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Infant Activity Rhythms During Sleep Measured in Largest Study of Its Kind

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How Babies’ Sleep Cycles Develop in Their First Year

A new study from the University of Surrey provides the clearest picture yet of how sleep patterns evolve in the first year of life, tracking the rhythmic cycles of inactivity in infants from just three months of age.

"The more we learn, the more we can pinpoint healthy from unhealthy sleep and help parents and doctors to catch problems early."
— Dr. Eva Winnebeck, Lecturer in Chronobiology, University of Surrey

The Study at a Glance

Researchers monitored sleep cycle development in 152 infants at three key ages: 3, 6, and 12 months old. To gather precise data, they used actigraphy devices—small motion trackers—attached to the infants’ ankles for 10 days at each age. The parents also wore wrist devices to provide a comparison.

Over 35,000 hours of sleep data were analyzed to identify rhythmic patterns of movement and inactivity.

Key Findings on Infant Sleep Rhythms
  • Early Rhythms: Rhythmic patterns of inactivity were detectable in infants from three months of age.
  • Cycle Length: At 3 months, cycles of inactivity averaged about 60 minutes. By 12 months, this cycle had lengthened by 10 minutes.
  • Contrast with Parents: For comparison, parent cycles of inactivity averaged 81 minutes.
  • Movement Over Time: Limb inactivity was highest at the start of a sleep period and steadily decreased as the night progressed.
The Role of Breastfeeding

A notable finding linked breastfeeding to sleep cycle length.

  • At 12 months, infants who were still being breastfed had longer inactivity cycles compared to non-breastfed infants.
  • Mothers who continued breastfeeding at 12 months also showed a difference: their own cycle length was longer by approximately 6.7 minutes.

"Our finding will help advance our understanding of the intricate relationship between sleep and development."
— Dr. Grégory Hammad, Visiting Researcher, University of Surrey (First Author)

Why This Matters

The first year of life is a period of dramatic change in sleep, shifting from multiple short naps throughout the day to more consolidated nighttime sleep. This study, published in the journal SLEEP, uses movement monitoring—a technique that predates the discovery of REM sleep—to gain new insights into how these fundamental rhythms stabilize in early development.