The Effect of Different Arm Angles When Throwing

Abstract

This experiment aims to determine how various throwing angles and forearm pronation affect the strain on elbow ligaments. The study focuses on identifying which combination of arm position and rotation produces the most significant ligament strain, as indicated by stretching and the formation of microtears. An anatomically accurate left arm model was constructed using 3D-printed bones to mimic the humerus, ulna, and radius, while rubber bands served as substitutes for natural ligaments. The rubber bands were securely attached to the bones using cyanoacrylate glue to ensure realistic ligament connections. Muscles and tendons were intentionally excluded to eliminate the variable of muscle contraction, and all throws were conducted manually.

Three distinct throwing angles were evaluated: 35 degrees (overhead), 45 degrees (three-quarters), and 75 degrees (sidearm). For each angle, two throwing conditions were tested: no rotation and pronation (inward rotation). In total, six throws were performed—three with no rotation and three with pronation. The forearm’s rotational movement during each throw was manually controlled to simulate the intended throwing mechanics. Ligament strain was assessed visually by examining elongation, tension, and the occurrence of microtears. Preliminary observations show that the rubber bands were not stretched or torn before the experiment was run. The results from this experiment will provide valuable insights into the biomechanics of throwing motions, potentially informing injury prevention strategies and contributing to improved sports performance and rehabilitation protocols.