Biomechanics of Chest Exercises

In the Fitbit “Building Bigger Stronger Chest Muscles” You wrote: "With the arms held in the front at the completion of the (fly) movement, the stress is shifted almost completely to the clavicular head. "Two questions: what is a source for that assertion, and how do you think that can be applied to training the "upper chest"?

(1)The source for all the assertions is from MRI analysis of muscular contractions, though I still have reservations of the accuracy of MRI analysis on the assertions made concerning "wide grip and narrow grip" chest presses effect of the chest muscles.

 (2) Incline presses and flys at 30 degrees of bench incline is still indicated as ideal for upper chest development. Above 30 degrees of incline, MRI analysis indicated the stress moves from upper chest to anterior deltoid.