From Ergo Log
Thanks to sports scientists at Inje University in South Korea, we now know that the good old push up is far more versatile than we realized. The Koreans discovered a way for athletes to develop the upper part of the chest muscle by doing push ups.
The way of doing push ups that the Koreans studied is shown on the right: the lower body is flexed at an angle of 30 degrees.
The researchers got 15 male students to do push ups in the traditional way and with a flexed trunk. They had attached electrodes to the muscles of the subjects’ upper body and core so that they could measure the electrical activity in these muscle groups.
The figure below shows the activity expressed as a percentage of the activity during maximum voluntary isometric contraction [MVIC].
When doing push ups with a flexed trunk the abdominal muscles worked less hard than when doing regular push ups. The activity in the lower part of the chest muscle – the sternocostal portion of the pectoralis major [S in the illustration] – was also a little less.
On the other hand, the activity in the upper part of the chest muscle – the clavicular portion of the pectoralis major [C in the illustration] – was higher when performing flexed-trunk push ups, as was the activity in the serratus anterior.
J Phys Ther Sci. 2014 Jun;26(6):909-10.