Evaluation of Physical Activity and Sedentary Behavior

Abstract

Physical activity (PA) is defined as any bodily movement produced by skeletal muscles that results in energy expenditure (EE) above the resting level. PA consists of exercise and non-exercise PA, also termed non-exercise activity thermogenesis (NEAT). NEAT is much larger than that of exercise-induced EE, and varies substantially between individuals. Questionnaires can provide qualitative information, such as type and purpose of PA, that differs from that provided by objective methods. However, the accuracy of questionnaires to measure PA intensity and EE is not sufficient. On the other hand, accelerometers are objective, small, non-invasive tools for measuring PA intensity and EE. Most NEAT is non-locomotive activities, and NEAT, especially NEAT due to non-locomotive activity, is difficult to measure under free-living conditions. Therefore, accurate metabolic equivalents (METs) estimation for non-locomotive and sedentary activities is required in addition to estimates of locomotive activity. Accelerometers can be used to study patterns of activity across time. A new generation of accelerometers will provide information on body posture and activity recognition to allow objective assessment of subjects’ habitual activities. Step counts mainly reflect moderate intensity PA, rather than total PA or physical activity level (PAL). The relationship between step counts and total PA depends on sex, age, and occupation. Accurate estimation of sedentary activities is important, because many people spend almost 10 h/day in sedentary behavior. The prediction accuracy of lower-intensity PA is generally poor. One possible reason is the low sensitivity of accelerometers. Predictive equations for sedentary behavior with high accelerometer sensitivity may improve the prediction accuracy.