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?

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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
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This. My lifting partner and I were trying to figure out how to “flex” our delts (which we were not successful at doing).

Please science, help.

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.

The deltoid *can’t* lift much more. Most skeletal muscles contract in pretty much the same way, throughout the skeletal structure. It appears that you’re comparing a compound movement with a single-joint movement.

When you raise something with a deltoid (i.e., lateral/front raises), it is guaranteed to be quite a bit less than if you curl something.

But if you *shoulder* *press* something, you’re using almost your whole body to hoist that weight (abs, back, legs, triceps, etc). No real comparison, there.

Oh, yeah – the bicep is easier to flex, because of its type of connection to your skeleton and range of movement.