|Activity, Energy Expenditure and Energy Requirements of Infants and Children (International Dietary Energy Consultative Group - IDECG, 1989, 412 pages)|
|Methods to assess physical activity and the energy expended for it by infants and children|
|2. Methods of acquiring information on the physical activity of infants and children|
Direct, or objective, measurements of activity have both advantages and disadvantages over a questionnaire or observational study. Firstly, because they involve an impersonal measurement and not a subjective impression, the data are more reliable. Secondly, because quantitative data are provided, more subtle assessments may be made than just gross subdivisions of activity. The disadvantages are both technical and financial. Studies that entail objective assessment of activity, require relatively expensive instruments. This may force the investigator to reduce the number of subjects from hundreds or even thousands of individuals who could be studied by a combination of questionnaire, or prospective diary records and observation, to no more than tens of individuals where instrumented, direct recording is performed. Lastly, many parents might be prepared to assist in the former method, and not wish the trouble and inconvenience of ensuring that a recording instrument continues to function properly.
Nevertheless, both approaches may be combined on occasion, with a large population being studied by questionnaire, and a subsample having objective measurements of activity to validate the larger data base.
Several techniques for measuring activity are available. Some simply record movement - such as pedometers, accelerometers, actometers, or electrical devices for counting steps. Others, such as the video-camera, may record activity in detail.
All of these techniques have been used in studies of physical activity in adults, and have been tried with varying degrees of success in children.
Pedometers have been in use for many years. While their design has improved recently, they can still occasionally give quite erroneous recordings and they do not, of course, necessarily detect activities performed in a more or less static position - arm movements, for instance. Even for a very rough estimation of activity they will have limited usefulness, and, for example, SARIS and BINKHORST (1977) found them very inaccurate.
An instrument, designed to provide an output similar to that of a pedometer but using a different principle, records an electrical impulse each time the shoe touches the ground. Even though, like pedometers, these instruments do not necessarily record all types of activity, they may have a role in a rough categorization of individuals into various groupings.
Accelerometers measure horizontal, lateral, or vertical movement, but counts may not differ in lying, sitting and standing, and work involving only the arms will not greatly increase the count rate of an accelerometer mounted on the trunk. These instruments are of most use in laboratory-based studies and are not particularly useful in large-scale field studies.
Actometers can be many different types of instrument; often they have the form of a modified wrist watch capable of recording acceleration and intensity of movement. They are inexpensive instruments and have been used successfully in adults and children for discriminating between groups of individuals with differing activity patterns. Studies have been described by SARIS and BINKHURST (1977), LAPORTE et al. (1979), TRYON (1987), and AVONS et al. (1988). However, they are not capable, as was originally hoped, of giving an indirect estimate of energy expenditure, and the fact that they need frequent calibration - for individual subjects, for the types of activity, and for the instruments makes it unlikely that they will be employed in large-scale studies in the near future.
Video-recording has a definite role in the assessment of children's activity patterns. However, obviously this is a technique which is unlikely to be practicable for large groups of individual children. The size of group which may be analysed by video-recording will vary depending on the objective of the study and, perhaps more importantly, on the financial resources available, since cameras and the actual analyses of the nature, frequency, and intensity of the movements of the child are all expensive.
There are obvious theoretical advantages of video-recording over direct observation and the recording of activity on a specially designed diary form. Direct recording requires immediate judgement of the actual activity and the noting down in some predetermined manner an abbreviated description of the activity. Often one observer may be required for one or, at the most, two children. If observations are needed over several hours, it may be difficult for the observers to maintain a satisfactory level of attention.
Video-recording can be used on several children simultaneously, and it can be played-back as often as required to make the appropriate decisions. It is also possible to use it in a more unobtrusive way, and it is more likely to be socially acceptable in both the developing and developed world. The practical problem, however, lies in the difficulty of analysing and quantifying the video-recordings to allow some ranking of individual children. It may provide the best way of assessing the activity of an infant or child in combination with some form of questionnaire or a diary record.