Physical Activity .. see also Be active

Issues

Physical activity has been considered a health benefit for many centuries. However, scientific evidence documenting the clear health benefits of moderate regular physical activity has only emerged over the past four decades. The best documented health gain is in the prevention of heart disease, and in the reduction of the risk of cardiovascular and all-cause mortality among those who are physically active, compared with those who are sedentary.

The relationship between physical activity and health involves four major issues.

1. The amount of physical activity required for health benefit remains to be clarified; new evidence points to benefits from moderate activity, but higher levels (or greater intensity) of physical activity will confer additional benefits.
   
2. Does fitness or simply activity confer a health benefit? Recent evidence suggest that both have a role. Physical activity (large skeletal muscle movement, which expends energy) may provide some benefits independently of fitness (cardiorespiratory fitness, which is a measure of how well oxygen is supplied to tissue during physical activity).
   
3. Identifying the population groups most likely to benefit from being physically active.
   
4. Developing interventions and programs to increase physical activity among all Australians, including the provision of brief, simple advice about physical activity by all health professionals.

Current levels and trends

No consistent monitoring of population physical activity has taken place in Australia, although slight increases in walking are apparent¹. Trend data from North America show little change over the past decade in the proportions of the population that are sedentary or engage in regular moderate activity².

Australian population data show that women, middle-aged and older adults, non-English speaking groups, parents of young children and those with lower educational attainment are less likely to be physically active^3,4. Overall, about half of Australian adults expend sufficient energy on physical activity for cardiovascular health gain^3,4.

Evidence

Recent consensus and meta-analytic evidence for a cardioprotective role for regular physical activity is compelling^2,5. Habitual physical activity reduces the risk of all-cause mortality, as well as the incidence of, and fatality rate from, cardiovascular disease, especially coronary heart disease. It also reduces the risk of high blood pressure and non-insulin dependent diabetes (NIDDM), and favourably influences HDL cholesterol, relative body weight and blood pressure². The US Surgeon General’s Report on Physical Activity (1996) found a positive relationship between protection against coronary heart disease and physical activity and fitness, evident for both men and women⁶. Consistently across studies, the maximal cardiovascular protection was evident in moderate activity or moderate-fitness groups compared with sedentary or low-fitness groups.

The evidence is based on longitudinal population-based (cohort) studies, rather than experimental evidence (similar to that for tobacco smoking and health). Better-designed studies, including improved measures of physical activity and outcomes of heart disease, show stronger associations, typically almost twice the risk of CHD in the most inactive people compared with those who are adequately active. There is evidence of a dose-response relationship, with more activity conferring additional benefit.

There is also consistency across studies, even after statistical adjustment for the effects of other risk factors. Finally, the evidence is strengthened by demonstrations that increases in physical activity or fitness confer subsequent protection⁷, even after as little as two years⁸. Further, increasing fitness to a moderate level confers a benefit at any age, suggesting that it is never too late to start some physical activity⁸.

The benefits of activity may be mediated through a range of biologically plausible mechanisms, including a direct effect on coronary atherosclerosis⁹, a favourable effect on other risk factors, an increase in coronary circulation, or an increase in myocardial stability (reducing the risk of fatal arrhythmias). Other cardiovascular-related health benefits are likely to be gained from physical activity, including reductions in the incidence of hypertension and NIDDM.

Physical activity may also favourably influence risk factors related to thrombosis, including fibrinogen and platelet function. There is some evidence suggesting a benefit of activity upon stroke incidence and mortality, but the amount of activity required, and the type of stroke prevented, are not yet clarified. More sustained levels of physical activity may be required to produce other benefits, including weight loss and increases in the HDL:total cholesterol ratio. It is recommended that physical activity be developed as a lifelong habit through childhood to prevent later atherosclerosis, but the cross-sectional correlates and benefits of activity in childhood are less clear¹⁰.

Physical activity is recommended for people with heart disease, but medical screening and assessment should precede the adoption of vigorous activity programs in this group. Although the risks of sudden death are transiently increased during vigorous exercise among those with heart disease, the population benefit substantially outweighs the risks¹¹.

National Heart Foundation Position

1. There is widespread recognition that physical inactivity is a major risk factor in cardiovascular disease, at least as great as the population risk attributed to smoking, high cholesterol or hypertension¹². As the rate of physical inactivity is high among adult Australians, its population impact is even greater.
   
