Often we tend to think of the hamstrings as one muscle and train them as such. However, this is a mistake because there can be a big difference in flexibility and strength amongst the three. For example, BioKinetic Athlete @iron_fit_rd has a strength deficit in her medial hamstrings – semitendinosis and semimembranosus, compared to the lateral hamstring – the bicep femoris. On the left, her feet are pointed inward, stretching and challenging the bicep femoris. On the right, her feet are pointed outward, challenging the medial hamstrings. You can see her lumbar round in this one. The reason for the rounding is that her medial hamstrings can not handle the load in this position and therefore can not stabilize her pelvis. If the pelvis did tilt to the normal angle, a hamstring injury would most likely occur because of the weakness. Therefore the nervous system does not allow it to go there. Since the pelvis is not fully tilted, the spine has to compensate by rounding.
To fix it, we need to reteach the medial hamstrings to load in full hip flexion.
