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close this bookActivity, Energy Expenditure and Energy Requirements of Infants and Children (International Dietary Energy Consultative Group - IDECG, 1989, 412 pages)
close this folderMethods to assess physical activity and the energy expended for it by infants and children
close this folder2. Methods of acquiring information on the physical activity of infants and children
View the document(introductory text...)
View the document2.1. Questionnaire or diary record
View the document2.2. Direct, objective measurements of activity
View the document2.3. Heart-rate recording
View the document2.4. Methods of acquiring information on energy expenditure

2.3. Heart-rate recording

It is technically relatively easy to record heart-rate over prolonged periods of time. If only a record of heart-rate is needed, this is not an expensive technique and instruments are readily available. If a more elaborate break-down of the data is desired - such as the duration of several different ranges of heart-rate, to indicate differing levels of activity - say 80-100, 100-120, 120-140, over 140 beats/min - then this will become expensive and somewhat complex.

Heart-rate recorders can be purchased to provide almost any information on heart-rate that is desired. However, there is some confusion about what exactly can be derived from heart-rates, and some basic physiological facts need to be repeated.

Firstly, the heart-rate is related to cardiac output. This relation is closer at higher levels of exercise than at moderate and low levels, because of the many other influences on heart-rate, such as posture, effect of meals, psychological factors, the muscle masses involved, and so on. At levels which are most common for infants and children in ordinary daily life, heart-rate has a highly variable relationship to the level of physical activity, and this relationship can also vary within and between individuals.

Thus, heart-rate can be a good general indicator of activity, but can not be a very precise indicator of energy expenditure. Moreover, analysing heart-rate records, even using computerized techniques, often requires some expert decision-making and is a tedious procedure. An additional problem with young infants is that they tend to tamper with electrodes and connecting electrical wiring. We had to discontinue a study on 2-3-year-olds for this reason. Heart-rate recording has a definite place in the methodology of assessing physical activity in children, but has to be employed with discretion.