Sprinting doesn’t just “strengthen” the hamstrings, the research shows that it actually changes how the hamstrings are built. Studies looking at muscle tendon behavior show that as speed increases, the hamstrings perform more negative work in late swing, not during stance. That high velocity deceleration is what drives the architectural changes we see in sprinters…longer fascicles, lower pennation angle, and a muscle tendon unit that’s better at handling fast lengthening without failing. Longer

Muscle Length Assessment Hamstring: Passive & Active