Yasuhiro Kunita, Naoki Ikeda, Takuya Nishioka, Shota Yamaguchi, Ayumi Yoshikawa, Daiki Hajima, Naoko Yabuno, Yuta Hashimoto, Kengo Harato, Takayuki Inami
The ATR group showed lower Achilles tendon SWV near neutral and consistently lower MG and SOL SWV across ankle angles. These findings suggest altered ankle-angle-dependent mechanical behavior of the Achilles tendon and MG-SOL components of the muscle-tendon unit in runners with Achilles tendinopathy.
PURPOSE: This study aimed to determine whether runners with mid-portion Achilles tendinopathy (Achilles tendinopathy runners [ATR]) show altered ankle-angle-dependent mechanical behavior of the Achilles tendon and triceps surae muscle-tendon unit during passive dorsiflexion.
METHODS: Twelve ATR and 11 control runners (CON) participated in this study (ATR: age 43.9 ± 12.0 years, running distance 38.3 ± 22.3 km/week; CON: age 41.2 ± 13.7 years, running distance 48.2 ± 29.7 km/week). The participants underwent device-controlled passive ankle dorsiflexion (DF) from 30° of plantar flexion (PF) to 80% of maximal DF at 1°/s in the prone position with the knee extended. Shear wave velocity (SWV) (m/s) was measured in the medial gastrocnemius (MG), lateral gastrocnemius (LG), soleus (SOL), and Achilles tendon (AT). The primary analysis used repeated-measures analysis of variance with angle (30/25/20/15/10/5/0° PF) and region (MG/LG/SOL/AT) as within-subject factors and group as the between-subject factor. A secondary triceps surae-only model (MG/LG/SOL) included 5/10/15° DF because the AT could not be measured beyond neutral.
RESULTS: In the primary model, the region × angle × group interaction was significant, and AT SWV was lower in ATR than in CON at 10° PF (ATR: 6.97 ± 0.49 vs. CON: 8.70 ± 0.51 m/s), 5° PF (ATR: 7.97 ± 0.43 vs. CON: 9.31 ± 0.45 m/s), and 0° PF (ATR: 9.15 ± 0.57 vs. CON: 11.30 ± 0.60 m/s) (all p < 0.05). The MG and SOL SWV were lower in ATR at all PF angles, whereas the LG showed no differences. In the secondary model, the MG and SOL remained lower in ATR across 5-15° DF.
CONCLUSION: The ATR group showed lower Achilles tendon SWV near neutral and consistently lower MG and SOL SWV across ankle angles. These findings suggest altered ankle-angle-dependent mechanical behavior of the Achilles tendon and MG-SOL components of the muscle-tendon unit in runners with Achilles tendinopathy.