Isotonic resistance jaw exercise alters jaw muscle coordination during jaw movements.

The aim was to investigate the effects of isotonic resistance exercise on the electro-myographic (EMG) activity of the jaw muscles during standardised jaw movements. In 12 asymptomatic adults surface EMG activity was recorded from the anterior temporalis and masseter muscles bilaterally and the right anterior digastric muscle during right lateral jaw movements that tracked a target. Participants were randomly assigned to a Control group or an Exercise group. Jaw movement and EMG activity were collected (i) at baseline, before the exercise task (pre-exercise); (ii) immediately after the exercise task (isotonic resistance at 60% MVC against right lateral jaw movements); (iii) after 4 weeks of a home-based exercise programme; and, (iv) at 8-weeks follow-up. There were no significant within-subject or between-group differences in the velocity and amplitude of the right lateral jaw movements either within or between data collection sessions (P > 0.05). However, over the 8 weeks of the study, three of the tested EMG variables (EMG Duration, Time to Peak EMG from EMG Onset, and Time to Peak EMG activity relative to Movement Onset) showed significant (P < 0.05) differences in the five tested muscles. Many of the significant changes occurred in the Control group, while the Exercise group tended to maintain the majority of the tested variables at pre-exercise baseline values. The data suggest a level of variability between recording sessions in the recruitment patterns of some of the muscles of mastication for the production of the same right lateral jaw movement and that isotonic resistance exercise may reduce this variability.

Human flexor pollicis longus: role of peripheral inputs in weight-matching.

We investigated the role of local cutaneous signals and of co-contraction of antagonists in repeated judgements of heaviness of weights lifted by flexor pollicis longus. A reference weight lifted by right thumb flexion was matched to a weight lifted by left thumb flexion. Anaesthesia of the right thumb, or of the superficial radial, dorsal ulnar or mixed radial nerves failed to impair accuracy of weight judgements. However, perceived heaviness significantly increased by 85% and 20% following anaesthesia of the thumb and dorsal radial surface of the hand, respectively, confirming a role for cutaneous inputs from these areas in motor control of the thumb.