BIA-assessed cellular hydration and muscle performance in youth, adults, and older adults

Alterations in body hydration can have an impact on muscle performance, with consequences not only at a sporting level, but on overall health and daily functional competence. Given that the estimation of body water from BIA is based on prediction equations involving assumptions on tissue hydration and body geometry, it is unclear if phase angle (PhA), which is not influenced by assumptions, is a better marker of muscle performance than the BIA estimated parameters of body water. Therefore, the aims of this investigation were to analyze the relationships of BIA-estimated body water compartments with muscle performance among youth, adults, and older adults, and to assess the added value of PhA as a marker of muscle performance.

BIA assessments were completed on 263 youth (ages 6-17), 249 adults (ages 18-64), and 75 older adults (ages 65+). Muscle performance was assessed by jumping mechanography (power and force) and handgrip strength. Partial correlations were used to compare the degree of association among the BIA measures with muscle performance for each age group, controlling for sex, age, and body weight.

TBW, ICW, and PhA were associated with muscle performance at the lower and upper limbs in all age groups (p < 0.05), with the exception of PhA with handgrip strength in adults and older adults and TBW with lower limb total force in the older adults. In youth, the highest associations observed were PhA with lower limb muscle power (r = 0.45, CI:0.35-0.54, p < 0.05) and with handgrip strength (r = 0.42, CI:0.32-0.52, p < 0.05). In adults and older adults, the major associations observed were those of ICW with lower limb muscle power (adults, r = 0.53, CI:0.43-0.61, p < 0.05; older adults, r = 0.52, CI = 0.33-0.67, p < 0.05). ECW had significantly lower associations (p < 0.05) with both lower limb force and power in adults and older adults compared to youth. In the older adults, ECW was negatively associated with lower limb total force (r = -0.24; p < 0.05).

BIA derived hydration parameters may be useful markers of muscle performance in all age groups. In particular, the ICW compartment was a better predictor of muscle performance in adults and older adults compared to youth. In youth, PhA had stronger associations with muscle performance than those of ICW. Thus, phase angle appears to be a useful marker of muscle performance, particularly in youth.