Stretching is a form of physical exercise in which a specific muscle or tendon (or muscle group) is deliberately flexed or stretched in order to improve the muscle's felt elasticity and achieve comfortable muscle tone. The result is a feeling of increased muscle control, flexibility, and range of motion. Stretching is also used therapeutically to alleviate cramps and in Yoga.
Stretching the buttocks a spanking technique
Stretching the buttocks in pauses of a spanking session can add to the sensual experience and also help to build sexual arousal. This technique is usually combined with the massage technique of kneading. The hands of the spanker dig into the flesh of the spankee's buttocks to pull them apart, opening up the anus (and vagina if the spankee is female). It is found especially in erotic spanking where more sexual activity after the spanking is likely to follow.
Stretching in BDSM
In BDSM, stretching limbs to the point where it hurts, or holding a stretch for some time, can be used as a punishment, for example in the technique of leg stretching. It can be combined with bondage.