Lack of time is the most often cited excuse for not exercising. I deliberately chose the word "excuse" over its less judgmental alternative "obstacle". Simply because I cannot see an "obstacle" when I compare two simple metrics: the hours people spend watching TV and the minutes needed to maintain one's health with exercise. With high intensity interval training, or HIT, health enhancing exercise can be compressed into an amazingly short amount of time. When done right. [tweet this].
According to the Nielsen "Three Screen Report" Americans spend 5.1 hours daily in front of their TV. But they admit to "only" half that time, according to a survey of the Bureau of Labor Statistics. To be fair, I take the survey's figure of 2.7 hours for the comparison with the American College of Sports Medicine (ACSM) current guidelines for quantity and quality of exercise . The ACSM's recommendations of 2.5 hours exercise PER WEEK vs. 2.7 hours in front of the TV PER DAY. Cut your 162 minutes of daily TV watching by just 21 minutes, and it still leaves you with more than 2 hours for mind numbing soaps.
On a cautionary note to my fellow German readers: don't think for one minute that our TV habits are in any way better than those of our U.S. friends. According to statista's "Daten & Fakten zur Mediennutzung" we spend on average 220 minutes in front of the dumb tube. So, either we have, for once, outdone our U.S. friends, or their self-admitted 2.7 hours are an understatement. Anyway, those figures tell you why I talk about excuses and not obstacles.
But I'm a realist. Whatever my view on the issue of having time, it won't change other people's views. Which is why my colleagues in public health have begun to look into ways of how to get the same health punch out of dramatically shorter exercise routines. And, as I mentioned in my previous post, the solution might have been found. It is called high intensity interval training, or HIT.
HIT is an exercise routine, which consists of brief bouts of vigorous activity, alternating with "active recovery" periods of more moderate intensity. Until very recently, researchers focused on the comparison of HIT with the conventional continuous endurance exercise of moderate-to-vigorous intensity, which is what those public health guidelines are all about. Most studies comparing those two exercise alternatives matched them for energy expenditure. Since energy expenditure is higher during the intense bout the overall time needed to expand the same amount of energy is shorter in HIT than in continuous exercise.
Latest research efforts, however, try to answer the question whether those high-intensity bouts might even compensate for an overall lesser energy volume. In other words, could we reduce not only the time spent on exercise but also the total exercise volume simply by doing HIT? Which means, reducing the time required for doing exercise even further? The latest study, conducted by Katharine D. Currie and her colleagues seems to suggest just that . Before I go into the details, let me explain why I find her line of investigation very appealing and important.
The overall purpose of exercise is to maintain functional health. The reason why exercise is key to human functional health is because humans are made to move. Only, today they don't move anymore. That's why my primary interest in exercise is about its link to health. Anything else, such as weight loss, is secondary. Because, if I can improve health by exercising, I have achieved my objective. Regardless of whether weight loss has materialized as a side effect or not. Weight loss for its own sake without any improvement in health is a purely cosmetic issue, which doesn't interest me that much.
One of the main health issues attached to exercise is arterial function. It's impairment is the first step that leads to atherosclerotic plaque build-up in your arteries and ultimately to heart attack or stroke. The entire process typically lasts decades, and our current portfolio of risk factors, such as high cholesterol, alert us way too late to this situation. I have written about this in my earlier post "When Risk Factors For Heart Attack Really Suck". Which is why I believe that arterial function is THE benchmark for testing the efficacy of exercise: It's an extremely sensitive early warning signal and a reliable tool to measure the effect of your exercise efforts. This is what Currie and colleagues had in mind. They wanted to see how a low-volume HIT routine affected the arterial function and fitness of 10 participants with existing heart disease.
Participants were tested individually for their fitness on a cycle ergometer. The researchers used the results of the fitness test to set the parameters for the two exercise routines, which all participants had to perform. The endurance protocol was set at 55% of each participant's peak power output as determined during the fitness test. In the endurance exercise bout, participants had to cycle at this intensity for 30 consecutive minutes.
The HIT protocol consisted of 10 1-minute bouts of exercise at 80% of peak power output, separated by 1-minute bouts at 10% of peak power output. That's 30 minutes of continuous exercise vs. 19 minutes of HIT, not considering warm-up and cool-down which were the same for both protocols.
Interestingly, while all participants completed the HIT protocol, 2 participants were unable to last through the endurance protocol. Arterial function improved after both exercise protocols similarly, despite the fact that the total work performed in the endurance protocol was significantly greater than in the HIT protocol.
Now, 10 participants is a rather small number of subjects for such a study. The problem with a small number is insufficient statistical power to detect a difference in arterial function between the two protocols, if there was a difference. Which is why we will be looking forward to seeing larger trials investigating this question using more participants.
The researchers also show one thing which is always close to my heart but which is rarely reported in study publications: the very different outcomes between individuals. After the endurance exercise one participant saw a dramatic improvement in arterial function, 4 participants had a more modest improvement, and the remaining 5 no improvement. Following the HIT routine, there were 2 participants with a dramatic improvement of arterial function, 2 with a more moderate improvement, 1 whose arterial function actually got worse and the remaining 5 with no change. Unfortunately the researchers do not tell us whether those who improved or didn't improve in one routine showed corresponding effects in the other routine. My guess is, for at least some of the participants, the reaction will have been different. But even if that was not the case, we can see again, that the presentation of group results masks the fact that different people react very differently to the same type of intervention. I have presented an example of this effect in my earlier post "Am I shittin' you? Learn to be a skeptic".
