.6 ± 2.9 years old, 78.3 ± 5.7 kg in weight, 184.6 ± 4.3 cm in height) were recruited. They performed four exercise performance tests throughout this study with 15 days washout period in between. Blood serum tests and urine tests were taken both pre- and post-exercise tests, and dynamic cardio-respiratory hardware (MetaMax 3B, Cortex Biophysik, Germany) was applied during each of their test. There were 2 different sport beverages available. The fluid replacement plan was a double blind crossover design. The volume of fluid intake was in accordance with ACSM recommendation for fluid replacement. Those who were assigned with sport beverage A (6% carbohydrate with 1% peptide) for the first and second performance tests, will be re-assigned to sport beverage B (6% carbohydrate without peptide) for the third and fourth performance tests, vice versa. Notes were taken for the volume of fluid intake to calculate the estimated Sweat Loss.&#x0D; Results We found 91.7% trials have increased LDH, 88.9% trials have increased CK, and 100% trials have been observed increased BUN right after exercise performance test. Even with sufficient water supply, athletes hydration status were getting worse after exercise performance test, their urine USG results were 1.024 ± 0.006 and 1.027 ± 0.006 for pre- and post-exercise performance test respectively. Their dehydration status quantified by the percentage change in body mass (%BM) was 1.86% ± 1.03% with a 95% confidence interval ranging from 1.57% to 2.15%.&#x0D; Conclusions Though, with sufficient water supply, athletes hydration status were getting worse after exercise performance test considering Sweat Loss and blood biochemistry indicators regarding fatigue and muscle injury.

Food Intake And Fluid Balance Varies Between Individuals During A 120 Km Running Race

Continuous data collection on fueling and food strategies of ultramarathoners during competition is scarce. Existing publications mostly report nutrient intake without much detail of fluid balance and foods consumed. PURPOSE: To provide an overview of the consumption of carbohydrates and fluids, fluid balance and types of foods during a race comprising 10-14 hours of continuous exercise. METHODS: Pre-race height, cm (Cescorf stadiometer) and pre- and post-race body weight, kg (Seca scale S760 mechanical) were measured. All food products were labeled and weighed (g) pre- and post-race (Cresta, CKS750). Continuous observation of food and beverage intake was performed as all runners were accompanied by a research team member on a bicycle using pre-defined lists and action cams (SJCAM, SJ4000) to record all items consumed. Fluid excretion collection was done using urine bags (Roadbag®). Results are expressed as mean±SD and range (min-max) or as percentage (%). RESULTS: The average temperature was 7.0°C with a humidity of 67%. Five runners performed the 120 km run with an average duration of 12:19±1:29 hours (9:50-13:49). They reported 38±10 (25-48) food and beverage consumption events over the race which consisted of 4-7 different preferred food items per person. This resulted in an average carbohydrate intake of 44±19 g/h and fluid intake of 421±127 ml/h. Runners lost 2.5±1.6 kg (-0.2-3.8) of total weight during the race. The average urine excretion was 0.8±0.5 kg (0.3-1.4). This resulted in an estimated sweat loss of 6.6±2.3 kg (4.6-10.1) and four out of five runners reported a lower post-race body weight of 4±2% (0-6). During the first 60 km of the race the preferred foods and beverages were energy gels, water and sports drinks. After this, food preferences suggested a more mixed pattern including the use of cola, chocolate milk and fruit. CONCLUSIONS: Runners consume, on average, fewer carbohydrates and fluids than recommended due to a high variability in intake. As urine excretion was relatively low, mostly a high sweat rate contributed to a lower post-race weight. Although non-specific sports nutrition foods and beverages were used, runners preferred the use of commercial sports nutrition products the most. Supported by regional grant Eat2Move of the province of Gelderland, The Netherlands.

Assessment of physical demands and fluid balance in elite female handball players during a 6-day competitive tournament.

Little data exists on drinking behavior, sweat loss, and exercise intensity across a competitive handball tournament in elite female athletes. Heart rate (HR), fluid balance and sweat electrolyte content were assessed on 17 international players across a 6-day tournament involving 5 games and 2 training sessions played indoors (23 ± 2 °C, 30 ± 2% relative humidity). Active play (effective) mean HR was 155 ± 14 bpm (80 ± 7.5% HRmax) with the majority of time (64%) spent exercising at intensities >80% HRmax. Mean (SD) sweat rates during games were 1.02 ± 0.07 L · h⁻¹ and on 56% of occasions fluid intake matched or exceeded sweat loss. A significant relationship was observed between estimated sweat loss and fluid intake during exercise (r² = .121, p = .001). Mean sweat sodium concentration was 38 ± 10 mmol · L⁻¹, with significant associations observed between player sweat rates and time spent exercising at intensities >90% HRmax (r² = .181, p = .001). Fluid and electrolyte loss appear to be work rate dependent in elite female handball players, whom appear well capable of replacing fluids lost within a tournament environment. Due to large between-athlete variations, a targeted approach may be warranted for certain players only.

