INTERVAL training is nothing new to fitness buffs. What may be new to some, though, are the multiple benefits of this intense training method, and the forms it can take.

Traditionally, when one thinks of interval training, one only thinks of a sprint-jog-sprint routine.

Indeed, interval training calls for a participant to sprint a certain distance, then jog slowly for about three minutes, before breaking into another sprint and not allowing the heart rate to return to normal. This routine is repeated several times.

The premise behind this is to put the heart and muscles under intense stress intermittently, with minimal recovery in between.

"Interval training pushes your heart harder than an endurance workout," says Dr Kelvin Chew, a consultant sports physician at the Singapore Sports Medicine Centre. "Heart rates for endurance workouts range from 65 to 75 per cent of maximum; with interval training, the heart rate goes into the 75 to 85 per cent range.

"The muscles work harder but actually different types of muscle fibres are also being trained.

"For endurance runs, slow twitch muscles get used to the long duration of your runs. For interval training, medium and fast twitch muscles get worked more."

Dr Lim Lian Arn, a specialist in orthopaedic surgery from Raffles Hospital, highlights that "interval training encourages the development of small blood vessels in and around your muscles, making them more efficient".

This same concept can be applied to other activities like cycling and swimming to break the monotony of running in interval training, and allow for targeted training in a certain activity.

Dr Lim also adds that the same physiological concepts can be used for any aerobic or cardiovascular sport such as cross-country skiing.

Some studies claim that a 30- to 45-minute session of interval training can equal, or better, the two hours of weekly exercise that doctors recommend.

Sharon Lim, the principal physiotherapist and manager of rehabilitation at Alexandra Health (AH), says there is some evidence to suggest that a single bout of maximal effort may be more effective than the traditionally prescribed moderate intensity workouts.

"Due to the periods of higher intensity during the interval training, the workout burns more calories than a moderate intensity session of the same duration," she says.

Dr Chew says a 70kg person can burn between 700 and 800 calories in a gym workout, while that for interval training ranges between 600 and 1000 calories.

Of course there are several factors to consider, such as the intensity, distance, speed and timing of the interval training; the length of the breaks between the sprints; and whether the two-hour workout is done in a single session or spread out during the week.

However, a 2005 study published by the Journal of Applied Physiology in the United States showed that six out of eight college-age men and women in a study group doubled their endurance, or the amount of time they could ride a bicycle at moderate intensity before exhaustion, after just two weeks of interval training.

Another group of eight did not do any interval training and showed no improvement in endurance.

Interval training can help improve aerobic capacity, anaerobic tolerance, lactate threshold, muscular strength and power, weight loss and heart functions.

A 2007 study by the same journal showed that interval training improved cardiovascular fitness and the body's ability to burn fat, even during low- or moderate-intensity workouts.

Eight women in their early 20s were first put through seven cycling interval workouts over two weeks. After that, the amount of fat they burnt in an hour of continuous moderate cycling went up by 36 per cent, while the ability of their heart and lungs to supply oxygen to working muscles improved by 13 per cent.

Some may find interval training lacks variety or muscle-building abilities, in which case, circuit training may be the answer. It is similar to interval training but participants go from station to station with no rest in between.

The stations can vary from simple exercises like burpees and sit-ups to rowing machines or weight-lifts.

However, the intensity of such workouts has led Dr Teh Kong Chuan, a senior consultant in AH's Sports Medicine Clinic, to warn: "With normal workouts, intensity is usually in the region of 70 to 80 per cent of maximum capability or lower. With interval training, you are typically working at over 90 per cent of maximum capability.

"With interval training at high intensity, the body is subjected to higher workloads and stress, which increase the risk of developing problems and injuries."

frankiec@sph.com.sg