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 1.

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. 

Fitback believes that measuring the direct long-term response of an individual child 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. Indeed, The American Heart Association has recommended that physical fitness be included on the vital health indicators list and is something that should be recorded during each doctor visit 2

Many countries are following the recommendations of several international physical health documents (e.g. health promotion activities, HEPAs) to establish their own systematic fitness surveillance and monitoring on the population level 3-6

To support such efforts, The European Network for the Support of Development of Systems for Monitoring Physical Fitness of Children and Adolescents (FitBack) was developed which provides web application for simple feedback on physical fitness testing as well as important information for stakeholders on establishing these kinds of monitoring systems.


  1. Adamo K.B., Prince S.A., Tricco A.C., Connor-Gorber S, Tremblay M. A comparison of indirect versus direct measures for assessing physical activity in the pediatric population: a systematic review. Int J Pediatr Obes. 2009;4(1):2-27.
  2. Ross R, Blair S.N., Arena R, et al. Importance of assessing cardiorespiratory fitness in clinical practice: a case for fitness as a clinical vital sign: a scientific statement from the American Heart Association. Circulation. 2016:CIR-0000000000000461.
  3. Andersen L.B., Andersen SA, Bachl N, et al. EU Physical Avtivity Guidelines: Recommended policy Actions in Support of Health-Enchanging Physical Activity Fourth Consolidated Draft, Approved by the EU-working group. 2008.
  4. Commission E. EU Action Plan on Childhood Obesity 2014-2020. A growing health challenge for the EU. 2014.
  5. Council E. Council Recommendation of 26 November 2013 on promoting health-enhancing physical activity across sectors. Off J Eur Union. 2013;56:1-5.
  6. Organization WH. Physical activity strategy for the WHO European Region 2016-2025. 2016.

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