Final answer:
Musculotendinous units play a key role in joint stability by producing isometric contractions that maintain joint position and resist external forces. This dynamic support is especially important in joints with relatively weak ligaments, like the shoulder.
Step-by-step explanation:
Musculotendinous units may indeed act isometrically to stabilize joints. During an isometric contraction, the muscles produce tension without changing the joint angle, making them crucial in maintaining posture and joint stability. This occurs due to the shortening of sarcomeres within the muscles, which increases tension but does not result in movement because these contractions resist the external load without overcoming it. In a supported joint such as the shoulder, where ligaments may be relatively weak, the muscle and its tendon act as a 'dynamic ligament' to resist forces and provide support. This function increases the contractile strength of muscles when needed, safeguarding joints against excessive forces that can occur during accidents or excessive exertion in activities like weightlifting.
Joint stability is further augmented by the lever system of muscle and bone interactions and the synovial joints, which are enhanced by the presence of tendons, muscles, and ligaments. Injuries to tendons, cartilage, and ligaments can occur when they are subjected to large forces, and physical therapy often employs exercises that apply specific forces and torques to recover muscle and joint function, sometimes utilizing the resistance provided by water to enhance muscle strengthening. Understanding the mechanics of muscles, tendons, and their interactions allows coaches and physical therapists to effectively treat and rehabilitate musculotendinous injuries.