Physical activity and the circadian rhythm of blood pressure.

1. Ambulatory blood pressure monitoring was carried out in 10 subjects for a period of 48 h, the first or second 24 h part of which was selected randomly to be a period of complete bed rest. 2. Heart rate was significantly lower throughout the period of bed rest except for the period 04.00-08.00 hours, when there was little difference. 3. The circadian variation of blood pressure was reduced during the day of bed rest but this was mainly due to higher night-time pressures.