I recently ruptured my distal biceps tendon and have to have surgery. My surgeon is one of the top doctors in the region and specializes in this procedure and works with our local NHL team.
Anyways, we got to talking about the biceps and how it move/works and activates. It’s strange, I can curl my arm, but I cannot supinate it. I have a big ball of muscle half-way up my upper arm with zero lower bicep. It’s nasty.
The doc was basically telling me that curling with your palms up uses the brachialis a great deal more than the biceps. He says the biceps is activated only when the wrist is rotated. He stated that the brachialis will pop the biceps up and the rotation of the wrist will flex it, giving the appearance that it is being stimulated more than it actually is.
He was athletic and lifted weights. He said that most trainees overworked the brachialis and undertrained the biceps. He said a good example would be to have half of your “biceps” training to involve supination moves like standing alternate DB curls and incline seated DB curls.
I thought it was interesting, because I thought supination was optional. Go figure.