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.
Want a simple yet brutal interval workout that will leave you crawling from the gym back to your car? (The answer is "yes, you do") Check out this burner from 98 Gym in Sydney and word of warning; don't skip the the pre-workout.
Choose an Assault Bike/Ski erg/Row machine
10 rounds :
30 seconds MAX EFFORT
2 min rest
*Done right this should feel like your legs are going to fall off
Now take 3 mins rest
Then a 60 second MAX EFFORT