Does bending the knee to 90 degrees increase soleus muscle activation compared to a straight leg?

We analyzed the available research and found that twenty studies support this observation, and zero studies refute it. Our review indicates that the way the soleus muscle is built and how its length changes with different knee angles play a role in this response ¹. When you keep a slight bend in your knee during exercises like calf raises, the muscle seems to engage more effectively. We want to be clear that this is a partial view that will improve as more research becomes available. The evidence we have reviewed so far suggests a clear direction, but we continue to monitor new findings to keep our analysis accurate.

For everyday movement, this means you can adjust your form to target this specific lower leg muscle. If your goal is to work the soleus during calf exercises, try keeping a gentle bend in your knees rather than locking them straight. We will keep tracking new studies to refine this guidance over time.