The Honeymoon Muscle
I just learned that the gracilis muscle, which is capable of clamping the thighs together with terrific force, is known as the anti-rape muscle. Some refer to its opposing muscle, which is responsible for opening the thighs, as the honeymoon muscle. The gracilis adducts and rotates the thigh medially; the sartorius abducts and rotates laterally. These muscles work together in opposition.
Muscles almost always operate in pairs: when one contracts, the opposing muscle relaxes. An obvious example would be the biceps and triceps. Or the hamstrings and quadriceps. The iliopsoas sometimes has this kind of reciprocity with the quadratus lumborum, but it depends.
If a muscle becomes engaged for a prolonged period, like if it’s chronically tense, the opposite muscle can become inhibited. And if one is much stronger than the other, then it can overpower, or even injure, the weaker one. In yoga, and also in sensible strength training, we try to keep balanced the muscles that work together.
When one muscle is much tighter than its opposite, we can use the principle of reciprocal inhibition to our advantage. If you activate the opposing muscle, this causes its partner muscle to relax, which is what we want when we’re trying to lengthen it.
A lot of people really, really want to touch their toes. They want long hamstrings and spend a lot of time and energy stretching. If you’re one of them, try engaging your quads (i.e., lift your knee caps and straighten your legs) to find more length in the hamstrings.