The effect of foot support on trunk strength assessment using isokinetic dynamometry

Abstract

BACKGROUND: The standardization of trunk-muscle strength assessment is important for clinical practice. OBJECTIVE: To compare trunk muscle strength and electromyographic (EMG) activation of the trunk and lower limb muscles during testing with and without foot support using an isokinetic dynamometer. METHODS: Trunk flexion and extension strength was evaluated in 34 young individuals using isometric and isokinetic contractions, with and without foot support. Concomitantly, EMG signals from the trunk and dominant lower limb muscles were recorded. RESULTS: With foot support, the muscle strength generated during isokinetic and isometric extension contractions was greater than that without foot support (p < 0.001). The use of foot support enhanced the activation of trunk muscles (lumbar iliocostalis and longissimus dorsi) only during isometric extension contractions, whereas increased isokinetic extension contractions were associated with greater medial and lateral gastrocnemius activation. CONCLUSIONS: Testing trunk extension strength with foot support is recommended because it results in a higher peak moment under isometric conditions, possibly due to greater EMG activation of the trunk muscles. During isokinetic conditions, the use of foot support promoted increased extensor strength without increased EMG activation of the trunk muscles. By contrast, testing of trunk flexion strength may be conducted with or without foot support.