OBJECTIVE:It has been suggested that atrophied or weak toe flexor muscles are associated with the formation of toe deformities, but there is little evidence to support this theory. This study aimed to determine whether the size of the toe flexor muscles differed in older adults with and without toe deformities. METHODS:Forty-four older adults (>60 years) were recruited for the study. Each participant had their feet assessed for the presence of hallux valgus or lesser toe deformities. Intrinsic and extrinsic toe flexor muscles were imaged with an ultrasound system using a standardized protocol. Assessor-blinded measurements of muscle thickness and cross-sectional area were taken using Image J software. RESULTS:Participants with lesser toe deformities (n = 20) were found to have significantly smaller quadratus plantae (P = 0.003), flexor digitorum brevis (P = 0.013), abductor hallucis (P = 0.004), and flexor hallucis brevis (P = 0.005) muscles than the participants without any toe deformities (n = 19). Female participants with hallux valgus (n = 10) were found to have significantly smaller abductor hallucis (P = 0.048) and flexor hallucis brevis (P = 0.013) muscles than the female participants without any toe deformities (n = 10; P < 0.05). CONCLUSION:This is the first study to use ultrasound to investigate the size of the toe flexor muscles in older adults with hallux valgus and lesser toe deformities compared to otherwise healthy older adults. The sizes of the abductor hallucis and flexor hallucis brevis muscles were decreased in participants with hallux valgus, whereas the quadratus plantae, flexor digitorum brevis, abductor hallucis, and flexor hallucis brevis muscles were smaller in the participants with lesser toe deformities.