Hamstring injury happens frequently in running-based sports such as athletics, football and rugby – But over 80% of these occur in the outer hamstring when the leg is swinging through – why is that?
It is often thought that hamstrings are injured from changes in direction, pushing off and explosive movements but in reality, most hamstring injury happens when the leg is swinging through, just before the foot touches down.
Here is a quick few stats and anatomy refresher to ground you:
The hamstrings are made up of three muscles
- The Biceps Femoris, which has two parts to it. The long head which cross’ both the hip and then knee joint and the short head which only crosses one joint
- And Semitendinosus at the inner thigh
There is a huge difference between how much each these muscles get injured. The Biceps Femoris long head (BFlonghead) is involved in a huge 80%hamstringirng injuries.(1)
As well as this, most hamstring injuries are thought to happen in late swing phase of running, just before the foot lands. So how does the BFlonghead taking the brunt of injuries and this mechanism of injury link in? Check out the video below first of all to ee how the hamstring works in walking:
As you can see in the video, the hamstrings fire into action before, during and after the foot lands. At this point when the knee is extended, the muscle is working while at it’s peak length and at maximal force development working hard eccentrically to slow leg swing down.
Note: An eccentric contraction is where the muscle controls lengthening out, which is far harder on the muscle than a concentric contraction where it contracts to push-off.
Recent studies have shown that the Biceps Femoris is more active, along with the other hamstring muscles when the hip is extending, rather than the knee flexing. The semitendinosus, however, is more active in knee flexion where it works to bend the knee. This means that as well as the BFlonghead working harder with eccentrically slowing the leg down, it is also not often strengthened as well as the other hamstrings because of this.
So there you have it, the BFlonghead of the hamstrings works harder eccentrically slowing down the momentum of the leg swinging forward and often gets missed in strengthening sessions – Stuck between a rock and a hard place! This gives athletes and health professionals better guidance as to what rehab exercises to add in post injury and also in injury prevention programmes depending on injury, leading to decreasing the nearly 30% re-injury rate.(1)