Ulf Ekelund
Medical Research Council Epidemiology Unit, Cambridge
Methods to measure physical activity
Physical activity is a complex multidimensional form of human behaviour that theoretically includes all bodily movement from fidgeting to participation in extreme sport activities such as marathon running or triathlon. Usually, physical activity refers to the use of large muscle groups, such as movements of the arms and legs, but it has been defined as "any bodily movement produced by skeletal muscles that results in energy expenditure". However, physical activity (defined as body movement) and energy expenditure are not synonymous. Body movement is a form of behaviour, whereas energy expenditure is an outcome of that behaviour. Furthermore, despite a large body of data supporting the associations between physical activity and health outcomes, the detailed relationship (i.e. dose – response) between the type and degree of physical activity and its effects on various aspects of health remains to be elucidated. The development and evaluation of different physical activity assessment methods is therefore of high priority.
Methods of physical activity assessment include both self-report methods, such as activity diaries, questionnaires and activity recalls, and objective assessment techniques. Objective assessment of free-living physical activity can be based on physiological (energy expenditure, heart rate [HR] monitoring) and biomechanical (accelerometry) principles. All assessment techniques have their inherent strengths and limitations and there is no method available which is able to accurately measure all different dimensions of physical activity. The choice of a specific method should ideally be based on the dimension(s) of activity which is most closely related to the research question, but is usually based on a trade-off between ease of assessment and measurement precision.
The aims of this presentation are; 1) to provide an overview of various methods for assessing physical activity; 2) to discuss the basic principles of different assessment methods; and 3) to discuss the strengths and limitations with different assessment methods. The presentation will focus on available methods that can be used for free-living physical activity assessment in epidemiological studies.
