These interval training workouts always had variety. As well, they were done without letting up on the effort. It was so hard it was called HIT (high intensity training). The goal was to complete more work at a higher level of intensity than could be done with longer, slower distance (LSD) running.

Work to recovery ratio

These workouts involve simple math. The idea is to alternate between periods of intense activity followed by slower movement. The advantage is that both the recovery period and workout duration can be manipulated. For instance, the intensity duration may be as short as five seconds, as with sprinting up a flight of stairs. If the recovery period lasts three times as long as the work period, then the work to recovery ratio (WR) is 1:3. You can also flip the ratio, doing 90 seconds of continuous activity followed by 30 seconds of recovery. In this case, the workout lasts three times as long as recovery (WR 3:1). The number of times you repeat the workout will depend on the level of intensity and your fitness level.

Individual intensity is key

The key to HIIT is that intensity relates to your ability to push yourself. HIIT can be modified for any fitness level or population, since each person does the activity at their own pace. For example, high level really fit athletes would start at an intensity of about 80 to 85 percent of their maximum heart rate. They would be breathing so hard that carrying on a conversation would be very difficult. In the slow interval that follows, the athlete would drop the intensity to 40 to 50 per cent of their maximum heart rate. This pace is now comfortable enough to allow recovery for the next intense interval.

Body benefits

Repeat interval training engages the nervous system. More muscle fibers are used (recruited), which is valuable for many reasons. HIT also challenges the metabolic system to increasingly select carbohydrate for fuel. Fat does not break down quickly enough to provide the necessary energy. The type of energy selected by the body serves two purposes.

First, repeated intervals use more calories than LSD workouts. The body’s metabolism keeps consuming calories after the exercise period is over. This post exercise ‘burn,’ as it is sometimes called, may last up to two hours after a workout. During this time, the body tries to return to pre-exercise levels, to restore or restock carbohydrate and fat stores (fuel), and repair any damaged muscle cells. To do this requires energy, hence the post exercise expenditure.

As well, the body’s resting metabolic rate (the number of calories the body burns at rest) rises as muscle mass increases. This increase is small but significant, since fat burns just two calories per pound but skeletal muscle burns six calories per pound over a day.

From HIT to HIIT

Example of calculating your maximum heart rate

To calculate your maximum heart rate (max HR), use the following equation. This predictive equation will provide your heart rate in beats per minute (BPM). It is based on a relationship between age and HRmax developed in a longitudinal study.

207- (Your Age x 0.7) = max HR

For example, at 40 years old your max HR = 180 bpm

To work at an intensity of 80 per cent,
multiply your max HR by 0.8 = 144 bpm
Your recovery should be 50 per cent,
multiply your max HR by 0.5 = 90 bpm
So your work out zone is between 90 to 144 bpm.

Remember it may take you a few minutes to recover to 90 bpm.

Fast forward to today, and a similar workout has a slightly different name and focus. High intensity interval training (HIIT) has been called the ‘time-efficient workout.’ These workouts are very similar to the track workouts. They involve quick bursts of strenuous exercise, which rapidly change breathing. Yes, you will most likely get a sweat on. The overall workout is shorter than the time needed for an aerobic workout. Both HIT and HIIT are based on the principle of work to recovery ratio (or work to rest ratio), as described in the sidebar.

HIIT can incorporate any type of exercise or activity. For example, you might engage in skipping or jumping jacks, as long as you follow the WR ratio with repeats. Intervals can be done in many ways. The goal is to focus on your own training intensity, as participating safely is always important.
Hard, easy, and repeat

HITT has been shown to benefit everyone, from sedentary adults to those with diabetes or heart failure and, of course, athletes. However, most research will say that to achieve the greatest health benefits, you must challenge yourself. Remember the simple mantra – hard, easy, and repeat. A 10-minute starter workout might involve walking quickly for 60 seconds, followed by 75 seconds of strolling. Repeat this pattern four times. Next, progress to doing the same routine twice more during the day, for a total amount of 30 minutes. SIT is a clever acronym for these short, intense bouts of low volume training. It can also remind us that prolonged sitting is a health risk. The beauty of SIT or any interval-like workout is that it can be applied to many different activities. As well, it can be done in almost any environment – inside or outside, pool or gym, hotel room or office.

Most people know that moderate physical activity, such as 30 minutes a day of brisk walking, is linked to living longer. An interval activity improves the ability of the circulatory and respiratory systems to supply the skeletal muscles with oxygen. Another benefit is that it also improves blood glucose control and the health of the body’s mitochondria, no matter how old you are.

Mitochondrial health

Mitochondria are the powerhouse cells of the body and muscle cells have a very high concentration of mitochondria. Mitochondria produce ATP, which is the energy currency of the body. So if muscles are working at their best, this will have a positive impact on your energy level. HIIT improves your cell health by increasing energy demands, creating more mitochondria. This is called mitochondrial biogenesis. The body adapts by encouraging cells to make more proteins to increase energy production. HIIT reverses the age-related decline in both mitochondrial function and proteins that build muscle. This makes it a very good exercise strategy.

If you have limited time and lack motivation to exercise, try a ten-minute HIIT workout. Remember the research – evidence overwhelmingly shows that the risk of not doing exercise greatly outweighs the risks of doing it. If you have a family history of heart disease or a prior health condition, talk with your doctor before starting this or any exercise program. Start gradually, and pay attention to your body. You may be surprised by how good you feel after a HIIT session, since this type of workout requires focus and can act as a distractor from stress. Perhaps knowing that that you will still burn calories after you finish your workout may put a positive spin on the rest of your day.

High Intensity Interval Training A better way to exercise