Differentiation of submaximal from maximal trunk extension effort: An isokinetic study using a new testing protocol

Study Design. An evaluation of the relations between concentric and eccentric contractions of the trunk extensors and extension effort performed at maximal and submaximal levels. Objective. To define quantitative parameter(s) derivable from isokinetic dynamometry that may differentiate submaximal from maximal trunk extension moment. Summary of Background Data. Using various consistency-related parameters, researchers in previous studies have not been able confirm the potential of isokinetic dynamometry for identifying submaximal effort during trunk extension. Methods. Twenty healthy subjects, 8 women and 12 men without low back pain history, aged 21 to 30 years, took part in this study. Testing consisted of three experimental conditions using four intermittent concentric and eccentric contractions at 20°and 60°/second. The first condition, in which subjects were asked to exert maximal concentric and eccentric effort, served as the baseline. In the second condition, subjects were asked to exert 50% of the force measured in the first condition. In the third condition, subjects repeated the second condition but were asked to exert the best reproducible level of force. Results. The highest differentiating power among the experimental conditions was attributed to the intervelocity difference between the concentric and eccentric contractions (P < 0.0001). Conclusions. This protocol effectively differentiates submaximal from maximal trunk extension effort in normal subjects.