MADISON, Wis. - The fitness industry is a big business, bringing in an estimated $24.4 billion annually. One in five Americans have a paid gym membership at one of the more than 37,000 gyms nationwide. But with so many choices, picking a type of workout can be intimidating. One of the hottest workout trends is high-intensity interval training, or HIIT.
Many gyms offer some form of HIIT training, but at Orangetheory franchises, HIIT training is all they do. Students at the fitness centers endure an hour-long workout while wearing heart monitors and following a trainer's instructions. The program involves treadmills, rowers and weights.
Adrian Lee, a former strength coach and a graduate of the University of Wisconsin-Madison, is the head trainer for both Madison Orangetheory Fitness studios. He said HIIT is based around anaerobic and aerobic exercise and centered on heart rate.
"The idea is we spend time in our anaerobic zone, which for us is the orange and red zone combined," Lee said. "You'll get something called EPOC (excess post-exercise oxygen), which occurs in the next 24-36 hours."
At Orangethory, heart rate, calories burned and time spent in five different heart zones are shown on big monitors. The zones are color-coded, with orange being the ideal zone, which gave the company its name.
"It's just a really good gauge, it's also a big motivator for a lot of members, so if they see they're truly working to their capacity by looking at the heart monitor, then as coaches it helps us because we know whether to pull a member back a little bit, not over-train or hurt themselves over time or to push them a little bit more to get to that next level," Lee said.
Laura Zeller, an exercise physiologist with UW's Preventive Cardiology program, has recommended HIIT training to some of her heart patients.
"In general, exercise gives you an opportunity to burn calories after exercise, but high-intensity interval training is more likely to burn more calories," she said. "In general, the higher the intensity of the workout, the more calories you're going to burn afterwards."
Exactly how many calories are spent in the afterburn is open to debate, but experts agree there is some positive post-workout effect.
"We know that high-intensity interval training can result in faster fitness gains and overall higher fitness level," Zeller said.
Most people will benefit from HIIT, but people with heart disease should check with their doctor before starting an intense training program, Zeller said.
"It's never too late," she said. "I have some amazing (people) who have been starting their exercise programs who are in their 80s and 90s who are just doing very well."
Experts also recommend leaving at least 24 hours between HIIT sessions.
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