How is plantarflexion MMT performed to differentiate gastrocnemius vs soleus?

How is plantarflexion MMT performed to differentiate gastrocnemius vs soleus?

• A. Have the knee extended to test gastrocnemius; have the knee flexed to test soleus; apply resistance on the forefoot
• B. Stand on tiptoes with knee extended
• C. Apply resistance on the heel with knee flexed
• D. Sit with foot flat on the ground

Answer: (A)

The key idea is using knee position to bias which calf muscle you’re testing during plantarflexion. The gastrocnemius crosses both the knee and the ankle, while the soleus crosses only the ankle. When the knee is extended, the gastrocnemius is stretched over both joints, making its contribution to plantarflexion more evident in the resisted movement. When the knee is flexed, the gastrocnemius is shortened (less available to contribute), so the soleus becomes the primary plantarflexor. So, to differentiate them, plantarflexion testing is done with the knee extended to test the gastrocnemius and then with the knee flexed to test the soleus, applying resistance to the ball of the foot. Standing on tiptoes with the knee extended isn’t a focused MMT to distinguish these muscles, and applying resistance on the heel with the knee flexed or sitting with the foot flat don’t provide the same reliable bias to isolate one muscle over the other.

The key idea is using knee position to bias which calf muscle you’re testing during plantarflexion. The gastrocnemius crosses both the knee and the ankle, while the soleus crosses only the ankle. When the knee is extended, the gastrocnemius is stretched over both joints, making its contribution to plantarflexion more evident in the resisted movement. When the knee is flexed, the gastrocnemius is shortened (less available to contribute), so the soleus becomes the primary plantarflexor.

So, to differentiate them, plantarflexion testing is done with the knee extended to test the gastrocnemius and then with the knee flexed to test the soleus, applying resistance to the ball of the foot.

Standing on tiptoes with the knee extended isn’t a focused MMT to distinguish these muscles, and applying resistance on the heel with the knee flexed or sitting with the foot flat don’t provide the same reliable bias to isolate one muscle over the other.