Effect of short foot exercise on plantar pressure during single leg standing in people with flatfoot: A randomized controlled trial

To investigate the effect of SFE and TC on plantar pressure in people with flatfoot during single-leg standing (SLS).

This randomized controlled trial recruited thirty-four participants with flatfoot, defined by a Foot Posture Index-6 more than seven. Participants were randomly assigned to the SFE or TC group and exercised for eight weeks. SLS assessments were conducted pre and post-intervention using a plantar pressure sensor (SR Soft Vision; Sumitomo Riko Co., Japan). The blind assessor divided the footprint of the sensor into eight regions according to a previous study (J.K. Gurney et al., 2008): heel; midfoot; medial, central, and lateral metatarsophalangeal joints (MTPJ); hallux; second toe, and 3rd, 4th, and 5th toes. The boundaries were defined as 70% ( heel and midfoot) and 45% ( midfoot and MTPJ) of the foot length. The MTPJ regions were defined as 30% (medial), 25% (central), and 45% (lateral) of the mediolateral axis. The peak plantar pressure and contact area of each region were calculated. Intention-to-treat (ITT) and per-protocol (PP) analyses were conducted using an 80% cut-off value for the implementation rate. Mixed model analysis of variance and Bonferroni correction were used for statistical analysis.

Thirty-four participants were equally assigned to the SFE and TC groups. In ITT analysis, the SFE group showed significantly increased peak plantar pressure in medial MTPJ (p = 0.016, 95% confidence interval(CI): -119.71－-544.28, effect size (d): -0.80), hallux (p 0.001, 95% CI: -522.09－-1072.92, d: -1.48) and second toe (p = 0.004, 95% CI: -131.57－-405.55, d: -1.0), and decrease in the midfoot (p = 0.0012, 95% CI: 591.16－146.83, d: 0.9) between pre and post-intervention. The TC group showed a significant increase in the heel (p 0.001, 95% CI: -145.51－-379.59, d: -1.15) between pre and post-intervention. The PP analysis showed similar results to the ITT analysis, but the PP analysis showed a significant increase in peak plantar pressure in lateral MTPJ (p = 0.032, 95% CI: -105.71－-523.08, d: -1.08) and the contact areas of the 3rd, 4th, and 5th toes (p = 0.008, 95% CI: -1.38－-4.29, d: -1.39) in the SFE group between pre and post-intervention in addition to the results of ITT analysis.

SFE can increase the medial MTPJ, hallux, and second toe, and decrease plantar pressure in the midfoot. In addition, if the participants performed SFE at an implementation rate > 80%, SFE could increase the plantar pressure of the lateral MTPJ and the contact area of the 3rd, 4th, and 5th toes. These findings suggest that SFE affects dynamic foot biomechanics in individuals with flatfoot.

SFE can be an appropriate intervention for flatfoot biomechanics.