The world’s favourite form of exercise, the early morning jog, can now rest in peace. Whether you are looking to lose weight, boost your general fitness, increase endurance, or build speed or muscle definition, there’s one workout philosophy that ticks all the boxes.

It’s called Interval Training.

Stripped to its basic, Interval Training is an exercise programme that simply alternates short periods of intense physical activity—fast running, cycling, swimming, jumping, etc.—with short periods of rest or light physical activity.

Stretch it: There is no added risk of injury if you adopt Interval Training practices.

“There is no reason for the quality or philosophy of training to differ for athletes and non-athletes, since athletes are put through the best, scientifically designed training programmes that will benefit everyone," says Kolkata-based Ranadeep Moitra, a coach certified by the National Strength and Conditioning Association (NSCA), US. “What differs is the quantity and intensity of training you do."

A study published by the American Journal of Applied Physiology in 2007 found that after only two weeks of Interval Training, participants in the study doubled their endurance and increased their fat-burning ability during subsequent low-to-moderate-intensity workouts by a massive 36%.

“Interval Training allows you to work at a higher intensity of aerobic capacity, at a higher level of heart rate, and it develops athleticism," says Heath Matthews, a sports rehabilitation specialist at the Kokilaben Dhirubhai Ambani Hospital and Medical Research Institute in Mumbai. “It’s a far more functional way of training than just steady cardio."

Matthews, who has worked with the Indian boxing squad and badminton player Saina Nehwal as a physiotherapist, says that most athletic training, even for long-distance runners, has shifted towards Intervals, with one or two long endurance sessions thrown in every week.

Moitra, who has worked with the Indian and Bengal cricket teams and the Kolkata-based East Bengal football club as a fitness expert, and now works with the Indian golf team, also relies solely on Intervals for cardio and overall fitness training.

“My endurance sessions are only based on Intervals," Moitra says. “The long, continuous run is not part of the programme. Even in off season—when you work the hardest on building endurance and power—I used to make the East Bengal team do 1km runs in 4 minutes, rest, then another 1km run in 4 minutes, and so on."

A typical Interval session for the East Bengal team would start with a 10-minute full-body warm-up, followed by a 280m run in a minute, then a minute’s rest, then a 140m run in 30 seconds, then rest for 30 seconds, then a 90m sprint at maximum speed, then a minute’s rest—this pyramid run was repeated four or five times. This would be followed by a set of 50m sprints over hurdles, with a 1:1 ratio of work and rest (that is, if it took 10 seconds to run the 50m, then rest for 10 seconds, and repeat). This would be followed by four or five sets of 10 repetitions of box jumps done quickly, with 20-second rest gaps between sets.

“All the activities were multi-joint, at high pulse rates," says Moitra. “Basically, in Intervals you are working at such a high intensity that you are repeatedly pushing your body to temporary failure, then resting to recover, and then pushing it back to failure. It’s the fastest way for a body to adapt to the workload you put on it."

Though this may sound like a risky proposition for people who don’t already possess high fitness levels, Matthews says there is no added risk of injury from training like this compared to normal cardio routines.

“Of course, people with serious conditions like heart disease always need to prepare their fitness plans in careful consultation with their doctor," Matthews says, “but that would hold true whether you want to just jog for 3km, or lift weights, or do Intervals."

Matthews, in fact, recommends Intervals for people coming back to fitness training after a long gap because it pushes the body to recover and regain fitness levels faster.

“Even while lifting weights in the gym, it is much more efficient to follow the Interval structure," says Moitra. “Instead of doing three sets of, say, chest press with long rest periods in-between, do a circuit routine—10 chest presses, followed by 10 squats, followed by 10 bicep curls with no rest in-between, forms one set. Then rest for a minute and repeat the circuit. You’ll get a workout that is way more effective, and in half the time."

Interval Training, in fact, is a boon for people pressed for time. Because it is done at such intensity, sessions never last more than 20 minutes.

“In those 20 minutes, you get the benefits of an entire hour’s exercise, and more," says Moitra.

While athletes follow Interval programmes carefully designed in accordance with the sport and their body type, Intervals can easily be done without such structuring. One popular style of Interval Training, called Fartlek or “speed play", is completely unstructured. Invented by Swedish Olympic athlete and coach Gösta Holmér in the 1930s, Fartlek involves a long run/walk combination with random bursts of speed and tempo change thrown in, a bit like a simulated soccer game without a ball.

Moitra offers a quick beginner’s guide: Imagine a bear is chasing you and you are running for your life—that’s your top speed. Now, run a 100m sprint at about 70% of this speed, and time yourself. Rest for double the time it took you to run the 100m. Repeat this five-six times. Remember to warm up and cool down, with 10 minutes of light running before and after the session to avoid injuries. Work at this intensity and pace till you can do 10 repetitions. Once you’ve worked on the volume, begin working on the intensity by increasing your speed.

How to design an interval session

Identifying the fitness benchmarks, and two sample workouts

Mumbai-based Praveen Tokas, a trainer certified by the NSCA and the Canadian Society for Exercise Physiology, who works with national athletes as well as Bollywood actors, shares the way an Interval Training programme is set up.

The two fitness benchmarks that define Interval sessions for an individual are VO2max and HRmax. VO2max or maximal oxygen uptake is basically the volume of oxygen an individual’s body can use while exercising at maximum intensity, and is a reflection of aerobic fitness and efficiency. HRmax is the beats per minute at which the heart rate of an individual plateaus while exercising at maximum intensity.

HRmax is usually calculated clinically through a treadmill or cycling stress test. The commonly used formula—220 minus (0.85 multiplied by age)—is also used to calculate HRmax, though research has shown it is not very accurate, especially in older people.

For an athlete

Warm-up: 10-15 minutes

Number of work intervals: 5

Duration of work intervals: 5 minutes

Work intensity: 85% HRmax (for example, sprinting at 85% of your maximum speed for 5 minutes)

Rest intervals: 1 minute

Work-rest ratio: 5:1

Frequency: 1-2 times a week

Cool down: 10-15 minutes

Total time: 67-77 minutes

For a fit non-athlete

Warm-up: 5 minutes

Number of work intervals: 5

Duration of work intervals: 1 minute

Work intensity: 85% of your top speed (note your heart rate after the first work interval, and use that as an approximation of your 85% HRmax for future reference).

Rest intervals: 1 minute

Frequency: 3 times a week

Number of rest intervals: 5

Total time: 20 minutes

Progression: Try decreasing the rest interval every third workout and increase speed when your heart rate is not reaching 85% of your HRmax during the work interval (which is a measure of progress, since your heart is not working as hard to run at the same speed).