Hamstring Injuries – Incidence and Causes

The most common injury in pitch sports is an injury to the hamstrings. Generally, hamstring injury incidence is between 18% and 20% per season among sprinters – one in five people! Injuries such as strains and avulsions (where the muscle tears from the bone) tend to happen more frequently when rapid eccentric strains are placed upon the hamstrings. Eccentric strain is normal to a degree – this occurs when a muscle is active yet lengthening (which is the opposite of concentric action, when a muscle is active and shortening). Eccentric movement is ‘harder’ on muscles than concentric movement, so at extremes it is the most risky kind of contraction.

Sprinting and kicking are often ’causes’ of hamstring injury.  In running, there is more risk during the late swing phase of the gait cycle – when the leg is reaching forward to strike the ground. In this period, the hamstrings are strongly decelerating the movement of the hip (slowing the flexing of the hip, which slows how far up your leg moves) AND they are also decelerating the straghtening of the knee….all so your leg can hit the ground at the right time.  Tears in the body of the muscle are most common, sometimes the strain is so great that the muscle actually pulls a bit of bone off at it’s insertion point (an avulsion fracture).  You are more likely to reinjure a hamstring your first week back to sport, and some sports such as Australian football have high rates of reinjury (up to 34% of players).

Hamstring injuries are classified as Grade I, II or III, depending upon the extent of the injury. Grade III injuries are total tears and avulsions from the bone and are extremely serious, whereas Grade I and II are less serious. However, someone with a Grade I or II injury may make themselves more prone to serious re-injury because they become pain free early in their rehabilitation and may take on too much too soon in their training.  We don’t know anyone like that, do we?