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Is it important to know how fit we are?

I think so. There is a link between physical activity (PA), cardiorespiratory fitness (CRF) and a variety of health problems. I will talk about some of the complexities of these relationships in a future Blog but a simple view is that taking exercise increases fitness and thus improves health. When it comes to our susceptibility to most of the chronic illnesses of mid to later life, CRF is a better predictor than PA.

As a society we take insufficient exercise and our physical fitness levels are less than they should be for ideal health. So it is important to measure CRF, both in individuals and in the population as a whole, if we are to identify who needs to do more. Indeed there are many doctors, particularly cardiologists, who believe that physical fitness is as important a measure as blood pressure, body mass index, blood cholesterol and smoking habit as a way of predicting future disease and life expectancy.

For older people a low CRF is an indicator of high risk for frailty and dependency – at a stage when something can be done about it.

How much do we know about population fitness levels?

Not enough. There are endless surveys of how much exercise people say they take but fewer studies of actual fitness levels in a population. This is not surprising because of the work involved in exercise testing each individual in such a survey.  Different surveys tend to produce very different results – partly because of different ways of measuring CRF but mainly  because of the differences in the populations surveyed.

The Allied Dunbar National Fitness Survey (ADNFS)

The ADNFS was the first attempt to assess our nation’s physical fitness and was published in 1990. The Survey was conducted in a representative sample of English adults aged 16 to 96 years, between February and November 1990. A total of 4,316 participants (76% response rate) were interviewed about a range of socio-demographic characteristics and lifestyle factors, such as diet, physical activity (type, frequency and duration), smoking, alcohol, sleep, stress and social support. A subsample of 2,767 participants also took part in a physical appraisal which included objective assessment of body dimensions, composition, flexibility, and cardio-respiratory and muscular fitness.

The findings were shocking. Over 7 out of 10 men and 8 out of 10 women fell below their age-appropriate activity level for achieving a health benefit. About 1 in 6 had done no activity for 20 minutes or more in the past month. The level of inactivity fell with age, 10% of 16-20 years olds took no exercise, increasing to 40% for 65-74 year olds. When tested on a treadmill the proportion of men unable to sustain uphill walking at 3mph rose from 4% in the 16-24 year olds to 81% in the 65-74 year group. For women the equivalent proportions were 34% rising to 92%. Interestingly, though fitness tended to decline with age, a number of older individuals were as fit as or fitter than some of the much younger subjects.

The figures for muscle strength were no more encouraging, 50% of women over 55 being unable to walk upstairs without assistance. Astonishingly, 80% of both men and women of all ages incorrectly believed that they did enough exercise to keep fit – yet more evidence of the human’s capacity for self-deception – the social desirability bias to which I referred last week.

Health Survey for England (HSE)

The HSE 2008 measured the CRF of a wide selection of the population. Adults aged 16 to 74 were tested by using a step test. This involves stepping up and down a single step of determined height at a fixed rate at increasing rate. This can give a reasonably accurate estimate of  fitness, expressed as maximal oxygen uptake (VO2max). The information in the HSE 2008 was analysed to allow comparisons to be made with the ADNFS. This involved converting the results of the step test from the HSE to indicate the percentage of adults who could sustain walking at 3 miles per hour (mph) on the flat and on 5 per cent incline. Key findings from HSE 2008 are:

  • Men had higher cardiovascular fitness levels than women, with an average level of VO2max of 36.3 ml O2/min/kg for men and 32.0 ml O2/min/kg for women. In both sexes, the mean VO2max decreased with age.
  • Cardiovascular fitness was lower on average among those who were obese (32.3 ml O2/min/kg among men and 28.1 ml O2/min/kg among women) than among those who were neither overweight nor obese (38.8 ml O2/min/kg and 33.9 ml O2/min/kg respectively).
  • Virtually all participants were deemed able to walk at 3 mph on the flat but 84 per cent of men and 97 per cent of women would require moderate exertion for this activity. Thirty two per cent of men and 60 per cent of women were not fit enough to sustain walking at 3 mph up a 5 per cent incline. Lack of fitness increased with age.
  • Physical fitness was related to self-reported physical activity. Average VO2max decreased, and the proportion classified as unfit increased, as self-reported physical activity level decreased.Although HSE annual surveys indicate that more of us are complying with the government’s exhortations to reach their exercise targets, there is evidence that this is not always translating into increased levels of fitness. For instance the number of British military reservists failing their fitness assessments increased from 20% in 2015 to 29% in 2018.

More recent surveys:

Last year a systematic analysis of all the recent population surveys of population CRF was published and included 87,000 individuals aged between 6 and 90. The authors were unable to produce a meaningful table of normal values which could be widely applied, mainly because of the varying characteristics of the populations studied. So for the time being I believe that my table in Blog of 29th February 2020 is about as good as you will find – and remember that you can measure your own CRF for yourself as described in the same Blog.

PS
I mentioned in my blog of 25th April the New Scientist article “Gotta Run” I am grateful to Ann who has written in to say that New Scientist articles are available free from your local library.
I am also grateful to Fin who has sent me another New Scientist article – “Discover your inner strength”1 which promotes and explains the benefits of including strength training in your exercise regime. Worth reading – your library should be able to provide it.

  1. Helen Thomson, New Scientist 18th April 2020; 34-38.