The Cooper Institute
 

Founded in 1970 by the "Father of Aerobics"
Kenneth H. Cooper MD, MPH

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Physical Activity vs. Physical Fitness: Which is More Important?

Posted in
Move more

Monday, Aug 15, 2016

Our everyday health behaviors shape our health future. Since the earliest studies performed over a half-century ago, we’ve known that regular physical activity decreases the risk of premature death from a number of causes. Physical activity (PA) is defined as any voluntary movement produced by skeletal muscles which results in energy expenditure. This includes raking leaves and walking the dog, as well as what you do in a structured formal exercise program. PA is often estimated by using questionnaires; better estimates can be obtained by wearing devices called accelerometers.  Since our level of PA is under our control to a great degree, it is considered a behavior.  Sedentary behavior is among the leading causes of chronic health problems in our society, with only about 20% of adults currently meeting minimal PA guidelines.  

Cardiorespiratory fitness (CRF) is defined as the ability to utilize oxygen at the cell level, and can be measured objectively in a clinical setting via a maximal treadmill exercise test (the gold standard measure). CRF can also be estimated outside of a clinical setting via the 1.5 mile run or 1 mile walk tests. While PA and CRF are related to one another, they are not the same thing. While PA is a behavior, CRF is an objectively measured characteristic. In fact, you may be surprised to learn the correlation between the two is only modest. Some individuals who don’t perform much PA will actually score quite well on an objective measure of CRF. Conversely, some individuals who perform quite a bit of PA will not score nearly as well as expected on a measure of CRF. Most experts feel that genetics is a major reason for these discrepancies that we sometimes see.  

This poses an interesting and important question: In terms of health, which is more important, physical activity or cardiorespiratory fitness? Since cardiovascular disease (CVD) is the leading cause of death in the U.S. for both men and women, Williams (2001) decided to compare PA versus CRF in terms of impact on CVD risk. He carefully examined 23 separate studies on PA and CRF representing over 1.3 million person-years* of data. A summary of his findings is shown in Figure 1 below. The percentiles across the horizontal part of the graph refer to levels of PA and CRF. For example, a percentile score of 25 means that 75 percent of the people were more active/fit than the people with the score of 25. So, as percentile score increases, this indicates higher levels of PA and CRF. As seen in the Figure, as percentile levels of PA and CRF increase, there is a decrease in the relative risk of CVD. However, the effects of PA and CRF on CVD risk are not the same! For increasing percentile levels of PA, the beneficial effects on CVD risk are not nearly as great as for increasing percentile levels of CRF. As shown, at the highest percentile of PA, the relative risk of CVD is about 0.7. This means that those with the highest levels of PA have about a 30% reduced risk of CVD compared to people with the lowest levels of PA. In contrast, there is a sharp decrease in CVD risk when moving from the 0 to the 25th percentile of CRF, with a further decrease beyond that point. Those at the highest percentile of CRF have a relative risk of about 0.35. This means that those with the highest levels of CRF have about a 65% reduced risk compared to people with the lowest levels of CRF.

This was the first study to prove that PA and CRF have significantly different relationships to CVD risk. Although they are both extremely important, having a high level of CRF results in a greater decrease in CVD risk than simply having high levels of physical activity. More recent studies have confirmed these results. So, it is still important to try to meet current public health guidelines for PA (at least 150 minutes of moderate intensity aerobic activity per week and at least 2 days per week of resistance training). However, it is even more important to get a good measure (or at least a good estimate) of CRF, regardless of your level of PA. Those with low levels of CRF need to increase their fitness level, even if they are already meeting the public health guidelines for PA. Numerous studies have shown that an increase in exercise intensity is more effective for increasing CRF than increasing the frequency or duration of exercise.
To learn more about how to help people change unhealthy behaviors such as sedentary lifestyle, take our Coaching Healthy Behaviors course. To learn more about physical fitness, take our Personal Training Education course either in Dallas or online. You need not be a health and fitness professional to take part in our courses, everyone is welcome!

*person-years of data are calculated by multiplying the number of persons by the number of years studied. For example, if 100 persons are studied for 10 years, then there are 1000 person-years of data available.

Reference
Williams, P. T. (2001). Physical fitness and activity as separate heart disease risk factors: a meta-analysis. Med Sci Sports Exerc, 33, 754-761.