Chapter 13Public health

Chapter overview

• Introduction• Recommendations for physical activity• Rationale for recommendations• Changing physical activity behaviours• Examples of good practice in public health• Walking: ‘The nearest to perfect exercise’• Physically active commuting• Benefits versus risks• A ‘best buy in public health’?• Summary

Introduction

• By 2030 non-communicable diseases, e.g. CVD, type 2 diabetes and many cancers, will contribute to 69% of deaths and 57% of the global burden of disease.

• These diseases share a rather small number of preventable risk factors.

• Some 80% of premature heart disease and stroke, 80% of type 2 diabetes and 40% of all cancers are preventable.

Population-attributable risk (PAR) for physical inactivity, Canada

Disease PAR (%)

Coronary artery/heart disease 19.4

Stroke 24.3

Hypertension 13.8

Colon cancer 18.0

Breast cancer 14.2

Type 2 diabetes 21.1

Osteoporosis 24.0

Physical activity recommendations: adults

 30 minutes of moderate-intensity aerobic activity on five days each week or  20 minutes vigorous activity on three days;

• moderate-intensity activities can be accumulated in bouts of  10 minutes;

PLUS

• activities that maintain or increase muscular strength and muscular endurance on at least two days each week;

• more benefit is gained from exceeding these recommendations.

Recommendations: avoidance of weight gain and older adults

• Prevention of unhealthy weight gain – 60 minutes moderate-to-vigorous on most days.

• Older adults:

– moderate-intensity related to individual level of aerobic fitness;

– include activities to maintain or increase flexibility and balance;

– activity plans should integrate preventive and therapeutic recommendations.

Recommendations: children

• 60 minutes or more of at least moderate intensity, preferably daily;

• 16,500 steps;

• use of electronic media restricted;

• some sessions that produce ‘high physical stress’.

Note: There are some differences between countries.

Evidence providing rationale for recommendations

• Frequent, preferably daily, activity – acute effects, e.g. on triglycerides, BP.

• ‘Trading’ intensity for duration – triglycerides similarly decreased after two sessions of walking, one twice the duration at half the intensity.

• Accumulating short bouts – triglycerides throughout day: decreased by similar amount with one 30-minute walk or three, ten-minute walks.

Acute effects of exercise – revealed by de-training studies

Trading intensity for duration

Accumulating ten-minute bouts: an example using triglycerides

Good practice: examples to facilitate active lifestyles

• Built environment: the more attractive and ‘walkable’ streets and parks are, the higher levels of walking.

• Denmark legislates that every child must have a safe route to school (50% of Danish children cycle or walk to school).

• In the Netherlands motorized traffic entering residential zones is restricted to a speed of ‘walking pace’.

‘Brisk’ walking at 3.5 mile h–1

• Light activity for the average young person;

• moderate for the majority of sedentary, middle-aged adults;

• vigorous for the elderly or individuals whose functional capacity is limited by disease.

Importance of intensity relative to VO2max or VO2max reserve

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Concept of VO2max reserve

• Definition: ‘Capacity above the resting metabolic rate of 1 MET’.

• Individuals with low VO2max reserve have little capability to increase oxygen uptake above the resting level.

• For such people brisk, or even normal-paced walking constitutes vigorous exercise.

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Walking: epidemiology of health benefits

Walking has been independently associated with a lower risk of:

• all-cause mortality;

• CHD/CVD;

• ischaemic stroke;

• type 2 diabetes;

• cognitive decline in older people;

• weight gain.

Summary I

• Non-communicable diseases are a major and increasing public health burden. Increasing physical activity levels would have an important impact on the incidence of such diseases.

• Adults need moderate-intensity activity for at least 30 minutes on five days each week, or vigorous-intensity aerobic activity for a minimum of 20 minutes on three days. Children need more.

• Changes to the built environment that facilitate walking and cycling will have an impact on population physical activity levels

Summary II

• Brisk or fast walking will improve fitness in most middle-aged and older men, and in almost all adult women. Walking for exercise is very injury-free.

• Adverse side-effects of exercise are mainly avoided if intensity is moderate. For the majority of individuals, benefits outweigh risks.

• For a society, the promotion of physical activity may lead to economic benefits