[Hydraulically controlled isokinetic strength testing]

Hydraulically controlled strength test devices provide a constant predetermined movement velocity, and as such may be specified as (quasi‑)isokinetic dynamometry. There are limited literature reporting comparisons with other strength testing modes. This work presents reference values and reliability analyses for trunk and knee maximum torques and their respective flexion-extension ratios for hydraulically controlled isokinetic dynamometry in comparison to isometric strength testing.

In a cross-sectional design, reference values (M, SD, percentiles) of 45 healthy adults (21 females, age 26.1 ± 3.9 years, BMI 23.2 ± 2.5 kg/m²) were assessed (trunk, knee: flexion, extension and their functional ratios) for the Factum® test devices (Frei medical) including, comparisons of the isometric or isokinetic test mode (Bland-Altman). For a sub-sample of 20 persons (50% females), time economy and reliability (ICC3.k) were assessed.

The (quasi‑)isokinetic test protocol was less time consuming (50%) and demonstrated higher reliability coefficients (ICC3.k 0.736-0.933) compared to isometric testing (ICC3.k 0.550-0.899). Flexion-extension ratios (isokinetic 68%, isometric trunk 63%) revealed a relation nearby 2:3, except for the isometric knee ratio (55% ≈ 1:2), due to smaller proportions of knee flexion forces.

Results indicated mode specific differences and are not directly comparable with clinical implications especially for the flexion-extension ratios. Each protocol showed to be sufficiently reliable with time economy advantages for the (quasi‑)isokinetic protocol. Distributions of body weight-adjusted peak torques and functional ratios may serve as device-specific benchmark values for strength testing in clinical environments.