Discussion
The study set out to explore the kinematics and impacts of junior and senior fast bowlers and how these relate to the retrospective and prospective presence of LBP. This study makes a number of novel contributions to the literature.
This study is the first of its kind to integrate IMUs to measure impacts and spinal movement during cricket fast bowling. The literature is dominated by the use of optoelectronic measurement systems and force plates which are high cost and require a dedicated environment for data capture.24–27 Portable miniature sensors like those used in this study may offer a viable alternative. Indeed the application of sensors for cricket bowling analysis is beginning to find its place in the literature,28–32 however this is the first time they have been used to explore LBP, spinal kinematics and limb impacts.
The prevalence of LBP in fast bowlers has been reported at 40%–64%6 8 33–35 which is similar to the 57% and 38% for the seniors and juniors of the current study. Incidence rates were lower at just 29% and 5% for senior and junior bowlers, respectively. This is in line with the 30% incidence of lower back injury in senior bowlers previously reported, however the present study is the first to report the incidence of LBP.13 All bowlers who developed LBP had a previous history of pain, suggesting this could be a good prognostic indicator. This is in agreement with earlier literature identifying previous back pain as a predictor of future back pain.36 37
Previous systematic reviews on bowling-related risk factors have either amalgamated the concepts of injury and pain making the extraction difficult,38 39 focused on a specific radiographically identifiable injury3 or focused on non-bowling related risk factors.22 In those studies investigating pain, the focus was either on muscle morphology35 40 or progression of radiographical findings;41 therefore the findings of the current study provide a novel addition.
Overall the results, while not statistically significant, did yield some large effect sizes. Junior bowlers without a history of LBP demonstrated around four times greater thoracic rotation at BFI, right rotation for the right handed bowler. Similarly senior bowlers without a history of LBP demonstrated 11o or 27% less range of thoracolumbar extension at BFI. These kinematics away from the direction of delivery are likely to serve as a ‘wind up’ mechanism for the generation of bowling pace, similar to the cocking phase in throwing. Using spinal rotation to generate wind-up is seen in other sports such as tennis and golf. However this is the first time separate thoracic and lumbar spinal regions have been investigated providing novel insights into the interplay or so-called ‘relative motion’ between spinal regions. The concept of relative motion between two neighbouring anatomical regions has been reported previously.42–44 In golfers, altered relative motion between the hips and lumbar spine was identified in those with LBP, suggesting greater relative contribution from the lumbar spine (and reduced contribution from the hips).44 45 This finding was mirrored in tennis where ROM, normalised to maximal range, during forehand strokes resulted in a range of rotation values beyond the maximum, in those with LBP during ‘wind up’.43 These suggest the potential for excessive relative contribution of motion from the lumbar spine resulting in high levels of tissue stress due to the utilisation of most or all of the available ROM. The findings of this study illustrate that in juniors the ratio of lumbar rotation to thoracic rotation at BFI was 1:1.3, whereas the equivalent was 1:3.1 for those without a history of LBP.
Prospective analysis was unfortunately limited to seniors due to an absence of the development of LBP in the junior sample. Seniors who developed LBP in the follow-up season had greater sagittal spinal movement during the delivery stride and greater lumbar extension at BFI. Previous studies have identified that SCR was associated with risk of lumbar injury,15 however the study did not include pain data. The relationship between radiographically diagnosed lumbar injury and pain is questionable, hence this study focused on pain and demonstrated no such relationship. In seniors, the posterior shifting of the shoulders compared with the hips has the potential for generating bowling pace by providing greater range to develop trunk and arm velocity. However, this is likely to place additional stress on the spine due to using more of the available range and positioning the spine closer to end-of-range extension. This is one mechanism for potential high levels of tissue stress.46 47 Similar findings have been identified in other sporting populations with LBP.48 It has been shown that positioning of the lumbar spine closer to the end of range was associated with pain in gymnastics, cycling, golf and rowing,49–52 and altering the position of the lumbar spine to be further from the end of range was associated with pain relief.52 53
In addition to these kinematic differences, high effect sizes were discovered demonstrating greater tibial acceleration along the z-axis at BFI in individuals with no history of LBP as well as greater time to peak resultant tibial acceleration in the no history of LBP group at FFI. A previous review of ground reaction force (GRF) studies demonstrated no link between GRF and lumbar injury or pain,5 therefore these findings are novel. The z-axis is most closely aligned to the mediolateral axis of the limb and suggests either a greater side-on posture or greater acceleration in line with the wicket with an externally rotated limb. The latter would be possible with a front-on bowler who alters the back leg orientation and uses the adduction/abduction plane to beginning to arrest or ‘check’ the forward momentum. Side on bowling postures are thought to offer less risk of back pain and therefore this may explain this finding in the group without a history of LBP.
Strengths and limitations
This is the first study to employ a number of IMUs to monitor spinal kinematics and impact during on the field cricket fast bowling. Such devices could offer a non-invasive and non-intrusive solution to monitoring of bowling over time, enabling coaches, clinicians and players to benefit from bowling-related biomechanics data. Additionally this study is the first of its kind to focus specifically on pain rather than low back injury, therefore offering new insights into the relationship between biomechanics and pain.
The current study was limited in its period of follow-up to just one season. It is not clear if additional incidence would have been determined over more than one season. Additionally the sample in this study investigated young adult fast bowlers, therefore it is not clear if similar results would be obtained from older senior bowlers.