Natural statistics of infants’ everyday motor experiences relate to sitting and walking development.

The present study reports the natural statistics of everyday motor experiences, measured throughout the day using wearable inertial sensors. Using a large data set of infants' real-time upright, sitting, prone, supine, and held experiences, we investigated how age and motor skill relate to the frequency and bout structure of body position. Our analyses replicated past survey and observational work by showing that older infants (11-14 months) spend more time sitting and upright compared with younger infants (4-7 months) and that the emergence of sitting and walking skills may contribute to these age differences. Furthermore, our analyses were novel in revealing that a larger share of younger infants' bouts were longer-lasting several minutes and even over an hour. In contrast, older infants had a greater share of shorter bouts less than 1 min long, suggesting they experience a greater mix of positions. Within older infants, bout duration distributions also varied according to walking skill. We discuss the importance of understanding the natural statistics of motor experiences at different timescales for characterizing infants' opportunities for motor learning and perceptual-motor exploration in daily life. (PsycInfo Database Record (c) 2026 APA, all rights reserved).