Objectives: To determine the differences in the morphology of foot soft tissues between runners using different types of running shoes.
Design: Cross-sectional study.
Methods: Thirty-eight recreational runners were divided into four groups based on running shoe type, namely, neutral shoes, motion control shoes, minimalistic shoes and neutral shoes with custom-made insoles. An arch height index and a relative arch deformation index were calculated for each participant. An ultrasound device was used to measure the cross-sectional area and/or the thickness of selected intrinsic foot muscles (abductor hallucis, flexor hallucis brevis and flexor digitorum brevis) and extrinsic foot muscles (flexor digitorum longus, tibialis anterior and the peroneus muscles), and the thickness of the plantar fascia, Achilles tendon and heel pad.
Results: Recreational runners using minimalistic shoes demonstrated stiffer foot arches than those using neutral shoes. Among the selected foot muscles, only abductor hallucis showed a significant morphological difference between shoe groups. Runners using minimalistic shoes had the thickest abductor hallucis. The minimalistic shoe runners also showed a thinner proximal plantar fascia and a thicker Achilles tendon than other runners. Insole runners had a thinner heel pad than neutral shoe runners.
Conclusions: This study suggests that the morphology of foot soft tissues is associated with running shoe type in recreational runners. A sudden change in running shoe type without adjusting training volume should be undertaken with caution, since it may take time for foot soft tissues to adapt to a new shoe condition.
Keywords: Achilles tendon; Heel pad; Intrinsic foot muscle; Plantar fascia; Ultrasound.
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