The Downside to High-Intensity Sprint Training
For beginners, explosive sprint training can cause serious damage, putting you at risk for certain diseases and even cancer
High-intensity interval training continues to be as popular as ever, and for good reason: HIIT has many benefits, including fat burn and a faster metabolism. But according to a new study published in The Official Journal of the Federation of American Societies for Experimental Biology, high-intensity sprint training, in particular, can cause serious damage, putting you at risk for certain diseases, if you're new to this type of explosive workout.
For the study, researchers had twelve male volunteers perform two weeks of every-other-day sprint training-30-second all-out sprints on leg and arm cycling machines, followed by four-minute rest periods in between. They performed this circuit three to five times. At the beginning and end of the two weeks, researchers measured peak aerobic capacity and peak power output, and took biopsies of their leg and arm muscles to analyze their mitochondria-the powerhouses of the cell that use the breakdown of food and oxygen to generate adenosine triphosphate (ATP), the body's energy resource needed for muscle function.
At the end of the two weeks, mitochondrial function was significantly suppressed, thus reducing the cells' capacity to consume oxygen and their ability to produce the energy needed to fight off damage from free radicals that are released during these sprints. This can harm healthy cells and cause damage to gene structures, which in turn increases the risk for inflammatory issues, degenerative diseases, and perhaps even cancer, says Robert Boushel, Ph.D., the study's senior author. And while the study was conducted in men, there's no reason to assume women wouldn't be at the same risk since mitochondria typically respond similarly in men and women, he adds.
It's fair to point out that previous research has led to somewhat opposing results, showing that HIIT can actually aid mitochondrial biogenesis, which essentially duplicates the mitochondria in your cells. The more mitochondria, the more ATP. The more ATP, the more energy your body has to pump blood to working organs and muscles.
So what gives? The men in this study were in good health but only considered 'moderately active', so the good news is that the more your body is conditioned to handle these types of workouts, the less the damage will be, says Boushel. "Our message is that people need to be a bit cautious about this sprint-type training," he says. "It's not to say high-intensity training is bad, but this type of explosive all out-sprinting may not be inducing a healthy response if you're untrained." If you've built up a solid training base, there's nothing wrong with implementing these types of explosive sprint training workouts, as long as you only do so a couple times per week as part of a larger program to give the body time to adapt.
The real health danger comes from jumping right into these types of explosive workouts without working your body up to them first, says Boushel. So, before you begin sprint training, try traditional HIIT training-3 to 4-minute bursts followed by a rest period-to build your body up to all-out sprints. This will stimulate antioxidants, enzymes that protect you from the high levels of free-radicals during the sprints. (Plus, check out these 12 surprising sources of antioxidants that can serve as natural defenders against free-radicals.)