Foot Placement During Sprinting And Its Effect On Biomechanics Of Sprint Performance In NCAA Division-I Female Track And Field Runners

Sprinting success is achieved by a fast start such that maximal horizontal 1 velocity can be achieved and maintained (Johnson and Buckley, 2000; Mann and Herman, 1985). Sprint velocity can be defined as the product of stride rate and stride length. Consequently, velocity can be increased by increasing stride rate or stride length or both; however, both factors are interdependent and individual morphologic and physiologic characteristics may influence the individual's motor abilities and utilization of the energy system (Coh et. al., 2001). Research indicates that elite and non-elite sprinters display significantly different joint angles during sprinting (Novacheck, 1998). It has been reported that world class sprinters demonstrate increases in stride length and cadence, thigh acceleration, trunk inclination, and trunk/thigh angle and decreases in components such as ground contact time, landing angle, and thigh angle (Kunz and Kaufmann, 1981). For instance, maximum knee flexion angles for elite and non-elite sprinters during the swing phase of sprinting reaches up to 130° and 105°, respectfully (Novacheck, 1998). However, it is the ratio between the contact time and the flight time that is the most crucial factor in the kinematic structure of the sprinting stride. Successful sprinters demonstrated a shorter contact phase and longer flight phase than less successful sprinters (Coh et. al., 2001). Reaction time, technique, electromyographic (EMG) activity, force production, neural factors, and musculoskeletal structures are other biomechanical factors that can influence performance in sprinting (Mero et. al., 1992). Hypothetically, a successful sprinter must have the ability to exert great force against the surface of the ground in a shorter time period than a less successful sprinter, which indicates that the successful sprinter generates greater power or ground reaction forces (Alexander, 1989; Kunz and Kaufmann, 1981; Weyand et. al., 2000). Ground reaction forces are only achievable when the body is instantaneously in contact with the surface of the ground, therefore, a delicate balance of stride length and stride rate contributes to normal human locomotion and sprinting success. Nett (1964) studied foot contact during sprinting and reported that running speed influenced ground contact. He reported that initial ground contact occurred on the lateral aspect of the 5th metatarsophalangeal joint, high on the ball. As the running speed decreased, the contact point shifted to a more posterior position, or toward the heel. This can be seen in the 400-meter run, where ground contact shifts back toward the heel and foot plant is somewhat flatter. In distances greater than 1500 meters, the initial ground contact of the 2 foot occurs on the lateral edge of the longitudinal arch between the heel and the head of 5th metatarsal. Nett further noted that during the load-phase of the ground contact of the foot, the heel strikes the ground, even in the case of sprinters; especially when the sprinters are fatigued (1964). Conversely, Mann (1980) and Novacheck (1998) reported that the heel of sprinters did not or "may never" touch the ground throughout the sprint, and that initial ground contact is dependent on gait speed, consequently, as speed increases initial contact changes from the hind-foot to the forefoot. This issue remains unclear because only five studies have involved examination of foot placement during sprinting and its effect on biomechanics of sprint performance (Nett, 1964; Mann, 1980; Payne, 1983; Novacheck, 1995, Novacheck, 1998). Differences between sprinters and non-sprinters have been observed biomechanically; however, present kinematic research generally does not extend to the influence of foot placement during the ground contact phase of the sprinting gait cycle. Although two main biomechanical factors - stride length and stride rate - have been widely accepted by researchers as key factors in sprint performance, it is also necessary to address the potential importance of foot placement during the ground contact phase. 3 Therefore, the purpose of this research study was to investigate ground foot contact and its effect on the biomechanics of the 200m sprint