Effect of rehydration schedule after four-hour head-out water immersion on running performance and recovery
Authors:   Ctr. for Research and Education in Special Environments, Dept. of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, New York, U.S., Hess Hayden W. , Schlader Zachary J. ,   Ctr. for Research and Education in Special Environments, Dept. of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, New York, U.S., Russo Lindsey N. ,   Ctr. for Research and Education in Special Environments, Dept. of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, New York, U.S., Stansbery Rebeccah L. ,   Ctr. for Research and Education in Special Environments, Dept. of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, New York, U.S., Carey Mary G. ,   University of Rochester, School of Nursing, Rochester, New York U.S., Pendergast David R. ,   Ctr. for Research and Education in Special Environments, Dept. of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, New York, U.S., Clemency Brian M. ,   Ctr. for Research and Education in Special Environments, Dept. of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, New York, U.S.,   Dept. of Emergency Medicine, Jacobs School of Medicine and Biomedical Sciences,  University at Buffalo, Buffalo, New York U.S., Hostler David ,   Ctr. for Research and Education in Special Environments, Dept. of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, New York, U.S.,   Dept. of Emergency Medicine, Jacobs School of Medicine and Biomedical Sciences,  University at Buffalo, Buffalo, New York U.S.
Published: October 2022

Introduction: Head-out water immersion (HOWI) results in diuresis, which could potentially limit performance after egress to land. We examined the effect of rehydration on endurance, cardiovascular stability, and overnight recovery following a four-hour thermoneutral HOWI on 12 subjects. Methods: Twelve males completed a crossover design consisting of no hydration, replacement of fluid loss during immersion (RD), and replacement of fluid after the immersion period (RA). Sixty minutes following immersion, subjects ran to exhaustion at ~80% maximum heart rate. After completing the run, each subject submitted to a head-up tilt test (HUTT). Vital signs and ECG were monitored overnight. Results: HOWI resulted in a transient diuresis in NH and RA, while it was sustained throughout immersion in the RD protocol, resulting in greater urine [l] output (1.27 ± 0.48 (NH), 1.18 ± 0.43 (RA), 2.32 ± 0.77 (RD) (p < 0.001). Body mass change (%) was greater in NH than RD, but not RA (-1.58 ± 0.56 (NH), -0.66 ± 0.47 (RD), and -0.92 ± 0.76 (RA)). Run times were 17% versus 20% in NH compared to RD and RA, respectively, but were not statistically different. Time to orthostasis during the HUTT did not differ by condition. Overnight heart rate variability and blood pressure were not different. Conclusion: Rehydration during water immersion resulted in a large, sustained diuresis without improving performance or recovery after exiting the water. Loss of body water during thermoneutral HOWI was modest, and both rehydration strategies minimally affected aerobic performance and overnight recovery in young, healthy males.