Foot placement modifies kinematics and kinetics during drop jumping

Purpose: Sprinting, bouncing, and spontaneous landings are associated with a forefoot contact whereas walking, running, and jumping are associated wit h heel-toe foot placement. Because such foot placement strategies influence landing mechanics or the ensuing performance, the purpose of this work was to compare lower extremity kinematics and kinetics and muscle activation p atterns between drop vertical jumps performed with heel-toe (HTL) and foref oot (FFL) landings, Methods: Ten healthy male university students performed two types of drop jump from a 0.4-m high box placed 1.0-m from the center of the force plate. They were instructed to either land first on the ball o f the feet without the heels touching the ground during the subsequent vert ical jump, i.e., forefoot landing jump (En), or to land on the heels follow ed by depression of the metatarsals, i.e., heel-toe landing jump (HTL). Thr ee successfully performed trials per jump type were included in the analysi s. The criteria for selection of the correct jumps was proper foot position at contact as judged from video records and the shape of force-time curve. Results: The first peak and second peak determined from the vertical force -time curves were 3.4 times greater and 1.4 times lower for HTL compared wi th those with FFL (P < 0.05). In the flexion phase of HTL, the hip and knee joints contributed 40% and 45% to the total torque, whereas during Fn the greatest torque contributions were 37% for both the knee and ankle joints. During the extension phase, the greatest torque contributions to the total torque were 41% and 45% by the knee and ankle joints during HTL and 34% and 55% during FFL. During the flexion phase, power production was 20% greater (P < 0.05) in HTL than in Fn, whereas during the extension phase power pro duction was 40% greater in FFL than in HTL. In the flexion phase of HTL the hip and knee joints produced the greatest power, and during the extension phase the knee and ankle joints produced the greatest power. In contrast, d uring both the flexion and extension phases of Fn, the knee and ankle joint s produced the greatest power. The EMG activity of gluteus, vastus laterali s, and plantar flexor muscles was similar between HTL and FFL in most cases except For the greater vastus lateralis EMG activity during precontact pha se in HTL than in FFL and the greater gastrocnemius activity in Fn than in HTL. Conclusion: Foot placement strategy modifies the individual joint cont ributions to the total power during drop jumping.