Association of appendicular extracellular-to-intracellular water ratio with age, muscle strength, and physical activity in 8,018 community-dwelling middle-aged and older adults

Arch Gerontol Geriatr. 2023 May:108:104931. doi: 10.1016/j.archger.2023.104931. Epub 2023 Jan 18.

Abstract

Background: The appendicular extracellular-to-intracellular water ratio (Ap ECW/ICW) has recently gained attention as a non-invasive measurable marker of muscle quality. However, there is a lack of basic evidence regarding age-related changes, sex differences, contribution to muscle strength independent of skeletal muscle mass (SMM), and potential improvement through physical activity (PA) in Ap ECW/ICW.

Methods: This cross-sectional study enrolled 8,018 middle-aged and older Japanese individuals (aged 45-75 years). The Ap ECW/ICW and SMM were measured using segmental bioelectrical impedance spectroscopy. Muscle strength was evaluated by measuring the handgrip strength (HGS) with a dynamometer, and the PA level (PAL) was measured with an accelerometer. We performed a linear regression analysis of the associations of the Ap ECW/ICW with age, HGS, and PAL.

Results: The Ap ECW/ICW increased by 0.019 for men and 0.014 for women per 5-year increase in age (p < 0.001), and the age-related increase was greater in men than in women (p for interaction <0.001). The Ap ECW/ICW was more strongly associated with the HGS than with the SMM in both men and women (p < 0.001). PAL showed a significant inverse association with the Ap ECW/ICW in both men and women (p < 0.001).

Conclusions: Ap ECW/ICW is higher with age, and it varies by sex. The Ap ECW/ICW may reflect muscle strength more than the SMM, suggesting that the Ap ECW/ICW may be improved by PA. The findings from this study may provide a framework for further Ap ECW/ICW research.

Keywords: Aged; Body composition; Body water; Electric impedance; Muscle strength.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Body Composition / physiology
  • Body Water*
  • Cross-Sectional Studies
  • Electric Impedance
  • Exercise
  • Female
  • Hand Strength
  • Humans
  • Independent Living
  • Male
  • Middle Aged
  • Muscle Strength / physiology
  • Water*

Substances

  • Water