Effects of speed on plantar forces in three-foot regions during treadmill walking: A preliminary study using force sensing insoles

Study aim: The foot has region-specific biomechanical functions for absorbing shock, however, the effects of walking speed on plantar forces in the foot regions are unknown. The purpose of this study was to investigate the measurement repeatability and changes of regional (forefoot, midfoot, and rearfoot) plantar force by a triple-sensor wireless insole by gait speed modifications during treadmill walking. Material and methods: Twenty young adults walked on treadmill at five speeds (self-selected, two slow and two fast conditions). Regional plantar forces were measured using a wireless in-shoe system (loadsol, Novel INc., St. Paul, MN). Intraclass correlation coefficients (ICC1, k) were used to assess repeatability. Repeated measures analyses of variance were used to determine differences in regional forces among speed conditions. Paired sample t-tests compared forces during self-selected speed and slow or fast conditions to determine foot regions influence. Results: Across foot regions and conditions, ICCs ranged from 0.799 to 0.971 for contact time and from 0.918 to 0.981 for peak force. Repeated measures analyses of variance showed that walking speed significantly affected contact time in all plantar regions and peak force in the forefoot and rearfoot (all values p < 0.01), but not in the midfoot (p = 0.85). Contact time in all foot regions increased at slower walking speeds and decreased at faster walking speeds. In forefoot, peak forces decreased at slower walking speeds and increased at very fast speeds. In rearfoot, peak forces increased at faster walking speeds. In midfoot, peak forces did not change at any walking speeds. Conclusions: The ability to measure plantar force data across three foot regions and at different walking speed has potential to broaden the research question investigated and explore clinical applications. The midfoot may be the most functional region to shock absorption from exposure to peak force during walking.