The biomechanics of the knee during the parachute landing fall.

Because anterior knee pain syndrome is common in young paratroopers, we studied the role of the extensor mechanism in deceleration during the parachute landing fall (PLF) and the extent of knee flexion resulting from use of proper and variant landing styles. The subjects were novice paratroopers. Data were gathered by electromyography and by cinematography. At impact, a period of myoelectric silence was found that increased during training. Knee flexion angles varied from 130 degrees in the proper PLF to a low of 110 degrees in the toes-knees-nose PLF and to a high of 160 degrees in the hypergenuflexion PLF. The improper PLFs had a duration of deceleration shorter than that of a proper PLF, with maximal knee flexion occurring later in the landing act. Our results give direction to more specific lower-body training.