There is a significant risk of injury when undertaking physical activities. Abnormal biomechanics of the lower limb has been implicated as a causative factor for injury. Although there have been a large number of studies in this field, many lack consistency of definitions and methodology. A large number of these studies have been retrospective, and it is often impossible to identify the baseline population. The evidence suggests that limitation of range of ankle dorsiflexion, limitation of range of hip eversion, excessive joint laxity, leg length discrepancy, an excessively supinated or pronated foot, excessively high or low arches of the foot and a large Q-angle are risk factors for injury. On the other hand, there is little convincing evidence that an abnormal range of ankle plantar flexion, genu varum or valgum or undue muscle tightness may be potential risk factors. All of these biomechanical abnormalities need further evaluation as potential risk factors for injury. Any trials undertaken must endeavour to define and describe their methods fully, and ensure that their results are reproducible.