Friday, November 06, 2009

Official Advice on Exercise Pt 2

Official advice on the amount of exercise needed is quite simple:

■ Children and young people should achieve a total of at least 60 minutes of at least moderate intensity physical activity each day. At least twice a week this should include activities to improve bone health (activities that produce high physical stresses on the bones), muscle strength and flexibility.
■ For general health benefit, adults should achieve a total of at least 30 minutes a day of at least moderate intensity physical activity on 5 or more days of the week.
■ The recommended levels of activity can be achieved either by doing all the daily activity in one session, or through several shorter bouts of activity of 10 minutes or more. The activity can be lifestyle activity or structured exercise or sport, or a combination of these.
■ It is likely that for many people, 45-60 minutes of moderate intensity physical activity a day is necessary to prevent obesity. For bone health, activities that produce high physical stresses on the bones are necessary.
■ The recommendations for adults are also appropriate for older adults. Older people should take particular care to keep moving and retain their mobility through daily activity. Additionally, specific activities that promote improved strength, co-ordination and balance are particularly beneficial for older people.

That’s all there is.

When I first read them I thought they were very soft. There is no mention of vigorous, nothing about raising the pulse rate or breathing heavily and nothing about being able to gradually do more with practice. As for breaking it up into 10 minutes units I thought it was the slippery slope to counting any slight movement as exercise.

But I was probably being a bit snooty because I run and know the feeling of wellbeing that sweeps through you after a good session. I therefore know in my bones that exercise is good for you. So my viewpoint is distorted especially as I have little understanding of the general level of inactivity in the population as a whole or how hard it is to start from a low base.

Reading the 2004 report by the Chief Medical Officer changed my mind (it can be downloaded here) as it shows the evidence base for the recommendations, which can be summarised by this quote:

The World Health Organization has reported that physical inactivity is one of the 10 leading causes of death in developed countries, producing 1.9 million deaths worldwide per year.21 It estimates that physical inactivity is responsible for the following proportions of ‘disability-adjusted life years’ in developed countries:

■ 23% of cardiovascular disease for men and 22% for women
■ 16% of colon cancer for men and 17% for women
■ 15% of type 2 diabetes
■ 12% of stroke for men and 13% for women
■ 11% of breast cancer. Becoming more active can bring substantial benefit.

There is a clear dose-response relationship between physical activity and all-cause mortality, and between physical activity and diseases such as coronary heart disease and type 2 diabetes: greater benefits occur with greater activity participation (see Figure 1). From a public health perspective, helping people to move from an inactive level to low to moderately active levels will produce the greatest reduction in risk. A physical activity energy expenditure of 500-1,000kcals per week (about 6-12 miles of walking for an average-weight individual, compatible with the current physical activity recommendations for adults) reduces the risk of premature death by 20-30%. These considerable health benefits hold for both women and men and are evident even up to the age of 80 years.

This is clear. If more people adopted this regime of moderate exercise there would be dramatic change. However in the back of my mind is the quote from Jerry Morris saying that vigorous activity was necessary and his survey of civil servant showed gardening was not enough. I presume later surveys have different results but is vigorous exercise really unnecessary?

It seems that there is might be some debate. In 2007 the American Heart Association modified its advice by incorporating vigorous exercise and resistance training. The base recommendation was still 30 minutes of moderate activity 5 times a week, but 3 sessions of vigorous exercise could be substituted, if preferred, or moderate and vigorous sessions could be mixed. The Guardian report of this change was exaggerated and had the headline “The era of gentle exercise is over: it’s official you’ve got to work up a sweat”, which is a complete misrepresentation (the NHS Behind the Headlines response is here). Although the American report was merely an enhancement of the existing recommendations, it did acknowledge that there were still some people who believed that only vigorous exercise had a health effect and that recent evidence gives some indication that vigorous exercise is more beneficial for cardiac disease.

However in terms of a public health message the last thing you want is debate. It is important to stand firm with advice and only change it when counter evidence is very clear. Any sign of confusion is an excuse for people to do nothing. You need only look at diet, where there is a perception of scientists always changing their minds (even if this is not the case) to see how that works.

Additionally getting people to move from nothing to something is very difficult and you do not want to make the task seem daunting. (Again diet is the example ‘5 a day’ for fruit and vegetables was chosen as a target that would not be too off-putting; it is not necessarily the optimum).

So I can now see why the current advice is good. It has a the maximum chance of making an impact but it needs to seep into the general consciousness in the same way as '5 a day'. If we walk on average only half a mile a day and 38% of adults have less than 30 minutes of moderate activity a week. There is a long, long way to go.

No comments: