Programmed vs. Thirst-Driven Drinking during Prolonged Cycling in a Warm Environment

We compared the effect of programmed (PFI) and thirst-driven (TDFI) fluid intake on prolonged cycling performance and exercise associated muscle cramps (EAMC). Eight male endurance athletes (26 ± 6 years) completed two trials consisting of 5 h of cycling at 61% V˙O2peak followed by a 20 km time-trial (TT) in a randomized crossover sequence at 30 °C, 35% relative humidity. EAMC was assessed after the TT with maximal voluntary isometric contractions of the shortened right plantar flexors. Water intake was either programmed to limit body mass loss to 1% (PFI) or consumed based on perceived thirst (TDFI). Body mass loss reached 1.5 ± 1.0% for PFI and 2.5 ± 0.9% for TDFI (p = 0.10). Power output during the 20 km TT was higher (p < 0.05) for PFI (278 ± 41 W) than TDFI (263 ± 39 W), but the total performance time, including the breaks to urinate, was similar (p = 0.48) between conditions. The prevalence of EAMC of the plantar flexors was similar between the drinking conditions. Cyclists competing in the heat for over 5 h may benefit from PFI aiming to limit body mass loss to <2% when a high intensity effort is required in the later phase of the race and when time lost for urination is not a consideration.

Impact of Exercise-induced Dehydration on Perceived Exertion During Endurance Exercise: A Systematic Review with Meta-analysis

Understanding the impact of stressors on the rating of perceived exertion (RPE) is relevant from a performance and exercise adherence/participation standpoint. Athletes and recreationally active individuals dehydrate during exercise. No attempt has been made to systematically determine the impact of exercise-induced dehydration (EID) on RPE. The present meta-analysis aimed to determine the effect of EID on RPE during endurance exercise and examine the moderating effect of potential confounders using a meta-analytical approach. Data analyses were performed on raw RPE values using random-effects models weighted mean effect summaries and meta-regressions with robust standard errors, and with a practical meaningful effect set at 1 point difference between euhydration (EUH) and EID. Only controlled crossover studies measuring RPE with a Borg scale in healthy adults performing ≥ 30 min of continuous endurance exercise while dehydrating or drinking to maintain EUH were included. Sixteen studies were included, representing 147 individuals. Mean body mass loss with EUH was 0.5 ± 0.4%, compared to 2.3 ± 0.5% with EID (range 1.7 to 3.1%). Within an EID of 0.5 to 3% body mass, a maximum difference in RPE of 0.81 points (95% CI: 0.36-1.27) was observed between conditions. A meta-regression revealed that RPE increases by 0.21 points for each 1% increase in EID (95% CI: 0.12-0.31). Humidity, ambient temperature and aerobic capacity did not alter the relationship between EID and RPE. Therefore, the effect of EID on RPE is unlikely to be practically meaningful until a body mass loss of at least 3%.

Relationships Between WUT (Body Weight, Urine Color, and Thirst Level) Criteria and Urine Indices of Hydration Status

