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.
Highlights
In the 1970s and 80s, Esther Thelen and colleagues described the developmental trajectory of infants’ spontaneous leg movements across the first year of life and explained how alternating kicking is a precursor to walking in typically-developing infants [1,2,3,4,5]
We were able to accurately identify the number of daily leg movements infants’ produced from wearable sensor data collected in their home environment while they went about their typical activities
There are two key points to our algorithm’s accuracy: (1) we set an acceleration threshold based on the unique movement characteristics of each infant, establishing a unique “noise” threshold based on the statistical properties of their movement; and (2) we require both acceleration and rotation to be present in order to count a movement, which ignores motion from cars, strollers and mechanical swings
Summary
In the 1970s and 80s, Esther Thelen and colleagues described the developmental trajectory of infants’ spontaneous leg movements across the first year of life and explained how alternating kicking is a precursor to walking in typically-developing infants [1,2,3,4,5]. They did not, quantify how many leg movements an infant makes in a day or how much leg movement practice is necessary in order to learn to walk. In our small sample we can identify there is an effect of leg movement quantity on walking onset, we cannot fully explain it
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