Hamstring function – How it assists in knee extension

While on the subject of knee extension….

The hamstring can flex the knee against gravity when prone or standing with the foot in non-weightbearing….but during most function, the action of the HAMSTRING is so much more complex.

During swing phase, the hip is flexing and the knee is extending. Both of these motions lengthen the hamstrings so that it is switched on before heel strike. At heel strike, the forward motion of the trunk tries to flex the hip. This is decelerated by the hamstring. At the same time, the tibia is moving forward with knee flexion, which the hamstrings can slow down when the foot is on the ground.

As the heel bone everts, the lower leg internally rotates and because of its greats attachment onto the lower leg and the pelvis, the hamstrings can decelerate both internal rotation of the tibia and the hip. In the frontal plane, the hamstrings also decelerate abduction of the knee after the heel has everted.

The lengthening and eccentric loading of the hamstring at multiple joints in many planes make it very eccentric with the front leg in gait. But once the ‘unload’ has started, the hamstrings become very concentric in all planes.

All of this eccentric control (loading) allows it then to do the opposite (explode) once it has been stretched and proprioceptively ‘turned on’.

So in function and gait…. the HAMSTRING is used so much more than to flex your knee as the books suggest.