Second Metatarsal Bone Stress During Running Is Independently Influenced by Running Speed and Load Carriage

Bone stress injuries occur in populations who engage in repetitive loading, such as distance runners and military recruits. The second metatarsal is a common bone stress injury site. Running speed and load carriage are modifiable factors which may influence metatarsal loading. The aim of this study was to determine how running at preferred, 90% of preferred, and 110% of preferred speed, with and without a weight vest carrying 10% body mass, influences second metatarsal bone stress. Data were collected from 28 runners (14 female, 14 male) during barefoot running using motion capture cameras, a pressure plate, and a force plate. Bone stress was calculated at the dorsal and plantar surfaces of the midshaft of the second metatarsal using a two-dimensional beam theory model. No interaction effect was found between running speed and load carriage. Running at 90% of preferred speed decreased peak dorsal and plantar stress by 2.1% and 2.3%, respectively, compared to preferred speed, while running at 110% of preferred speed increased peak dorsal and plantar stress by 4.2%. Running with 110% of body mass increased peak dorsal and plantar metatarsal stress by 3.1% and 2.9%, respectively, compared to running with no additional mass. The mean coefficient of variation across all conditions was 25%, indicating variation in peak stress between participants. Running at faster speeds and with additional loads may increase the risk of second metatarsal bone stress injury. The high variation in peak bone stress between participants demonstrates the importance of considering the individual when assessing injury risk.