The relationship between knee-ankle muscle strength and performance tests in young female adults with flexible pes planus

Background A decrease in muscular activation of the knee and ankle is one of the primary reasons for pes planus. The muscle strength of the knee and ankle in patients with pes planus may affect the performance tests which consists of daily life activities. The aim of the study was to determine the relationship between knee and ankle muscle strength with performance tests in young female adults with flexible pes planus. In addition, we also aimed to observe whether the severity of pes planus affects the ankle muscle strength and performance test scores. We carried out a cross-sectional single-center study. The muscle strength measurement of knee flexion-extension, ankle dorsal-plantar flexion, and ankle inversion-eversion movements were evaluated with the manual muscle test (MMT) device. The timed up and go test (TUG), 5-repeat sit-and-stand test (5STS), and 10-m walk test (10MWT) were used to evaluate knee and ankle performance. Results A significant difference was found only for the five-repetitive sit-and-stand test among the classified groups considering the pes planus grade ( p < 0.05). There was no significant difference between groups for other parameters ( p > 0.05). In correlation analysis, there was only a relationship between the timed up and go test (TUG) with left foot dorsal flexor muscle strength and between 10-m walk test (10MWT) with right foot invertor muscle strength ( r 1 = − 0.288, r 2 = − 0.288, p < 0.05). Conclusions The results of this study reveal that the duration of 5STS was significantly lower in the second degree pes planus group. TUG test score showed low negative correlation with left foot dorsal flexor muscle strength. In addition, the scores of 10MWT exhibited poor negative correlation with right foot invertor muscle strength. Regarding other parameters, no significant correlations were found.