The influence of subject and test design on dynamometric measurements of extremity muscles

In the context of broader discussions of clinical dynamometry, earlier reviews have raised concerns about the potential effects of variations in subject factors and test procedures on measurements. None, however, have dealt exclusively with these effects. We therefore reviewed more than 200 articles to evaluate in detail the effects of variations in subject factors and test procedures on measurements. Factors relating to subjects that affected measurements were age, gender, weight, athletic background, disability, and limb dominance. Test conditions that led to variations in measurements were range of movement in which values were obtained, type of contraction or movement (concentric, eccentric, isokinetic, isometric, isotonic), pretest procedures (warm-up and gravity-correction procedures, starting position, stabilization, axes alignment, lever arm length, preload, damp/ramp settings), test conditions (speed, test sequence, rest intervals, feedback), and type of data analysis (the data selected and how they are manipulated). In the majority of the publications, the authors failed to provide sufficient detail for accurate replication of test procedures or for comparison with other studies. We advocate that the factors identified in this review be included whenever measurements obtained with a dynamometer are reported. Effective development of normative data, formation of ratios, comparison of measurements across studies, and relating measurements with other performance criteria (eg, measurements of functional performance) all require descriptions of variables relating to subjects and testing. Similarly, meaningful use of these measurements in clinical practice requires consideration and documentation of these variables.