Which of these mechanisms causes golgi tendon organs to start firing action potentials?

• A. As the muscle contracts, collagen fibers 'squeeze' the nerve endings of the golgi tendon organ.
• B. As the muscle relaxes, collagen fibers 'squeeze' the nerve endings of the golgi tendon organ.
• C. As the muscle contracts, free nerve endings in the golgi tendon organ are compressed by muscle fibers.
• D. As the muscle stretches, free nerve endings in the golgi tendon organ are compressed by muscle fibers.