Initial hydration status, fluid balance, and psychological affect during recreational exercise in adults

There is little information on the impact of hydration status on the psychological response to exercise despite potential implications for adherence to an exercise programme and for overall health and fitness. We investigated initial hydration status, fluid balance, and psychological responses associated with a typical recreational exercise session in healthy adults. Fifty-two participants performed a freely chosen gymnasium-based exercise session at a fitness centre, with ad libitum access to fluids. Urine samples were collected on arrival for analysis of osmolality. Sweat loss was estimated from the change in body mass after correction for fluid intake and urinary losses. Subjective psychological ratings were recorded before and after exercise. Pre-exercise urine osmolality was above 900 mOsmol · kg−1 (used as a threshold for hypohydration) in 37% of participants. Fluid intake during exercise was 390 ± 298 mL, while estimated sweat loss was 794 ± 391 mL. The percentage change from pre-exercise body mass was –0.62 ± 0.20%. Physically active adults who arrived to take part in exercise hypohydrated reported more negative changes in psychological affect in response to their subsequent freely chosen recreational exercise session than those classified as euhydrated prior to exercise (−0.2 ± 0.7 vs. 0.8 ± 0.7; P < 0.005).

Voluntary Fluid Intake And Core Temperature Responses In Children During Exercise In The Heat

Hydration can play an important role in maintaining performance and reducing clinical risk related to heat strain in young athletes. However, there remain a limited number of studies that describe core body temperature and other related responses to voluntary fluid intake in children during exercise in the heat. PURPOSE To examine the effects of ad libitum fluid intake, using chilled (∼10°C) water (W) vs. an 8% carbohydrate-electrolyte ([Na+]: 11.8 mmol·l−1) solution (CHO-8%), on core temperature and other physiological, behavioral, and perceptual responses in children during exercise in a hot environment. METHODS 29 healthy, active children (14 boys, 15 girls; age: 11.4 ± 1.2 y, 9–12 y; height: 151.4 ± 7.8 cm; weight: 42.4 ± 6.6 kg; BMI: 18.4 ± 1.7) completed two 80-min intermittent exercise (treadmill: 70% VO2max; cycle ergometer: 60% VO2max) sessions (using W or CHO-8%) on separate days (randomized, crossover design) in a hot (33°C) and humid (relative humidity: 54.7 ± 3.8%) environment. During each exercise session, fluid intake, urine volume, body weight (BW), core temperature, heart rate (HR), perceived exertion (RPE), thirst, taste, and gastrointestinal discomfort were measured at selected time points. Pre- and post-exercise urine specific gravity and osmolality were also determined. RESULTS CHO-8% consumption was greater compared to W (838.5 ± 50.7 g vs. 560.4 ± 47.9 g; p < 0.0001). Accordingly, with a similar post-exercise urine output (CHO-8%: 75.0 ± 12.7 g; W: 88.5 ± 13.5 g; p=0.3358), there was greater fluid retention during exercise in the CHO-8% trial compared to W (763.5 ± 49.0 g vs. 471.9 ± 49.6 g; p < 0.0001). Estimated sweat loss (by BW) was similar in both trials (CHO-8%: 591.8 ± 22.6 g; W: 568.8 ± 25.2 g; p=0.2634), resulting in a positive BW change (adjusted for urine output) in the CHO-8% trial and a BW-indicated fluid deficit in the W trial (+171.7 ± 56.4 g vs. −106.4 ± 52.6 g; p=0.0001). Core temperature was slightly higher (0.16 ± 0.01°C; p=0.0125) during CHO-8%, though the rate of change was similar in both trials. Moreover, this subtle difference did not translate into any statistical difference in physiological stress between trials, as indicated by HR or RPE. CHO-8% was consistently preferred over W (p < 0.001) in all selected taste perception categories. CONCLUSION CHO-8% appears more effective than W in keeping healthy, active children hydrated, by encouraging greater fluid intake and maintaining body weight, during exercise in the heat. However, greater consumption and retention of CHO-8% did not provide any measurable thermoregulatory or perceived exertion advantages over W during this exercise protocol. Supported by Kraft Foods Global, Inc.