2. Physical activity benefits men and women of all ages, and there is increasing evidence that such benefits occur relatively soon after the adoption of an active lifestyle^6,8.
   
3. The total amount of physical activity seems to be more important than the intensity, so that moderate activity may be accumulated through the week.
   
4. Physical activity should start as a lifelong habit in childhood, and its benefits are maximal if maintained throughout life. Physical activity is also important for those with coronary heart disease, with the benefits outweighing the risks. Activity is an important and effective component of cardiac rehabilitation programs for people following myocardial infarctions, cardiac procedures or surgery.
   
5. The amount of physical activity required for health benefit has moved from the 1980s recommendations of ‘aerobic’ (vigorous) levels towards a current consensus of moderate levels (30 minutes a day) on most or all days of the week².
   
6. Activity may be in a single session, or ‘accumulated’ in multiple bouts of eight to 10 minutes during the course of the day^2,12.
   
7. This moderate physical activity message suggests a lifestyle approach to physical activity. Strategies need to be developed to increase incidental physical activity, regular brisk walking and other forms of active recreation¹³.
   
8. Both physical activity and improved fitness appear to have health benefits. Reducing the risk of cardiovascular disease may result from moderate activity alone, but more sustained changes (to produce a cardiorespiratory training effect) may be required to favourably influence other risk factors.
   
9. Effective physical activity promotion also has an adjunctive role in weight control and maintenance, although more sustained activity and dietary change may be needed to achieve sustained weight loss among the overweight and obese.
   
10. The overall goal is to develop general population strategies and programs to increase physical activity.
    
11. Specific populations who are more likely to be sedentary or minimally active deserve special efforts.

References

1. Australia’s Health Trends, AIHW, 1995. AGPS Canberra.
   
2. Surgeon General’s Report: Physical activity and health. US Department of Health and Human Services, Center for Diseases Control, Atlanta, Georgia 1996.
   
3. Bauman A., Bellew B., Booth M., Hahn A., Stoker L., Thomas M., ‘Towards best practice for physical activity in the areas of NSW’. NSW Health Department, December 1996.
   
4. Booth, M., Owen N., Bauman A., Gore C.J., Active and Inactive Australians, Department of Environment, Sport and Territories, AGPS, Canberra 1995.
   
5. Berlin J, Colditz G.A., ‘A meta-analysis of physical activity in the prevention of coronary heart disease’. American Journal of Epidemiology 1990, 132:612-628.
   
6. Blair S.N., Kohl H., Barlow C.E., ‘Physical activity, physical fitness and all-cause mortality in women: Do women need to be active?’ American College of Nutrition 1993, 12:368-371.
   
7. Paffenbarger R., Hyde R.T., Wing A.L. et al, ‘The association of changes in physical activity level and other lifestyle characteristics with mortality among men’. New England Journal of Medicine 1993, 328:538-545.
   
8. Blair S.N., Kohl H.W., Barlow C.E. et al. ‘Changes in physical fitness and all cause mortality: A prospective study of healthy and unhealthy men’. JAMA 1995, 273:1093-1098.
   
9. Hambrecht R., Niebauer J., Marburger C. et al, ‘Various intensities of leisure-time physical activity in patients with coronary artery disease: Effects on cardiorespiratory fitness and the progression of coronary atherosclerotic lesions’. Journal of American College of Cardiology 1993, 22:468-477.
   
10. Armstrong N., Simons-Morton B., ‘Physical activity and blood lipids in adolescents’. Pediatric Exer Science 1994, 6:381-405.
    
11. NIH (National Institutes of Health, USA) ‘Consensus statement on physical activity and cardiovascular health’, 18.3.96 (reproduced in ‘Surgeon General’s Report’, pp 41-48).
    
12. Fletcher G.F., Balady G., Froelicher V.F. et al. ‘Exercise standards. A statement for healthcare professionals from the American Heart Association’. Circulation 1995, 91:580-615.
    
13. Pate R.R., Pratt M., Blair S.N. et al. ‘Physical activity and public health. A recommendation from the Centres for Disease Control and the American College of Sports Medicine’. JAMA 1995, 273:402-407.

March 1997

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