Dry Run: I ask Brent Carter, an instructor at Focus Personal Training Institute in new York City, to take me through a sample workout. he recommends alternating a minute of kettlebell swings with a minute of burpees. "Your heart rate needs to be at about 90 percent of its max to see benefits," he explains. The intensity taps into the body's anaerobic energy system, stimulating production of growth hormones that will supposedly help me torch more calories. We warm up, then Carter sets a timer. Two minutes in, I am gasping for breath and my thighs are on fire. at the four-minute mark, my last burpee barely leaves the ground, and I'm only at 84 percent of my max heart rate.
Verdict: On a busy week, I may do three short sessions, but I won't switch permanently. The intensity sucks all the enjoyment out of exercise.