What is High Intensity Interval Training and Why Should I Consider Using It?

This is an exciting topic and relevant to any person who likes to challenge themselves and would like to increase their fitness and lose weight. For those that take it to heart, this type of training is not an easy street. If it came in a box, it would probably have a warning label. In this respect, interval training is an effective means to burn calories, improve fitness and health, but if you haven’t exercised in several years, have a family history of problems, have been diagnosed with some form of condition or experience complications of any kind, you should consult with your physician before progressing to this type of a program.

High-intensity training, otherwise known as HIT or HIIT training has become increasingly popular (6). Traditionally, exercise prescription would suggest an individual who wishes to see cardiovascular benefit (decrease in heart rate, increase in maximal oxygen consumption, decrease in blood pressure, etc.) should train in a continuous fashion. Continuous training infers that you get dialed into your speed on the treadmill or bike and you stay there…continuously. This type of exercise is still extremely popular and prescribed often as it is effective for cardiovascular benefits, metabolic benefits (i.e., improve glucose and insulin status) and can help lead to weight loss (when added to a sound dietary program). It’s also popular because it’s simple meaning it takes less mental effort because you get your intensity dialed in and you stay there. The American College of Sports Medicine (ACSM), a large professional organization that is looked upon as the premier organization devoted to exercise recommends that individuals train continuously for 20 – 60 min at an intensity of 60–80% (1). While effective and still popular, this type of training is “old school” to many people who keep up to date with literature associated with fitness and such.

In the last decade, new information has highlighted the use of interval training as a means to promote positive changes (6). In the simplest of explanations, interval training consists of brief periods of time where the intensity of your exercise is increased to a level that is higher than where you would normally train and then you decrease the interval back down to a level just slightly below where you normally train. In this respect, some could argue that resistance training is interval training, but also participation in sports like soccer, basketball and football all have interval aspects to them. For example, if you like to run on a treadmill at 6.5 mph for 40 min, you could easily adapt this workout to an interval format. The great thing about intervals is by keeping it simple and sticking to the principle of increasing to a higher intensity and then decreasing to a lower intensity; you can develop many different combinations and thus keep your workouts changing and more interesting. In theory, every single workout could be different. Three things are often manipulated: 1) the work: rest ratio, 2) the length of time for each component and 3) the speed/intensity of your intervals. For example, a great place to start is to look at the clock on your treadmill and at the turn of every minute change the speed in a 1:1 fashion or a 1:1 work: rest ratio. So you could go up to 7.5 mph for one minute and down to 6.0 mph for one minute and then back up to 7.5 mph for a minute and back and forth in this manner every minute. This is called a 1:1 work: rest ratio. Your ‘work’ period is at 7.5 mph (where you are ‘working’ harder) and your rest is at 6.0 mph (not true rest, but it’s slower than where you normally workout). You can change your work: rest ratio from 1:1 to 2:1, 3:1, 4:1 or down to 0.5:1. If it’s 1:1 the work and rest proportions are intended to be the same amount of time (1 min and 1 min or 1:1). If it’s 2:1, it’s 2 min of work and 1 min of rest and so forth.

The second area where you can make changes is to change the amount of time of the rest interval (which will then automatically change the work interval). Using our example from before, you could run in a 2:1 work:rest ratio, but instead of making the rest interval one minute make it 3 min. If the rest interval is 3 min, then you will “work” for 6 min because your ‘work’ interval is 2x your rest interval or 2 x 3 min. If it’s a 3:1 ratio you’ll “rest” for 3 min (1 x 3 min) and “work” for 9 min (3 x 3 min). As stated before, a tremendous amount of flexibility can be instilled just by altering these two aspects. In the simplest of terms, the longer your work period is in comparison to your rest period, the more intense your workout.

The last area typically modified with interval training is the speed/intensity at which you establish the intervals. It’s important you understand this is arbitrary. It’s up to you, how hard you want to work, your health status, your fitness status, etc. My recommendation is to pick an upper and lower level that when averaged together is slightly higher than where you normally train. Thus, if you typically run at 7 mph on a treadmill, picking a ‘work’ interval of 8 mph and a ‘rest’ interval of 6 mph would average to 7, so instead pick 8 mph as your ‘work’ or 6.5 mph as your ‘rest’ speed, which averages to 7.25 mph. When you consider you are running at this harder interval for longer periods of time, the average speed of your workout will be a good bit higher than your typical 7 mph.

The combinations are literally hundreds. Fortunately, a good bit of research has been completed here recently and studies have nicely supported this type of training. Hickson and colleagues had eight previously sedentary and recreationally trained folks complete ten weeks of high-intensity exercise training. All individuals trained six days per week and ran one day using high-intensity intervals on a treadmill and cycled the next day using high-intensity intervals. They reported that maximal endurance capacity increased by an average of 44% following this style of training (5). Looking for a change in your same workout time to burn more fat? Essen and associates compared one hour of continuous exercise at 50% maximal capacity to one hour of intermittent (15 s hard, 15 s rest) cycle exercise. Both groups averaged the same amount of work throughout the hour-long exercise bouts, but those who exercised intermittently burned more fat and less carbohydrate (3). Using untrained people, an additional study found that completing five sets of four minute at 100% max capacity followed by two minutes of rest increased the oxidative capacity of the muscle when compared to people who exercised continuously at the same average intensity (2). Finally, continuous and HIT exercise were compared in recreational runners (4). Subjects were matched into three groups: 1) continuous exercise for 26 min, 2) long HIT (four to six, four minute intervals with two minutes of inactive rest) or 3) short HIT (30 to 40, 15 second intervals at a faster speed with 15 seconds of inactive rest). All groups only trained three days per week and exercised at a mean intensity of ~65% maximum heart rate for six weeks. Both continuous and long HIT improved aerobic capacity more than the short HIT group. Also, the time taken to reach exhaustion was actually longer in the continuous group (a 93% increase), but also increased by 67% and 65% for the long and short HIT group, respectively.

I recommend everyone to implement at least one day of interval training into their day. I had lunch with Andy Frisella and his cousin, Scott, the other day. Both of those guys are big guys (220+ lbs plus) and were anaerobic athletes in high school and college. Like many guys, they get light-headed and sick to their stomach thinking about pounding away on a treadmill. I was this way for a long time, but overcame this by doing intervals. Intervals challenge me like resistance training does where I have to go hard for a brief period and then I know a break is coming. It’s a completely different mental scenario that running for block after block on your city streets. The natural competitor in you comes out and I’ve seen it to be a great way for guys to begin doing some more cardio type exercise and burn a few extra calories. The same can be said for women. Intervals are awesome for women who will log hours upon hours on the road, treadmill or elliptical. Not for the entire time, but develop an interval program using this article and I’m sure you’ll find it’s a great new challenge that you have complete control over and makes your old workout something new and exciting. Intensity in all of your workouts is the key to changes. Don’t be afraid to work hard, your body will thank you for it.

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