The effect of knee angle and subject position on plantar flexors isokinetic performance and muscular activity

Abstract

BACKGROUND: Assessment of the plantar flexion (PF) isokinetic performance has been greatly diverse and based on personal preferences rather than standardized guidelines. OBJECTIVE: To examine the performance of the plantar flexors under different settings including knee joint angle and subject position. METHODS: Thirteen women and 20 men took part in this study. The isokinetic protocol (60∘/s) was set to ankle movement between 10∘ dorsiflexion to 30∘ PF. Participants performed three repetitions of concentric PF in randomly-ordered knee angles; 15∘, 45∘ and 90∘, and in seated and supine positions. Surface electromyography (EMG) data were collected from the Soleus (SOL) and Gastrocnemius. RESULTS: Knee angle impacted the PF moment (P⩽ 0.001–0.026) and work (P⩽ 0.05) measures in both genders. The moment and work measures were significantly less in the 90∘ than those in the 45∘ and 15∘ positions. The 45∘ position had the highest values, particularly in sitting in the male participants. Only the GL EMG data was significantly impacted (P= 0.017) by the subject position. However, the difference was trivial (1.6%). The SOL muscle showed a consistent pattern of increased activity when the knee was in flexion. CONCLUSION: The 45∘ position seems to be optimal for obtaining the highest isokinetic PF scores.