Let's face it, if exercise was really that much fun, everybody would do it and we wouldn't be fat, diabetic or die of heart disease. So when your doctor tells you that you better start exercising, your immediate question might be: how much do I have to do? The answer is, it depends. It depends on whether you want to hear the polite version or the truth.
The polite version goes something like this: As long as you do some exercise, you will see some health benefits. When your doctor gives you this advice, he probably has studies in mind like the one performed by Hamer and colleagues [1]. They show us that as few as 1-2 exercise sessions per week protect against heart disease. I don't really buy it, and neither should you. Here is why:
The researchers took data from 23,747 people of the English and Scottish health surveys and grouped them into one of two groups, depending on the status of their metabolic health. The latter was defined along the risk markers of high blood pressure, low good cholesterol, diabetes status, high waist circumference and inflammatory status. People who had less than 2 of those risk factors made it into the metabolically healthy group, the rest into the unhealthy group.
Since these surveys had also asked people to self-report their physical activity levels, the researchers were able to investigate, how exercise volume correlates with health outcome. And, lo and behold, over the average follow-up period of 7 years those among the metabolically unhealthy people, who reported exercising just once or twice a week, had the same risk of developing heart disease as the metabolically healthy people. I'm not trying to discredit this study. It is a valid method to look at associations between exercise and health. But we have to keep in mind that it only answers the question whether PA, at this low volume of 1-2 times per week, is associated with heart health. What the study doesn't tell us is, whether this association is of a causal nature. In other words, it really does not tell us whether low-volume PA "...is protective in men and women with clustered metabolic abnormalities" as the authors suggest.
If studies like the one of Hamer and colleagues are used to entice the couch potatoes to pick up exercise, even if it is only once or twice a week, then, by all means, that's a good start. In public health we love this type of message for a simple reason: We can throw it at the media in the hope of encouraging sedentary people to take up exercise. If the message is effective, there will be fewer heart attacks and early deaths. What we deliberately do not tell you, though, is how effective this exercise is for YOU. We have a number for that. It is called the 'number needed to expose' (NNE). It tells you how many couch potatoes need "to be exposed" to a change in exercise habits in order to prevent one single case of heart attack or death. In the case of Hamer's study that number stands at more than 40. Meaning, for every 40 people, which we convince, we can prevent 1 death from any cause. Good for us. But probably not good enough for you. If you take up our advice, the 1 in 40 simply means a 2.5% chance that this avoided death would have been yours. Not very motivating. Which is why you don't read so much about these numbers.
Now, if you were my client, I would ask you, whether you were interested in getting the best out of the limited time you are willing to invest in exercise. Which brings us to the second version of the answer, which I promised you in the beginning of this post: the truth.
Evidence is accumulating that the intensity at which you exercise is far more important for your health than the total volume of exercise. In an earlier post (Shortcut to Longevity) I introduced the results of the Copenhagen City Heart Study, which showed an association between heart disease mortality and the intensity, but not the volume, of habitual cycling. Of course, what applies to the Hamer study, applies to this study too. An association is not necessarily of a causative nature. But if we take it as an indication that exercise intensity is so important, isn't that bad news and bad news for the couch potato? Not only does he have to exercise, he also has to exercise hard? No, this is where the good news are: There is method of milking this high-intensity effect to the point where it saves you oodles of time.
It is called high intensity interval training, or HIT for short. This acronym should get you excited, because it super-charges the benefit:time ratio of exercising. In fact, if done correctly, you can expect to improve your fitness and endurance to the same extent as you would with traditional continuous endurance exercise while spending 90% less time on exercise [2]! But let's take it a step at a time.
What is HIT? As the name implies, HIT sessions consist of alternating intervals of vigorous and moderate intensity exercise. One-minute intervals of sprinting, interspersed with 3 minutes of jogging at a moderate pace, would be one of a virtually infinite number of variations of HIT. Do this for 16 or 20 minutes thrice a week and I promise you, within 2 weeks, you'll be excited about the noticeable progress you make. That's 60 minutes a week! Should be possible for the tightest of time budgets. After all, time is the most often cited obstacle to taking up exercise. Understandably, because there are only 24 hours in a day, of which statistically, every German spends 4 hours in front of the TV and every American 6 hours. Which really leaves us so little time to do something meaningful, aside from working and sleeping. If that comes across as sarcastic, I'm guilty as charged.
