Until the past few years, it seemed to me that most physicians who were trained in internal medicine, as I was, were uninterested in anything that moved faster than 3 miles per hour. Not so, now. At the American College of Physicians (ACP) annual meeting last month on San Diego's spectacular harbor, the sessions on sports medicine were jammed. People who were not in their seats 10 minutes early were kept out in the hallway by fire marshals. Why all the interest?