Reliability of isokinetic dynamometer for isometric assessment of ankle plantar flexor strength

Objective: To evaluate isokinetic dynamometer reliability for isometric assessment of plantar flexor (PF) strength.

Design: Cross-sectional.

Setting: Testing by the same physiotherapist twice during a first session (repeatability) and once during a second session (reproducibility).

Participants: Twenty-two healthy subjects (44 ankles, 11 men/11 women).

Main outcome measures: Isometric PF peak torque, with and without body mass normalization, at 0° and +20° of plantar flexion. Measurement reliability was evaluated using intraclass correlation coefficient (ICC), standard error of measurement (SEM) and minimal detectable change (MDC).

Results: Without normalization, measurement repeatability was excellent at 0° of plantar flexion (ICC, 0.94; SEM, 6.6%; MDC, 18.4%) compared with good repeatability at +20° (ICC, 0.85; SEM, 11.1%; MDC 30.6%). Measurement repeatability following normalization was good at 0° (ICC, 0.88; SEM, 5.2%; MDC, 14.4%) and +20° (ICC, 0.79; SEM, 10.2%; MDC, 28.1%). While reproducibility was good at 0° with normalization (ICC, 0.84; SEM, 5.9%; MDC, 16.3%) or excellent without (ICC 0.92; SEM 7.5%; MDC, 20.8%), it was moderate at +20° with normalization (ICC 0.71; SEM 11.3%; MDC, 31.3%) or good without (ICC 0.78; SEM 13.0%; MDC, 36.1%).

Conclusion: The reliability of PF maximal isometric strength is good/excellent at 0° of plantar flexion but moderate/good at +20°.