title: Daily Quantity of Infant Leg Movement: Wearable Sensor Algorithm and Relationship to Walking Onset.
abstract: BACKGROUND
  Normative values are lacking for daily quantity of infant leg movements. This is critical for understanding the relationship between the quantity of leg movements and onset of independent walking, and will begin to inform early therapy intervention for infants at risk for developmental delay.
  
  
  METHODS
  We used wearable inertial movement sensors to record full-day leg movement activity from 12 infants with typical development, ages 1-12 months. Each infant was tested three times across 5 months, and followed until the onset of independent walking. We developed and validated an algorithm to identify infant-produced leg movements.
  
  
  RESULTS
  Infants moved their legs tens of thousands of times per day. There was a significant effect of leg movement quantity on walking onset. Infants who moved their legs more walked later than infants who moved their legs less, even when adjusting for age, developmental level or percentile length. We will need a much larger sample to adequately capture and describe the effect of movement experience on developmental rate. Our algorithm defines a leg movement in a specific way (each pause or change in direction is counted as a new movement), and further assessment of movement characteristics are necessary before we can fully understand and interpret our finding that infants who moved their legs more walked later than infants who moved their legs less.
  
  
  CONCLUSIONS
  We have shown that typically-developing infants produce thousands of leg movements in a typical day, and that this can be accurately captured in the home environment using wearable sensors. In our small sample we can identify there is an effect of leg movement quantity on walking onset, however we cannot fully explain it.
authors.affiliation: Division of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, CA 90089-9006, USA. beth.smith@usc.edu.
authors.forename: Beth A
authors.initials: BA
authors.lastname: Smith
authors.affiliation: Division of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, CA 90089-9006, USA. itrujill@usc.edu.
authors.forename: Ivan A
authors.initials: IA
authors.lastname: Trujillo-Priego
authors.affiliation: Department of Preventative Medicine, Division of Biostatistics, Keck School of Medicine, University of Southern California, Los Angeles, CA 90089-9234, USA. christianne.lane@med.usc.edu.
authors.forename: Christianne J
authors.initials: CJ
authors.lastname: Lane
authors.affiliation: Division of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, CA 90089-9006, USA. jmfinley@usc.edu.
authors.forename: James M
authors.initials: JM
authors.lastname: Finley
authors.affiliation: Department of Neurology, Oregon Health & Science University and Portland Veterans Affairs Medical Center, Portland, OR 97239-3098, USA. horakf@ohsu.edu.
authors.forename: Fay B
authors.initials: FB
authors.lastname: Horak
mesh_terms: D000054:Acceleration; D000465:Algorithms; D000886:Anthropometry; D005260:Female; D006801:Humans; D007223:Infant; D007866:Leg / Q000502:physiology*; D008297:Male; D009068:Movement / Q000502:physiology*; D010827:Physiology / Q000295:instrumentation*; D016138:Walking / Q000502:physiology*
keywords: growth and development; infant; movement; wearable sensors