Field measurement of physical activity in epidemiology
The gold standard for physical activity estimation is based on measurements of total energy expenditure by direct calorimetry using doubly labelled water [34]. Physical activity can then be calculated based on total energy expenditure and basal energy expenditure, with the ratio or difference between these variables representing physical activity-related energy expenditure. Such techniques are obviously inappropriate for epidemiological studies, but are to be used to validate field methods. Similarly, behavioural observation (by direct observation or filming) cannot be easily implemented on a large scale, and is actually not fully validated yet as a gold standard. Heart rate and ventilation monitors are influenced by factors other than physical activity [34]. Indirect calorimetry methods, based on the determination of overall oxygen consumption by respirometers, also provide data of debated validity. Therefore, until recently, physical activity assessment for epidemiological purposes mostly relied on questionnaires [35]. Although activity monitors might provide more accurate and reliable (i.e. objective) evaluations, it has long proven difficult to implement their general use in field studies due to cost and feasibility issues, as well as uncertainties regarding the best monitor to choose (pedometer and/or accelerometer). In addition, the need for a conceptual framework in the field of activity measurement has been outlined [36]. In recent years, several epidemiological studies using activity monitors have been published and several initiatives are currently ongoing regarding their use in the field of COPD [37].
Field measurement of physical activity in epidemiologyThe gold standard for physical activity estimation is based on measurements of total energy expenditure by direct calorimetry using doubly labelled water [34]. Physical activity can then be calculated based on total energy expenditure and basal energy expenditure, with the ratio or difference between these variables representing physical activity-related energy expenditure. Such techniques are obviously inappropriate for epidemiological studies, but are to be used to validate field methods. Similarly, behavioural observation (by direct observation or filming) cannot be easily implemented on a large scale, and is actually not fully validated yet as a gold standard. Heart rate and ventilation monitors are influenced by factors other than physical activity [34]. Indirect calorimetry methods, based on the determination of overall oxygen consumption by respirometers, also provide data of debated validity. Therefore, until recently, physical activity assessment for epidemiological purposes mostly relied on questionnaires [35]. Although activity monitors might provide more accurate and reliable (i.e. objective) evaluations, it has long proven difficult to implement their general use in field studies due to cost and feasibility issues, as well as uncertainties regarding the best monitor to choose (pedometer and/or accelerometer). In addition, the need for a conceptual framework in the field of activity measurement has been outlined [36]. In recent years, several epidemiological studies using activity monitors have been published and several initiatives are currently ongoing regarding their use in the field of COPD [37].
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