For decades, it has been an article of faith for parents of young pitchers: Do not let them throw curveballs. The reason was simple. Contorting elbows — all in the service of ever more competitive baseball at ever younger ages — puts more strain on the joint than arms can handle.

But as the research into the biomechanics of pitching has evolved, the debate has grown more robust, and more perplexing. A recent major study shows curveballs pose no greater risk than that of other pitches. And many studies lately have shown that the greatest threat to young arms is not throwing curves but making too many pitches of any kind.

“Science is banging heads with intuition and gut instinct,” said Glenn Fleisig, the research director of the American Sports Medicine Institute, who has conducted studies on breaking balls and young arms since 1996. “For years, we told people that curveballs were bad. Then we set out to prove it. We did not prove curveballs are safe, but we could not prove they were dangerous.”

Like a pitcher and a catcher disagreeing on pitch selection, the opposing sides in the debate could not be more closely allied. Dr. James Andrews, the orthopedic surgeon to many athletes, is a founder of the American Sports Medicine Institute and has written with Fleisig some of the studies that have failed to prove that curveballs are hazardous to young arms. It has not stopped Andrews from challenging the results.