Muscle Performance and muscle-specific strength in Adults Assessed by Handgrip Strength and Isokinetics: Age-related Findings and Rehabilitation considerations

Abstract

Introduction.

Handgrip strength is widely used as a proxy for global muscle strength, its accuracy in reflecting functional performance across different age groups remains controversial. Isokinetic assessments may offer greater sensitivity, particularly in eccentric strength. To compare muscle performance assessed by handgrip strength and isokinetic knee extensor testing, and to explore muscle-specific strength differences across age groups.

Methods
A cross-sectional analytical study was conducted in healthy self-referred adults divided into three age groups: young (18–35 years), middle-aged (50–64 years), and older adults (≥65 years). Assessments: Handgrip strength using Jamar® dynamometer, body composition via DXA, and isokinetic knee extensor concentric and eccentric low and high velocities assessment. Muscle-specific strength was calculated force unit/mass unit. Group comparisons and effect sizes were analyzed using ANOVA or Kruskal–Wallis tests as appropriate.

Results
A 152 participants were evaluated. Handgrip strength showed significant differences only between the older group and the other two. In contrast, isokinetic strength (concentric and eccentric) demonstrated stronger age-related declines, with large effect sizes. Eccentric/concentric torque ratios were significantly higher in older adults at low velocities and in middle-aged adults at high velocities. Muscle-specific strength derived from eccentric strength detected age-group differences, whereas those based on handgrip strength did not. Moderate correlations were found between handgrip and isokinetic strength.

Conclusions
Eccentric muscle strength is relatively preserved in older adults and may serve as a more sensitive marker of muscle-specific strength than handgrip strength. Rehabilitation programs for aging individuals should consider eccentric training strategies tailored to age-specific muscle performance patterns.