Author(s): KOYAMA, K., YAMAUCHI, J., Institution: TOIN UNIVERSITY OF YOKOHAMA, Country: JAPAN, Abstract-ID: 1764

INTRODUCTION:
The human foot arch could have a function to utilize elastic energy from a muscle and tendon complex during bipedal locomotion. During running and jumping, foot arches store and release elastic energy when they compress and reform. This stretch-shortening process increases mechanical energy and improve physical performance. Also, the force generating capacity of the foot increases when the foot arch height decreases due to loading. We suggest that the force amplification mechanism is mechanically regulated by the dynamic function of the foot arch in conjunction with the stretching of a muscle and tendon complex of the foot. These functions of the foot could play an important role in enhancing the initiation of jump performance. Indeed, we showed that toe flexor strength was required for the force reacting on the ground during the jump performance while the foot arch function might help to potentiate energy in a countermovement jump (Yamauchi and Koyama, 2020). However, there have been no studies addressing how the dynamic function of the foot arch affects the muscles that generate force during the ground contact phase in the jump performance. The aim of this study was to use kinetic and kinematic motion analysis to examine how changes in the foot arch with increased vertical force affect the jump performance in drop jumping.
METHODS:
Twenty-six subjects performed drop jumping from a box of 45-cm hight under the barefoot condition. Vertical ground reaction force (GRF) was measured on a force plate on a right foot during the contact phase of a drop jump, and GRF valuables were calculated. Three-dimensional position data of retroreflective markers and vertical ground reaction force data were synchronously collected with an eight-camera three-dimensional optical motion capture system and a force plate, respectively. The medial longitudinal arch was represented as three retroreflective markers, which were placed on the skin: the navicular tuberosity, the medial border of the first metatarsal head and the medial tubercle of the calcaneus. The foot arch dynamics was analyzed from these kinematic data, and was quantified as the amount of changes in foot arch height and angle at the landing phase and the take-off phase.
RESULTS:
The jump height of the drop jumping was 27.6 ± 5.2 cm. The foot arch height and angle on the landing phase were 1.82 ± 0.28 cm and 18.2 ± 4.4 degrees, and those on the take-off phase were 1.78 ± 0.38 cm and 19.4 ± 4.2 degrees. There was no significant relationship between drop jump heights and foot arch variables on the landing phase; however, a significant relationship between drop jump heights and foot arch variables on the take-off phase.
CONCLUSION:
The results of this study suggests that the mechanical contribution of the foot arch dynamics could help to enhancing human jump performance. The foot arch has an ability to integrate and generate force in the take-off phase of human countermovement jumping.