Moving away from traditional foci may help us understand sporting performance and injuries

The three biomechanics papers in this issue Gabbe et al., Dichiera et al., and Hrysomallis et al. may seem to be quite disparate, but on closer inspection they have something in common. Foremost, the authors have presented research that is directing our attention away from traditional foci. The papers also show why we need to investigate the neuromuscular biomechanics of sporting injuries and performance, for which there has been some research already performed, but moreover it points us to where future research needs to be carried out.

Studies that have examined factors related to hamstring injuries have traditionally focused on isokinetic strength studies of the knee joint, in particular hamstring-quadriceps ratios. Even though there have been many studies on this issue, controversy still exists over the ability of these ratios to predict injury. Some studies suggest there is a relationship,1, 2 but others none.3, 4 In fact Bennell et al.3 evaluated a range of hamstring-quadriceps ratios in a large group of players but found no relationships to risk of hamstring injury. Now it could be that different player groups may have different factors that predict injury, as suggested by the results of Gabbe (this issue). However, Gabbe's et al. (this issue) results also suggest that we need to look at other joints in kinematic chain.

Most clinicians and researchers would agree that hamstring injury is caused by eccentric contractions of the hamstrings to slow the lower leg at the end of the swing phase in running.3, 5 Biomechanical studies of running have shown that leg swing speed is determined by how much power the hip flexors can generate during the first half of swing.6 In addition, the hip flexors and extensors also control sagittal plane posture of the pelvis and trunk, while walking7 and probably running. Pelvic posture directly affects hamstring length. The hamstrings’ moment arms at the hip are approximately twice the size of those at the knee for the postures at the end of swing phase running, determined using the kinematics of running6 in the SIMM (© Musculographics, IL, USA) musculoskeletal modelling package. Therefore, this means changes that increase hip flexion angle will affect hamstring length more than changes in knee extension angle, placing the hamstrings at risk of injury. The importance of the paper by Gabbe et al. (this issue) is that this confirms this muscular-skeletal and biomechanical logic, suggesting that hip flexor tightness, which causes hamstring lengthening, may contribute to the risk of hamstring injury, at least in older AFL players. Gabbe's et al. (this issue) results also suggest that we need to investigate the hip and knee motion of players while running. The relative lengths of the hamstrings5 and hip flexors are important, but we also need to investigate how these muscles are used in running. It is likely to be the combination of muscle architecture and how the muscles are used in the task that dictates performance and injury in sport.

The paper by Dichiera et al. (this issue) has also clearly shown that we need to examine the role of other joints in the kinematic chain to understand the reasons for kicking accuracy. These authors showed that hip flexion and anterior pelvic tilt of the kicking leg are related to kicking accuracy. Even though it is sill not entirely clear what the link may be, the stance leg's knee flexion appears to be important for kicking accuracy. Compared to an extended knee, a change in the angle of a flexed knee will result in greater change in height of the hips. Therefore, it could be that greater knee flexion could be related to a better ability of the person to correct for height of the swing leg above the ground.

Static standing postural measurement has allowed researchers to establish the basic mechanisms that maintain balance. However, Hrysomallis et al. (this issue) have alerted us to the fact that even though some tasks in sport require maintenance of static balance, more often dynamic balance needs to be maintained. The paper by Hrysomallis et al. (this issue) has also cleverly shown in essentially very similar tasks that the control of balance in dynamic conditions are only weakly related to those in static cases. This should be expected as quiet standing balance seems to be an ankle-based strategy.7, 8, 9 However, dynamic tasks are quite different in that hip-based strategies are the focus for standing when the surface is unstable and, importantly, to maintain balance while walking.7, 9 Winter and colleagues have clearly shown that walking balance relies on the ability to maintain control of upper-body posture,7 which is probably the case in many sporting tasks.

In many sporting situations, control of balance and posture of the upper-body are important aspects of sports performance and injury. Control of the pelvic posture is the basis upon which control of upper-body posture is established. We have already seen the important role of the hip flexors, and also the extensors, in maintaining posture of the pelvis and Gabbe and colleagues (this issue) showed how this is related to hamstrings injury in older players. Our work on ACL injuries has suggested that control of upper-body posture is probably related to the size of the ground reaction forces10 and the loads experienced by the knee.11 Therefore, research into the control of movement and posture of the upper-body may allow us to examine ways to prevent injuries in sport.

These three papers have reminded us to look beyond traditional foci and examine other joints in the kinematic chain of movement. If performance is to be improved and injuries prevented in sport, future research will need to focus on joints removed from the obvious joint of inquiry. It will also be important to examine muscle architectures and the joint biomechanics during the relevant sporting tasks.