Objectives: To assess the effects of hydration status and ice-water dousing on physiological and performance parameters. Design: Randomized, crossover. Methods: Twelve athletes (mean[M] ± standard deviation [SD]; age, 20 ± 1 years; height, 174 ± 8 cm; body mass, 72.1 ± 11.0 kg; VO 2max 53.9 ± 7.3 mL⋅kg −1 ⋅min −1 ) completed four trials (euhydrated without dousing, hypohydrated without dousing, euhydrated with dousing, and hypohydrated with dousing), which involved intermittent treadmill running (five 15-minute bouts) in the heat (M ± SD; ambient temperature, 34.7 ± 2.1°C; relative humidity, 46 ± 3%; wet-bulb globe temperature, 28.0 ± 0.4°C). Participants also completed four cognitive, power, agility, reaction time, and repeated sprint performance tests throughout each trial. Heart rate (HR) and rectal temperature (T rec ) were measured continuously. Repeated measures ANOVAs were performed to assess differences between physiological and performance variables. Alpha was set at ≤0.05, a priori. Data are reported as mean difference ± standard error (MD ± SE). Results: HR was significantly lower in euhydrated trials compared to hypohydrated trials, irrespective of dousing (8 ± 2 bpm; p = 0.001). Dousing did not significantly impact HR (p = 0.455) and there was no interaction between hydration and dousing (p = 0.893). T rec was significantly lower in euhydrated trials compared to hypohydrated trials (0.39 ± 0.05°C, p < 0.001), with no effect from dousing alone (p = 0.113) or the interaction of hydration and dousing (p = 0.848). Dousing resulted in improved sprint performance (11 ± 3 belt rotations, p = 0.007), while hydration status did not (p = 0.235). Conclusions: Athletes should aim to maintain euhydration during exercise in the heat for improved physiological function and cooling with ice-water dousing elicits additional performance benefits.

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.

Reproductive hormones can have significant non-reproductive physiological effects, including altering the regulation of body fluid volume. The purpose of this investigation was to explore the impact of sex and menstrual cycle (MC) phase on volume regulatory responses to 24-hour fluid restriction (24-h FR). Participants (men: n=12, 20±2y; women: n=10, 20±1y) were assigned two randomized and counterbalanced fluid prescriptions (Euhy: euhydrated, urine specific gravity, USG<1.020; Dehy: 24-h FR, USG>1.020). Men completed both (MEuhy, MDehy) while women completed both in the late follicular (days 10-13; FDehy, FEuhy) and mid-luteal (days 18-22; LDehy, LEuhy) phases. We measured body mass, plasma and urine osmolality (Posm, Uosm), USG, urine color (Ucol) and serum copeptin. 24-h FR yielded mild dehydration with no influence of sex or MC phase (P>0.05). Men exhibited higher copeptin following Dehy (pre: 8.2±5.2, post: 15.8±12.6, P=0.04) but women did not (FDehy - pre: 4.3±1.6, post: 10.5±6.9, P=0.06; LDehy - pre: 5.6±3.5, post: 10.4±6.2, P=0.16). In FDehy women, Posm increased following FR (pre: 288±2, post: 292±1, P=0.03) but not in men (pre: 292±3, post: 293±2, P=0.46). No MC differences were observed between %BML, Posm, Uosm, USG, Ucol, and serum copeptin (P>0.05). These results suggest that copeptin responses to mild dehydration elicited via 24-h FR were present in men only, regardless of MC phase in young healthy adults.

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