Why does my bicep look nonexistent when I flex with fist facing away from shoulder?

[soccerballtux]

It gets a lot larger when I curl it around to face my shoulder/bicep like the bodybuilders do when in a show or something.

I know that there are 2 muscles in the bicep, does this mean I'm working only one of them entirely out and I need to work the other one too? Or is this normal?

Thanks.

[Attacus]

The more your twist your hand inward (supinate) the more you activate your biceps, the more you twist your hand outward (pronate) the more you activate your brachialis.

To target your brachialis: hammer curls, reverse curls.

[crupiea]

I guess you aint going to be no Jesse the Body anytime soon.

get back in the gym and in one year repost.

Thanks,

The Management

[Mourning Tide]

flexing with fist facing outwards (or even to the front of your body) elongates the bicep head, reducing the gap between ur bicep and forearms

flexing biceps with hands facing = more peak

^just simple terms from blatant observations

[SDFlip]

post a pic.

[kjonson]

The basic reason is that you have a couple major muscles involved in this:

Biceps Brachii
Brachialis

When you pronate your forearm, you shift the tension off the biceps and on to the brachialis. The reason for this is that the biceps has two insertions on the forearm, at the radius (bicipital tendon) and in the forearm flexors over the ulna (bicipital aponeurosis...it merges with the fascia instead of attaching to a bone).

So when you pronate, the bicipital aponeurosis is no longer able to put as much tension on the forearm flexors and the bicipital tendon is wrapped around the radius, hence neither is able to put much tension on the bicep muscle (it's dropped by at least 20% tension, but reports vary).

This causes you to put most of your tension on the brachialis which attaches on the ulna, and the ulna stays in the same position during pronation. Hence, this becomes the superior concentric flexor, whereas normally the biceps muscle is the strongest concentric flexor (don't get confused with the fact that the brachialis is the strongest muscle at this joint because the brachialis is only the strongest during isometric flexion).

So basically, twisting the attachment points of the biceps away from the direction of tension reduces the ability of the muscle to flex hard, and since it's the superficial muscle, it will not appear as visibly flexed. This is also the reason that pronated curls are great for building overall strength in elbow flexion - you're working the strongest muscle at the joint which normally gets ignored during supinated curls.

[soccerballtux]

Kjonson thanks for your post, very helpful.

Is there any way to isolate (or at least preferentially stress) the long head (outer) shown here? I'm doing seated curls.
http://www.exrx.net/Muscles/BicepsBrachii.html