Maximal Versus Non Maximal Muscular Exertions: A Study of Valid Measures Using Isokinetic Dynamometry

Abstract

Muscle strength capabilities are a determinant in the ability to successfully accomplish everyday tasks. As such, the quantification of this aspect of human performance is of interest in many settings. Currently, the validity of muscle strength test results is reliant on the notion that during testing, the participant exerted an effort that is sincere, and that consisted of maximal voluntary contractions. Therefore, the ability to differentiate between maximal and non maximal muscular exertions is of importance. The purpose of this dissertation was to develop and validate probability-based decision rules for differentiating between maximal and non-maximal voluntary exertions of the knee and shoulder joint musculature during isokinetic dynamometry-based testing. For development of the decision rules, healthy participants performed a series of maximal and non-maximal exertions at different testing velocities through a prescribed range of motion. Two different theory-based approaches were subsequently used for decision rule development: the first approach was based on expected better consistency in strength waveform shapes and relative magnitudes during performance of maximal efforts in comparison to non-maximal efforts. The second approach was based on the known force-velocity dependency in skeletal muscles. In terms of discriminatory performance, several of the decision rules pertaining to the knee joint markedly improve upon those previously reported. In addition, a separate investigation demonstrated that the decision rules offer excellent discriminatory performance when applied to test results of participants that have undergone surgical reconstruction of their anterior cruciate ligament. As such, clinicians and researchers may be able to ascertain voluntary maximal effort production during isokinetic testing of the knee joint musculature with a high degree of confidence, and thus be able to rely on such scores for decision-making purposes With regards to the shoulder musculature decision rules, several methodological issues related to test positioning and signal processing need to be addressed prior to consideration of their use in the clinical domain.