Final answer:
The magnitude of muscle torque through a joint's range of motion changes due to the movement of the pivot point and alterations in mechanical advantage, which impacts the required muscle force for movements like holding or lifting objects.
Step-by-step explanation:
The magnitude of an internal (muscle) torque changes through a joint's range of motion (ROM) because of the varying positions of the pivot point and changes in the mechanical advantage due to the perpendicular lever arms. As the joint flexes, the location of the pivot point can shift, affecting how much force the muscle needs to exert to maintain a position or movement. For example, the force the biceps muscle must exert to hold up a book changes as the forearm is flexed, and setting a bicycle seat at the proper height can reduce leg strain due to these mechanical advantages.
In addition to the pivot point and lever arms, muscle and joint torque also depend on the force direction and the point of application of the force. It is important for physical therapists and training coaches to understand these concepts for the effective treatment of musculoskeletal issues and the design of rehabilitation exercises, such as those performed underwater to increase muscle strength. However, the large forces involved in these activities can sometimes lead to damage in the connecting tissues like tendons and cartilage.