Abstract
Human steady-state locomotion modes are symmetrical, leading to symmetric mechanical function of human feet in general; however, track distance running in a counterclockwise direction exposes the runner’s feet to asymmetrical stress. This may induce asymmetrical adaptation in the runners’ foot arch functions, but this has not been experimentally tested. Here, we show that the plantar fascia (PF), a primary structure of the foot arch elasticity, is stiffer for the left than the right foot as a characteristic of runners, via a cross-sectional study on 10 track distance runners and 10 untrained individuals. Shear wave velocity (index of tissue stiffness: SWV) and thickness of PF and foot dimensions were compared between sides and groups. Runners showed higher PF SWV in their left (9.4 ± 1.0 m/s) than right (8.9 ± 0.9 m/s) feet, whereas untrained individuals showed no bilateral differences (8.5 ± 1.5 m/s and 8.6 ± 1.7 m/s, respectively). Additionally, runners showed higher left to right (L/R) ratio of PF SWV than untrained men (105.1% and 97.7%, respectively). PF thickness and foot dimensions were not significantly different between sides or groups. These results demonstrate stiffer PF in the left feet of runners, which may reflect adaptation to their running-specific training that involves asymmetrical mechanical loading.
Highlights
Human steady-state locomotion modes are symmetrical, leading to symmetric mechanical function of human feet in general; track distance running in a counterclockwise direction exposes the runner’s feet to asymmetrical stress
Even in a lefty runner (n = 1), plantar fascia (PF) shear wave velocity (SWV) at the proximal site was higher for his left (10.0 m/s) than right foot (9.1 m/s)
The most striking finding of the present study was that track distance runners showed stiffer PF at the proximal site in their left than the right feet, unlike the untrained participants
Summary
Human steady-state locomotion modes are symmetrical, leading to symmetric mechanical function of human feet in general; track distance running in a counterclockwise direction exposes the runner’s feet to asymmetrical stress. This may induce asymmetrical adaptation in the runners’ foot arch functions, but this has not been experimentally tested. Human steady-state locomotion modes are symmetrical, leading to symmetric mechanical function of human feet in general; track distance running is performed always in a counterclockwise direction, i.e., the left leg being inside during curve running In this phase, runners are required to generate greater forces with their left legs[19,20] to exert centripetal force[21]. A profound understanding of PF adaptability is essential for improvements in their performance as well as prevention of plantar fasciitis
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