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Interval Training - HIIT or Miss?

Mike Boyle explains how to carry out high-intensity Interval Training (HIIT).

Every fat loss article we read espouses the value of interval training for fat loss. HIIT (for high-intensity Interval Training) is thrown around so much that many people assume they know what it is. However, among all the recommendations I see to perform HIIT, very few articles contain any practical information about what to do or how to do it.

Two different processes converged to understand that I might be a fat loss expert and not know it. In my method of professional reading, I read both Alwyn Cosgrove's Afterburn and Craig Ballantyne's Turbo Training. What struck me immediately was that what these experts recommending for fat loss looked remarkably like the programs we used for conditioning. When I was reading these programs, I was also training the U.S. Women's Olympic Ice Hockey team members. It seemed all of the female athletes I worked with attempted to use steady-state cardio work as a weight loss or weight maintenance vehicle. I was opposed to this idea as I felt that steady-state cardiovascular work undermined the strength and power work we were doing in the weight room.

My policy became "intervals only" if you wanted to do extra work. I did not do this as a fat loss strategy but rather as a "slowness prevention" strategy. However, a funny thing happened. The female athletes we prevented from doing steady-state cardiovascular work also became remarkably leaner. I was not bright enough to put two and two together until I read the manuals mentioned above and realized that I was doing what the fat loss experts recommended. We were on a vigorous strength program, doing lots of intervals.

With that said, the focus of this article will be not why but how. How do I perform HIIT? To begin, we need to understand what interval training is? In the simplest sense, interval training is nothing more than a method of exercise that uses alternating periods of work and rest. The complicated part of interval training may be figuring out how to use it. How much work do I do? How hard should I do it? How long should I rest before I do it again?

Interval training has been around for decades. However, only recently have fitness enthusiasts worldwide been awakened to the value. The recent popularity of interval training has even given it a new name in the literature. Interval training is often referred to as high-intensity Interval Training (HIIT), and it is now the darling of the fat loss and conditioning worlds. The truth is, you can also do low-intensity interval training. Most people should not start with HIIT but LIIT. HIIT may make you vomit if you do not work into it.

Research Background

A recent study by Gibala et al. (2006)[1], done in Canada at McMaster University and often referenced as the Gibala Study after lead researcher Martin Gibala, compared 20 minutes of high-intensity interval training, consisting of a 30 second sprint followed by a four-minute rest, with 90 to 120 minutes in the target heart rate zone. The result was amazing. Subjects got the same improvement in oxygen utilization from both programs. What is more surprising is that the 20-minute program only requires about two minutes and 30 seconds of actual work.

A second study by Tabata et al. (1996)[2] that has become known as the Tabata study again shows the extreme benefits of interval training. Tabata compared moderate-intensity endurance training at about 70% of VO2 max to high-intensity intervals done at 170% of VO2 max. Tabata used a unique protocol of 20 seconds work to 10 seconds rest done in seven to eight bouts. This was a series of 20-second intervals performed for four minutes. Again, the results were nothing short of amazing. The 20/10 protocol improved the VO2 max and the anaerobic capabilities more than the steady-state program.

Swain (2006)[3] stated, "running burns twice as many calories as walking." This is excellent news for those who want to lose body fat. I am not a running advocate, but we can rest another high-intensity (running) versus low-intensity (walking) debate.

Let us look at the maths. Swain states that a 136-pound person walking will burn 50 calories/mile and proportionally more as the subject's weight increases. In other words, a 163-pound person would weigh 20% more and, as a result, burn 20% more calories. This means that expenditure goes from 50 to 60 calories, also a 20% increase. Swain states that running at seven mph burns twice as many calories as walking at four mph. This means a runner would burn 100 calories in roughly eight and one half 8.5 minutes or about 11 calories a minute. At four miles per hour, the walker would burn 50 calories in 15 minutes (the time it would take to walk a mile at four MPH). That is less than four calories per minute of exercise. Please understand that this is less a testament for running and more a testament for high-intensity work versus low-intensity work. More intensity equals higher expenditure per minute.

Interval Training Methods

There are two primary ways of performing interval training. The first is the conventional Work to Rest method. The first is the conventional Work to Rest method, a logical approach. The Work to Rest method uses a set time interval for the work period and a set time interval for the rest period. Ratios are determined, and the athlete or client rests for generally one, two or three times the length of the work interval before repeating the next bout. The big drawback to the Work to Rest method is that time is arbitrary. For many years, we have always guessed as we had no other "measuring stick." We have no idea what is happening inside the body.

Heart Rate Method

With the mass production of low-cost heart rate monitors, we are no longer required to guess. The future of interval training lies with accurate, cheap heart rate monitors. We no longer look at time as a measure of recovery, as we formerly did in our rest to work ratios. We are now looking at physiology. What is important to understand is that heart rate and intensity are closely related. Although heart rate is not a direct and flawless measure of either intensity or recovery status, it is far better than choosing a time interval to rest. To use the heart rate method, choose an appropriate recovery heart rate. We use 60% of the theoretical max heart rate in our case. After a work interval of a predetermined time or distance is completed, the recovery is set by the time it takes to return to the recovery heart rate. When using the HR response, the whole picture changes. Initial recovery in well-conditioned athletes and clients is often rapid and shorter than initially thought.

