This sounds like the stuff of grocery-store tabloids, but it has a lot of science to back it up. Way back in 2008, the Journal of Physiology published a study showing that subjects who performed four to six 30-second all-out intervals (we're talking nearly to the limit of what their bodies could handle), with rests in between, three days per week showed the same muscular and fat-burning benefits as subjects who cycled at a moderate pace for a single 40–60-minute session five days per week. (That's 90 minutes versus four and a half hours of exercise a week, for those keeping score at home). In 2014, researchers at McMaster University in Ontario published a study in Experimental Physiology showing that 30-second interval training may actually be superior to continuous workouts when it comes to certain improvements in muscle tissue.
Perhaps most surprising are the results from another McMaster University study published in PLOS One in 2016. For this 12-week study, scientists slashed the intervals, having subjects perform three all-out cycling intervals of only 20 seconds each with two minute rests in between, three times a week. With warmup and cooldown, the workout lasted a measly 10 minutes. Compared with people who performed the same number of weekly workouts but simply cycled at a moderate pace for 45 minutes (with the same warmup and cooldown), the interval group showed the same improvements in endurance, insulin resistance, and the microscopic muscle structures responsible for energy production and oxygen consumption.