NEW YORK —
Growing pains are "bilateral," too, in that they typically affect both sides of the body. This doesn't mean that both sides have to hurt every time — the right leg might hurt one night, and a few days later the left one will act up — but kids who only ever get pains on one side probably aren't having growing pains. And growing pains aren't visible. Your kid might be screaming his head off about his shin, but you should never actually see anything wrong with his shin. If you do — if you see redness or swelling or bruising, for instance — you should take your little one to the doctor, pronto.
So, the definition of "growing pains" is based on when and where the pain happens, not on what causes it. And even today, no one is sure what produces growing pains, but there are several theories backed by (limited) research, and together they suggest that growing pains might have a range of physiological causes. One possibility is that kids who get growing pains have abnormally low pain thresholds. In a 2004 study, Philip Hashkes, at the time a pediatric rheumatologist at the Cleveland Clinic, tested the pain thresholds of 44 children with growing pains by putting pressure on various parts of their bodies, including points that are particularly sensitive to individuals who have chronic pain syndromes like fibromyalgia. After conducting similar tests on 46 children who didn't have growing pains, Hashkes found that much less pressure was needed to incite pain in the children who had nightly growing pains.
Growing pains could in part be the result of overactivity, too. This theory meshes with parental observations that growing pains are often worse on nights after sports practices. These aren't your typical post-workout pains, though — kids are much more at risk for true sports overuse injuries, such as shin splints, in part because growing bones don't handle stress very well. In another study, Hashkes measured, using ultrasound, the bone densities and qualities of 39 kids who experienced growing pains and found they were lower than average. The density and quality of bone drops when it has been overused without having a chance to recover, so the findings suggest that some growing pains may be associated with too much running around. But some researchers aren't convinced by the overuse theory, in part because growing pains often start suddenly in the middle of night, and overused muscles should ache more consistently.