Gastrocnemius and soleus are selectively activated when adding knee extensor activity to plantar flexion

Area of Science:

• Biomechanics
• Human Physiology
• Musculoskeletal System

Background:

• The gastrocnemius and soleus muscles are primary plantar flexors, but the gastrocnemius also acts as a knee flexor.
• Anatomical differences suggest selective activation patterns during combined movements like simultaneous plantar flexion and knee extension.

Purpose of the Study:

• To investigate the selective activation of the gastrocnemius and soleus muscles.
• To determine how concurrent knee extensor activation influences these plantar flexor muscles.

Main Methods:

• Ten male volunteers performed isometric plantar flexion at varying intensities (10-30% maximum effort).
• Isometric knee extension was superimposed at 0%, 50%, and 100% maximum effort during plantar flexion tasks.
• Electromyographic (EMG) activity of the medial gastrocnemius and soleus was recorded and analyzed.

Main Results:

• Medial gastrocnemius EMG activity was significantly depressed when knee extension effort was added (P=.002).
• Soleus EMG activity was significantly increased with concurrent knee extension (P<.001).
• These effects were consistent across different plantar flexion levels.

Conclusions:

• Concurrent knee extensor activity during plantar flexion leads to selective soleus muscle activation.
• The synergistic activity of the gastrocnemius is depressed under these conditions.
• This suggests a neural control mechanism for differential muscle recruitment during complex movements.