Final answer:
The medial ulnar collateral ligament experiences the most tensile stress during forceful extensions of the forearm, commonly seen in actions by baseball pitchers, which can lead to injury and the need for Tommy John surgery.
Step-by-step explanation:
The medial ulnar collateral ligament is subjected to the greatest tensile stress during actions that involve forceful extensions of the forearm, such as those performed by baseball pitchers. This ligament, which is an intrinsic part of the elbow joint, spans from the medial epicondyle of the humerus to the medial ulna. It is especially vulnerable during pitching because it resists hyperextension of the elbow.
The anterior portion of this ligament is known for its strength and its ability to withstand the force during these extensions. However, repetitive stress can lead to injury, which may necessitate surgical intervention, commonly known as Tommy John surgery.