The adaptation of the foot to heavy loads: plantar foot pressures study

INTRODUCTION:: The foot serves as the main shock absorber during various activities as walking running and jumping. There are static and dynamic mechanisms which play a role in the adaptation of the foot to weight bearing walking with weights. The function of the foot while weight bearing was studied mainly under static conditions. We designed an experiment to explore dynamically the adaptation of the foot to weight bearing walking with weights. METHODS:: Ten healthy subjects participated the study. They walked barefoot over an EMED force plate which based on multiple pressure capacitance sensors. Each subject walked three times. The first walk was without any weight, the second walk with weight of 20 kg in backpack and the third walk with weight of 40 kg. Contact area, peak pressures, peak forces and duration of contact time were measured in seven areas of interest of the foot-heel, midfoot, lateral, central and medial forefoot, lateral toes and hallux. RESULTS:: The pressure time integral and force time integral increased in most areas of the foot except for the midfoot in the 20 kg walk. The largest increase was at the central and medial forefoot. Adding additional 20 kg to the load did not increased the loads on the midfoot but increased further the loads mainly at the central and medial forefoot. CONCLUSIONS:: The human foot adapts itself under loading condition by maintaining the medial longitudinal arch. Increasing the loading further activates compensatory mechanisms which maintain the longitudinal arch and shifts the the loads to the central and medial forefoot.