CrossFit, P90X, tabata, kettlebells—there are more offerings than ever when it comes to high-intensity workouts. And metabolic conditioning is a sure way to see results, as it burns calories and stimulates anabolic hormones (such as testosterone, growth hormone, and insulin-like growth factor) that are responsible for increasing lean muscle mass, McCall says. “Plus it can be fun to compete against the clock and watch your performance improve as you work to completing more reps in the same or less time,” he adds.
