A more reasonable look at exercise guidelines

We are going to revisit the exercise guidelines because there is a new meta analysis in JAMA of Leisure Time Physical Activity and Mortality: A Detailed Pooled Analysis of the Dose-Response Relationship that tries to answer the question of how much training is optimal in a more precise way. As we discussed previously, the official exercise recommendations can be hard to understand from an amateur or elite athlete's perspective. Training at that level is not focused on health benefits per se, but on improving performance. The problem lies in the rough dichotomies for both time and intensity in the guidelines. For example:

"Adults aged 18–64 should do at least 150 minutes of moderate-intensity aerobic physical activity throughout the week or do at least 75 minutes of vigorous-intensity aerobic physical activity throughout the week" (WHO exercise guidelines 2010)

In my previous post we saw that I managed 164 minutes per week on average over a two year period including about 20% strengthening that should be counted separately. If we work that out, it is about 132 minutes aerobic training (mostly judo) and 32 minutes strength training per week. That is enough exercise if we count judo as a vigorous activity, which seems reasonable. However, we note that it does not reach the optimum of 300 minutes of moderate-intensity or 150 minutes of vigorous-intensity exercise plus two sessions of strength training per week. At the same time it is at the top level of recreational judo. So, something is not quite right.

The first problem we will tackle is the amount of exercise. The best way of measuring physical activity is using prospective logging. That is, each participant maintains a detailed log of all activities, usually for a week. This measure corresponds well with energy expenditure measured using doubly labelled water. However, for the kind of large epidemiological studies used to base the exercise guidelines on that is too much work. Instead they rely on seven-day recall questionnaires, which basically means asking the participants what they did last week hour by hour. This is a poor estimate of actual exercise but an acceptable measure for comparing different groups of people or the same people at different time points. As expected people tend to over estimate their physical activity using the recall method. One study found an average under estimation of 40% for total duration of exercise but a massive four-fold over estimation of vigorous exercise using recall instead of logs. The result was a 70% over-estimate of exercise amount when corrected for intensity. In addition, being part of a study means that logged exercise will probably be larger than exercise during an average non-logged week. Importantly, any of the methods will probably over estimate the average amount of exercise compared to a long-term exercise log, which includes vacations, injuries, and general laziness. Anyway, this is an important part of the reason why the guidelines basically give two intervals for training amount: Less than 150 minutes/week is bad for you, and more than 150 minutes/week is good for you.

Our second scab to pick is the intensity, which is dichotomised to moderate or vigorous both in the guidelines and in the original publications. Moderate is walking or bicycling in a brisk pace, but not strenuously. Vigorously is anything more intensive than walking or bicycling, for example jogging or swimming. Behind this artificial dichotomy lies the actual activities and in research about physical activity the intensity of different forms of exercise is quantified in metabolic equivalents or METs. The number of METs that an activity has is determined by how many times the resting energy expenditure the activity consumes. Using the kind of exercise and the number of hours we can then calculate an amount of exercise corrected for intensity. This is called MET-hours, that is the number of hours of exercise at a given MET-intensity. The minimum exercise in the guidelines correspond to 7.5 MET-hours per week, and the higher goal for additional benefits is accordingly 15 MET-hours/week.

Using the Compendium of physical activities we can calculate how many MET-hours my training actually corresponds to. Judo has a MET of 10 and weightlifting 6. This works out to 22 MET-hours Judo and 3 MET-hours strengthening for a total of 25 MET-hours, which is satisfyingly above the goal for maximum benefit.

Figure 1 adapted from Leisure Time Physical Activity and Mortality: A Detailed Pooled Analysis of the Dose-Response Relationship by Hannah Arem and co-workers, JAMA Internal Medicine 6 Apr 2015.

Finally, we can get back to the new analysis. What they did was go back to the original data and use the MET-hours recorded for each participant at leisure-time physical activity (i.e. exercise). This was then compared to the risk of death for different amounts of intensity corrected exercise. In figure 1 we can see that we can lower our risk of death by up to 40% by training more than 22 MET-hours per week and less than 75 MET-hours per week. However, we also see that the dichotomy holds. If we train at least 7.5 MET-hours per week we get the bulk of the benefit.

We can conclude that how long we, or our patients, should train depends very much on the type of training. When using these guidelines, even with correction for type of training, we should remember that they are based on reducing the risk of death. They are not meant to help you improve performance, certainly not at the serious amateur or elite level. Finally, while we can understand the reasoning behind making the guidelines as easy as possible, it would be useful to explain how to grade different forms of exercise quite early in the actual guidelines instead of leaving it to the reader to find in original sources.

Books for anaesthesiology - General textbooks

Having properly started my residency in anaesthesiology and intensive care medicine I have started looking for textbooks to help me.

In my view medicine has four important levels of knowledge: basic science, clinical practice, evidence based medicine, and epidemiology. Clinical practice will be the focus of your general textbook, but each level deserves its own book because the general textbooks are never good enough. For basic science and EBM the demand for detail and precision is much greater, and epidemiology is often ignored completely.

What follows will be a number of book-reviews of books that I have read, which are useful for anaesthesiology residents. If you have any suggestions, please leave a comment.

So far I have these three general anaesthesia books, which I will say something about.

Morgan & Mikhail's Clinical Anesthesiology (2013, 5 ed. edited by John F. Butterworth IV, David C. Mackey and John D. Wasnick), which is actually available in electronic form through the university library. It's an easy read, unless you are easily annoyed by typos and trivial errors. Instead of references it has suggested reading, which is a mix of reviews, book-chapters and original research. To say that it lacks depth is to state the obvious, but it seems to reflect the state of clinical anaesthesia fairly well.

With that I mean that there is sufficiently scarce evidence that the personal opinion and experience of the individual mentor makes huge differences in how and what you are taught. It is a bit annoying, because you spend a couple of weeks with one specialist behind you, until they are confident to let you run things. Then you change to the next specialist, and they basically think you are insane.

Anestesi (2005, 2 ed. edited by Matts Halldin and Sten Lindahl), a swedish textbook, which is helpful for some practices that are more specifically swedish, and it is generally a good book. Not very thick though, so rather basic.

Anestesikompendium (2004, 8 ed. edited by Rainer Dörenberg), the pocket reference produced by the department in Uppsala. It's brilliant for working in Uppsala for obvious reasons, and includes important practical knowledge like which syringes to use for which drugs, and pre- and postoperative guidelines for different operations and different post-op wards at the hospital.

This early in the residency I am in a read and re-read mode for trying to remember and understand the different anaesthetic regimens and why different specialists prefer different ways of doing things, so it is a good thing to have a couple of books to compare. However, in many cases where practice is significantly different between different specialists they give no, or little guidance, which is why I am seriously considering getting a more complete work. Like 500 pages thicker Clinical Anesthesia by Barash and coauthors, or the two-volume over three thousand pages thick Miller's Anesthesia. In addition there are more specific books covering specific subfields of which I will write more later when I have had time to read them.