Autogenic inhibition, where one muscle group's contraction relaxes its antagonist, is a mechanism by which PNF stretching increases range of motion.

“And we talked about why PNF works, things like the spindle and the Golgi tendon organ reflexes that are built into all of us that we arrive in this world with.”

“The GTOs have multiple functions. In fact, I think even though GTOs are in every medical textbook, every physiology textbook, every first year neuroscientist learns about them when learning about the neuromuscular junctions and the mechanisms of interoception, et cetera, they're likely to have other functions as well. And one of the reasons why PNF stretching does work, whether or not you're doing that by using a strap to pull back a limb, or whether or not you're actively contracting your quadriceps to then release and emphasize stretch range of motion for your hamstrings and related muscle groups is that activation of those GTOs, meaning putting loads and tension into that system can inhibit the spindles in the opposite antagonistic muscle groups.”

“What changed was the patterns of neural activation that were restricting you from in the first case stretching your hamstring or having a... To be more accurate we should say having a certain range of motion about the hamstring and its related joints and those brake mechanisms were removed. And, of course, then when you contract your hamstring, you're removing some of the neural brakes, the spindle acting as a brake and inhibiting that quadricep range of motion.”