Gastrocnemius function – How it assists in knee extension

Gastrocnemius function – How it assists in knee extension

This attaches above the knee into the femur and into the achilles tendon. It acts in a similar way to soleus, but as it attaches to the femur, its influence on the proximal joints and structures is more significant.

Gastrocnemius decelerates internal rotation of the femur when the foot is on the ground, but it is lengthened at both ends. One end in the frontal plane, the other end in the transverse plane. In the sagittal plane, it controls ankle dorsiflexion.

The knee flexion is transformed into knee extension by a number of muscles along with mass and momentum. As the front leg in gait is moving through towards swing phase, the tibia is slowed down by eccentric lengthening of the gastrocnemius and a number of other calf muscles. This slowing along with the momentum of the body creates knee extension as it pulls back on the distal femur as ankle dorsiflexion is decelerated.

So in function and gait…. the Gastrocnemius are a powerful knee extensor!

Hamstring function – This is not just a knee flexor!

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.