title: Artificial neural networks to predict activity type and energy expenditure in youth.
abstract: Previous studies have demonstrated that pattern recognition approaches to accelerometer data reduction are feasible and moderately accurate in classifying activity type in children. Whether pattern recognition techniques can be used to provide valid estimates of physical activity (PA) energy expenditure in youth remains unexplored in the research literature.
  
  
  OBJECTIVE
  The objective of this study is to develop and test artificial neural networks (ANNs) to predict PA type and energy expenditure (PAEE) from processed accelerometer data collected in children and adolescents.
  
  
  METHODS
  One hundred participants between the ages of 5 and 15 yr completed 12 activity trials that were categorized into five PA types: sedentary, walking, running, light-intensity household activities or games, and moderate-to-vigorous-intensity games or sports. During each trial, participants wore an ActiGraph GT1M on the right hip, and VO2 was measured using the Oxycon Mobile (Viasys Healthcare, Yorba Linda, CA) portable metabolic system. ANNs to predict PA type and PAEE (METs) were developed using the following features: 10th, 25th, 50th, 75th, and 90th percentiles and the lag one autocorrelation. To determine the highest time resolution achievable, we extracted features from 10-, 15-, 20-, 30-, and 60-s windows. Accuracy was assessed by calculating the percentage of windows correctly classified and root mean square error (RMSE).
  
  
  RESULTS
  As window size increased from 10 to 60 s, accuracy for the PA-type ANN increased from 81.3% to 88.4%. RMSE for the MET prediction ANN decreased from 1.1 METs to 0.9 METs. At any given window size, RMSE values for the MET prediction ANN were 30-40% lower than the conventional regression-based approaches.
  
  
  CONCLUSIONS
  ANNs can be used to predict both PA type and PAEE in children and adolescents using count data from a single waist mounted accelerometer.
authors.affiliation: School of Biological and Population Health Sciences, Oregon State University, Corvallis, OR 97331, USA. stewart.trost@oregonstate.edu
authors.forename: Stewart G
authors.initials: SG
authors.lastname: Trost
authors.forename: Weng-Keen
authors.initials: WK
authors.lastname: Wong
authors.forename: Karen A
authors.initials: KA
authors.lastname: Pfeiffer
authors.forename: Yonglei
authors.initials: Y
authors.lastname: Zheng
mesh_terms: D000203:Activities of Daily Living; D000293:Adolescent; D002153:Calorimetry, Indirect; D002648:Child; D002675:Child, Preschool; D004734:Energy Metabolism / Q000502:physiology*; D015444:Exercise / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D018670:Monitoring, Ambulatory / Q000379:methods*; D009043:Motor Activity / Q000502:physiology*; D016571:Neural Networks, Computer; D012044:Regression Analysis; D013177:Sports / Q000502:physiology