Interval Training – HIIT or Miss?
By: Mike Boyle
Please note: the following article is based on the lecture, Interval Training done at the Perform Better Summits.
I think every fat loss article we read espouses the value of interval training for fat loss. In fact, the term HIIT (for High Intensity Interval Training) is thrown around so much that many people just assume they know what it is. However, among all the recommendations I see to perform HIIT, very few articles contain any practical information as to what to do or how to do it.
I have to confess that I stumbled into this area somewhat accidentally. Two different processes converged to make me understand that I might be a fat loss expert and not know it. In my normal process 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 were recommending for fat loss looked remarkably like the programs we used for conditioning. At the time I was reading these programs, I was also training members of the US Women’s Olympic Ice Hockey team. 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 diametrically 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 that we prevented from doing steady state cardiovascular work also began to get remarkably leaner. I was not bright enough to put two and two together until I read the above-mentioned manuals and realized that I was doing exactly what the fat loss experts recommended. We were on a vigorous strength program and we were doing lots of intervals.
With that said, the focus of this article will be not ‘why’, as we have already heard the ‘why’ over and over, but ‘how’. How do I actually perform HIIT? To begin, we need to understand exactly 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 around the world 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. Truth is, you can also do low intensity interval training. In fact, most people should not start with HIIT but LIIT. HIIT may make you vomit if you don’t work into it.
In case you have been in a cave for the last decade, let’s quickly review some research. A recent study done in Canada at McMaster University and often referenced as the Gibala Study, after lead researcher, Martin Gibala, compared the following: 1) 20 minutes of high intensity interval training consisting of a 30 second sprint followed by a four-minute rest, with 2) 90 to 120 minutes in the target heart rate zone. The results were amazing. Subjects got the same improvement in oxygen utilization from both programs. What is more amazing is that the 20- minute program only requires about two minutes and 30 seconds of actual work performed.
A second study 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 percent of VO2 max to high intensity intervals done at 170 percent of VO2 max. Tabata used a unique protocol of 20 seconds work to 10 seconds rest done in seven to eight bouts. This was basically a series of 20 second intervals performed during a four-minute span. 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.
Further evidence for the superiority of higher intensity work can be found in the September/October 2006 issue of the ACSM Journal. Dr. David Swain stated, “running burns twice as many calories as walking.” This is great news for those who want to lose body fat. I am not a running advocate, but we can put to rest another high intensity (running) versus low intensity (walking) debate.
Do the math. Swain states that a 136-pound person walking will burn 50 cal/mile and proportionally more as the subject’s weight increases. In other words, a 163-pound person weighs 20 percent more and, as a result, burn 20 percent more calories. This means that expenditure goes from 50 to 60 calories, also a 20 percent increase. Swain goes on to state 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 minutes or about 11 calories a minute. The walker at four miles per hour would burn 50 calories in 15 minutes (the time it would take to walk a mile at four MPH). That’s 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 greater expenditure per minute.
Interval Training Methods
There are two primary ways to performing interval training. The first is the conventional Work to Rest method. This is the tried and true method most people are familiar with. 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. We have no idea what is actually happening inside the body. We simply guess. In fact, for many years, we have always guessed as we had no other “measuring stick.”
Heart Rate Method
With the mass production of low cost heart rate monitors, and the development of systems like MyZone, we are no longer required to guess. The future of interval training lies with heart rate monitors. We are no longer looking 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 simply choosing a time interval to rest. To use the heart rate method, simply choose an appropriate recovery heart rate. In our case, we use 60 percent of theoretical max heart rate. After a work interval of a predetermined time or distance is completed, the recovery is simply set by the time it takes to return to the recovery heart rate. When using HR response, the whole picture changes. Initial recovery in well conditioned athletes and clients is often rapid and shorter than initially thought. In fact, rest to work ratios may be less than 1-1 in the initial few intervals. An example of a sample workout using the heartrate method for a well-conditioned athlete or client is shown below.
- Interval 1 – Work 60 sec rest 45 sec
- Interval 2 – Work 60 sec rest 60 sec
- Interval 3 – Work 60 sec rest 75 sec
- Interval 4 – Work 60 sec rest 90 sec
*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 rest up to eight times as long as the work interval. In fact, we have seen athletes who need two minutes rest after a 15 second interval. In the heart-rate method, the rest times gradually get longer. The first interval is 1 to 0.75 while the last interval is 1 to 1.5.
The Problem with Formulas
At least 70 percent of the population does not fit into our age-old theoretical formulas. The 220 minus age formula is flawed on two key points: it doesn’t fit a significant portion of the population, and it is not based on research. 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 Karvonen formula.
(Max HR- Resting HR) x %+ RHR= THR
Ex- (200-60) x 0.8 +60 = 172
The key to the Karvonen formula is that it looks at larger measures of fitness by incorporating the resting heart rate and is therefore less arbitrary. However, the 220 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. 3-1 will work better for beginners.
Interval Rest Recommendations (Work to Rest Based)
Just remember, as the intervals get longer, the recovery time, as it relates to the interval, may not need to be as long. In other words, a fifteen second sprint may require 30-45 seconds rest but a two minute interval may only need to be followed by a two minute rest.
The biggest benefit of interval training is that you can get a tremendous aerobic workout without the boredom of long steady state bouts of exercises. In fact, as the Gibala study demonstrated, you can get superior benefits for both fitness and fat loss by incorporating interval training. If the heart rate is maintained above the theoretical 60 percent threshold proposed for aerobic training, then the entire session is both 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 minutes of actual work.