Anyway, I haven't answered the next logical question, whether HIT also translates into real health benefits. You bet it does. In fact those benefits are so profound, that even heart attack and heart failure patients are now being put on HIT routines. Wisloff and colleagues randomized 27 heart failure patients into 3 training groups [3]: a HIT group which walked three times a week four 4-minute intervals at close to maximal heart rate, with 3-minute intervals of walking at 50% to 70% of maximal heart rate between the high intensity intervals; a moderate-intensity exercise group which walked thrice weekly continuously for 47 minutes at 70% to 75% of maximal heart rate; and a control group which met every 3 weeks for a 47-minute walk. After 12 weeks, the control group showed no improvement in fitness, measured as maximal oxygen uptake. The moderate-intensity group had improved fitness by 14%, whereas the HIT group, which had spent 50% less time on exercise, had an improvement of 54%. Moreover HIT improved arterial function, cholesterol and heart function, significantly better than the continuous moderate-intensity exercise protocol.
In another study, diabetics were put on a HIT protocol consisting ten 60-s sprints interspersed with 60-s moderate-intensity cycling. After only 6 sessions, participants' glucose metabolism had improved substantially and so had their muscles' oxidative capacity [4]. Unfortunately, this study was not controlled, meaning there was no control group to compare the relative benefits of HIT vs. continuous moderate intensity exercise. Which shows, we are still in the early days of finding our ways to optimal protocols for different people with different health issues.
In my lab, we wanted to know whether the high benefit:time ratio of HIT, together with its quickly noticeable results, would entice couch potatoes to do more than a prescribed weekly minimum of three 20-minute hit sessions. After 6 months 76% of our 120 study participants had acquired the habit of exercising more than 150 minutes per week. When they started on our program they had all been sedentary and mostly overweight, but they were otherwise healthy. Over the 6 months they not only improved their fitness substantially but also reduced their weight and improved their risk factors for heart diseases and diabetes [5].
I prefer telling a couch potato that, to gain a health benefit, (a) he or she has to do exercise, that (b) the exercise has to be of sufficient intensity, and that (c) this benefit can be his or hers at a modicum of time spent on exercise. I prefer that to making polite noises about the benefits of very little exercise, no matter what intensity and volume, because the benefit I would be talking about wouldn't be the benefit she or he is thinking of.
In the next post I will show you how to design your own HIT routine, how to find the optimal intensities and what to keep in mind when you bring such a routine into a hitherto sedentary life.
Seeing you again coming Monday.
1. Hamer, M. and E. Stamatakis, Low-Dose Physical Activity Attenuates Cardiovascular Disease Mortality in Men and Women With Clustered Metabolic Risk Factors. Circulation: Cardiovascular Quality and Outcomes, 2012.
2. Kent, W., The effects of sprint interval training on aerobic fitness in untrained individuals: a systematic review. British Journal of Sports Medicine, 2011. 45(15): p. A8.
3. Wisloff, U., et al., Superior cardiovascular effect of aerobic interval training versus moderate continuous training in heart failure patients: a randomized study. Circulation, 2007. 115(24): p. 3086-94.
4. Little, J.P., et al., Low-volume high-intensity interval training reduces hyperglycemia and increases muscle mitochondrial capacity in patients with type 2 diabetes. Journal of Applied Physiology, 2011. 111(6): p. 1554-1560.
5. Kraushaar, L., Improving the Efficiency of Lifestyle Change Interventions for the Prevention of Cardiometabolic Disease, in School of Public Health Medicine2010, University of Bielefeld: Bielefeld. p. 239.
Hamer, M., & Stamatakis, E. (2012). Low-Dose Physical Activity Attenuates Cardiovascular Disease Mortality in Men and Women With Clustered Metabolic Risk Factors Circulation: Cardiovascular Quality and Outcomes DOI: 10.1161/CIRCOUTCOMES.112.965434
Kent, W. (2011). The effects of sprint interval training on aerobic fitness in untrained individuals: a systematic review British Journal of Sports Medicine, 45 (15) DOI: 10.1136/bjsports-2011-090606.26
Wisloff, U., Stoylen, A., Loennechen, J., Bruvold, M., Rognmo, O., Haram, P., Tjonna, A., Helgerud, J., Slordahl, S., Lee, S., Videm, V., Bye, A., Smith, G., Najjar, S., Ellingsen, O., & Skjaerpe, T. (2007). Superior Cardiovascular Effect of Aerobic Interval Training Versus Moderate Continuous Training in Heart Failure Patients: A Randomized Study Circulation, 115 (24), 3086-3094 DOI: 10.1161/CIRCULATIONAHA.106.675041
Little, J., Gillen, J., Percival, M., Safdar, A., Tarnopolsky, M., Punthakee, Z., Jung, M., & Gibala, M. (2011). Low-volume high-intensity interval training reduces hyperglycemia and increases muscle mitochondrial capacity in patients with type 2 diabetes Journal of Applied Physiology, 111 (6), 1554-1560 DOI: 10.1152/japplphysiol.00921.2011
