Day length associates with activity level in children living at 60 degrees north.

The associations between day length and activity, rest-activity rhythm, and psychiatric symptoms were studied. Sixty-six healthy children participated in the study during one year. They were monitored for 72 consecutive hours with belt-worn activity monitors (actigraphs) to obtain objective data on their activity levels during the day and night. In addition, the parents filled out the Child Behavior Checklists. It was found, that the mean total and day and night time activity levels were increased and the relative circadian amplitude blunted with the longer day length. It was concluded that day length was associated with activity level and rest-activity rhythm and this association may reflect the seasonal changes in these parameters.