Knee position affects medial gastrocnemius and soleus activation during dynamic plantarflexion: no evidence for an inter-muscle compensation in healthy young adults.
Level 3 - non-randomized controlled study
Within-subject controlled physiological laboratory study in healthy volunteers
PubMed 39786921 · doi:10.1242/bio.061810
What was done
Thirty healthy young male participants performed dynamic concentric plantarflexions (15° dorsiflexion to 30° plantarflexion) on a custom dynamometer at five velocities (30, 60, 120, 180, and 210°/s). Testing was conducted under two conditions: supine with the knee fully extended and kneeling with the knee fixed at 90° flexion. Surface electromyography (EMG) was measured using 16-channel linear arrays over the medial gastrocnemius and soleus muscles alongside ankle plantarflexion torque.
What was found
Averaged across the five contraction velocities, dynamic plantarflexion torque was 31% lower (P=0.002) and overall medial gastrocnemius EMG activity was 35% lower (P=0.002) in the knee-flexed compared to the knee-extended position. During the first half of plantarflexion at slower contraction velocities, soleus EMG activity was 15% and 28% higher (both P=0.002) in the knee-flexed position, but this did not prevent the overall 31% drop in torque output.
Why it matters
These findings clarify the neuromuscular coordination of the triceps surae, showing that while knee flexion reduces medial gastrocnemius output and selectively increases early soleus activation at low velocities, soleus upregulation does not compensate for lost net ankle torque.
Limits
The study included only healthy young males (n=30), limiting generalizability to females, older populations, or clinical cohorts. Dynamic movements were tested in differing body postures (supine vs kneeling) which may alter hip angle or stability, and the abstract does not report lateral gastrocnemius activity.