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Disclaimer, I'm not a biology undergrad and I only know the basics about muscle movement.

I know that doing a bench press works the chest, and specifically the Pectoralis Major because, well, I feel muscle soreness. However, it is not obvious to me what the Pectoralis Major has to do with extending the arm.

Thinking about muscle contraction, I see clearly how, for example, the Bicep flexes the elbow when it contracts. In a similar way, when the Pectoralis Major contracts you get horizontal shoulder adduction.

But what about the bench press? The majority of the movement consists of raising the arms upwards from a tucked position, and the is little shoulder adduction.

Thanks!

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  • $\begingroup$ The bench press is almost entirely shoulder adduction.... $\endgroup$
    – theonlygusti
    Apr 21, 2021 at 9:55

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The pectoralis muscle attaches to the top to the inner half of the clavicle, just underneath the biceps on the inner part of your arm and the breastbone (a.k.a the sternum) which is found in the middle of your ribs. See below: Pectoralis major muscle attachments

So taking that in account the pectoralis muscle helps bring your arm closer to your body (adducts your arm), pulling it forward in front of you (flexes the humerus) to push up like you would when you bench press. This action can be seen below.

enter image description here

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  • $\begingroup$ Oh okay, pretty stupid on my part. There is a lot of adduction in a bench press. The only difference is that the triceps also extend the arm. Thanks! $\endgroup$
    – Gonate
    Feb 22, 2015 at 17:23
  • $\begingroup$ Not a stupid question :) It also assists in forward flexion which is part of a bench press. $\endgroup$
    – AndroidPenguin
    Feb 22, 2015 at 17:27

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