Tabata biking

A regrettably small sample size, but that is a pretty cool room-calorimeter they used for this experiment.

Though other studies have shown that sprint interval training can markedly improve fitness and athletic performance, little was known about how this type of exercise affects energy expenditure, a factor that motivates many people to exercise. To determine how many calories a typical sprint interval training workout might burn, Sevits and his colleagues recruited five healthy male volunteers, all between the ages of 25 and 31 years old. These volunteers made an initial visit to Colorado State University in Fort Collins in which they performed an exercise stress test to make sure their hearts were healthy enough to participate. The researchers also analyzed the volunteers' body compositions and their resting metabolic rates.

Over the next three days, the volunteers ate a diet precisely calibrated to meet their metabolic needs so that they'd be in "energy balance," Sevits explains, with just enough calories so they weren't over- or under-eating. At the end of those three days, the men then checked in to a research facility at the University of Colorado Anschultz Medical Campus that was outfitted much like a typical hospital room. However, this room was completely enclosed, with air intake and exhaust regulated and equipment installed to analyze oxygen, carbon dioxide, and water content. Based on the results of this analysis, the researchers could determine how many calories the volunteers burned while each stayed in the room.

For two days, each volunteer lived in the room, continuing to eat the prescribed diet and spending the majority of their time in sedentary activities, such as watching movies or using a computer. However, on one of the days, they engaged in a sprint interval workout that involved pedaling as fast as possible on a stationary bicycle in the room that was set at a high resistance for five 30-second periods, each separated by four-minute periods of recovery in which they pedaled slowly with very little resistance. During the intense, 30-second bouts, the researchers coached the volunteers over an intercom system, encouraging them to give 100 percent effort.

Sprint Interval Trainer?

Analyzing results from the room calorimeter system showed that the volunteers burned an average of an extra 200 calories on the sprint interval workout day, despite spending just 2.5 minutes engaged in hard exercise. Though the researchers can't yet speculate on whether such efforts could translate into weight loss, Sevits and his colleagues suggest that engaging in intense, but brief, bursts of exercise could aid in weight maintenance. "Burning an extra 200 calories from these exercises a couple of times a week can help keep away that pound or two that many Americans gain each year," Sevits says.

Steve Hsu notes that running consumes around 100 calories per mile. So depending on how fast you run, the interval workout tested here isn't actually faster. There are variants of the interval workout, such as the tabata, which would get you to about the same place eight minutes.