A.D. Wayne, C.L. Chapman, S.M. Holt, S.C. Brazelton, C.T. O’Connell, H.N. Medved, W.A.B. Howells, E.L. Reed, K. Wiedenfeld Needham, J.R. Halliwill, FACSM, C.T. Minson, FACSM

University of Oregon, Eugene, OR

An overwhelming majority of the scientific literature investigating the effects of hypohydration on muscular strength has been performed in male participants. One study recently reported that passive heat-stress induced hypohydration reduces upper body muscular strength in females. To our knowledge, there are no data on whether prolonged mild hypohydration, in the absence of heat stress, similarly reduces upper body strength in females. This knowledge gap has implications for female athletes and workers in physically demanding occupations. PURPOSE: To test the hypothesis that maximum voluntary isometric handgrip strength is reduced in females following prolonged mild hypohydration compared to a hydrated state (i.e., euhydrated) and to investigate whether this response differs between males and females. METHODS: In a block-randomized crossover design, twenty-two healthy adults [11 females (F), 11 males (M); 21 (3) years] completed 24 hours of fluid deprivation (HYPO) or 24 hours of normal fluid consumption (EUHY). Protocols were separated by ³72 hours. Body fluid losses were estimated via the percent change in body mass (∆BM) over 24 hours. Participants performed three maximal voluntary isometric handgrip strength on a hand dynamometer with one minute rest between sets. Data are presented as mean with 95% confidence intervals. RESULTS: ∆BM was not different between sexes (P=0.5393) during HYPO [F: -2.2% (-2.9, -1.6); M: -2.8% (-3.4, -2.3)] or EUHY [F: -0.1% (-0.8, 0.5); M: 0.1% (-0.3, 0.6)]. Maximal handgrip strength was reduced in HYPO vs. EUHY in males [48 kg (43, 54) vs. 51 kg (45, 57), P=0.0468)] but there were no differences between conditions in females [27 kg (24, 30) vs. 28 kg (25, 32), P=0.3166)]. During HYPO, there was a trend toward greater reductions in handgrip strength between the first to third attempts in females vs. males during HYPO [-2.7 kg (-5.2, -0.2) vs. 0.8 kg (-1.6, 3.3), P=0.0762]. CONCLUSION: These findings suggest that prolonged hypohydration caused by fluid deprivation causes modest reductions in maximum handgrip strength in males but not females. However, unlike males, our data suggest that females are not able to reproduce initial handgrip strength on subsequent attempts when mildly hypohydrated.

Supported by NIH R01HL144128 and F32HL164021.

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