Consider the squat. Too upright (excessive dorsiflexion, vertical shins) and the quads dominate, but the posterior chain is underutilized. Too horizontal (excessive hip flexion, forward lean) and the lumbar spine becomes a lever arm for shear forces. The optimum kinematic crack for a squat is the torso angle and shin angle that keep the barbell over midfoot while maximizing glute and hamstring contribution.
Elite sprinters achieve hip extension of 10–15 degrees less than sub-elite athletes at toe-off. This seems counterintuitive—shouldn't more extension mean more propulsion? optimum kinematics crack