Comparative effects of selective posterior tibialis strengthening and Achilles tendon stretching on static balance and walking speed in university students with flexible flatfoot: a randomized controlled trial

Background and Study Aim. Flexible flatfoot is a common condition associated with altered foot biomechanics, impaired balance, and reduced functional performance. Strengthening and stretching exercises are commonly prescribed to address these impairments, as different interventions may produce distinct patterns of neuromuscular adaptation and recovery over time. Although these approaches are widely applied, their relative effectiveness in improving balance and walking speed over time remains of practical interest. This study aimed to compare the time course, rate, and magnitude of changes in balance and walking speed following posterior tibialis strengthening and Achilles tendon stretching in individuals with flexible flatfoot. Materials and Methods. A single-blinded, parallel-group, repeated-measures randomized controlled trial was conducted on 64 university students aged 18–26 years with flexible flatfoot (navicular drop > 10 mm). Participants were randomly allocated to a Posterior Tibialis Strengthening Group or an Achilles Tendon Stretching Group. Interventions were performed five days per week for four weeks. Balance (Berg Balance Scale) and walking speed were assessed at baseline, at the 2nd week, and at the 4th week by a blinded assessor. Data were analyzed using repeated-measures ANOVA to evaluate time, group, and time × group interaction effects (p < 0.05). Results. Both interventions demonstrated significant improvements in balance and walking speed over time. At the 2nd week, the posterior tibialis strengthening group showed higher Berg Balance Scale scores (45.56 ± 1.24 vs. 44.56 ± 1.24) and walking speed (1.2875 ± 0.0227 m/s vs. 1.2381 ± 0.0166 m/s) compared to the Achilles tendon stretching group (p < 0.001). At the 4th week, further improvements were observed. The strengthening group demonstrated higher balance scores (48.56 ± 1.24 vs. 45.56 ± 1.24) and walking speed (1.3559 ± 0.0247 m/s vs. 1.2694 ± 0.0166 m/s) (p < 0.001). Significant time × group interaction effects were found for balance (F = 67.435, p < 0.001) and walking speed (F = 278.459, p < 0.001). Conclusions. Posterior tibialis strengthening and Achilles tendon stretching both improve functional performance in individuals with flexible flatfoot. However, strengthening produces a faster and clinically greater trajectory of improvement over time. This highlights the importance of examining time-dependent functional adaptation in addition to overall effectiveness.