Final answer:
Excess muscle on joint movement slightly restricts the movement. While muscles can limit flexibility, they are necessary for joint motion and work in pairs, with one contracting and the other relaxing to allow movement.
Step-by-step explanation:
The effect of excess muscle on joint movement is that the joint movement is slightly restricted. Since muscles can only contract but not extend beyond their resting length, the presence of excess muscle mass can limit the range of motion. Synovial joints are designed to allow certain movements, and while muscles are necessary to move bones at the joints, too much muscle can occupy the space needed for that motion, effectively reducing flexibility. In some cases, strong ligaments can also limit the movement of joints, providing stability during weight bearing, as seen in the hip joint compared to the more flexible shoulder joint.
However, muscles must work in pairs to facilitate movement. The contracting muscle, called the flexor, bends the joint, while the opposing muscle, the extensor, straightens it. When one muscle contracts, the other relaxes, allowing for motion. Therefore, even with excess muscle, some movement is still possible, though it may be reduced compared to the normal range of a less muscle-bound joint.