Comparison of hamstring and opposing forces in late swing and early stance
| Opposing moments | |||
|---|---|---|---|
| Phase | Hamstring action and moments | Internal (quadriceps and hip flexors) | External |
| Late swing | Strong eccentric contraction (whilst at sub-maximal length) to decelerate the shank, producing in particular a high knee flexion moment. | Vastus muscles begin to activate at the end of swing producing a weak (early) contraction.15 Hip flexors are almost inactive.15 | Minimal opposing forces (the light force of air resistance would actually assist hamstring in decelerating the shank). |
| Early stance | Strong concentric contraction to resist opposing forces and help produce a hip extensor moment.1–46 | Vastus muscles increase their activation in early stance, producing a stronger contraction, whilst rectus femoris starts to contract.15 | Potentially large hip flexor & knee extensor joint reaction moments (i.e. GRF vector is anterior to the knee and hip joints, due to forefoot-strike).1–46 |