Rest to work ratios may be less than 1-1 in the initial few intervals. An example of a sample workout using the heart rate method for a well-conditioned athlete or client is shown below.

  • Interval 1 - Work 60 seconds rest 45 seconds
  • Interval 2 - Work 60 seconds rest 60 seconds
  • Interval 3 - Work 60 seconds rest 75 seconds
  • Interval 4 - Work 60 seconds rest 90 seconds

In a conventional 2-1, time-based program, the rest period would have been too long for the first three intervals, rendering them potentially less effective. The reverse may be true in a de-conditioned athlete or client. I have seen young, de-conditioned athletes need to rest up to eight times as long as the work interval. We have seen athletes who need two minutes of rest after a 15second interval. In the heart rate method, the rest times gradually get longer. The first interval is 1-.75 while the last interval is 1 to 1.5,

The Problem with Formulas

The 220 minus age formula is flawed on two key points: it does not fit a significant portion of the population and is not based on research. At least 70% of the population does not fit into our age-old theoretical formulas. Even the developer of the now-famous formula admits that his thoughts were taken out of context. The more accurate method is called the Heart Rate Reserve Method or the Karvonen formula.

Karvonen Formula

  • (HRmax- HRrest) x %+ HRrest= HRtarget
  • (200-60) x.8 +60 = 172

The key to the Karvonen formula is that it looks at more significant fitness measures by incorporating the resting heart rate and is, therefore, less arbitrary. However, the two twenty minus age formula will suffice for establishing recovery heart rates.

Interval Training Basics

The longer the interval, the shorter the rest period as a percentage of the interval. In other words, short intervals have a high muscular demand and will require longer rests when viewed as a percentage of the interval. Fifteen-second intervals will need at least a 2-1 rest to work ratio. Three to one will work better for beginners.

Interval Rest Recommendations (Work to Rest Based)

  • 15 sec. Beginners at least 45 sec (3-1), more advanced 30 sec (2-1)
  • 30 sec. Rest 1:00 to 1:30 (3-1 or 2-1)
  • 60 sec. Rest 1:00- 2:00 (2-1 or 1-1)

Just remember, as the intervals get longer, the recovery time may not need to be as long as it relates to the interval. In other words, a fifteen-second sprint may require a 30-45 seconds rest, but a two-minute interval may only need to be followed by a two-minute rest.

Aerobic Intervals?

As the Gibala study demonstrated, you can get superior benefits for both fitness and fat loss by incorporating interval training. The most significant advantage of interval training is that you can get a great aerobic workout without the boredom of long steady-state bouts of exercise. If the heart rate is maintained above the theoretical 60% threshold proposed for aerobic exercise, the entire session is aerobic and anaerobic. This is why my athletes do almost no "conventional" aerobic training. All of our aerobic work is a by-product of our anaerobic work. My athletes or clients can get their heart rate in the recommended aerobic range for 15 to 20 minutes, yet in some cases, they do only three to minutes of actual work.

Modes of Interval Training

Although most people visualize interval training as a track and field concept, our preferred interval training method is the stationary bike. Although running is the theoretical "best" mode of training, the facts are clear. Most Americans are not fit enough to run. Statistics estimate that 60% of those who begin a running program will be injured. In a fitness or personal training setting, that is entirely unacceptable. Females, based on the genetics of the female body (wider hips, narrower knees) are at potentially even higher risk. Physical therapist Diane Lee says it best in her statement, "You cannot run to get fit. You need to be fit to run."

Interval training can be done on any piece of equipment. However, the most expeditious choice, in my opinion, will be a dual-action bike like the Schwinn AirDyne. The bike allows, in the words of performance enhancement expert Alwyn Cosgrove, "maximum metabolic disturbance with minimal muscular disruption." In other words, you can work hard and not injure yourself on a stationary bike.

Fit individuals can choose any mode they like. However, the bike is the best and safest choice. In my mind, the worst decision might be elliptical trainers. Another noted training expert, Charles Staley, has a concept I believe he calls the 180 Principle. Staley advocates doing precisely the opposite of what you see everyone else in the gym doing. I agree. Walking on a treadmill and using an elliptical trainer seem to be the two most popular training modes in a gym. My conclusion, supported by Staley's 180 Principle, is that neither is of much use.

