Throughout my Masters I have worked on various projects related to shoulder biomechanics, fatigue induced exercise, kinesio taping, and shoulder impingement syndrome. Specifically, my master thesis focused on the effect of exercise induced muscle fatigue on the acromiohumeral distance in people with normal shoulder joints compared with people with hypermobile joints.
Acromiohumeral distance is a narrow distance (approximately 10 mm) on top of the shoulder. There are different structures passing through this space including the supraspinatus tendon and the bursae.
This space is important as narrowing of the space can compromise the supraspinatus tendon or cause inflammation within the bursae. All of which could result in pain and restricted range of motion of the shoulder. One of the factors that can reduce acromiohumeral distance is muscle fatigue which can occur because of repetitive movement either during work or sporting activities.
In addition, the previous research has shown that the risk of developing musculoskeletal pain is higher in people with hypermobile joints. As these groups of people have laxity within their ligaments supporting their joint it makes them more susceptible to musculoskeletal injuries including shoulder joint problems.
In my master thesis, with collaboration of Dr Ann Cools who is one of the very known professors in the field of shoulder rehabilitation (Ghent Uni, Belgium), we measured the acromiohumeral distance by ultrasonography and muscle strength before and after shoulder fatigue exercise. The result of this study showed that following fatigue the acromiohumeral distance and strength reduced, however could not find any difference between the healthy shoulder and the hypermobile joint.
The conclusion from this study was that fatigue could increase the risk of injuries within the shoulder joint; however, people with hypermobile joints did not show any difference to the normal shoulder.
The result of this study has been published in the Journal of Applied Biomechanics (2017) Razie J Alibazi et al. The effect of shoulder muscle fatigue on acromiohumeral distance and scapular dyskinesis in women with generalized joint hypermobility.