Final answer:
The humerus experiences both compressive and tensile loading during a push-up due to muscle contraction and the body weight force exerted at the joints.
Step-by-step explanation:
During a push-up, the humerus is under compressive and tensile loading due to the action of the muscles and the force exerted by the weight of the body. As the person lowers their body, the muscles of the arm, specifically the bicep, contract to control the movement, placing the humerus under tension. Conversely, as the arm pushes the body away from the ground, the humerus endures compressive forces especially at the elbow joint where the downward force (FE) exerted by the humerus equals 407 N, which is significant compared to the total weight supported.
Muscles typically contract and cannot expand beyond their resting length; hence during a push-up the muscles and joints exert forces in opposite directions. For instance, the upward force of the muscle subtracts from the downward force of the joint, supporting the body weight throughout the exercise. Furthermore, the forces in muscles and joints are largest when their load, in this case, the body weight, is a long distance from the joint, creating large lever arms and thus larger forces required by the muscles.