Ensuring Consistency and Examining the Reliability of Isokinetic and Isometric Knee Extension Strength Testing in Older Women over a Four-Week Interval

This study evaluates the inter-session reliability of isokinetic knee extension testing at 60°/s and 180°/s, along with isometric testing, over four weeks in older women. Sixteen participants, averaging 62.75 years, underwent assessments using a Biodex System 4 Pro dynamometer at baseline and after 30 days. The testing protocols included isometric (3 repetitions at 90° knee flexion) and isokinetic (maximal contractions at both speeds) assessments. Results showed non-significant increases in peak torque for isometric (0.92%) and isokinetic (60°/s: 4.13%) tests, while the 180°/s test demonstrated a significant increase (5.24%). Intraclass Correlation Coefficients (ICCs) ranged from 0.55 to 0.94 for isometric tests and from 0.62 to 0.97 for isokinetic tests, indicating moderate to excellent reliability. The Standard Error of Measurement percentage was lowest for isometric tests (3.24%) and highest for the 180°/s tests (8.23%). Bland-Altman analysis revealed small mean biases across all tests, suggesting that both isometric and isokinetic extension strength assessments exhibit reliable test-retest performance in older women. The findings have significant implications for accurately evaluating the effectiveness of interventions and rehabilitation programs tailored for older women, allowing for precise monitoring of strength changes and progress.