Transversal and Longitudinal Twitch Response of Biceps Brachii

Abstract. Isometric transversal displacement (TD) and torque responses were simultaneously recorded during graded electrically elicited isometric twitch contractions on the human biceps brachii muscle. The amplitude of electrical stimulation was increased in 5 mA steps from a threshold up to a supramaximal response. Muscles’ belly transversal displacement was measured by a high precision mechanical displacement sensor using a slight pre-tension to the muscle belly. The results were compared to simultaneously measured muscle torque on a distal limb. The results indicate parabolic relation between the TD and the torque twitch peak amplitudes. Significantly shorter contraction time was found for the TD response than for the torque response. Variation of the contraction time measured from threshold to supramaximal stimulation was notably different for the TD response and the torque response. This suggests that different mechanisms affect longitudinal (torque) and transversal (TD) deformations during contraction. Delay time was similar at submaximal and supramaximal responses but much larger in TD at just above threshold contractions. Half relaxation time has a similar linear trend in both responses, however, the magnitude is much larger in the TD than in the torque responses. Parameters extracted from the transversal displacement of the muscle belly on a twitch could serve as an appropriate predictor of the muscle contraction velocity and of the muscle composition.

Key words: tensiomyography, mechanomyography, transversal displacement, skeletal muscle, joint torque