(37) CHANGES IN BODY WATER DISTRIBUTION ACROSS THE MENSTRUAL CYCLE

Purpose: To examine changes in body water distribution across the early follicular (EF), late follicular (LF), and mid-luteal (ML) phases of the menstrual cycle (MC). Methods: Sixteen healthy women (62.5% White/Caucasian; age, 22±5 y; age of menarche, 12±2 y; body mass index, 23.7±4.1 kg∙m-2) with a history of regular menstruation, abstinence from hormonal contraception use, and no current or past eating disorders participated in this study. Three lab visits per participant were scheduled to coincide with the EF (within 5 days of self-reported onset of menstruation), LF (within 48 hours of a positive at-home urinary ovulation test), and ML (7-9 days after the positive ovulation test) phases of the MC. Body water distribution was assessed at each visit with whole-body bioimpedance spectroscopy and quantified using total body water (TBW), intracellular fluid (ICF), and extracellular fluid (ECF) volumes. Urine specific gravity (USG) and hematocrit were measured as indices of hydration status. Statistical significance of the mean differences between MC phases for TBW, ICF, and ECF was determined using repeated measures ANOVA with an alpha level of significance of 0.05. Magnitudes of the differences were expressed using the partial eta squared (ηp2) effect size. Results: Means and standard deviations for outcome variables are presented in Table 1. Standardized residuals of all outcome variables were approximately normally distributed with equal variances between all within-subject conditions. Mean hematocrit (≤41.4%) and USG (≤1.0187) values were similar (all p>0.05) at each study visit. Differences in TBW volumes across MC phases were small (ηp2=0.06) and non-significant (p=0.394). ICF volumes were lower (ηp2=0.10) during the EF phase compared to the LF and ML phases, although these differences were not significant (p=0.207). ECF volumes were significantly (p=0.007) higher (ηp2=0.28) during the EF phase compared to the later phases. Conclusions: Consistent TBW volumes and hydration status across the three study visits with concomitant changes in ICF and ECF suggest that body water may shift from the intracellular fluid space to the extracellular fluid space during the EF phase. Practical Applications: The observed shifts in body water suggest that fluid needs may vary across the MC. Specifically, a reduction in ICF during the EF phase (i.e., during menstruation) may lead to dehydration-related performance decrements if large enough. Strength and conditioning professionals and sport coaches working with female athletes should be particularly cognizant of fluid intake during the early phase of the MC. Acknowledgements: None