Loads on Elbow
During pushup: Greater posterior and varus forces (distal segment ie forearm closer to the body midline than proximal segment) are generated at the elbow when the hands are medially rotated compared to when the hands are either neutral or laterally rotated. (Lou S., Lin C, Chou P, Chou Y, Su F. Elbow load during pushup at various forearm rotations, Clin Biomech 16:408, 2001)
The triceps tendon attachment at the ulna is closer to the elbow joint center than the attachments of brachialis to the ulna or biceps brachii to the radius. Thus the extensor moment arm is shorter than the flexor moment arm, so the former must generate more force than the latter to produce the same amount of joint torque. Thus there are larger compression forces at the elbow during extension than flexion, when comparing movements of similar speed/force.
The triceps moment arm (because of the shape of the olecranon process where the tendon inserts) varies with the position of the elbow. The moment arm is largest during full elbow extension, compared to when there is flexion past 90º