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

“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.”

“This has a name, it's called autogenic inhibition, it's a fancy name for contraction of one muscle group providing a relaxation of the other muscle group that's antagonistic to it.”

“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.”