A powerlifter attempting a maximum deadlift suddenly releases the barbell when tension peaks. The reflex responsible for dropping the load senses which stimulus, travels in which afferent, and produces what effect on the agonist muscle?

• A Muscle tension, Ib afferent, inhibition of the agonist ✓
• B Muscle length, Ia afferent, excitation of the agonist
• C Joint angle, group II afferent, excitation of the antagonist
• D Muscle tension, Ia afferent, inhibition of the agonist

Explanation

Golgi tendon organs sit in series with extrafusal fibers at the musculotendinous junction and encode force, not length. Excessive tension fires Ib afferents, which excite inhibitory interneurons acting on the homonymous alpha motor neuron, relaxing the agonist: the inverse stretch reflex or autogenic inhibition. This protects tendon and bone from rupture under dangerous loads. The Ia afferent arises from the spindle, which lies in parallel and senses length, and it produces excitation of the agonist, so those combinations are wrong.

Reference: Guyton and Hall Textbook of Medical Physiology, 14th ed.

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