The following study published in the Journal of Applied Research by Petrofsky and colleagues showed that only six minutes of high-intensity training (HIT) can elevate metabolism for up to 36 hours.
The exercise protocol, conducted by researchers from Azusa Pacific University in CA, consisted of a one-minute warm-up, four-minutes of high-intensity work followed by one-minute of recovery. All ten subjects followed an exercise video for six minutes. All subjects had a personal trainer present to ensure the protocol was followed especially during the four-minute HIT component. The HIT consisted of 8 intervals; each interval was 20 seconds of exercise followed by 10 seconds of recovery. The body weight exercises included squats, jumping in place, lunges, and split squats. The experiments were conducted over a 4 day period.
The top subject in the group burned 112 calories during the six minute protocol and 345 calories over the next 24 hours for a total of 457 calories. At three and six hours post exercise, oxygen consumption was still significantly elevated at 26% and 20% respectively compared to resting values. The study showed that the substrate used during exercise was mainly carbohydrate but following exercise, more fat was utilized. This study compared well with other studies that demonstrated excess post-oxygen consumption was significantly greater for 24 hours but extended out to 36 hours.
Petrofsky J et al. (2011). Post exercise Basil Metabolic Rate Following a 6 Minute High Intensity Interval Workout. The Journal of Applied Research 11(2):65-72.