Extrinsic and intrinsic factors associated with non-contact injury in adult pace bowlers: a systematic review protocol

Review question: which extrinsic and intrinsic factors are associated with non-contact injury in adult cricket pace bowlers?Review objective: the objective of this review is to determine the extrinsic and intrinsic factors associated with non-contact injury in adult pace bowlers.Cricket is generally considered to be a sport of low injury risk compared to other sports. In cricket, the pace bowler strives towards the adoption of a bowling technique with a relatively low injury threat that will, at the same time, allow for a fast (120km/hr) and accurate delivery to the opposing batsman. However, of all the various roles of the cricket player, the pace bowler has the highest risk of injury, especially for low back and lower limb (lower quarter) injury. The reason for this high risk of injury is due to the inherent, high-load biomechanical nature of the pace bowling action. The high prevalence of injury amongst pace bowlers highlights the great need for research into factors associated with injury.Both extrinsic and intrinsic factors work in combination to predispose the bowler to injury. Extrinsic or environment-related factors include bowling workload (the numbers of overs a bowler bowls), player position (first, second or third change) and time of play (morning or afternoon). A high bowling workload has been linked with a higher risk of injury in pace bowlers. Foster et al. found in an observational study that bowling too many overs in a single spell or bowling too many spells may increase the pace bowler's risk of sustaining a low back injury. In another observational study, Dennis et al. found that an exceptionally high bowling workload as well as an uncommonly low bowling workload is associated with injury risk. The major extrinsic factors for bowling injury identified by Orchard et al. are a high number of match overs bowled in the previous week, number of days of play and bowling second (batting first) in a match. Extrinsic factors are known to make the bowler more susceptible to injury, especially in the presence of intrinsic factors.Intrinsic, or person-related, factors include muscle strength, flexibility, balance and biomechanics. Intrinsic, strength-related factors, such as shoulder depression, horizontal flexion strength for the preferred limb and quadriceps power in the non-preferred limb are also significantly related to back injuries in fast bowlers. Both upper limb and lower limb-related intrinsic factors are known to be associated with injury. A prospective study by Dennis et al. aimed to identify the risk factors for injury in adolescent cricket fast bowlers. Their findings concluded that bowlers with a hip internal rotation range of motion of ≤30° on the leg ipsilateral to the bowling arm were at a significantly reduced risk of injury compared with bowlers with40° of rotation. Moreover, bowlers with ankle dorsiflexion lunge of 12.1-14.0 cm on the leg contralateral to the bowling arm were at a significantly increased risk of injury compared to bowlers with a lunge of14 cm. Reduced hamstring flexibility was also associated with lumbar disc abnormalities. Bowling-related biomechanical risk factors for injury have been established such as trunk rotation of the shoulders by to a more side-on position during the delivery stride. Portus et al. also reported that shoulder counter-rotation was significantly higher in bowlers who reported lumbar spine stress fractures, while the non-trunk injured group displayed a more flexed knee at front foot contact and ball release. In addition to the above kinematic risk factors, there are high ground reaction forces associated with the power phase - between the front foot placement and ball release components of the pace bowling action. A combination of kinematic bowling related issues as described above and high ground reaction forces may predispose the bowler to injury.Morton et al. conducted a systematic review on pace bowlers between the ages of 13.7 and 22.5 years on risk factors and successful interventions for cricket-related low back pain. Young cricketers between the ages of 13 and 18 years are different to adults in terms of their physiology which impacts on their predisposition to injury and phases of healing. Young cricketers may differ from an adult population in that young pace bowlers who sustain injuries during their bowling career may have given up on the sport by the time they approach adulthood, and the composition of the adult pace bowler population group is therefore affected by natural selection which may cause this group to differ from the original population. Caution is thus advised when generalizing findings from this young population group to adult pace bowlers which emphasizes the need for studies amongst adult pace bowlers. Furthermore, the review by Morton et al. included articles that specifically investigated factors associated with low back pain. However, due to the interconnectedness between the spine and the lower limbs, kinematic variables affecting the spine will also affect the load placed on the lower limbs with subsequent risk of injury. The interdependent mechanical interactions in a linked segment system such as the system of motion of the low back can be caused by movement coordination patterns in other body segments. The systematic review by Morton et al. only included intrinsic factors while the proposed review will also look at extrinsic factors. Therefore, the primary objective of this review is to determine extrinsic and intrinsic factors associated with non-contact injury in adult pace bowlers.