Just as there is an optimum dose for any medicine, to which most people respond, and an overdose which will seriously harm a significant number of people, so too there is a minimum does for exercise and an overdose.
Previously I wrote about exercise non-responders and how, it seems, that everyone responds to some sort of exercise, you need to find the type of exercise that suits you, just as some people respond better to paracetamol and others to ibuprofen. However, there is another factor involved; dose.
The ibuprofen packet tells you to take 2 ibuprofen and then 1 to two after that. That’s because most people respond to that dose (400mg) but the packet also says not to exceed 6 tablets in 24 hours, because above that dose the drug starts to be dangerous.
Similarly, there seems to be an optimum dose for exercise. In a study in the Journal of Physiology scientists divided people into 5 groups. Each group exercised for 60 minutes either 1, 2, 3, 4 or 5 days per week. Some lucky people in the once a week group showed an improvement in their fitness but there were a lot of non-responders in that group. At four days per week, however, the average fitness improvement takes a big leap, compared to the 3-a-week group, and there were no non-responders at all in the 4 and 5 days a week groups.
Then the non-responders from the 1, 2 and 3 sessions per week groups were given an extra 2 days of training per week, i.e. they were now doing 3, 4 and 5 sessions per week. Everyone of the non-responders became responders with the extra 2 days.
So it seems that if exercise came in pill form the dose would be 4 sessions a week, but what about the maximum dose?
Say hello to James O’Keefe, a cardiologist and self-confessed exercise freak, who has a lot to say on the subject of exercise dose in this enlightening TED talk. The same information, published in the British Medical Journal, can be found in written form here.
First of all, it seems that for moderate exercise, like tidying up after the kids, a bit of a stroll or some gardening, has an infinite dose response. The more you move, the longer you’ll live, while the rewards for vigorous activity start to plateau at 50mins per day.
According to O’Keefe, strenuous exercise for more than 30-50 minutes per day begins to damage your heart. There are actually no pain receptors in your heart, so you can be merrily stressing the poor thing and it has no way of telling you!
A trial randomised 60 male patients with CHD to vigorous exercise sessions of either 30 or 60 min. The 30 min exercise workouts improved arterial elasticity and produced minimal oxidant stress. In contrast, the 60min sessions increased oxidant stress and worsened vascular stiffness as measured by pulse wave velocity, particularly in those over the age of 50.
Dr O’Keefe cites many studies showing increased fibrosis in the hearts of marathon runners, increase in coronary plaque in marathon runners and some poor mice, forced to train for the “iron-mouse competition” showing enlarged hearts, scarring and dysrhythmias. He then goes on to discuss mortality vs running distance and exertion.
Two very recent studies presented in abstract form at major national meetings may revolutionise our thinking about running and its health effects. One is a prospective observational study that followed 52 600 people for up to three decades. The 14 000 runners in that study had a 19% lower risk of death compared with the 42 000 non-runners. Yet, when they sub-grouped the runners by weekly mileage, those who ran over 20 or 25 miles per week seemed to lose their survival advantage over the non-runners. On the other hand, those who ran between 5 and 20miles total per week enjoyed a 25% decrease in risk of death during follow-up. The same pattern emerged for speed of running: the fast runners, those running typically over 8 miles an hour, appeared to get no mortality benefit compared with the non- runners, whereas those who fared best usually ran about 6–7 miles per hour—a comfortable jog for most people. In addition, the individuals who ran 6 or 7 days per week appeared to lose the mortality benefits, whereas the survival advantages accrued best for those who ran 2–5 days per week.
As you can see from the graph above, those who ran more than 25miles/week, in terms of mortality, were no better off than couch potatoes.
If you want to win endurance races, then you’re going to have to train long and hard, but if you are exercising for your health then relatively short exercise sessions, no more than 50minutes, about 4 times per week is the way to go and from my point of view, that’s just perfect!