Is the 'crunch factor' an important consideration in the aetiology of lumbar spine pathology in cricket fast bowlers?

The 'crunch factor' is defined as the instantaneous product of lateral flexion and axial rotational velocity of the lumbar spine. It was originally implicated in the development of lumbar spine pathology and lower back pain in golfers and, although empirical evidence supporting or refuting the crunch factor is inconclusive, it remains an intuitively appealing concept that requires further investigation, not only in golf, but also in other sports involving hitting and throwing motions. This article considers whether the crunch factor might be instrumental in the aetiology of contralateral lumbar spine injuries sustained by cricket fast bowlers. Based on recent empirical research, it is argued that the crunch factor could be important in cricket fast bowling especially considering that peak crunch factor appears to occur just after front foot impact when ground reaction forces are known to be at their highest. The crunch factor may also occupy an integral role in lower back injuries sustained in other sports involving unilateral overhead throwing (e.g. javelin throwing) and hitting (e.g. tennis serving) actions where the spatial orientation of the arm at release or impact is largely determined by lateral flexion of the trunk and where the transfer of energy and momentum along the kinetic chain is initiated by a rapid rotation of the pelvis. Further research is required to empirically verify the role of the crunch factor in the development of lower back injuries in cricket fast bowling and sports that involve similar lower trunk mechanics. This research programme should ideally be supported by modelling work examining the stresses imposed on bony, disc and joint structures by lateral flexion and axial rotation motions so that their respective contribution to injury can be identified.