Purpose: The purpose of this study was to analyze existing data and compare the effects of an 8-week intervention of either aerobic exercise, resistance exercise, or a combination of both on changes in total body water (TBW), intracellular (ICW) and extracellular (ECW) water volumes and body composition between groups and compared with a non-exercise control group in younger and older adults.

Methods: 69 pre- or stage-1 hypertensive, overweight or obese, and sedentary adults (age 58 ± 7 y) were randomized to one of three training programs: aerobic (AT), resistance (RT), or a combination of aerobic and resistance (COMB), or a non-exercise control group (CON) for a total of 8 weeks. Body composition and body water compartments were measured with bioelectrical impedance analysis (BIA, InBody720) and a three-day diet diary was recorded at baseline and post-intervention. Statistical analyses were performed on changes between groups, all exercise (INT) vs. control (CON), between sexes, and between younger (<60 y) and older (60+ y) adults. Values are reported as mean ± standard deviation (SD).

Results: INT had larger volumes of TBW, ICW, and ECW than CON, but the differences were not significant (P > 0.05 for all). INT increased TBW more than CON, but the difference was not significant (0.1 ± 1.3 l and -0.3 ± 1.2 l, P = 0.11, for INT and CON, respectively). COMB had the greatest change in TBW compared with CON (P = 0.05) and had a significantly greater increase in ECW compared with CON (P = 0.03). There was a negative association between age and LBM, TBW, ICW, and ECW volumes (Effect size (ES) > 1.0 for all). TBW, ICW, ECW, and LBM differed between groups in younger adults (P ≤ 0.05 for all), but did not differ between groups in older adults (P > 0.05 for all).

Conclusions: 8 weeks of AT, RT, COMB, or no exercise training can alter body water compartments in younger and older adults, via changes in body composition, but the changes are more variable in young adults. Body water compartment volumes are different between younger and older adults, in support of declining body water with age. Future research in this area is warranted with a larger sample, longer intervention, and more diverse population.