To isolate the gastrocnemius during plantarflexion testing, which knee position should be used?

To isolate the gastrocnemius during plantarflexion testing, which knee position should be used?

• A. Knee extended (neutral) to recruit gastrocnemius; apply resistance to plantarflexion at the forefoot
• B. Knee flexed; resistance at the heel
• C. Knee flexed; resistance at the forefoot
• D. Knee extended; resistance at the midfoot

Answer: (A)

Gastrocnemius is a biarticular muscle that crosses both the knee and the ankle. When the knee is kept straight, the gastrocnemius is stretched into a favorable length-tension range, so it can contribute more to plantarflexion and stand out as the primary plantarflexor compared with the soleus. Using resistance at the forefoot aligns with the muscle’s line of pull through the Achilles tendon, challenging plantarflexion in a way that emphasizes the gastrocnemius rather than other muscles. If the knee were flexed, the gastrocnemius would be slackened and the soleus would contribute more, making it harder to isolate the gastrocnemius. Resistance at the heel or midfoot can alter leverage and recruit additional stabilizers, reducing specificity to the gastrocnemius.

Gastrocnemius is a biarticular muscle that crosses both the knee and the ankle. When the knee is kept straight, the gastrocnemius is stretched into a favorable length-tension range, so it can contribute more to plantarflexion and stand out as the primary plantarflexor compared with the soleus. Using resistance at the forefoot aligns with the muscle’s line of pull through the Achilles tendon, challenging plantarflexion in a way that emphasizes the gastrocnemius rather than other muscles. If the knee were flexed, the gastrocnemius would be slackened and the soleus would contribute more, making it harder to isolate the gastrocnemius. Resistance at the heel or midfoot can alter leverage and recruit additional stabilizers, reducing specificity to the gastrocnemius.