People tend to confuse the stretch reflex mechanism with the function of Golgi tendon organs, which attach between muscles and tendons. Golgis monitor tendon stretch at the end of the tendons; if tendons are overstretched, the Golgi organs shut down (inhibit) that stretch. But Golgi’s only operate at very high levels of stretch, and do not activate until after the stretch reflex mechanism has been triggered. Golgi’s don’t operate at low levels of stretch because if they did, they would be in the way all the time.
Another confusion is that the term ‘tendon reflexes’ refers to Golgi tendon organ activation. Again, Golgi organs inhibit muscle reaction. When the doctor checks your tendon reflexes with a tap to the knee, that tap actually activates the muscle spindle’s stretch reflex mechanism; the confusion comes from the term ‘tendon reflex’, so-called because it is indeed the tendon that is struck just under the patella. But the Golgi organ is located above the knee at the end of the muscle belly. Striking up there would be striking in the deflective portion of the muscle belly, where only a local action from the deflection of the giving fibers of the muscle could be measured. Striking the less deflective tendon below the knee activates the entire muscle. Also, the only neurology to the Golgi organs are collateral nerve branches to the tendons that cause them to stiffen when their muscles contract.
Again, Golgi organs actually inhibit muscle contraction, and all tendon reflexes ~ knee, elbow, ankle etc. ~ are measured by striking the tendon, not a Golgi organ; and the resulting muscle contraction is caused by a dynamic, or myotatic stretch reflex reaction via the muscle spindles.
Incidentally, because Golgi’s do inhibit muscle contraction, it is sometimes erroneously thought that mashing down on the Golgi organ will turn off a spastic muscle. As just said, smashing the Golgi activates the spindle-driven stretch reflex, and additionally, in trying to get in deep enough to work on a Golgi organ, the spindles would turn the muscle on so tight, the deeper layers where Golgi’s are located could never be reached.