Non-noxious stimulation of the glenohumeral joint capsule elicits strong inhibition of active shoulder muscles in conscious human subjects.

Information about the function of joint afferents in humans is scarce. Therefore, we investigated the influence of non-noxious electrical stimulation of the glenohumeral joint capsule on the activity of shoulder muscles in conscious human subjects. Stimulation electrodes were inserted in the joint capsule during arthroscopy. Only when the anterior inferior part of the capsule including the glenohumeral ligament was stimulated a strong and rather long latent general inhibition in voluntarily activated shoulder muscles was observed (average latency and duration: 33 ms and 76 ms, respectively). The inhibition was followed by an excitation and a few but inconsistent oscillations in the muscle activity. The results suggests a potent proprioceptive feedback pathway for the motor control of the human shoulder joint. However, further investigations are needed to clarify the involvement of several possible afferent pathways.