Pennation angles and fiber length of ankle dorsiflexor and plantarflexor muscles depending on muscle contraction intensity

Abstract

In this study we investigated pennation angles and fiber lengths of major ankle dorsiflexor and plantarflexor muscles depending on muscle contraction intensity (MCI) and ankle joint angles. Ten male subjects with no history of musculoskeletal injuries participated. For each patient the ankle joint was fixed at 15° dorsiflexion and 0°, 15° and 30° plantarflexion. Ultrasound images (SonoAce Pico, Samsung Medison, Korea) were taken to measure pennation angles of tibialis anterior (TA), gastrocnemius medialis (GCM), gastrocnemius lateralis (GCL), and soleus (SOL). Pennation angles and fiber lengths in ankle muscles on sub-maximal muscle contraction were determined. A torque dynamometer (Biodex system 3, Biodex Medical System, USA) was used to simultaneously measure torques in different MCIs (0, 30, 70 and 100% MVC). Results showed that significant differences in pennation angles and fiber length were found between 0% MVC and sub-maximal MVCs, between 0° and 15° of dorsiflexion, and between 15° of plantarflexion and 15° of dorsiflexion. Based on this study, the pennation angle surface model (PASM) was proposed in order to improve EMG-driven model. This study showed that pennation angles and fiber length should be measured at different MCIs, and would be beneficial in implementing a more realistic muscle model to predict muscle forces.