Punching the heavy bag is a great resistance exercise that can tire out an athlete quickly. At Title Boxing Club, participants do three straight minutes of heavy bag punching (mimicking a three-minute boxing round) before taking a short water break. Then they're back at it. Participants often leave exhausted thanks to the added calisthenics (like squats, lunges and high knees) and core exercises (crunches, planks) that are scattered throughout the hour-long session.
Various boxing clubs claim that the one-hour workout can burn between 800 and 1,000 calories. Campbell encourages his clients to do three one-hour classes a week for the biggest impact.
"After four, five, six months, they're getting incredible results," Campbell said. "We do a newsletter every month highlighting people who have lost 150, 165 pounds. It's life-changing."
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Before the boxing-for-fitness boom, most clubs existed within the inner city and targeted local kids hoping to box competitively. These days clubs like Title Boxing and LA Boxing are finding huge success in suburban areas, with an interesting demographic dominating their membership—women. Campbell estimates 80 percent of his clients are females.
Coaches at boxing clubs can be demanding—often barking orders and adding 'If you do them wrong, we'll do them again!' Ultimately, each participant decides how hard and how much they want to get out of a boxing workout. Participants who stuck with the workouts have seen remarkable changes in their bodies.
"Women have gone from a dress size of 14 to a 3...just incredible results," Campbell says. "I knew it would be a great workout, but I didn't think about the results people would get."
More: Core Workout: 5 Moves for Flat Abs
Stay in shape in a fitness class.