Modes of Interval Training
Although most people visualize interval training as a track and field concept, our preferred method of interval training is the stationary bike. Although I think running is the theoretical “best” mode of training, the facts are clear: most Americans are not fit enough to run. In fact, statistics estimate that 60 percent 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 greater risk. Physical therapist, Diane Lee, says it best in her statement, “You can’t 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 Assault Air Bikes or the Schwinn AirDyne. The bike allows, in the words of Alwyn Cosgrove, “maximum metabolic disturbance with minimal muscular disruption.” In other words, you can work really 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 choice might be the elliptical trainers. Charles Staley, another noted training expert, has a concept I believe he calls the 180 Principle. Staley advocates doing exactly the opposite of what you see everyone else in the gym doing. I’m in agreement. Walking on a treadmill and using an elliptical trainer seem to be the two most popular modes of training 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 fairly large area is needed.
- 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 (author assumes no responsibility for those thrown on the floor attempting this. Do not try this in a normal health club where the treadmills are packed in like sardines. You must have room to fall off without striking an immovable object).
Additional Treadmill Drawbacks
- Lack of true active hip extension may under-train the hamstrings.
- In treadmill running, the belt moves, you just stay airborne. Treadmill times do not translate well to running on the ground. This may be due to lack of ground contact time.
- Time based. Try 15 seconds on with 45 seconds off at 7 MPH and 5% incline. For safety, decrease speed and increase incline.
- Heartrate based (max HR of 200 used for example). Try a 15 second sprint at 7/5 and simply rest until the heartrate returns to 120 beats per minute. Rest is rest, don’t walk or jog or your heartrate will lower slowly.
- Dual action bikes like the Assault and the Airdyne produce a higher HR. This is due to the combined action of the arms and legs. There is no better affordable option than the Assault. It is the perfect interval tool as it does 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. This is probably the best “safe” tool.
- Requires limited skill.
- Limited potential for overuse injury.
Stationary Bike Recommendations
- Same time recommendations as for the treadmill. For the Assault simply use RPM’s as a measure of intensity. For a well-conditioned male, a 15 second sprint should be at a level of 70-80 RPM’s. Do not go all out as this will seriously undermine the ability to repeat additional intervals. Well-conditioned female athletes will be at 80 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. AirDynes (older models) will have slightly different work levels than the newer smaller fan models.
- Slideboards (add link) provide the best “bang for the buck” after the Assault. However, in a fitness setting there is a skill requirement. Clients must be warned that they may fall and potentially be injured. This may sound stupid but be sure to inform the client that the board is slippery. I can’t tell you how many clients have stepped on a slideboard and remarked “this is slippery”. Remember what they say about assuming.
- The slideboard provides the added benefits of a standing position and getting hip ab and adductor work.
- Slideboards are also great for groups. No adjustments are needed. You just need extra booties. We order 4 pairs for every board.
- Safe in spite of “experts.” Some so-called experts have questioned the effect of the slideboard 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. Just put a heartrate monitor on and keep the hands of and watch the heartrate skyrocket. If clients complain about lack of balance, slow down the machine and develop the balance but, don’t allow them to hold on.
- The StepMill is the least popular, and as Staley points out, the most effective. Think 180 again. If it’s popular, it’s probably not good.
- Conventional Stairclimbers are easier to abuse than the StepMill. Many users ramp up the speed while allowing the arms to do the majority of the work. As we mentioned before, keep your hands off the rails.
- The elliptical machine is most popular because it is easiest. This is nothing more than human nature at work. Discourage your clients from using an elliptical trainer. If they insist, let them do it on their off days.
Research continues to mount that interval training may improve fitness better than steady state work. The big key is not what to do any more but, how to do it. For maximum effect, get a heartrate 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. Don’t 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.
- Resistance Exercise Reverses Aging in Human Skeletal Muscle.” Simon Melov, Mark Tarnopolsky, Kenneth Beckman, Krysta Felkey and Alan Hubbard PLoS ONE 2(5): e465. doi:10.1371/journal.pone.
- “Short Term Sprint Interval Versus Traditional Endurance Training: Similar Initial Adaptations in Human Skeletal Muscle and Exercise Performance Journal of Physiology Sept 2006, Vol 575 Issue 3.
- Effects of moderate-intensity endurance and high-intensity intermittent training on anaerobic capacity and VO2max. Tabata I, Nishimura K, Kouzaki M, Hirai Y, Ogita F, Miyachi M, Yamamoto K. Department of Physiology and Biomechanics, National Institute of Fitness and Sports, Kagoshima Prefecture, Japan.
- September/October ACSM Health and Fitness Journal. Dr. David Swain Moderate or Vigorous Intensity Exercise: What Should We Prescribe?
About the Author
Michael Boyle is the Co-Founder of Mike Boyle Strength and Conditioning in Woburn, MA. He is known internationally for his pioneering work in the field of Strength & Conditioning and is regarded as one of the top experts in the area for Sports Performance Training.
He has made his mark on the industry over the past 30 years with an impressive following of professional athletes, from the US Women’s Olympic teams in Soccer and Ice Hockey to the Boston Bruins, Boston Breakers, New England Revolution, and most recently the Boston Red Sox.
His client list over the years reads like a “Who’s Who” of athletic success in New England and across the country including legendary Boston names such as Nomar Garciaparra, Cam Neely, and Ray Bourque. He’s served as a Strength & Conditioning Consultant for the 2013 World Champion Boston Red Sox and coached World Champions, National Champions and Olympic Medalists in football, basketball, baseball, soccer, ice hockey, rowing, judo, and gymnastics.
He has been a featured speaker at numerous strength and conditioning and athletic training clinics across the world and has produced over 20 instructional videos in the area of strength and conditioning. He has also lectured all over the world.
Mike and his wife Cindy have 2 children, Michaela and Mark and reside in Reading, MA.