ABSTRACT
STUDY DESIGN: Controlled laboratory study. OBJECTIVES: To compare the neuromuscular function of the triceps surae muscle bilaterally in elite athletes with unilateral chronic Achilles tendinopathy. BACKGROUND: Previous studies suggest that tendinopathies or chronic pain may lead to a spinal/supraspinal level modulation of the excitability or voluntary activation of ipsilateral motor units. However, this has not been studied in Achilles tendinopathy. METHODS: Fourteen college athletes (mean ± SD age, 24.2 ± 1.7 years) who had unilateral chronic middle-portion tendinopathy in their Achilles tendons were recruited. Bilateral measurements of soleus reflex tests, including H-reflex and V wave, and rate of force development (RFD), as well as corresponding electromyography of the tibialis anterior and triceps surae muscles, were performed. Statistical within-subject and between-leg comparisons were made. RESULTS: In the leg with tendinopathy, the V wave of the soleus muscle was significantly increased (P<.001). The side with tendinopathy also had a reduced normalized RFD (0-30, 0-50, and 0-100 ms) in plantar flexion, and concomitant higher electromyography ratios between the tibialis anterior and soleus (0-30 and 0-50 milliseconds) during the early stage of explosive contractions (P<.05). No significant differences were found for H-reflex, maximal plantar flexion and dorsiflexion torque, and absolute RFD. CONCLUSIONS: Higher volitional supraspinal reflexes and lower maximal-strength independent force development occur in the triceps surae of elite athletes with unilateral middle-portion Achilles tendinopathy. These changes potentially indicate an acquired compensatory mechanism for maximal force production and deficits in explosive strength. The RFD is also suggested as a sensitive parameter to depict neuromuscular changes during treatment of chronic tendinopathies.
