Physical activity or physical fitness: which is better to monitor in children?
Fitback believes that measuring the direct long-term response of individuals to physical activity – their physical fitness – is a more reliable indicator of habitual physical activity, as well as providing a more stable factor in assessment of health risks.
Objectively assessing physical activity remains a very challenging task despite many technological advances in the field over the past several years. Using any kind of wearable device to assess physical activity in daily life introduces numerous problems, that in reality boil down to one issue: that any two devices will provide two different estimations of the physical work that was performed.
Therefore, it is difficult to accurately assess: exercise intensity thresholds, frequency of data collection, wear time, the inability of the device to differentiate between different types of movement (e.g. cycling, walking, water activity), and how to condense all this information into one useful metric encompassing all physical activity completed in a day. In addition, environmental factors like changes in weather conditions can independently affect the usual behaviour of a child on any given day. Finally, just wearing a new, shiny device can itself affect the behaviour of an individual.
Despite these well-documented shortcomings, accelerometer-based measuring devices (i.e. objectively measured physical activity monitors) are much more reliable for assessing physical activity and energy use than subjective information obtained from activity questionnaires alone .
Keep in mind: there are considerable differences in energy metabolism between different individuals. Existing recommendations on the frequency, intensity, duration and type of physical activity espoused generally ignore individual differences, and propose universal solutions to specific needs. This means that two children involved in the same physical activity of identical duration and intensity may achieve different energy values even if they are of the same age, sex, height and body mass. Each child will respond differently physiologically when exposed to an identical physical activity stimulus.