The CLOCK 3111T/C polymorphism is associated with hour-by-hour physical activity levels only on weekends among Japanese male and female university students

•CLOCK 3111T/C polymorphism is associated with sleep-wake rhythms including activity.•No study has examined CLOCK 3111T/C or physical activity (PA) for an entire week.•PA among genetically evening-oriented students was low only on Saturday.•PA among genetically evening-oriented students was low only on Saturday.•Social obligations may mask the genetically determined biological rhythm of PA on weekdays.