This is James Smith
The question regarding the degree to which the hamstrings are recruited in the squat is most simply answered relative to the magnitude of rotation occurring at the axis of the hip and knee.
- As the knee flexes the hamstring shortens
- As the hip flexes the hamstring lengthens
- Squatting with less hip flexion + more knee flexion equates to less hamstring lengthening
- Squatting with greater hip flexion + less knee flexion equates to more hamstring lengthening
It is for these reasons why even a quarter squat, with sufficient hip flexion + forward trunk rotation, will yield substantial hamstring recruitment and why a rock bottom, high bar/minimal forward trunk rotation, Olympic squat will yield less (the magnitude of knee flexion off-sets the magnitude of hip flexion)