If you struggle to find time for the gym, research suggests that high intensity exercise for less than 15 minutes a day may improve fitness.
Repeated, four-second bursts of intense exercise, performed three times a week, was found to boost cardio and muscle power, according to a study published July 12, 2021 in Medicine & Science in Sports & Exercise.
Researchers from the University of Texas at Austin studied 11 healthy, active adults in their 20s during eight weeks of training. Researchers tested participants' VO2 max (ability to use oxygen during exercise) as well as anaerobic capacity (ability to generate power in short bursts without oxygen) to analyze whether short exercise sessions could improve fitness.
During the training, participants exercised for four seconds at maximum effort, rested for 30 seconds, and then repeated the cycle for 30 rounds.
After following this program three days a week for eight weeks, participants saw a 13% increase, on average, to their VO2 max and a 17% increase to their anaerobic capacity. In other words, they got fitter, although the total exercise they did was about two minutes per day.
Intense exercise could be more efficient for fitness than previously believed
Trying to cram the benefits of exercise into a shorter time period isn't new. High-intensity interval training (HIIT) and Tabata workouts are both popular styles of calorie-torching exercise that involve 20-30 second bursts of intensity.
But as anyone who's tried HIIT can attest, it's challenging to go hard even for that short period of time.
This study aimed to reduce some of the pain associated with intense exercise, according to Edward Coyle, senior author of the study and director of the Human Performance Lab at the University of Texas at Austin.
"When you go all out for 20 or 30 seconds, you build up lactic acid in your muscles and it becomes very hard," he told Insider.
In contrast, his team theorized that a four-second interval isn't long enough to build up lactic acid, so athletes wouldn't feel the burning muscles and extreme fatigue of longer intervals.
Participants in this study had many of the same fitness improvement shown with longer intervals, with fewer side effects, the data suggests. The participants even wanted to continue with the workouts after the study, and said they'd recommend the workouts to others.
More research could show how to reap the most benefits from exercise with less work
A previous study from Coyle found that four-second exercise intervals could also help prevent some of the risks of a sedentary lifestyle by revving up metabolism and boosting fat-burning ability.
That study required participants to complete a short sprinting workout every hour during their eight-hour sedentary period.
However, not everyone can duck out for an hourly sprint break. And one major limitation of the research is that the benefits of four-second sprints are difficult to replicate without an exercise bike.
"For a running scenario, you'd have to be sprinting and accelerating for four seconds, and that's pretty hard on your body and your joints," Coyle said.
A possible solution might be adding some elevation, such as a hill or some stairs, to ramp up the intensity.
Coyle is continuing to study how to reap the most benefits from exercise with the least amount of work. For now, he said the research is a good reason to add exercise to your day, even if you don't have time for a long workout.
"If people can't do what we're recommending, it's helpful to just take a few flights of stairs," he said.