Background: A Venn diagram consisting of percentage body mass loss, urine color, and thirst perception (weight, urine, thirst [WUT]) has been suggested as a practical method to assess hydration status. However, no study to date has examined relationships between WUT and urine hydration indices. Thus, the purpose of this study was to investigate relationships between urine specific gravity, urine osmolality, and the WUT criteria. Hypothesis: Urine specific gravity and urine osmolality indicate hypohydration when the WUT criteria demonstrate hypohydration (≥2 markers). Study Design: Laboratory cohort study. Level of Evidence: Level 3. Methods: A total of 22 women (mean ± SD; age, 20 ± 1 years; mass, 65.4 ± 12.6 kg) and 21 men (age, 21 ± 1 years; body mass, 78.7 ± 14.6 kg) participated in this study. First morning body mass, urine color, urine specific gravity, urine osmolality, and thirst level were collected for 10 consecutive days in a free-living situation. Body mass loss >1%, urine color >5, and thirst level ≥5 were used as the dehydration thresholds. The number of markers that indicated dehydration levels were counted and categorized into either 3, 2, 1, or 0 WUT markers that indicated dehydration. One-way analysis of variance with Tukey pairwise comparisons was used to assess the differences in urine specific gravity and urine osmolality between the different number of WUT markers. Results: Urine specific gravity in 3 WUT markers (mean ± SD [effect size], 1.021 ± 0.007 [0.57]; P = 0.025) and 2 WUT markers (1.019 ± 0.010 [0.31]; P = 0.026) was significantly higher than 1 WUT marker (1.016 ± 0.009). Urine mosmolality in 2 WUT markers (705 ± 253 mOsmol [0.43]; P = 0.018) was significantly higher than 1 WUT (597 ± 253 mOsmol). Meeting at least 2 WUT markers resulted in sensitivities of 0.652 (2 WUT criteria met) and 0.933 (3 WUT criteria met) to detect urine osmolality >700 mOsmol. Conclusion: These results suggest that when 3 WUT markers are met, urine specific gravity and urine osmolality were greater than euhydration cutoff points. The WUT criterion is a useful tool to use in field settings to assess hydration status when first morning urine sample was used. Clinical Relevance: Athletes, coaches, sports scientists, and medical professionals can use WUT criteria to monitor dehydration with reduced cost and time.

Sex differences in the physiological responses to exercise-induced dehydration: Consequences and mechanisms?

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

23 Nutritional Intake and Weight Change in Severely Burned Patients

Introduction Nutrition is crucial for recovery from burn injuries, as severe weight (wt.) loss can lead to impaired immunity and wound healing, infections, skin graft failure, and mortality. Previous studies recommended avoiding more than 10% wt. loss, as this level resulted in increased infection rates. However, wt. loss is often not quantifiable during the critical illness phase, with severe edema masking non-fluid related body wt. changes. Energy (kcal) deficits can be used to estimate wt. loss until the edema has resolved, but previous studies in non-burn patients indicate that actual wt. loss is less than the commonly used 3500 kcal per pound of fat (7700 kcal per kg of fat). The objective of this performance improvement project was to evaluate nutritional intake and the resulting dry wt. change in severely burned patients. Methods This performance improvement project was approved by our regulatory compliance division. We performed a retrospective evaluation on patients with at least 20% total body surface area (TBSA) burns admitted for initial burn care to our intensive care unit over a 7-year period. Patients who died or who had major fascial excisions or limb amputations were excluded. Patients who did not achieve a recorded dry wt. after wound healing were not included in this analysis. Retrospective data were collected, including sex, age, burn size, kcal intake, kcal goal per the Milner equation using activity factor of 1.4, admission dry wt., dry wt. after wound healing (defined as less than 10% TBSA open wound), and days to dry wt. after wound healing. Descriptive statistics and linear regression were performed using JMP. Significance was set at p&lt; 0.05. Results The 30 included patients had the following characteristics: 90% male, 30 ± 11 years old, 45% ± 15% TBSA burn. They received 2720 ± 1092 kcal/day, meeting 68% ± 24% kcal goal, and took approximately 53 ± 30 days from injury to achieve dry wt. after wound healing. These patients had wt. loss of 8 ± 8 kg from the kcal deficit of 69,819 ± 51,704 during this time period. The kcal deficit was significantly associated with wt. change [p &lt; 0.001, R2 = 0.49, wt. change in kg = (-0.000103 x kcal deficit) – 1]. This translates to one kg of body wt. loss resulting from 9709 kcal deficit. Conclusions This performance improvement project found that an energy deficit of approximately 9700 kcal in our patients equates to 1 kg of body mass loss (4400 kcal deficit equates to 1 pound of body mass loss). These findings are similar to wt. loss studies in other patient populations and contrary to the commonly used 3500 kcal per pound of fat (7700 kcal per kg of fat).