A similar degree of inter-individual difference was seen in a study which used the same protocol of low-volume HIT, but this time on healthy sedentary adults. The question was whether 2 weeks of performing the HIT routine 3 times per week would improve the participants' ability to burn fat instead of carbohydrates. This so called oxidative capacity is a marker of metabolic health and gives you a clue about your diabetes risk. True enough, the results support the idea, that this minimal amount of exercise can substantially improve metabolic function. But again, the wide standard deviation of the group results points at substantial differences between the individuals .
These inter-individual differences make prescription of exercise always a trial-and-error effort. As much as you would like to hear from your coach or doctor that a specific type of exercise will have a specific effect on your health, nobody can give you that certainty. In fact, if you encounter a coach who talks certainty, you know a coach whose knowledge is too limited to make him recognize his own limitations. That's something to be wary about.
Now, what if you would like to try HIT for yourself? How would you design a HIT routine? Before I give you a few pointers, let me warn you first: Do not take my advice as a medical recommendation. You follow it at your own risk. If you have been sedentary, and you have any doubt as to whether exercise at high intensity is good for you, seek medical advice first.
Obviously the best way of designing a maximally effective HIT routine is to go through a fitness test first. Ideally, one which tests things like your maximal oxygen consumption. The gold standard is the cardiopulmonary exercise test during which gas exchange is measured together with heart rate or ECG. The measured values will allow your coach to tailor the intensity of the intervals to maximum effect. But there is a simple do-it-yourself way, too. Here is how it works:
In exercise research we know that people's perception of exertion correlates quite reliably and closely with biomarkers of exertion (e.g. heart rate, oxygen consumption). We call this subjective perception the "rate of perceived exertion" or RPE. And we have scales for you to express this RPE. The most commonly used one is the Borg scale of perceived exertion. I personally prefer the OMNI version because its 0-10 scale is so much more intuitive than Borg's 6-20 scale.
The picture to the right is a copy of the OMNI scale.
It doesn't matter whether you run or cycle or do any other type of endurance exercise. What you would describe as "extremely hard" (9-10) is the most strenuous intensity at which you can currently perform your exercise. Regardless of your personal maximal oxygen capacity. That means, an Olympic marathon runner has his 100% max at 10 and so do you as a couch potato. Even though both of you have vastly different capacities. Since we want to exercise at 80% of that capacity it doesn't matter what it's absolute value is. The only thing that matters is that we hit the 80%. Which is what these scales are so good for.
At the left end (0) of the scale you find the descriptor "extremely easy", which is the way you would describe an exercise that you could perform for very long durations without any distress. The point is to get your exercise intensity during the high-intensity intervals to where you would describe the feeling as "hard", that is, at a 7-8 out of 10. That point correlates pretty closely with the 80-85% of maximal effort used by the researchers. The period of active recovery, which separates two high-intensity intervals, should get you to a perception in the range of 4-6.
Keeping this scale in mind you can now perform your own interval training with whatever exercise you fancy, whether its cycling, running, skating, swimming, or whatever. From experience with our own study participants I find a HIT routine of 1-minute high-intensity intervals, separated by 4-minute active recovery intervals, the most agreeable to start with. If that's too tough, cut the high-intensity interval down to 45 or 30 seconds. Try to get 3 to 4 high interval bouts into one exercise. And don't be frustrated if initially you can manage only two. Do this 3 times a week, always with one day between 'HIT days', and you'll find your fitness level responding very fast to this minimal effort. Increasing this effort will be no problem. You can play around with different ways of doing that. Shortening the active recovery period is one way. Stringing more intervals into your exercise bout is another. The variations are limitless.
If there is one particular biomarker which you want to improve, be it blood pressure, blood sugar or arterial function, get it tested before you start and then a couple of weeks after you have persisted with the weekly HIT routine. To see the health effects of your efforts can be a strong motivator to go on, or to do even more. To get from 20 minutes three times a week to 20 minutes daily will be a huge improvement. It still leaves you with plenty of TV time, and probably with enough time to wonder how you could have ever thought of time being an obstacle to exercise.
You'll probably not be tempted to do what I did 10 years ago: I threw out my TV and never replaced it. Which is why I can now work, study, exercise and write a blog. Which also means that to compensate for my zero TV time, somebody must spend a lot longer in front of the TV than the average 2.7 hours. Could that be you? Or someone you know, who would benefit from reading this? [tweet this].
1. Garber, C.E., et al., Quantity and Quality of Exercise for Developing and Maintaining Cardiorespiratory, Musculoskeletal, and Neuromotor Fitness in Apparently Healthy Adults: Guidance for Prescribing Exercise. Medicine & Science in Sports & Exercise, 2011. 43(7): p. 1334-1359 10.1249/MSS.0b013e318213fefb.
2. Currie, K.D., R.S. McKelvie, and M.J. Macdonald, Flow-Mediated Dilation Is Acutely Improved following High-Intensity Interval Exercise. Medicine and Science in Sports and Exercise, 2012.
3. Hood, M.S., et al., Low-volume interval training improves muscle oxidative capacity in sedentary adults. Medicine and Science in Sports and Exercise, 2011. 43(10): p. 1849-56.
Currie KD, McKelvie RS, & Macdonald MJ (2012). Flow-Mediated Dilation Is Acutely Improved following High-Intensity Interval Exercise. Medicine and science in sports and exercise PMID: 22648341
Hood MS, Little JP, Tarnopolsky MA, Myslik F, & Gibala MJ (2011). Low-volume interval training improves muscle oxidative capacity in sedentary adults. Medicine and science in sports and exercise, 43 (10), 1849-56 PMID: 21448086