If your idea of a workout consists, as mine did, of a pleasant run and a few sit-ups, your first CrossFit session isn’t just a shock—it’s like being tased.
The answer, some scientists are finding, is: maybe.
In recent years, researchers have been making counterintuitive discoveries about how our bodies get in shape. In a 2006 study, scientists at Ontario’s McMaster University divided 16 young men into two groups. One group rode stationary bikes at a moderate pace, for up to two hours at a stretch, six times over two weeks. The other did up to six 30-second, balls-out sprints. Researchers then took tissue samples from participants’ thighs and compared them.
The results were stunning. By several key measures of exercise performance—number of mitochondria (an indicator of how efficiently a muscle is using oxygen), buffering capacity against lactic-acid buildup, and the presence of glycogen (sugar) for fuel—the groups “showed remarkably similar improvements in exercise performance.” The difference: one group exercised for more than 10 hours, the other for only 15 minutes. In another study, just two weeks of sprints nearly doubled cyclists’ endurance when they pedaled at a fairly vigorous pace, from 25 to 50 minutes.
Serious endurance athletes are aware that some speed work is beneficial, but this was a surprise. “What was unique about our study was that maybe you only had to sprint to increase endurance,” says Martin Gibala, chair of McMaster’s department of kinesiology. A weekend athlete who relies solely on interval training won’t become Meb Keflezighi, says Gibala, but he will experience many of the adaptations long attributed to endurance training—and likely improve his 10K time to boot. The studies also raise questions about how much of the “base layer” miles that many dedicated athletes pile on is really needed. “People do a lot of junk mileage,” Gibala says.
A vocal spokesman for the less-is-more philosophy is Guy Petruzzelli, 39, a personal trainer and professional triathlete from Chicago who tried CFE—skeptically at first—during his recovery from a car-bike collision in June 2010. Previously, Petruzzelli’s training had been “swim-bike-run: a pretty standard diet for most triathletes.” Three weeks after starting his new regimen, he went to the track and ran 5:15-mile repeats—30 seconds faster than his usual time. “That’s a huge difference,” he says. On the bike, his average power output for a 40K effort leaped 33 percent.
Petruzzelli was sold. Last August, he won the Olympic-distance MidEast Duathlon Championships in Ohio—5K run, 40K bike, and 10K run—despite cutting his training volume roughly in half since before the accident. “I get a lot of criticism because I follow this model,” he told me. But, he says, “it can be applied at an elite level.”
Endurance athletes have scoffed at MacKenzie and CFE for their emphasis on weight lifting—skepticism born of a long-held fear that lifting bulks you up and slows you down. But recent science is showing that, if you do it right, you can get strong and powerful without adding body weight. “You want to lift heavy weights, which means lower reps,” says Anthony Turner of Middlesex University’s London Sport Institute. “A good workout would be four sets of four repetitions.”
Well-trained runners in Norway who followed a similar program—heavy half-squats a few times a week for two months—increased the time they could run at their maximum speed by 21 percent before exhaustion set in, according to a 2008 study. Physiologists think this is thanks to an increase in running efficiency, the idea being that a stronger body uses less energy to move.
