Eli5 Why are some muscles, like a bicep, easier to flex than other muscles, like a deltoid (shoulder), when the deltoid can lift much more?

Question

Eli5 Why are some muscles, like a bicep, easier to flex than other muscles, like a deltoid (shoulder), when the deltoid can lift much more?

In: Biology

Answer 1

When you flex your bicep you are pulling between your forearm and your chest which tightens muscle as it contracts. When you are lifting with your delts you are pulling or pushing from your shoulders against gravity. Nothing to push or pull against means there is nothing flexing. You can almost do it if you put your hands behind your back above your head, but it’s not exactly a striking pose.