Background: Flatfoot is an alteration of the normal structure of the foot, characterized by a partial or total reduction of the medial longitudinal plantar arch, valgus deformity of the heel, and abduction of the forefoot. While treatments often include strengthening of the intrinsic foot muscles, evidence of its efficacy in adults with flatfoot remains limited. Objectives: The main objective of this review was to evaluate the effects of strengthening the plantar intrinsic muscles in adults with flatfoot. Methods: Searches were conducted in PubMed, Embase, Cochrane, PEDro, and Web of Science databases up to October 2023. The review protocol was developed and followed according to the PRISMA Extension for Scoping Reviews (PRISMA-ScR) guidelines. Studies included were those published on intrinsic muscle strengthening in adult populations. A qualitative synthesis of all included articles was performed, along with a quantitative sub-analysis of randomized controlled trials and a critical methodological assessment. Results: Eleven studies involving a total of 374 participants were selected. Most studies identified the “short foot exercise” as the optimal exercise for isolating and training the plantar intrinsic foot muscles. The most commonly analyzed variables were the Foot Posture Index and the Navicular Drop Test. Conclusions: Strengthening the plantar intrinsic muscles enhances the height of the medial longitudinal arch, improves hindfoot posture and balance, and increases hallux abductor muscle activity. This strengthening, whether achieved through short foot exercises alone or in combination with other techniques, is effective in treating adult flatfoot. Current literature suggests that a duration of 4–6 weeks may be sufficient to achieve beneficial outcomes.
Moreno-Fresco et al. (Fri,) studied this question.