Anyone who has ever engaged in rock climbing or bouldering, the name for climbing on low rock formations without a rope, can testify to the strain the activity puts on the body. When positioned vertically, the muscles in your hips and torso strain to keep your lower body in place against the wall. Arching your back, you move one hand up to grasp on to the next hold - your thighs and calves leaving the sensation of a deep burn as they struggle with the pressure being exerted upon them. Eventually, as you lodge your hand into the next hold, the muscles that are close to giving up are relieved as the muscle group in focus shifts. The process is repeated methodically as you gradually scale the wall.