“Why does cracking your back feel so good?”

Summary of neurophysiologic effects of manual therapy:
Peripheral mechanisms
• Significant reduction in blood and serum level cytokines in joint-biased manual therapy
• Changes of blood levels of b-endorphin, anandamide, N-palmitoylethanolamide, serotonin
• Endogenous cannabinoids increases
Spinal mechanisms
• Joint-biased manual therapy is speculated to bombard the central nervous system with sensory input from the muscle proprioceptors
• Hypoalgesia
• Afferent discharge
• Motoneuron pool activity
• Changes in muscle activity
Supraspinal mechanisms
• Joint-biased manual therapy to the lower extremity of rats after capsaicin injection. Functional MRI of the supraspinal region quantified the response of the hind paw to light touch after the injection. A trend was noted toward decreased activation of the supraspinal regions responsible for central pain processing.
• Autonomic responses
• Opioid responses
• Expectation of effectiveness of manual therapy is associated with functional outcomes
• Joint-biased manual therapy is associated with improved psychological outcomes
• Dopamine production
• Central nervous system

Some people like to crack their knuckles to. It feels good because it frees up joints. Motion is lotion. It may also release endorphins, which are the "feel good" molecules. He would really enjoy a visit to the chiropractor! (yes, it's safe and even good for kids)

An adjustment stimulates a large amount of nerve endings that creates a hyper stimulation to the area, thus disbursing the stimulate areas. Similar to hitting your knee on a coffee table...the first response is to rub the are to disburse the pain, but you not fixing the underlying condition. He should go for an exam.

Cracking your back feels good for many reasons. It improves mobility of the joints, it can decrease pain in the joint, and it can decrease inflammation. There are also psychological components to hearing and feeling the back cracking.