Investigation into lumbar spine injury risk factors during fast bowling in junior cricketers

Background
Fast bowlers experience the highest incidence of injury in cricket, with most injuries occurring in the lumbar spine region attributed to aspects of fast bowling technique, such as the mixed action that displays greater shoulder counter-rotation. Coaching interventions afford a potentially valuable strategy whereby correction of the fast bowling technique has shown positive outcomes in reducing potential risk factors associated with lumbar spine injury.
Thesis Aim
The purpose of this thesis was to determine the biomechanical differences between the main action types and whether particular biomechanical bowling variables can account for lumbar spine abnormalities on diagnostic imaging in junior fast bowlers. A secondary aim was to explore a coaching intervention that targeted proposed biomechanical injury risk factor mechanisms for lumbar spine injury in junior fast bowlers.
Methods
Sixty junior district/zone (pre-state) male fast bowlers completed five consecutive overs across two cohorts. Three-dimensional kinematics and kinetics of the bowling action were recorded and analysed in Visual3D software. A randomly selected group completed a seven-week coaching intervention program. Magnetic resonance imaging (MRI) scans of the lumbar spine region were carried out pre-, mid- and post-season to monitor lumbar spine health.
Results
Significant differences affecting elbow, shoulder, trunk and pelvic angles between front-on, semi-open and mixed action types were observed. The mixed action displayed greater trunk rotation and higher thoraco-lumbar rotational range of motion during the back-foot contact phase. Significantly greater knee extension at ball-release, hip internal rotation at arm-horizontal and reduced thoraco-lumbar range of motion were seen in the front lower-limb for participants with lumbar spine abnormality compared to the control group. Crunch factor analyses (trunk flexion/extension multiplied by pelvis rotation) were shown to be significantly correlated with increased L5-S1 and T12-L1 mediolateral shear force but reduced compressive force, but were not significantly linked with lumbar spine abnormality. The coaching intervention demonstrated that the coaching group demonstrated more positive improvements (45%) than the control group.
Conclusions
This thesis has shown that biomechanical differences exists between fast bowling action types, particularly in the mixed action during the back-foot contact phase. Due to the absence of differences in lumbar loading between actions during front-foot contact phase, lumbar region kinetics during back-foot contact phase need to be analysed in future research to determine if kinematic differences during this phase contribute to increased lumbar injury risk in junior fast bowlers. Traditional injury risk mechanisms were not associated with increased risk of lumbar spine injury. Rather, junior fast bowlers may be unable to dissipate load due to restricted thoraco-lumbar rotation and the motion of the front lower limb may affect injury risk via the inefficient transfer of load to the lumbar spine. Crunch factor was also found to be influential on lumbar load during fast bowling. This relationship may be detrimental to spinal health in junior fast bowlers as increased mediolateral shear joint force was associated with injury and requires further investigation. This thesis has also shown that a coaching intervention can reduce known injury mechanisms such as shoulder counter-rotation, shoulder-pelvis separation angle and trunk lateral flexion.