Chapter 1Introduction

Chapter overview

• Early observations

• Modern trends

• Prevalence of activity/inactivity world-wide

• Trends over time in physical activity levels

• National surveys of fitness

• Definitions of key terms

• Summary

After the Second World War …

• Hypothesis: ‘Deaths from coronary heart disease would be less common among men engaged in physically active work than among those in sedentary jobs’ (Jeremy Morris et al.).

• Conductors on double-decker buses climbed 600 stairs per day; drivers on the buses sat for 90% of their shift.

• The incidence of CHD in conductors was less than half that of drivers (1953 paper in the Lancet).

Modern trends

Three modern trends will increase the prevalence of CHD, stroke, cancer and diabetes in the twenty-first century. These are:

• the epidemic of obesity;

• inactivity in children; and

• the increasing age of the population.

Obesity trends in England

Decrease in percentage of children walking to school, Australia

Projected changes in age structure of population, New Zealand

Reporting data on population levels of physical activity

There are two frequently used approaches.

• the proportion of individuals in a specified age/sex-group judged to be inactive;

or

• the proportion of individuals meeting the criteria that identify the minimal ‘dose’ of activity needed for health benefits.

Percentage of adults classified as ‘inactive’ in European countries (2005)

Percentage of adults meeting national guidelines in England (2006)

Note: Dashed lines represent targets.

Trends in adult activity levels, Canada

National Fitness Survey, England (1992)

Nearly one-third of men and two-thirds of women would find it difficult to sustain a walking pace of about 4.8 km h–1 (3 mile h–1) up a 1-in-20 (5%) slope for more than a few minutes.

The proportion of men who could not do this rose sharply with age, from 4% of 16–24-year-olds to 81% of 65–74-year-olds. Figures for women rose from 34% to 92%.

Inactivity prevalence

‘More than 60% of the world population is inactive or insufficiently active to gain health benefits.’

(World Health Organization)

Health is …

‘a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity’.

(World Health Organization)

Physical activity is …

‘any bodily movement produced by contraction of skeletal muscle that substantially increases energy expenditure’.

Exercise is …

‘a sub-category of leisure-time physical activity in which planned, structured and repetitive bodily movements are performed to improve or maintain one or more components of physical fitness’.

Summary I

• After the Second World War epidemiologists began to study the role of exercise in protection against heart disease.

• The epidemic of obesity is leading to an increase in obesity-related diseases.

• In many countries, less than one-third of young people are sufficiently active to benefit their present and future health.

• Improvements in life expectancy mean that the number of older people is increasing, changing the age-structure of populations.

Summary II

• Physical activity levels decline rapidly with increasing age; levels are higher in men than in women.

• A decline in physical activity follows in the wake of economic growth. The prevalence of inactivity may be expected to rise as the economies of developing countries progress.

• In England, nearly one-third of men and two-thirds of women could not sustain a normal walking pace up a modest slope for more than a few minutes (National Fitness Survey 1992).