Effects of Speed, Orthosis, and Load on Calf Muscle Electromyography Signal During Treadmill Walking

Background: Achilles tendon rupture rehabilitation protocols often emphasize two key factors, namely plantar flexion and load restriction during the early recovery stages. However, we hypothesize that variations in walking speed also play a significant role in affecting the load on the Achilles tendon. This study aims to explore the combined impact of plantar flexion angle and walking speed on the surface electromyography (EMG) activity of the calf muscles. Methods: Surface EMG measurements on 24 healthy volunteers assessed the activity of the calf muscles (gastrocnemius lateralis, gastrocnemius medialis, and soleus). Participants walked on a treadmill using two designs of ankle foot orthoses set at three different angles of the ankle joint (mainly 0 degrees, 15 degrees, or 30 degrees plantar flexion), as well as barefoot and in sports shoes. The tests were performed at full loads of 1, 2 and 4 km/h or with additional measurements at 1 and 2 km/h with a partial load of 20 kg. The walking speed of 4 km/h in sports shoes was used as reference, corresponding to the maximum load on the calf muscles during walking. Results: Both orthoses demonstrated a significant reduction in EMG activity by more than half even at a 0 degrees setting and 1 km/h compared to walking barefoot or in sports shoes. However, as walking speed increased to 2 km/h and especially to 4 km/h, EMG activity significantly increased, approaching the level of walking with sports shoes at 1 km/h. The results indicated that even minor changes in walking speed had a significant impact on muscle activity, underscoring the importance of this parameter. Conclusions: This study suggests that walking speed should be considered a crucial factor in rehabilitation protocols for Achilles tendon ruptures, alongside plantar flexion and load restrictions, to optimize recovery outcomes.