Exercise as it relates to Disease/Is walking an effective exercise intervention in the prevention of cardiovascular disease in elderly women?
This article is a critical analysis of the following paper: Manson J, Greenland P, LaCroix A. Walking compared with vigorous exercise for the prevention of cardiovascular events in women. ACC Current Journal Review. 2003;12(1):29 
What is the background to this research?
Cardiovascular disease (CVD) is one of the leading causes of mortality, not only in Australia, but also across the globe.  It is classified as a condition relating to the heart and its surrounding blood vessels.. A strong relationship between regular physical activity and the prevention of CVD has been found in a large number of studies.      Prevalence data shows that one in six Australians is affected by CVD. Both men and women are equally affected. Although, only a small amount of research focussed on women at the time. Most physical activity guidelines have focussed on providing recommendations of intensities between moderate and vigorous physical activity, without any emphasis on the effects of walking, which is recognised as the most common form of exercise in women.  Evaluating the effects of walking on CVD could have a great impact on health in especially elderly women, by making PA guidelines more accessible and achievable, without the pressure of vigorous activity.  In addition, this study highlights the effect of sedentary behaviour and its contribution to CVD, which hasn't been accounted for in previous studies.
Where is the research from?
The study population involved an ethnically and diverse cohort of postmenopausal women, who were enrolled in the Women's Health Initiative. The WHI is an American national health study, which aims to develop strategies in preventing major disease factors in postmenopausal women and is highly recognised by the American health care system. 
The main author ,Dr. JoAnn Manson, is a well-respected professor of medicine at the Harvard medicine school, who's main focus of research is in women's health and chronic disease.  As well as one of her co-authors, Philip Greenland, who is a reputable professor of medicine and published well over 400 papers in relation to his focus on cardiovascular epidemiology and prevention.
What kind of research was this?
This research was a prospective study as part of the Women’s health initiative observational study. A large cohort of 73,743 women was observed for an average of 3 years, while looking for development of any sign of cardiovascular disease and analysing how this related to other factors of the individual’s lifestyle.
Prospective observational studies have high validity and provide high quality data, even though a high follow-up rate is necessary. The study claims of a follow-up rate of 95%. In addition, a prospective cohort study seemed more appropriate than a retrospective cohort study, due to the benefit of being able to target for a specific outcome, with less bias.  Observational studies are not controlled and need to take into account any factors that could influence or bias the outcome, known as confounders.  This study used Cox Proportional hazards model to account for these potential confounding variables, such as age, smoking, BMI etc. 
Due to the large sample size, the follow-up rate and duration of this study, the methodology seemed appropriate.
What did the research involve?
At baseline, all subjects had to be free of any diagnosed cardiovascular disease or cancer. The first screening included self-administered questionnaires relating to personal and family medical history and other lifestyle factors that could be of significance. This was followed by repeated physical activity questionnaires, that focussed on the type, frequency and duration of exercise, including information on walking and sedentary behaviour. This data was analysed and calculated into weekly energy expenditure, measured in metabolic equivalents, for different intensities of physical activity and walking. The end points of this study were classified as newly diagnosed coronary heart disease and total cardiovascular events in individuals, which were strictly classified.
- Large cohort and long-term follow up
- Racial and ethnic diversity
- End points were classified very accurately and consistently
- Questionnaires - this leads to misclassification and over-reporting of physical activity. It is also to consider that different individuals have a different perception of what to classify as moderate and vigorous exercise
- Usage of standardised classifications of energy expenditure associated with certain activities, which remains to be an estimate. Calculating energy expenditure from these estimates won't be as accurate, compared to measuring energy expenditure from different sources. Although, due to the large sample size, it seemed appropriate.
What were the basic results?
The study displayed significant results in the relationship between physical activity and CVD:
- Strong inverse relationship between base line physical activity score and risk of cardiovascular event during the follow-up period
- Similar risk reductions between walking and vigorous physical exercise
- A combination of both walking and vigorous exercise showed the greatest risk reduction (approximately 0.37 for individuals in the highest energy expenditure quintiles)
- Greater sedentary behaviour increased the risk factors
|Type of Physical Activity||1st Quintile (lowest MET scores)||3rd Quintile||5th Quintile (highest MET scores)|
However, the most significant indicator, for developing risk factors for CVD, was energy expenditure, without any relation to the type of activity. Therefore, it should be considered that any type of activity, as long as it reaches a certain threshold of energy expenditure will very likely be effective in reducing the risk for CVD.
What conclusions can we take from this research?
Both walking and vigorous physical activity seemed to have a similar positive effect on the reduction of risk factors related to CVD. However, total energy expenditure is a better indicator of risk reductions in CVD, compared to type and intensity of physical activity. Recent studies suggest that even small amounts of exercise are better than none although, increasing the amount will have significant benefits on health and preventing CVD.   
This study is supporting recent guidelines for Physical activity, of recommended 150 minutes of moderate exercise per week.   Findings from this study encourage especially elderly women to exercise, because of taking away the pressure of having to exercise vigorously. A recent systematic review and meta-analysis of randomised control trials also highlights the importance of regular walking in the prevention of cardiovascular disease. 
In addition to overcoming physical inactivity, it is important to note that emphasis should also be on reducing sedentary behaviour. In particular, recent studies focus on the reduction of sedentary behaviour in the population which is affecting health and CVD significantly.  
Adding walking to your physical activity routine will have significant benefits to your health. Not only for the prevention of cardiovascular disease, but also on daily life and general health.   
- Some exercise is better than none.
- Identify preferences for physical activity, that YOU enjoy doing(e.g. walking, swimming etc.), but be consistent.
- Integrate increased walking into your lifestyle and break up sedentary patterns. (social walking, walking with a destination in mind)
- If you have any concerns about exercising - Consult a professional. See further readings.
- Start slow and increase duration and intensity over time.
- Visit Heart Foundation. Walking Solo or in a Group. https://walking.heartfoundation.org.au
- Are you at risk for Cardiovascular disease? Find out. https://www.heartfoundation.org.au/for-professionals/clinical-information/absolute-risk
- Physical Activity Fact Sheet. Get Active. https://www.heartfoundation.org.au/active-living/get-active
- Adult Pre-Exercise Screening Tool. https://www.essa.org.au/Public/ABOUT_ESSA/Adult_Pre-Screening_Tool.aspx
- Find Exercise Professionals near you https://www.essa.org.au/find-aep
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