The excuse that there is not enough time to exercise effectively is beginning to wear thin according to evidence from a study by scientists in Canada who found that short term high-intensity interval training (HIT) can deliver in significantly less time the same health benefits as moderate long term "endurance" training.

The scientists who did the study are based at McMaster University, Hamilton, Ontario. A paper on it is about to come out in print in the The Journal of Physiology, although an online issue has been available to view since January.

Scientists have known for years that doing regular moderate long term exercise like cycling or running for several hours a week improves oxygen delivery to muscles and elimination of waste products: it also improves the efficiency of fuel burning in the tiny power houses inside cells, the mitochondria.

Such a regime also widens the blood vessels to the muscle cells and boosts the number of mitochondria they contain. The result is an ability to do every day things more effectively, without strain, and with lower risk of heart attack, stroke and diabetes.

But there is one drawback that puts many people off: the amount of time such an approach consumes. Corresponding author Professor Martin Gibala and colleagues took it upon themselves to show that you can get the same results in less time with short spurts of "HIT".

As Gibala explained to the press:

"We have shown that interval training does not have to be 'all out' in order to be effective."

"Doing 10 one-minute sprints on a standard stationary bike with about one minute of rest in between, three times a week, works as well in improving muscle as many hours of conventional long-term biking less strenuously," he added.

HIT is where you do a number of shorts bursts of highly intense exercise with short recovery breaks in between.

In previous research involving college students, Gibala and colleagues discovered that HIT delivers the same physical benefits as traditional endurance training, even though it takes considerably less time, and surprisingly, involves doing less exercise.

But in their previous research they used an extreme set-up where the participants had to pedal "all out" on a specially adapted lab exercise bike.

In this new study they used a standard stationary bike and a workout that was still beyond the comfort zone of most people (about 95 per cent of maximal heart rate), but was only half of what might be regarded as an "all out" sprint.

This less extreme form of HIT should work well for people whose doctors might be a little worried about them taking up the "all out" form: that is people who are older, less fit and likely to be overweight.

For the study, they set out to show that unlike most HIT research that employs an "all out" approach (such as repeated Wingate Tests) that may not be safe or practical for many people, it was possible to achieve similar results with a more practical model of low-volume HIT.

They recruited seven men of average age 21 years and got them to perform 6 training session over 2 weeks. Each session comprised between 8 and 12 one-minute intervals at around 100 per cent of peak power output (they monitored their performance using a measure of their peak VO2). Each interval was separated by 75 seconds of rest.

The results showed that the training significantly increased exercise capacity in two cycling time trials (one for 50kJ and the other for 750kJ).

The researchers also compared biopsy samples of vastus lateralis muscle (the largest part of the quadriceps) taken before the 2 weeks of training with samples taken after, and found that the later samples showed increased maximal activity of mitochondrial capacity and other relevant chemical processes.

The researchers concluded that:

"This study demonstrates that a practical model of low volume HIT is a potent stimulus for increasing skeletal muscle mitochondrial capacity and improving exercise performance."

Gibala said that to achieve the same results by endurance training over the same period (two weeks) you would have to do over 10 hours of continuous moderate cycling exercise.

Although the study does not explain why HIT is so effective, it suggests that HIT stimulates many of the same signalling pathways as those stimulated by endurance training.

Gibala said "no time to exercise" is now no longer a valid excuse as HIT can be tailored for the average adult.

"While still a demanding form of training," he explained, "the exercise protocol we used should be possible to do by the general public and you don't need more than an average exercise bike."

He and his colleagues are now working on developing HIT to help people who are overweight or who have metabolic disorders like diabetes.

"A practical model of low-volume high-intensity interval training induces mitochondrial biogenesis in human skeletal muscle: potential mechanisms."
Jonathan P Little, Adeel S Safdar, Geoffrey P Wilkin, Mark A Tarnopolsky, and Martin J Gibala.
J Physiol, jphysiol.2009.181743; published ahead of print January 25, 2010
DOI:10.1113/jphysiol.2009.181743

Source: Wiley-Blackwell.

Written by: Catharine Paddock, PhD