Interval Training Modes in Detail


  • Maybe the most effective method but also most likely to cause injury
  • Shuttle runs (running to a line and back repeatedly) have both high muscular demand (acceleration and deceleration) and high metabolic demand
  • Running is relative. Running straight ahead for 30 seconds is significantly easier than a 30-second shuttle
  • Shuttle runs produce more muscular discomfort due to the repeated acceleration and deceleration
  • Running for the average gym-goers is impractical as a reasonably large area is needed

Treadmill Running

  • A close second to ground-based running in both effectiveness and unfortunately injury potential.
  • Getting on and off a moving treadmill is an athletic skill and can result in serious injury. Therefore, treadmill interval running is probably not for the average personal training client.
  • Treadmill speeds are deceiving. For example, 10 MPH is only a six-minute mile yet can feel very fast. However, 10 MPH is not a difficult pace for intervals for a well-conditioned athlete.
  • High-quality interval treadmills should be able to go to 15 MPH.
  • For treadmill running, first practice the skill of getting on and off the moving treadmill (the author assumes no responsibility for those thrown on the floor attempting this. You must have room to fall off without striking an immovable object). Do not try this in a standard health club where the treadmills are packed like sardines.

Additional Treadmill Drawbacks

  • Lack of correct active hip extension may undertrain the hamstrings
  • In treadmill running, the belt moves. You stay airborne. Treadmill times do not translate well to running on the ground. This may be due to a lack of ground contact time

Treadmill Recommendations

  • Time-based. Try 15 seconds on with 45 seconds off at 7 MPH and 5% incline
  • For safety, decrease speed and increase the incline
  • Heart rate based (max HR of 200 used, for example). Try a 15-second sprint at 7/5 and rest until the heart rate returns to 120 beats per minute. Rest is rest, do not walk or jog or your heart rate will lower slowly

Stationary Bike

Dual-action bikes like the Airdyne produces a higher HR. This is due to the combined action of the arms and legs. There is no better affordable option than the AirDyne. Although they require periodic maintenance, they are the perfect interval tool as they do not need any adjustments to belts or knobs when interval training. The fan is an accommodating resistance device. This means that the harder you push, the more resistance you get back. Most athletes and clients dislike the large fan AirDynes as they cannot work up a sweat without a windscreen. This is probably the best "safe" tool as it requires limited skill and limited potential for an overuse injury.

Stationary Bike Recommendations

Use the same time recommendations as for the treadmill. For the AirDyne, set the top display to Level. For a well-conditioned male, a 15-second sprint should be level 12-15. Do not go all out, as this will seriously undermine the ability to repeat additional intervals. Well-conditioned female athletes will be Level 8-10 for 15 seconds. Levels should be adjusted down for fitness level and up for body size. Larger athletes or clients will find the bike easier. Large fan AirDynes (older models) will have slightly different work levels than the newer smaller fan models

Slide board

  • Slide boards provide the best "bang for the buck" after the AirDyne. However, in a fitness setting, there is a skill requirement. Clients must be warned that they may fall and potentially be injured. Be sure to inform the client that the board is slippery. I cannot tell you how many clients have stepped on a slide board and remarked: "This is slippery". Remember what they say about assuming.
  • The slide board provides added benefits of standing and getting hip ab and adductor work.
  • Slide boards are also great for groups. No adjustment is needed. You need extra booties. We order four pairs for every board.
  • Safe despite "experts." Some so-called experts have questioned the effect of the slide board on the knees. However, there is nothing more than the anecdotal evidence of a few writers to support this theory.

Climbers and Ellipticals

  • The key to using any climbing device is to keep the hands and arms off of the equipment. This is critical. Put a heart rate monitor on and watch the heart rate skyrocket. If clients complain about lack of balance, slow down the machine and develop the balance but do not allow them to hold on.
  • The StepMill is the least popular, and as Staley points out, the most effective.
  • Conventional Stair climbers are easier to abuse than StepMill. Many users ramp up the speed while allowing the arms to do most of the work. As we mentioned before, keep your hands off the rails.
  • The elliptical machine is the most popular because it is the easiest. Discourage your clients from using an elliptical trainer. If they insist, let them do it on their off days. This is nothing more than human nature at work.

The big key is not what to do anymore but how to do it. Research continues to mount that interval training may improve fitness better than steady-state work. For maximum effect, get a heart rate monitor and go to work.

One warning

Deconditioned clients may need three weeks to a month of steady work to get ready to do intervals. This is OK. Do not kill a beginner with interval training. Begin with a quality strength program and some steady-state cardiovascular work. The only good use for steady-state work in my mind is preparing an athlete or client for the intervals to come.


  1. GIBALA, M.J. et al. (2006) Short Term Sprint Interval Versus Traditional Endurance Training: Similar Initial Adaptations in Human Skeletal Muscle and Exercise Performance", Journal of Physiology, 575 (3), p. 901-911
  2. TABATA, I. et al. (1996) Effects of moderate-intensity endurance and high-intensity intermittent training on anaerobic capacity and VO2 max. Med Sci Sports Exerc, 28 (10) p. 1327-1330.
  3. SWAIN, D. (2006) Moderate or Vigorous Intensity Exercise: What Should We Prescribe? ACSM Health and Fitness Journal, 10 (5) p. 7-11

Page Reference

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  • BOYLE, M. (2010) Interval Training - HIIT or Miss? [WWW] Available from: [Accessed

About the Author

Michael Boyle is a Boston based strength and conditioning coach.