Neuromuscular Factors Related to Hamstring Muscle Function, Performance and Injury

Hamstring function is influenced by a number of neural, architectural and morphological factors, and the adaptability of these characteristics has important implications for optimizing performance and reducing injury risk. High rates of maximal or near-maximal hamstring force development are required to generate peak horizontal velocities during running, and this is largely determined by the extent to which these muscles can be voluntarily activated. Greater eccentric hamstring strength also correlates with better acceleration capacity and likely improves the ability to decelerate the lower limb during the presumably injurious terminal swing phase of high-speed running. The intra- and intermuscular coordination of the hamstrings appears to influence both hamstring muscle fatiguability and the risk of muscle strain injury. Muscle volume and architectural features such as fascicle length and pennation angle also influence hamstring function, and these vary considerably between hamstring muscles, between individuals and with training status. The adaptability of these features has been explored to a significant extent in recent times, and careful exercise selection allows selective targeting of individual hamstring muscles or muscle segments and this appears to influence the pattern of chronic adaptations such as muscle hypertrophy. Short fascicles within the often-injured long head of biceps femoris may predispose athletes to strain injury but these appear to respond in a contraction-mode-specific manner; lengthening after eccentric training and shortening after concentric training of 4 or more weeks. Conventional training with eccentric and concentric phases in each repetition can also lengthen fascicles, possibly in an excursion (muscle length)-dependent manner. A large biceps femoris muscle to proximal aponeurosis width ratio has been proposed as a potential risk factor for hamstring strain injury, although this is only supported by biomechanical modelling at the time of writing. High levels of anterior pelvic tilt and lateral trunk flexion during sprint running may also predispose athletes to hamstring strain injury, although the quantity of evidence for this is small at the moment. At present, the optimal methods for altering coordination and running technique are not known