Final answer:
The latissimus dorsi muscle is mainly used in pull-ups, climbing, and swimming, as it is responsible for adduction, extension, and internal rotation of the shoulder joint.
Step-by-step explanation:
The muscle predominantly used in activities such as pull-ups, climbing, and swimming is the latissimus dorsi. This muscle is one of the largest in the upper body and plays a crucial role in the movement of the shoulders and arms. When engaged in pull-ups, the latissimus dorsi works to adduct, extend, and internally rotate the shoulder joint. In addition, climbing requires back and shoulder strength, where this muscle is also heavily implicated. Swimming involves various muscle groups, but the latissimus dorsi is essential for the pulling motion during strokes like freestyle and butterfly.
In contrast, neither the quadriceps nor the biceps are primarily responsible for these activities. The quadriceps are primarily involved in knee extension, such as when straightening the leg or standing up. The biceps, which are flexors of the elbow joint, also assist in pull-ups but are not the main muscle used. The triceps are the extensors of the elbow and would be active in the pushing motions, not activities primarily involving pulling.