Learn more about the role activity and fitness play in health risk.
Reed H. Humphrey, Ph.D., P.T., FACSM, is professor and chair of the School of Physical Therapy & Rehabilitation Science at the University of Montana. He completed a 4-year term as head of the World Council for Cardiovascular and Pulmonary Rehabilitation in 2004 and is a past president of the American Association of Cardiovascular & Pulmonary Rehabilitation. He is associate editor of ACSM's Resources for Clinical Exercise Physiology and past associate editor of ACSM's Guidelines for Exercise Testing and Prescription, fifth edition. Humphrey currently serves as an associate editor for ACSM's Health and Fitness Journal®.
If you haven't come across the phrase "there is nothing as constant as change," well, you probably have just forgotten when you did come across it. In health and fitness, we accept some fundamental principles about the positive effects of exercise, most of which were learned during professional training. As careers evolve, meetings and continuing education seminars modify some of the techniques we use to bring about those positive effects. Moreover, our views on reducing a client's risk for chronic disease and the levels of exercise necessary to improve function as parallel objectives are gleaned from our specific education and experience. I think it's probably also fair to speculate that many of you reading this column likewise are periodically frustrated by the inconsistent views about the relative importance of physical inactivity and chronic disease risk. Many clinicians-and the public via overwhelming messages in the advertising media and print news-continue to view elevated lipids, hypertension, and smoking to be the three critical factors for illness despite the overwhelming evidence that diminished fitness conveys just as high, if not higher, risk for a cardiovascular event (1).
In the September/October 2006 issue of this Journal, David Swain, Ph.D., FACSM, wrote about the relative importance of vigorous exercise for a variety of health and fitness outcomes (2). Certainly, the argument that fitness is crucial to reduce risk of a cardiovascular event has gained considerable traction in recent years, where exercise capacity is used as the measure of improved fitness. In four important articles published between 2002 and 2004, involving nearly 18,000 subjects (contrary to the popular criticism that studies focus only on men, more than half of these subjects were women), exercise capacity consistently was associated with lower risk; a single metabolic equivalent increase in exercise capacity resulted in a decrease in risk ranging from 12% to 20%, depending on the study (3-6). In the context of the fitness setting, it seems that the reasonable approach to the advisement of clients is to stress an improvement in fitness as measured by a test of exercise capacity. Perhaps as importantly, the client's exercise prescription should be focused on an improvement in fitness above other considerations.
But how does this evolving understanding of fitness square with the popular notion that overall physical activity also is important in the reduction of cardiovascular risk? In fact, there is a long and storied history of elegant epidemiological studies that associate higher levels of habitual physical activity and reduced cardiovascular risk, and it is this literature base that has long been the basis for the argument that health risk can be substantially reduced through moderate intensity and habitual activity. But attention to more recent studies confirm the importance of examining both activity and graded levels of activity intensity, and it is clearer that many different physical activities at a variety of exercise intensities yield significant incremental reductions in risk. Published in 2002, a study of more than 44,000 men followed over a 12-year period reported that, although reduction in health risk was evident in a wide variety of activities that included aerobic and resistance exercise, compared with those who were inactive, increasing intensity still conferred additional protection (7). Although this study was limited to men, similar patterns are observed in women. In a large scale study of women (8), researchers evaluated a total physical activity score, amount of brisk walking, and other vigorous activities to look at the health of more than 73,000 postmenopausal women. The results demonstrated a clear graded inverse relationship between total physical activity score and cardiovascular health risk. Likewise, estimates of activity intensity showed a similar inverse relationship. In other words, greater overall activity significantly reduced cardiovascular risk, but those engaging in higher intensity activities added to the reduction in risk.
In an effort to be more specific about the quantification of physical activity while examining the fitness and physical activity question in the same group of subjects, Jonathan N. Myers, Ph.D., FACSM, and his colleagues found that a 4,200-kJ (1,000-kcal) increase in overall physical activity was similar to the 1 metabolic equivalent increases in exercise capacity that conferred to lower cardiovascular event risk (9). Paul T. Williams, Ph.D. (10), published a meta-analysis of 8 fitness cohorts and 30 activity cohorts to illustrate the degree of risk reduction between the cohorts from lowest to highest percentiles. Both activity and fitness were associated with a progressive and steady decline in risk between the 20th and 80th percentiles, with fitness showing a stronger degree of risk reduction.
In summary, Health/fitness professionals need to stress the importance that there are significant health benefits accrued even when there may not be a change in fitness as measured by exercise testing, and both exercise capacity and overall weekly energy expenditure are important, with an additive effect provided by higher intensity exercise. It is hoped that the recent studies have provided some confirmation that although there is nothing as constant as change, it's also important to not let the "best" (increased fitness) be the enemy of the "good" (increased overall activity) in the context of improving public health.
1. Wei, M., J.B. Kampert, C.E. Barlow, et al. Relationship between low cardiorespiratory fitness and mortality in normal-weight, overweight, and obese men. JAMA: Journal of the American Medical Association
2. Swain D.P. Moderate- or vigorous-intensity exercise: What should we prescribe? ACSM's Health & Fitness Journal
® 10(5):7-11, 2006.
3. Myers, J.N., M. Prakash, V.F. Froelicher, et al. Exercise capacity and mortality among men referred for exercise testing. New England Journal of Medicine
4. Mora, S., R. Redberg, Y. Cui, et al. Ability of exercise testing to predict cardiovascular and all-cause death in asymptomatic women: a 20-year follow-up of the lipid research clinics prevalence study. JAMA: Journal of the American Medical Association
5. Gulati M., D.K. Pandey, M.F. Arnsdorf, et al. Exercise capacity and the risk of death in women. The St James Take Heart Project. Circulation
6. Balady, G.J., M.G. Larson, R.S. Vasan, et al. Usefulness of exercise testing in the prediction of coronary disease risk among asymptomatic persons as a function of the Framingham risk score. Circulation
7. Tanasescu, M., M.F. Leitzmann, E.B. Rimm, et al. Exercise type and intensity in relation to coronary heart disease in men. JAMA: Journal of the American Medical Association
8. Manson, J.E., P. Greenland, A.Z. LaCroix, et al. Walking compared with vigorous exercise for the prevention of cardiovascular events in women. New England Journal of Medicine
9. Myers, J., A. Kaykha, S. George, et al. Fitness versus physical activity patterns in predicting mortality in men. American Journal of Medicine
10. Williams, P.T. Physical fitness and activity as separate heart disease risk factors: a meta-analysis. Medicine & Science in Sports & Exercise
® 33(5):754-761, 2001.