The COVID-19 pandemic has an impact on people’s ability to exercise and walk. Decreased exercise habit leads to decreased muscle mass, which may hamper social activities. The decline in exercise habit is a particular challenge among older people, as it may lead to frailty. In this paper, we report that creating arches at the cuboid boneand adductor muscles activates toe movement. We examined whether the arches could be built into shoe insole to correct left–right differences in leg skeletal muscle mass. A prototype insole with arches created at the cuboid boneand transverse head of adductor hallucis musclewas designed, and a prospective cohort study was conducted to examine its effects. Plantar pressure during walking was recorded in 10 subjects, and a 3-month intervention study was conducted in 40 subjects. The results showed an increase in toe pressure from before to after wearing the prototype insoles. In addition, leg skeletal muscle mass increased in the group wearing the prototype insole, and a significant difference compared to the control group was detected by Wilcoxon signed-rank test. The results from this study demonstrate that the prototype insole promotes toe movement and increases leg skeletal muscle mass.