Physical Inactivity and Measurement

Physical inactivity is a major driver of non-communicable disease (NCD). The World Health Organization (WHO) identifies it as a leading risk factor for global mortality, and insufficiently active adults have a markedly higher risk of early death than active adults. In 2022 the WHO estimated that around a third of adults worldwide, some 1.8 billion people, were insufficiently active. In England, the most recent Active Lives survey found that around a third of adults did not meet the 150-minute aerobic guideline. Inactivity contributes to coronary heart disease, stroke, type 2 diabetes, several cancers including breast and colon, obesity, poor bone health and depression, and it places a large, avoidable cost on health services.

It is important to separate two related ideas. Physical inactivity means not achieving recommended activity levels, whereas sedentary behaviour means waking time spent sitting, reclining or lying with low energy expenditure, such as prolonged desk work, driving or screen time. A person can meet the weekly activity target yet still sit for most of the day. High sedentary time is associated with additional health risk; being sufficiently active attenuates part of this association, but prolonged sitting remains harmful for some outcomes even in people who meet the guidelines, which is why the advice is to move more and sit less. Terminology also matters: the WHO describes people who do not meet the guidelines as insufficiently active, while England's Active Lives survey groups adults as active (at least 150 minutes a week), fairly active (30 to 149 minutes) and inactive (fewer than 30 minutes), so inactive has a specific, narrower meaning in UK surveillance. Inactivity follows a social gradient, being more common in people from more deprived areas, some ethnic groups, disabled people and women, which makes it an issue of health inequality as well as individual behaviour.

Activity can be measured subjectively or objectively, and the two approaches trade accuracy against cost and scale. Subjective methods rely on self-report, using validated questionnaires such as the International Physical Activity Questionnaire (IPAQ) and the Global Physical Activity Questionnaire (GPAQ), along with activity diaries and recall interviews. They are cheap and easy to use in large populations, which is why national surveys depend on them, but they are prone to recall error and tend to overestimate activity, particularly at moderate intensity.

Objective methods measure movement more directly. Accelerometers, worn on the wrist or hip, record acceleration and estimate the volume and intensity of activity using processing algorithms and thresholds; they are the mainstay of research but capture activities such as cycling, swimming and resistance exercise less well, depending on the device and where it is worn. Pedometers count steps as a simple, motivating measure, and heart rate monitoring estimates intensity. The reference method for total energy expenditure is the doubly labelled water technique, which is accurate but expensive and confined to research. A common currency across methods is the metabolic equivalent of task (MET), a standardised measure of energy expenditure relative to rest; by absolute intensity, moderate activity is conventionally about three to six METs and vigorous above six, though the relative intensity of a given task varies with a person's fitness. Activity is often summarised as MET-minutes per week to combine intensity and duration. Sedentary behaviour is measured separately, using self-reported sitting time or device-based methods such as inclinometers that detect posture, since a step counter alone does not capture how long a person sits.

Promoting activity is a whole-system task shared across many sectors. In the NHS, primary care is a key setting: brief advice during routine consultations, exercise referral schemes and social prescribing link workers connect patients to activity, supported by the Making Every Contact Count (MECC) approach. Secondary care contributes through rehabilitation, prehabilitation and initiatives that keep inpatients moving.

Beyond the NHS, in England local authorities hold public health responsibility and run or commission leisure services, parks, active travel schemes and community programmes, often targeting the least active, although these arrangements differ across the four UK nations. National bodies such as Sport England and the Office for Health Improvement and Disparities (OHID) fund and coordinate this work, and Active Partnerships help join it up locally. The voluntary and community sector, from walking groups and parkrun to disability sport organisations, delivers much of the activity people actually take part in, frequently reaching groups that clinical services do not. For the SEM clinician, knowing this landscape means being able to signpost effectively and to work across the system, recognising that increasing activity at a population level depends on the environment and opportunity as much as on individual advice.

• •Physical inactivity is a leading global risk factor for death and non-communicable disease, and insufficiently active people have a substantially higher mortality risk.
• •Around a third of adults worldwide are insufficiently active, and in England around a third of adults do not meet the aerobic guideline, following a clear social gradient.
• •Physical inactivity (not meeting activity targets) is distinct from sedentary behaviour (prolonged sitting); both matter, and prolonged sitting is associated with additional risk even in active people.
• •Self-report tools such as the International Physical Activity Questionnaire and the Global Physical Activity Questionnaire are cheap and scalable but overestimate activity; accelerometers estimate movement more objectively.
• •One metabolic equivalent of task is a standardised measure relative to rest; by absolute intensity, moderate activity is about three to six and vigorous above six, summarised as MET-minutes per week.
• •Activity promotion is delivered across the NHS, local authorities, Sport England and the voluntary sector, with the environment and opportunity as important as individual advice.