Reciprocal inhibition is a neuromuscular reflex where if one muscle group contracts, the opposing muscle group must relax to allow movement through a joint.
Getting a muscle to relax can stop a cramp. Contracting or stretching a cramping muscle can make it worse. First, figure out which muscle is cramping and needs to relax. Next, determine the opposing muscle group for an action of the complaining muscle. Perform an isometric contraction of the opposing muscle group with no change to muscle length which sends a signal through the tendon to relax the target or cramping muscle group.
For example, if the hamstrings are cramping, hold the leg in a static position by resting the other leg on top of it, and try to lift the lower leg, against resistance and without stretching the hamstrings. to extend the quadriceps. The patellar tendon of the quadriceps will send a signal to the hamstrings to relax.
The same concept will work for tight muscles. By understanding the pairings of agonist and antagonist muscle groups for any single motion, movement can be performed in an isometric contraction to inhibit opposing muscles from contracting, which essentially lets them take a break and reset proprioception and other neurological signals of the surrounding area.
If the isometric contraction is done gently while lying face up, the muscles will contract, and posture functions will not be in play as they are not needed in that position. This is especially important if the muscles are weak, and the posture system or fascia is overworked and locked down.