I like to exercise. I run, I play soccer, I'm a Jillian Michaels devotee.

I like to exercise. I run, I play soccer, I'm a Jillian Michaels devotee. I like my workouts to end with a lot of sweat and a couple sore muscles; I like to feel the changes as they happen to my body. As such, I loved Orangetheory. It was fun, fast and, at times, brutal. At Orangetheory, it's all about HIIT: high-intensity interval training that keeps your body guessing.

The idea is simple: By sustaining a target-zone heart rate, you're giving your metabolism a kick in the pants. The result is extra calorie burn and increased energy. Each class participant wears a heart-rate monitor synched up to one of several TVs lining the wall, and you're expected to monitor your own output throughout class. Workouts vary each day, but my experience included 30 minutes on the treadmill or rowing machine-I opted for the run, having been scarred by leg-killing high-school crew practices-followed by a plyometric workout that utilized TRX bands and included plenty of burpees. The instructor was spot-on-encouraging, tough, funny-as was the upbeat music. When I left, I was soaked in sweat with a smile on my face. Were there a gym near me, I'd do this every day. orangetheoryfitness.com