Same but different: a comparison of antigravity muscle moment outputs when measured by isokinetic dynamometer versus inverse dynamics

Isokinetic dynamometers (IKD) and inverse dynamics (ID) approach are the two primary methods used to study muscle moment outputs during isolated and natural movements, respectively. However, it remains unclear whether these methods provide comparable moment values. This study, therefore, examined the maximum moment outputs of the main antigravity muscle groups as measured by IKD and ID methods. Maximum isometric moments were measured at matched joint angles from ankle plantarflexors, knee extensors, hip extensors, and hip abductors using a commercially available IKD and a force plate integrated apparatus, which enabled ID computation. On average, a 44 % (P = 0.002) greater ankle plantarflexor moment was obtained in ID than IKD condition, whereas the opposite - a 27 % (P = 0.037) greater extensor moment in IKD - was measured at the knee. No significant differences in moment outputs were found between the two methods for hip abductor and hip extensor muscles. Observation that IKD and ID methods produce significantly different moment outputs for ankle plantarflexor and knee extensor muscles should be considered when interpreting the results derived from these two methods.