What's the basic concept?
The idea is that 15 minutes of high-intensity interval training (HIIT) can deliver the same physiological benefits (such as improved endurance, and reduced risk of heart attack, stroke and diabetes) as three hours of long, slow running.
It seems that short bursts of high intensity exercise – 30-second all-out sprints with a work-to-recovery ratio of around 1:6 – may stimulate the same cellular pathways as long, steady state aerobic exercise. In other words: the same health gains of running but in a fraction of the time. But, of course, there’s a catch: as lead researcher Martin Gibala says, “Those short bursts hurt.”
What’s the risk?
HIIT sessions require maximal, or close to maximal, efforts. This means you rely primarily on your anaerobic system for energy. If the aerobic system uses oxygen on a ‘pay as you go’ basis, the anaerobic system generates an oxygen ‘debt’, which needs paying off as soon as you back off from the full-on effort. (That is why heartrate monitors aren’t particularly good for gauging the intensity of HIIT intervals: your heartrate continues to climb sharply during recovery as the body pays off the oxygen debt.)
But as long as you have the OK from your doctor to exercise, this is entirely safe. Just remember that maximal exercise of any sort puts considerable stress on your muscles and connective tissues. There’s no further benefit to be had from doing more than two days of HIIT per week. And you need time to recover, so allow at least one full day of recovery between sessions. Prioritise longer, low-intensity sessions in your training week, and include strength and conditioning work to help prevent injury.
Endurance is more important to me than explosive speed. Can I still benefit?
Yes. There’s no doubt that long, slow runs are the most effective means of training for an endurance race. They boost the fatigue resistance of slow-twitch muscle fibres; HIIT has its greatest impact on fast-twitch fibres. So why should you include HIIT sessions in a distance training programme?
One good reason is that although the fast-twitch fibres may not be as fuel-efficient or resistant to fatigue, they join in the action when leg muscles start to tire in the latter stages of a race. So you may get a boost to your overall muscular endurance.
Do I have to run my HIITs?
No – HIITs work well on the elliptical trainer, stair climber or stationary bike. In Gibala’s study, the subjects used a bike: it’s not only a very time-efficient way of getting in a quality workout, but because cycling is non-weight bearing, it’s the mode of exercise least likely to cause – or exacerbate – injury.
As for whether the improvement in leg speed developed by cycling crosses over to improved leg speed during running, that’s up for debate. But it certainly won’t hurt!
Three simple high-intensity sessions
On a track
Warm up with five laps at an easy pace - gradually speed up so that you end up running briskly. Then do 200m at maximal sprint effort followed by 400m gentle jog. Repeat six times.
On a treadmill
Set the incline to one per cent. Warm up by running gently, gradually building speed, for 10 minutes. On an effort scale of one to 10, you should be at five to six by the end. Run 30 seconds at close to maximal speed (which is at least 18km/h on the treadmill for most people); jog gently for three minutes. Repeat four to six times.
On a bike
Following a short warm-up, try four to six bouts of maximal sprint efforts, each lasting for 30 seconds, and follow with four minutes of easy spinning recovery.