Hydration and cooling in elite athletes: relationship with performance, body mass loss and body temperatures during the Doha 2019 IAAF World Athletics Championships

PurposeTo characterise hydration, cooling, body mass loss, and core (Tcore) and skin (Tsk) temperatures during World Athletics Championships in hot-humid conditions.MethodsMarathon and race-walk (20 km and 50 km) athletes (n=83, 36 women) completed a pre-race questionnaire. Pre-race and post-race body weight (n=74), Tcore (n=56) and Tsk (n=49; thermography) were measured.ResultsMost athletes (93%) had a pre-planned drinking strategy (electrolytes (83%), carbohydrates (81%)) while ice slurry was less common (11%; p<0.001). More men than women relied on electrolytes and carbohydrates (91%–93% vs 67%–72%, p≤0.029). Drinking strategies were based on personal experience (91%) rather than external sources (p<0.001). Most athletes (80%) planned pre-cooling (ice vests (53%), cold towels (45%), neck collars (21%) and ice slurry (21%)) and/or mid-cooling (93%; head/face dousing (65%) and cold water ingestion (52%)). Menthol usage was negligible (1%–2%). Pre-race Tcore was lower in athletes using ice vests (37.5°C±0.4°C vs 37.8°C±0.3°C, p=0.024). Tcore (pre-race 37.7°C±0.3°C, post-race 39.6°C±0.6°C) was independent of event, ranking or performance (p≥0.225). Pre-race Tsk was correlated with faster race completion (r=0.32, p=0.046) and was higher in non-finishers (did not finish (DNF); 33.8°C±0.9°C vs 32.6°C±1.4°C, p=0.017). Body mass loss was higher in men than women (−2.8±1.5% vs −1.3±1.6%, p<0.001), although not associated with performance.ConclusionMost athletes’ hydration strategies were pre-planned based on personal experience. Ice vests were the most adopted pre-cooling strategy and the only one minimising Tcore, suggesting that event organisers should be cognisant of logistics (ie, freezers). Dehydration was moderate and unrelated to performance. Pre-race Tsk was related to performance and DNF, suggesting that Tsk modulation should be incorporated into pre-race strategies.

Pre-competition body mass loss characteristics of Brazilian jiu-jitsu competitors in the United Kingdom

Background: Brazilian jiu-jitsu (BJJ) is a grappling-based combat sport in which competitors engage in pre-competition acute ‘weight’ loss (AWL) and rapid ‘weight’ loss (RWL) to achieve the body mass (BM) required for their desired division. AWL/RWL practices of UK BJJ competitors have not previously been reported. Aim: Our aim in this study was to determine the prevalence, magnitude and stakeholder influences of AWL and RWL amongst BJJ participants in the United Kingdom (UK). A secondary aim was to explore whether there is any influence of time spent in the sport or competition frequency on AWL/RWL practices. Methods: In this study we used the rapid weight loss questionnaire (RWLQ) adapted for BJJ to determine the prevalence and magnitude of AWL/RWL in UK BJJ, the prevalence of methods used and the key stakeholder influences on these practices. As a secondary investigation we aimed to determine whether there was any effect of age starting BJJ on AWL/RWL. Results: Of 115 completed responses, 59% stated they performed AWL/RWL before competition. Mean BM loss for this competition was 1.9 ± 3.8 kg (2.3 ± 4.6%), with 34% of participants starting BM loss 3–7 days prior and 16% starting 0–2 days prior. Methods used tend to be achieving calorie deficit via exercise and diet rather than hypohydration, with little advice from formally qualified personnel. Participants who perform AWL/RWL started training (BF10 = 199, d = .72) and competing (BF10 = 107, d = .68) in BJJ younger than those who do not perform AWL/RWL. Conclusions: AWL/RWL is prevalent in UK BJJ, but not at the magnitude of other combat sports or countries. Though negative effects of extreme hypohydration are unlikely, there may be a higher chance of eating disorders in BJJ, particularly due to the young age of AWL/RWL commencement.