Joint stability in the shoulder

- biomechanics and gamma reflexes

	Joint stability is determined by the muscular stiffness in 'soft' joints such as the neck knee and shoulder. Muscular tension generates stability at the glenohumeral jnt the outward curves represent the stabilising influence when the prime mover muscles act on the shoulder
	To enable stability at the glenohumeral joint during arm elevation  the scapula muscles position the glenoid to provide  optimal orientation  for the rotator cuff stabilising function
If the rotator cuff and scapular muscles do not operate synergistically then the potential for glenohumeral subluxation & subacromial impingement is generated

Summary

• the rotator cuff muscles provide glenohumeral stability
• the scapular muscles provide the positioning for inferior stability of the glenoid labrum for a snug fitting humeral head
• with the deep joint stabilizing muscles providing the stability, the prime movers may provide the 'action'
• generally speaking the stabilizing muscles of most joints are one joint muscles with an endurance function; whereas the prime movers are the muscles which lend power to the movement e.g. Pectoralis Major.  Therefore when designing an exercise regime the client must begin with good muscular stability before commencement of training of the prime movers.
• Frequently, clients compensate for lack of stability by increasing the speed at which they do the task.  This then leads to further in-coordination, poor timing between muscles, loss of synergy, and more dysfunction.  
• Closed kinetic chain training to gain scapula and rotator cuff stability may encourage gamma afferent feedback from the annulospiral endings, as well as activate the nuclear bag and nuclear chain fibres 
• Plyometric type exercises using theraband are designed to encourage eccentric-concentric control of the prime movers.

Plyometrics  

EMG biofeedback

Interesting article

Commerford & Mottram (2001). Functional stability re-training: principles and strategies for managing mechanical dyfunction.  Manual Therapy, 6,1, 3-14

Commerford & Mottram (2001). Movement and stability dysfunction - contemporary developments.  Manual Therapy, 6,1, 15-26

• these articles are particularly interesting in respect to synergistic 'timing' of muscle action in the upper and lower limbs

Animated muscular synergistic interaction for shoulder abduction - refer to Climbing section Shoulder Problems(English) Schulter Probleme (Deutsch)

Last update : 22 July 2006

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Copyright Martin Krause 1999 - material is presented as a free educational resource however all intellectual property rights should be acknowledged and respected