While some of you are well immersed in your holiday debauchery, others amongst us (present company not included, of course) are already getting a head start on those New Year’s Resolutions…to the extreme. From Thursday’s New York Times and Stephanie Cooperman (link courtesy Sam Frank).

A controversial exercise program has attracted a growing following of thousands nationwide, who log on to CrossFit.com for a daily workout, said its founder, Greg Glassman. Participants skip StairMasters and weight machines. Instead they do high-intensity workouts that mix gymnastics, track and field skills and bodybuilding, resting very little between movements.

The emphasis is on speed and weight hoisted, not technique. And the importance placed on quantifiable results has attracted hard-charging people like hedge fund managers, former Olympians and scientists. But some exercise experts are troubled by the lack of guidance for beginners, who may dive into stressful workouts as Mr. Anderson did. (He had not worked out regularly for two years.) “There’s no way inexperienced people doing this are not going to hurt themselves,” said Wayne Winnick, a sports medicine specialist in private practice in Manhattan, who also works for the New York City Marathon.

Other critics say that even fit people risk injury if they exercise strenuously and too quickly to give form its due, as CrossFit participants often do. For people who like to push the limits of fitness and strength – there are many police officers, firefighters and military personnel in the ranks of CrossFit athletes – the risks are worth it, because they consider it the most challenging workout around.

The short grueling sessions aren’t for the weekend gym warrior. The three-days-on, one-day-rest schedule includes workouts like “Cindy”: 20 minutes of as many repetitions as you can of 5 pull-ups, 10 push-ups, 15 squats. “Fight Gone Bad” entails rotating through five exercises, including throwing a 20-pound ball at a target 10 feet away. And only veteran CrossFit devotees even attempt, and few complete, “Murph,” a timed mile run, 100 pull-ups, 200 push-ups, 300 squats and then a second mile run. (A weighted vest is optional.)

Mr. Glassman, CrossFit’s founder, does not discount his regimen’s risks, even to those who are in shape and take the time to warm up their bodies before a session.

“It can kill you,” he said. “I’ve always been completely honest about that.”

But CrossFitters revel in the challenge. A common axiom among practitioners is “I met Pukey,” meaning they worked out so hard they vomited. Some even own T-shirts emblazoned with a clown, Pukey. CrossFit’s other mascot is Uncle Rhabdo, another clown, whose kidneys have spilled onto the floor presumably due to rhabdomyolysis.