How much exercise do we take?
There are a number of answers to this question depending upon who is making the estimate and how they have measured it. Some of the regular surveys which assess physical activity in the population include the Health Survey for England (HSE), Active People Survey, National Travel Survey and The General Household Survey.
What people say they do
The most representative survey is given in the annual HSE report. The HSE compares current population activity with the Department of Health recommendations. It uses validated questionnaires completed by wide sections of the population to assess the level of compliance with these guidelines. Different types of activity are summarised into a frequency-duration scale which takes into account the time spent participating in physical activities and the number of active days in the last week. By this measure the proportion of adults meeting the recommendation has increased steadily since 1997 for men and 1998 for women. In 1997, 32 per cent of men met the recommendation, increasing to 43 per cent in 2012. Among women, 21 per cent met the recommendation in 1997 and 1998, increasing to 32 per cent in 2012.
After 2012 the recommendations changed to include shorter bursts of activity so the figures in the past few years cannot be compared with the earlier figures. Currently the estimates are that 66% of men and 58% of women meet the guidelines. Be aware, however, that these results depend upon the accuracy of the self-assessment of the individuals completing the questionnaires and are therefore likely to be substantial overestimates – see below.
The 2008 HSE report found that, based on the participants’ self-reported data, 39% of men and 29% of women met the exercise recommendations of the CMO. Increasing age and increasing BMI were associated with decreasing levels of activity. At age 16-24, 52% of men and 35% of women met the recommendations. The numbers fell steadily over the next three decades of life to 41% and 31%. Thereafter the fall was more precipitate to 9% and 6% for the over 75s.
Like other HSE surveys, the report gives a huge amount of additional data including the effect of obesity and social status on activity and also the different activities included in different age and sex groupings.
In 2011 the Department of Health modified its recommendations as indicated previously: “Adults should aim to be active daily. Over a week, activity should add up to at least 150 minutes (2½ hours) of moderate intensity activity in bouts of 10 minutes or more – one way to approach this is to do 30 minutes on at least five days a week. Alternatively, comparable benefits can be achieved through 75 minutes of vigorous intensity activity spread across the week or a combination of moderate and vigorous intensity activity” The recommendations also added muscle strengthening activities on two or more days per week that work all major muscle groups (legs, hips, back, abdomen, chest, shoulders and arms).
Using the new guidelines the HSE 2012 estimated that 34 per cent of men and 24 per cent of women aged 16 and over met their recommendations. In both sexes, the proportion who met the guidelines generally decreased with age, reduced household income and increased BMI. Compared with the 2008 survey there was an increase in those meeting the recommendation for aerobic activity; it does seem that we are improving a bit in our exercise habit – or getting better at self-deception.
What people really do
The HSE 2008 report broke new ground by adding a separate assessment of activity levels – it actually measured what people did. The comparison with what they said they did is startling.
They used accelerometers (a sort of sophisticated pedometer) to record information on the frequency, intensity and duration of physical activity in one minute “epochs” – showing accurately the actual daily activity of their subjects over a period of one week. Based on the results of the accelerometer study, 6 per cent of men and 4 per cent of women achieved the government’s recommended physical activity level – just 15% of the level of compliance indicated by individuals’ own questionnaire responses – revealing a staggering level of either self-deception or just downright lying! Men and women aged 16 to 34 were most likely to reach the recommended physical activity level (11 per cent and 8 per cent respectively), the proportion of both men and women meeting the recommendations fell in the older age groups. On average men spent 31 minutes in moderate or vigorous activity (MVPA) in total per day and women an average of 24 minutes. However, most of this was sporadic activity, and only about a third of this was accrued in bouts of 10 minutes or longer which count towards the government recommendations.
Questionnaire estimates of activity levels rely entirely on self-reporting and the unreliability of this measure is made starkly obvious by these HSE figures. It is a human tendency is to exaggerate both to ourselves, and perhaps more to others, the amount of good stuff we do. This has been termed “social desirability bias” and extends into assessments of how much food we eat. When measured, actual average calorie intake is between 50 and 100% greater than is indicated by the answers to questionnaire surveys.
Does the difference matter?
When the effects of physical fitness are compared with stated activity levels, it is physical fitness which is a far better predictor of future heart disease and mortality, particularly in younger subjects. Hardly surprising is it? Our fitness level is an excellent reflection of how much exercise we actually take as compared with what we might like to think we take.
So just how fit are we? I will try to answer that next week.