With great interest we read the article by Kelly et al. on the measurement of physical activity (PA) and sedentary behavior (SB) (Kelly P et al. Int J Behav Nutr Phys Act 13:(1) 32, 2016). We appreciate the invitation of the authors to provide feedback on their ideas and we take this opportunity to contribute to the discussion. Our main proposition is that this field can learn much from the field of quality of life research and the methodology developed for validating quality of life questionnaires.
Keywords: Physical activity; Reliability; Sedentary behavior; Validity.