Question

what is the health assessment of physical activity

what is the health assessment of physical activity

Answer 1

Behavioral observation is one of the earliest methods to assess physical activity. It has evolved by direct entry of data in a computer (McKenzie 2002). The method exceeds other measures of physical activity in providing contextual information as well. Disadvantages are that the method is time consuming, the presence of an observer might interfere with the activity behavior of the subject and the classification of observed activities, especially activity intensity, is subjective. There are no doubly labeled water validations available in literature, possibly because observations do not last for intervals of 1 week or more as required for the application of the doubly labeled water technique in humans (Speakman 1997).

Activity questionnaires, including interviews and diaries, are the most common tools for the assessment of physical activity. The methodology is cheap and allows application in large populations. Despite the large-scale application, reliability and validity of the measurement of habitual physical activity by questionnaires is low  

Heart rate monitoring is one of the first objective methods for the assessment of physical activity. Validation studies generally include 2–4 days continuous heart rate monitoring during the 7–14 day observation intervals with doubly labeled water. Observation days were weekdays as well as weekend days and results are weighted in a ratio according to the doubly labeled water interval. Studies apply individually assessed heart-rate energy-expenditure calibration equations for the estimation of daily energy expenditure, where equations comprise two linear regression lines, one for heart rates below and one for heart rates above the average value for sedentary activities; the so-called flex heart rate. The results of 11 different studies were reviewed in 1999 and 2005 (Westerterp 1999; Torun 2005). The total energy expenditure assessed with heart rate monitoring was not different from total energy expenditure assessed with doubly labeled water at group level in all studies. However, individual differences were large as shown by the SD of the mean. The reported extremes ranged between −17% (Livingstone et al. 1992) and 52% (Livingstone et al. 1990). The heart rate monitoring is an objective method. However, the heart rate is affected by more factors than physical activity; data conversion needs individual measurements of heart rate in combination with oxygen consumption. Nowadays, the heart rate is applied especially as an indicator of activity intensity (Rennie et al. 2005). A new application is the measurement of the heart rate in combination with body movement as a measure of physical fitness (Plasqui and Westerterp 2005, 2006). Those with a higher level of physical fitness can generate more activity at a lower heart rate than unfit subjects. Additionally, the combining heart rate with accelerometry as described below, may improve precision of physical activity measurement. However, the general shortcoming of heart rate monitoring over longer time under free-living conditions still is the data quality (Brage et al. 2006).

Motion sensors are the most promising for the assessment of physical activity. Sensors can be applied in free-living subjects over prolonged periods of time. When equipped with a data memory to store information on body movement, they can also be used to study patterns of physical activity in time. Various sensors have been developed from mechanical devices to electronic accelerometers. Accelerometers can provide information about the total amount, the frequency, the intensity, and the duration of physical activity. Eight different devices have been evaluated with doubly labeled water as a reference (Plasqui and Westerterp 2007). However, most of the studies should be interpreted with care. The validity is generally based on a comparison between accelerometer output and doubly labeled water assessed energy expenditure in a multiple regression analysis with subject characteristics as additional covariates. The separate contribution of accelerometer counts to the explained variation in energy expenditure is often not presented and standard errors or limits of agreement are large or not presented. The best results were found for the Tracmor (Philips Research, Eindhoven, The Netherlands), a device with the first published doubly labeled water validation (Bouten et al. 1996) that is expected to become commercially available shortly.