Effects of upper limb muscle vibration on human voluntary wrist flexion-extension movements.

The effect of upper limb muscle tendon vibration during alternating step flexion-extension movements about the wrist was studied in 6 normal humans. A vibrator was mounted over either the wrist flexor muscle or the elbow flexor and extensor muscles. Vibration was applied either to a single muscle or simultaneously to both muscles during wrist flexion-extension movements. After a period of practice, subjects learned the required movements and were able to make them with their eyes closed. Simultaneous application of subthreshold vibration to the wrist flexor and the elbow extensor or flexor muscles during extension movements produced an undershooting of the required end-movement position. The observed results indicated the pattern of transjoint projections from elbow extensor and flexor muscles to motoneurons supplying wrist extensor and flexor muscles. It is also suggested that those transjoint projections play an important role in coordinated movement of wrist and elbow joints.