Are shoulder counter rotation and hip shoulder separation angle representative metrics of three-dimensional spinal kinematics in cricket fast bowling?

This study aimed to investigate the relationship between shoulder counter-rotation (SCR), hip shoulder separation (HSS) and three-dimensional spinal kinematics during fast bowling in cricket. Thirty five elite male fast bowlers were analysed using three-dimensional inertial sensors on the spine. Lumbar, thoracic and thoracolumbar kinematics were determined during the delivery stride. Spearman's pairwise correlations displayed significant associations between SCR, thoracic and thoracolumbar lateral flexion between the back foot impact and max contralateral rotation phase of the delivery stride (rs = -.462 and -.460). HSS and thoracolumbar lateral flexion displayed a significant correlation between back foot impact and max contralateral rotation (rs = -.552). No other significant correlations were observed. These results suggest SCR and HSS are modestly related to lateral flexion, leaving a large component of SCR and HSS unrelated to specific three-dimensional spinal kinematics. It is possible that this represents changes in whole spinal orientation and not resultant spinal motion. Despite this, SCR remains the only metric currently related to injury and therefore is important; however it is only a very modest proxy for more traditional descriptions of spinal motion.