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

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.