Final answer:
The greatest valgus load occurs during the late cocking and early acceleration phases of the throwing cycle. These phases are marked by maximal external rotation of the shoulder and flexion of the elbow, subjecting the elbow's medial structures to significant stress.
Step-by-step explanation:
The phase of the throwing cycle where the valgus load is at its greatest is typically during the late cocking and early acceleration phases. During these phases, the shoulder is maximally externally rotated and the elbow is flexed, creating a scenario where the medial (inner) structures of the elbow are subjected to significant stress. This stress, known as a valgus load, occurs as the thrower's arm moves from the position of maximal external rotation to the rapid internal rotation and elbow extension of the acceleration phase.
Valgus stress is pertinent in sports medicine and orthopedics because it can lead to injuries such as ulnar collateral ligament (UCL) tears, which are common in overhead athletes like baseball pitchers. Understanding the mechanics of throwing and the risks associated with high valgus loads is crucial for injury prevention and management.