Biomechanical measures of muscular effort

This paper identifies those particular force and torque quantities that arise most frequently in biomechanical investigations, and which, when appropriately combined with the system's kinematic behavior, appear to be related most directly to muscular effort, i.e., the metabolic cost associated with producing muscle tension, in a joint neighborhood. Depending upon whether the joint distribution problem has been solved, muscular effort is best determined either by the individual variable muscle force magnitudes or by the magnitude of the variable muscle force-dependent component of the resultant joint torque. Discrete biomechanical measures that can be used to represent these continuously-varying scalar functions are identified and examined critically. These include instantaneous measures (e.g., the extremes and other characteristic force, torque, and power values) and interval measures (e.g., average force, torque, and power values, work performed, change in mechanical energy, and linear and angular impulses). If the variation of the effort function is negligible, instantaneous measures may suffice provided there exists a reliable scaling factor relating these quantities to metabolic cost. If the variation of the effort function is appreciable, then properly weighted impulse measures may be the most appropriate because they appear to reflect muscular effort over the widest range of human activities, including those that involve isometric contractions.