Evaluation of voluntary and elicited dorsiflexor torque-angle relationships.

The purposes of this study were to determine the relative influence of mechanical (muscle force and moment arm) and neural (activation) factors on the shape of dorsiflexor torque-angle relationships and to determine the interday reliability of measurements of such relationships. Dorsiflexor torque-angle relationships produced with maximal voluntary contractions (MVCs) and with electrically elicited contractions (twitch, 20-Hz tetanic, 40-Hz tetanic) were obtained for seven male subjects on 2 separate days. MVC torque-angle relationships were reproducible between days. Elicited relationships were less reproducible than the MVC relationships, with the 40-Hz relationship the most reproducible of the elicited relationships. The shapes of the MVC and elicited twitch torque-angle relationships were significantly different. The shapes of the MVC, 20-, and 40-Hz elicited relationships were similar. The simplest explanation for this latter finding is that the shape the MVC relationship is determined primarily by mechanical factors and is not strongly dependent on neural factors. The results of this study may affect the interpretation of comparisons of torque-angle relationships between subject groups or pre- and posttraining.