Accelerometric estimates of physical activity vary unstably with data handling.
    
    
        
    
    
        
        PLoS ONE 12:e0187706 (2017)
    
    
    
      
      
	
	    BACKGROUND: Because of unreliable self-report, accelerometry is increasingly used to objectively monitor physical activity (PA). However, results of accelerometric studies vary depending on the chosen cutpoints between activity intensities. Population-specific activity patterns likely affect the size of these differences. To establish their size and stability we apply three sets of cutpoints, including two calibrated to a single reference, to our accelerometric data and compare PA estimates. METHODS: 1402 German adolescents from the GINIplus and LISAplus cohorts wore triaxial accelerometers (Actigraph GT3x) for one week (mean 6.23 days, 14.7 hours per day) at the hip. After validation of wear, we applied three sets of cutpoints for youth, including the most common standard (Freedson, 2005) and two calibrated to a single reference, (Romanzini uni- and triaxial, from Romanzini, 2014) to these data, estimating daily sedentary, light, moderate, vigorous and moderate-to-vigorous PA (MPA, VPA, MVPA). Stability of differences was assessed by comparing Romanzini's two sets of cutpoints. RESULTS: Relative agreement between cutpoints was closer for activity of lower intensities (largest difference for sedentary behaviour 9%) but increased for higher intensities (largest difference for light activity 40%, MPA 102%, VPA 88%; all p<0.01). Romanzini's uniaxial and triaxial cutpoints agreed no more closely with each other than with Freedson's. CONCLUSIONS: Estimated PA differed significantly between different sets of cutpoints, even when those cutpoints agreed perfectly on another dataset (i.e. Romanzini's.) This suggests that the detected differences in estimated PA depend on population-specific activity patterns, which cannot be easily corrected for: converting activity estimates from one set of cutpoints to another may require access to raw data. This limits the utility of accelerometry for comparing populations in place and time. We suggest that accelerometric research adopt a standard for data processing, and apply and present the results of this standard in addition to those from any other method.
	
	
	    
	
       
      
	
	    
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        Publication type
        Article: Journal article
    
 
    
        Document type
        Scientific Article
    
 
    
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        Keywords
        Adolescents; Validation; Tracking; Children
    
 
    
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        Publication Year
        2017
    
 
    
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        2017
    
 
    
    
        ISSN (print) / ISBN
        1932-6203
    
 
    
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	    Volume: 12,  
	    Issue: 11,  
	    Pages: ,  
	    Article Number: e0187706 
	    Supplement: ,  
	
    
 
    
        
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            Publisher
            Public Library of Science (PLoS)
        
 
        
            Publishing Place
            Lawrence, Kan.
        
 
	
        
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        Peer reviewed
    
 
    
        Institute(s)
        Institute of Epidemiology (EPI)
    
 
    
        POF-Topic(s)
        30503 - Chronic Diseases of the Lung and Allergies
    
 
    
        Research field(s)
        Genetics and Epidemiology
    
 
    
        PSP Element(s)
        G-503900-001
    
 
    
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        Erfassungsdatum
        2017-11-14