In case you're new to the concept of interval training, the scientific theory goes that even though you may burn more kilojoules during a 50-minute moderate workout than you would during a 10-minute interval session, your 'joule burn as you recover from your workout will be greater after sprint intervals.
It's all about that after-burn adding to your total burn thanks to a greater metabolic demand, burning more kilojoules restoring the energy that was depleted during the sprints. It's a whole big science thing, that you can read up about here.
So how long should your intervals be in order to really stoke that metabolic fire and get the most out of your workout? I'm glad you asked, and so are the researchers behind a new study in The Journal of Physiology
The researchers behind the study, from the University of Copenhagen, analysed the effects of interval training on 12 male cyclists through blood and muscle biopsies post exercise. The cyclists were reportedly put through 3 workouts on different days;
- Cycling at a steady pace for 50 minutes at 70 per cent effort
- 18 rounds of 5 second sprints, followed by 30 seconds of rest
- 6 rounds of 20 second sprints, followed by 20 seconds of rest
According to the results, the total of kilojoules burnt during the interval sessions were equal, despite the time under pressure differing between the workouts, however the 20-second sprints created a spike in adrenaline and lactate. An increase in lactate results in a mitochondria boost - the energy force in the cells - meaning a greater increase in health and fitness benefits.
The findings are significant because it demonstrates although shorter bursts of high-intensity exercise have the potential to burn significant 'joules, there's clearly a point where the effectiveness drops off. Jens Bangsbo, a professor of physiology at the University of Copenhagen and co-author of the study suggests that five seconds isn't enough time to sufficiently stress the muscles. Bangsbo suggests that 20 seconds is the "sweet spot" for athletes wanting to unlock the greatest physiological gains, and the minimum amount of time for such improvements.
He does acknowledge that intervals of 10-15 seconds would hold benefits over 5 seconds... but really, how much of a push can you build up to in 10 seconds. Hold out for the 20, and witness the greater gains. It's not that long and sure beats one 50 minute interval.
This article originally appeared on Men's Health.