Complexity of spatio-temporal plantar pressure patterns during everyday behaviours

The human foot sole is the primary interface with the external world during balance and walking, and also provides important tactile information on the state of contact. However, prior studies on plantar pressure have focused mostly on summary metrics such as overall force or centre of pressure under limited conditions. Here, we recorded spatio-temporal plantar pressure patterns with high spatial resolution while participants completed a wide range of daily activities, including balancing, locomotion and jumping tasks. Contact area differed across task categories, but was only moderately correlated with the overall force experienced by the foot sole. The centre of pressure was often located outside the contact area or in locations experiencing relatively low pressure, and therefore a result of disparate contact regions spread widely across the foot. Non-negative matrix factorization revealed low-dimensional spatial complexity that increased during interaction with unstable surfaces. Additionally, pressure patterns at the heel and metatarsals decomposed into separately located and robustly identifiable components, jointly capturing most variance in the signal. These results suggest optimal sensor placements to capture task-relevant spatial information and provide insight into how pressure varies spatially on the foot sole during a wide variety of natural behaviours.

Automated summary

The human foot sole plays a crucial role in balance and walking, and provides important tactile information about contact. This study examined plantar pressure patterns during various daily activities and found that contact area differed across tasks, but was only moderately correlated with overall force. The center of pressure was often located outside the contact area or in regions experiencing low pressure. Non-negative matrix factorization revealed low-dimensional spatial complexity, which increased during interaction with unstable surfaces. These findings offer insights into optimal sensor placements and spatial pressure variations on the foot sole during natural behaviors.