Variability of isometric and isotonic leg exercise: Utility for detection of submaximal effort.

A number of studies have investigated the use of variability measures in the detection of submaximal or insincere efforts in strength testing. The underlying assumption of these approaches is that submaximal efforts will be more variable than maximal efforts. Previous studies have investigated the variability of torque production in isometric or isokinetic tasks with mixed results. The present study investigated the variability of torque production and velocity in isometric and isotonic leg extension tasks, respectively. Fifteen asymptomatic subjects participated in a within-subject counterbalanced design in which they were asked to perform maximally and submaximally in both isometric and isotonic leg extension tasks. Results indicated that both isometric and isotonic tasks showed greater variability (measured by coefficient of variation) in the submaximal effort condition. However, the sensitivity to detect submaximal efforts was much greater for the isotonic velocity variability condition. It was concluded that the isotonic approach showed promise for clinical application, but that the isometric task had unacceptably poor classification rates, consistent with previous research.