Twitch response of intact human tibialis anterior muscle to doublet stimulation at graded strengths.

The purpose of this project was to determine if the properties of doublet force twitches change with recruitment level. Isometric, human tibialis anterior force twitches were measured in response to singlet and doublet stimulation at several recruitment levels for eight healthy subjects. All doublets showed nonlinear force summation. When normalized to singlet responses at the equivalent recruitment level, doublet peak force, torque-time integral, half pulse width and half decay time changed with recruitment while start time and contraction time did not. Although the number of subjects was small, the results suggest that caution must be exercised when extending doublet properties at full recruitment to partial recruitment conditions.