Training muscles while they are stretched leads to more muscle growth in muscles that cross two joints, like the calf's gastrocnemius, but does not lead to more growth in muscles that cross one...

We analyzed one assertion on whether training at long muscle lengths causes more hypertrophy in biarticular muscles than in monoarticular muscles, and the evidence we’ve reviewed so far supports this idea. Specifically, it suggests that when muscles crossing two joints — like the gastrocnemius in the calf — are trained while stretched, they may show greater muscle growth compared to muscles crossing only one joint, like the soleus, due to differences in their structure [1]. Biarticular muscles, such as the gastrocnemius, span two joints — in this case, the knee and ankle — which may make them more sensitive to stretch under load. Monoarticular muscles, like the soleus, only cross one joint and may not respond the same way when trained in a lengthened position. The evidence we’ve reviewed indicates this structural difference could explain why one responds more to stretch-based training than the other. We did not find any studies or assertions that contradict this pattern. However, the total number of assertions analyzed remains very low — just one — and the evidence does not explain how this applies to other biarticular or monoarticular muscles beyond the calf. It also doesn’t clarify whether the same pattern holds across different training volumes, intensities, or populations. What we’ve found so far is limited but points to a possible difference in how these two types of muscles adapt to stretch-loaded training. For now, if you’re training the calf, focusing on exercises that fully lengthen the gastrocnemius — like standing calf raises with a deep stretch — might be more effective for growth than exercises that don’t stretch it as much. But whether this applies to other muscles like the hamstrings or rectus femoris remains unclear based on the current evidence.