RESUMO
BACKGROUND: Flat feet change lower extremity alignment, and it may change the load distribution on Achilles tendon during exercise. The purpose of the present study was to investigate the immediate effect of cumulative transverse strain via resistive ankle plantarflexion exercise on the Achilles tendon in individuals with flat feet. METHODS: Fourteen individuals with flat feet and 14 age-matched individuals with normal foot posture were enrolled in the present study. Achilles tendon thickness was measured by an ultrasonography device with a linear probe at 3 points: 1 cm (AT-1), 2 cm (AT-2), and 3 cm (AT-3) proximal to the superior aspect of the calcaneus. Ultrasonography measurements were performed before and after participants completed 90 repetitions of double-leg calf raise exercises which included moving the foot from full ankle dorsiflexion to full ankle plantarflexion. RESULTS: Achilles tendon thickness at all points measured was thinner in the flat feet group at both pre- and post-exercise conditions compared with that of the control group (p<0.05). Achilles tendon thickness at AT-1, AT-2, and AT-3 decreased after the exercise in both groups (p<0.001). The differences in Achilles tendon thickness at all points measured between pre- and post-exercise conditions were lower in individuals with flat feet than those of the control group (p<0.05). CONCLUSION: There was a significant decrease in Achilles tendon thickness after exercise in both groups; however, the tendon thickness markedly diminished in individuals with normal foot posture. The results are thought to result from changes in tendon structure and in load distribution on the Achilles tendon.
RESUMO
The purpose of the present study was to investigate the changes in stiffness, tone, and elasticity of extrinsic foot muscles and Achilles tendon in adults with pes planus at rest and during standing. The study was conducted with 59 participants, 29 with pes planus and 30 with normal foot posture. The oscillation frequency (indicator of tone), dynamic stiffness (indicator of stiffness), and logarithmic decrement (related to elasticity) of the Achilles tendon, peroneus longus, tibialis anterior, and medial and lateral gastrocnemius muscles were measured with a myotonometer (MyotonPRO, Myoton AS, Estonia). The passive mechanical properties of the selected muscles and tendon were measured at rest and during standing. The oscillation frequency, dynamic stiffness, and logarithmic decrement of the peroneus longus, tibialis anterior, and medial and lateral gastrocnemius muscles were similar in individuals with and without pes planus (p < 0.05). Individuals with pes planus had higher dynamic stiffness of the Achilles tendon at rest (p = 0.042; d = 0.431), whereas they had lower dynamic stiffness of the Achilles tendon with a moderate effect size during standing compared to controls (p = 0.028; d = 0.640). The logarithmic decrement of the Achilles tendon in individuals with pes planus was significantly lower with a large effect size during standing (p = 0.025; d = 0.945). The results obtained suggest that pes planus is not related to the passive mechanical properties of the foot extrinsic muscles. A decrease in stiffness and an increase in elasticity during standing, and an increase in stiffness at rest in the Achilles tendon were found in individuals with pes planus.