When doing a push-up on the floor, the motion at the elbow joint during the down phase is called ________ and the type of muscle action is called ________.

The joint motion is incorrectly labeled as extension; the elbow is bending (flexing) as the body moves toward the floor, not straightening.

During the down phase of a push-up, the elbow angle decreases as the body lowers, which is defined as flexion. The triceps brachii controls this descent by producing force while lengthening - this lengthening-under-load action is the definition of eccentric muscle contraction, making flexion and eccentric the correct pairing.

While the joint motion (flexion) is correct, the muscle action is wrong - concentric describes a muscle shortening under load, which is the opposite of what occurs during the controlled lowering phase.

Both terms are incorrect; extension describes the up phase of the push-up, and concentric action occurs when the elbow straightens during the upward push, not during the descent.