Krishnaveni, et al.(3) measured physical activity in children with uni-axial accelerometers (MTI Actigraph AM7164, MTI Health Services, Florida, USA). Time spent in sedentary-, light-, moderate- and vigorous intensity activity, as calculated with self-defined cut-off levels for accelerometer counts, was compared with simultaneously kept diaries of the child’s activities by parents and teachers. The wide limits of agreement between accelerometer-assessed and diary-assessed time spent in activities of varying intensity was seen as a limitation of the data accelerometers generate.

One can argue on the conclusion derived from the data as stated by the authors. The interrelation of accelerometers with diaries may be of some value, but because there are potentially errors in both methods, it is impossible to determine the true validity of any one of them in doing so. Calorimetry, more specifically the doubly labeled water method, has become the gold standard for the validation of field methods of assessing physical activity(4). Then, accelerometers show a high potential as a field method for the assessment of volume, pattern, intensity, type, and energy expenditure of physical activity.

The conclusion as derived by Krishnaveni, et al.(3) generalizes the results as derived with one type of uni-axial accelerometer (MTI Actigraph AM7164, MTI Health Services, Florida, USA) to accelerometers in general. However, the capacity of accelerometers to assess physical activity dimensions like volume, pattern, intensity, type, and energy expenditure of physical activity is a function of the characteristics of the sensor and the data processing. Again, doubly labeled water is the indicated reference for evaluation. Thus, it appeared using a tri-axial instead of a uni-axial accelerometer impro-ved the performance significantly(5).

The study by Krishnaveni, et al.(3) shows modest relations between Actigraphs and diaries for time spent in sedentary-, light-, moderate intensity activity, but not for vigorous intensity activity. Future evaluations on physical activity assessment in children should specifically focus on the capacity to detect high-intensity activity. Hoos, et al.(6) did a study on physical activity in similar aged children with a tri-axial accelerometer, showing that to obtain a higher physical activity level in children, they should be given opportunities to perform high-intensity activities.

Funding: None.

Competing interests: None stated.

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