Survival of the Fittest

by Paul Rogers on July 1, 2009

Pic - Flickr - sdpitbull

Pic - Flickr - sdpitbull

We all know that exercise and physical activity is good for us: authorities have been belting out the message for decades. Even so, it all gets a little confusing trying to decide how much, what type of exercise, and how to know if you’re doing enough by any measurable parameter.

Now it seems we have some real numbers to work with.

Kodama and colleagues at the Department of Internal Medicine, University of Tsukuba in Japan completed a meta-analysis of cardiorespiratory fitness as a predictor of all-cause mortality and cardiovascular events in healthy men and women. (A meta-analysis combines all relevant studies focusing on a particular outcome and analyses the collective results.) Thirty-three studies were included in the analysis.

Fitness Lowers Heart Attack Risk and Increases Longevity

The results were quite informative, even though these types of observational study cannot provide too much certainty at the detail level. However, we do know that fitness generally has positive, preventive effects on heart disease and some cancer risks, and possibly other longevity factors such as immunity, but this study has given us some practical working numbers in terms of  fitness and performance by age group.

 The researchers classified participants by their measured fitness and aerobic power in terms of METS or metabolic equivalents. A MET is the amount of  energy consumed at rest and 8 METS would be the ability to exercise at 8 times the energy expenditure of sitting still, or the ‘resting metabolic rate’. Participants were categorized as low cardiorespiratory fitness (CRF) (less than 7.9 METs), intermediate CRF (7.9-10.8 METs), or high CRF (greater than or = 10.9 METs).

Here are the results:

  1. Compared with participants with high CRF, those with low CRF had a relative risk for all-cause mortality of 1.70; and for CHD/CVD events of 1.56. 
  2. Compared with participants with intermediate CRF, those with low CRF had a relative risk for all-cause mortality of 1.40 and for CHD/CVD events of 1.47

Those risk numbers, 1.70 and 1.56, for example, describe the increase in risk comparing those with lower fitness (1.70, 1.56) to those with higher fitness 1.0, 1.0). You can see that as you get fitter, your risks of a heart event (heart attack or stroke or similar) or death decrease rather dramatically. Or, you can look at it the other way around: the less fit you are, the greater your risks of a heart event or death compared to a much fitter person.

What This Means in Practical Terms

 Why this study is so useful is that the authors interpreted the results in language  that is explanatory to non-specialists. For example, the minimum cardiorespiratory fitness level that seems to be protective is 9 METs for men at age 40, 8 METs for men at age 50, and 7 METs for men at age 60. For women, it is 7 METs at age 40, 6 METs at age 50, and 5 METs at age 60.

To translate this into walking or jogging speeds, based on Kodama’s data, the speeds would be (in miles or kilometres per hour):

8 METS — 4 mph or 6.4 kmh (very fast walk)

10 METS — 5 mph or 8.0 kmh (slow jog)

12 METS — 6 mph or 9.6 kmh (jog)

If, at 60, you can do 6 miles or 10 km in an hour (12 METS), then you are in the super fit category, because this would even be highly protective fitness for a 40-year old — according to the data from this study.

This is encouraging for people who are not really into hard-core fitness programs. You do have to be fit to walk at 8 METS for an hour, but not exceptionally so. A regular walking program will likely see you achieve this performance well past age 60. For comparison, an amateur fun runner or marathon runner can run at 15 to 18 METS for an hour, and professional endurance athletes at up to 25 METS. 

Add a few sessions of weight training per week for muscle maintenance — at home will do — to your regular walking or jogging, and you can see that keeping fit needs commitment, but it does not have to be too onerous.

– Satoru Kodama; Kazumi Saito; Shiro Tanaka; at al. Cardiorespiratory Fitness as a Quantitative Predictor of All-Cause Mortality and Cardiovascular Events in Healthy Men and Women: A Meta-analysis JAMA, May 20, 2009; 301: 2024 – 2035.

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