High-intensity interval training (HIIT) is the fastest way kick your body into fat-burning full-athlete mode. In fact, studies show that these short, intense bursts of exercise coupled with recovery periods can increase your endurance, VO2 max, and post-workout calorie burn—plus actually help make a grueling session more enjoyable.
But a new study in The FASEB Journal warns that if you're not actually at peak fitness status, you may be doing serious damage to your body.
A group of Canadian and European researchers put a handful of untrained subjects through a test of ultra-intense leg and arm interval exercises. After the workout, researchers analyzed muscle tissue samples and found that the Average Joe’s mitochondria were only firing at half-power thanks to the taxing training.
The powerhouse of cells, mitochondria are in charge of regulating your cells’ capacity to consume oxygen and fight off damage from harmful free radicals. Why does this matter? High levels of free radicals have been linked to serious health conditions, including cancer, premature aging, and organ damage.
"If you're new to going to the gym, participating in high-intensity 'sprint' classes may increase your performance but might not be healthy for you," said senior study author Robert Boushel, director of the University of British Columbia's School of Kinesiology in a press release.
When you've been training for a while, your body builds up antioxidant enzymes to protect against these free radicals, the authors explain.
So where is that line drawn? Well, the guys participating in the study self-identified as being in good health, but as "untrained” or “only moderately active." Basically, if you’re new to the gym, don’t hit the HIIT class right away. Build up your intensity over time. If sprint and interval training has long been part of your workout repertoire, you probably have nothing to worry about—which means you have no excuse, so get to it.