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HIIT (high intensity interval training) has had lots of press over the last 2 years, from the BBC Horizon programme “The truth about exercise” to the well publicised Andrew Marr incident. Many accredited studies have shown that HIIT will increase aerobic fitness (VO2 max) as well as providing all the health benefits of longer duration exercise. Its time efficiency and effectiveness have made it very popular; but what are the optimal number of intervals?
In the BBC Horizon programme, Dr Michael Moseley was tested doing a single 3 minute routine, containing several 30 second, maximal bursts. Some complete just one sustained, flat-out 3-4 minute burst, whereas others practice a more conventional training routine of more intervals – as many as 10, all close to maximum heart rate. Each interval is followed by periods of slower recovery.
Frequency of training also varies greatly. Some may train every day, others a few times a week with days off between exercise. Dr Mosley Was completing just two sessions a week.
Although scientific studies have proved that intense interval training can increase your aerobic fitness up to 10 times faster than moderate exercise, no studies had been done to determine the optimum amount of intervals. Until now. A study by Mcmaster University in Ontario tested 17 young men and women on different HIIT regimes. 10 of the 17 were asked to exercise on 2 separate days a week. On the first day they did a standard HIIT session of four 30 second intervals of excruciating effort alternated with one minute of recovery. On the other day they did a single, non-stop interval of around 4 minutes, after which they had used the exact amount of energy as in the first session. Blood samples were gathered after each session.
The remaining 7 volunteers did the non-stop, single four minute interval for 6 weeks, completing it 3 times a week. Again blood samples were taken.
Although there were gains for the single interval training group immediately after exercise, these did not translate into lasting improvements over the 6 week study. Only the group who were doing multiple intervals gained in the medium term.
In another study by the University of Science and Technology in Norway, volunteers were asked to perform 24 HIIT workouts over three or eight weeks. This meant that some of the subjects did sessions every day (sometimes twice on the same day), while others only exercised three times a week. At the end of the study, those exercising 3 times a week had improved aerobic fitness by 11%, while those who were at it daily showed no improvements; in fact some of them showed a small decline. Only after they stopped exercise did the daily group show signs of improvement, with aerobic capacity creeping up by 6% some 12 days after cessation of activity.
The conclusion of both of these studies is that the best gains come from more standard interval training. Several intervals interspersed with recovery are best. So try to do 60-90 seconds off full on swearing-inducing effort with 60 seconds of slow recovery. Repeat at least 4 times, but 8 is better. The less recovery you have the faster you will improve lactic tolerance. The longer recovery you have the more you will improve speed and power.
By Adam Atkinson