Musculoskeletal modelling of the shoulder during cricket bowling

Abstract

Shoulder injuries affect athletes who participate in overhead sports, such as swimming, baseball or basketball. This is due to the high loading, large range of motion and repetitive nature of the sporting task. Impingement has been identified as the most common cause of shoulder pain in overhead athletes. Cricket bowling involves one of the more complex sporting tasks where the arm goes through a large range of motion during circumduction to project the cricket ball at varying degrees of speed and spin where injury surveillance research estimates that over 20% of cricket injuries are related to the upper limb with the glenohumeral joint being the second most injured site. Similar to other overhead athletes, cricket bowlers have a prevalence of shoulder injury and pain with loss of internal rotation. It is hypothesised that this is due to large distraction forces and muscle imbalance at the glenohumeral joint. A second, specific hypothesis is that bowlers who have greater internal rotation after delivering the cricket ball are more likely to suffer from impingement. The motivation for this study is derived from these hypotheses. The aim of this thesis was to test the hypotheses above and investigate potential shoulder injury risk in cricket bowlers. A full body 3D kinematic analysis of fast and slow bowling actions was conducted and a musculoskeletal model used to investigate joint forces and muscle activations at the shoulder. Technical advances were made in musculoskeletal modelling; these included a new kinematic optimisation routine and improvements in the muscle wrapping method. The performance of a scapula tracker in full speed bowling trials showed good repeatability. There was however, significantly greater posterior/anterior tilt and internal rotation underlining the effect of speed of movement on the scapula tracker that was used. At ball release, the glenohumeral adduction angle for fast bowlers was between 36°- 80° and 59°- 66° for slow bowlers with the humerus externally rotated within a range of 90°- 140° and 71°- 131° for both sets of bowlers respectively. The analysis showed that one potentially vulnerable position was in the region between upper arm horizontal and ball release due to the location of the joint reaction force and its magntiude. A large distraction force was reported for bowlers where the superior shear forces was also a key factor in determining the risk on injuries at the joint. Predicted activation pattern for subscapularis substantiate the risk of impingement injuries due to overuse and fatigue during rotation of the arm from upper arm horizontal to ball release. In addition, internal/external glenohumeral joint torque values were similar for both sets of bowlers with the peak value occuring midway between upper arm horizontal and ball release. Further work should concentrate on the link between technique and musculoskeletal loads and thus allow training to mitigate the risk of shoulder injury.