Arch height flexibility is associated with plantar fascia tension during running.

Background: Plantar fascia tension is considered to cause plantar fasciitis, and medial longitudinal arch decrease is believed to be a risk factor for plantar fasciitis. Arch height index (AHI) and arch height flexibility (AHF) are useful indicators for evaluating medial longitudinal arch. However, the relationship between plantar fascia tension during running and these indicators remain unclear.

Research Question: Are the foot characteristics in AHI and AHF that represent medial longitudinal arch related to plantar fascia tension during running?

Methods: Twenty-two male participants enrolled in this study. Foot characteristics required for calculating AHI and AHF were measured using the AHI measurement system. AHI was defined as the height from the floor to the dorsum of the foot divided by the truncated foot length with 10% or 50% load. AHF was defined as the change in arch height from the 10% and 50% loads. Marker trajectories of the foot and force plate data during running were measured using a three-dimensional motion analysis system and a force plate. Based on the measured data, the peak values of the plantar fascia tension were analyzed. Pearson's correlation was used to determine the relationship between foot characteristics and plantar fascia tension.

Results: No significant correlation was found between AHI in the 10% load condition and plantar fascia tension (r = -0.36, p = 0.09) or between AHI in the 50% load condition and plantar fascia tension (r = -0.148, p = 0.515). In contrast, a significant moderate positive correlation was observed between AHF and plantar fascia tension (r = 0.568, p < 0.01).

Significance: AHF is a change in arch height between sitting and standing positions, can be easily used to evaluate plantar fascia tension in clinical settings. This study implies that evaluating AHF is a useful tool in considering plantar fascia tension during running.