Prior exercise lowers blood pressure during simulated night-work with different meal schedules

Abstract

Background: Shift-work and a sedentary lifestyle are risk factors for raised blood pressure (BP). Exercise can reduce BP in diurnally-active individuals, but it is unknown whether postexercise hypotension persists when people are active and eating at night. We present the first investigation into the acute effects of exercise on BP monitored during simulated night-work.

Methods: Nine normotensive participants, aged 20-42 years, completed at least two crossover trials beginning at 1800 hours. Between 1900 and 2000 hours, participants either rested or exercised at 50% peak oxygen uptake (VO(2peak)) and then remained awake throughout the night, completing various tasks until 0515 hours. Six participants completed a total of four trials in which they exercised or rested, whereas either one standardized (60 kJ/kg) meal at 2200 hours or two smaller (30 kJ/kg) meals at 2200 and 0200 hours were eaten. Systolic and diastolic BP, mean arterial pressure (MAP), heart rate (HR), and wrist activity were recorded every 30 min.

Results: Following exercise, MAP was significantly (P < 0.0005) lower throughout the night-shift compared with no prior exercise (95% confidence limits for reduction: 4-7 mm Hg). The postexercise reductions in systolic BP and MAP were not moderated by diet, but the reduction in diastolic BP was slightly greater when only one meal was eaten (P < 0.0005). BP was lower even though wrist activity and HR were significantly higher following exercise (P < 0.0005).

Conclusions: These data indicate that prior exercise lowers BP throughout a subsequent 8-h night-shift in healthy individuals within the normotensive range. Therefore, regular low-intensity exercise might moderate the well-known association between shift-work participation and raised BP.

Figure 1

Mean ± s.e. systolic blood pressure measured every 30 min during a simulated night-shift with, and without, exercise prior to the beginning of the shift. (a) Consumption of two smaller (30 kJ/kg body mass) meals during the shift at 2200 and 0200 hours. (b) Consumption of one larger (60 kJ/kg body mass) meal during the shift at 2200 hours. The gray panel indicates time of exercise or rest. Black vertical lines indicate time of meal consumption.

Figure 2

Mean ± s.e. diastolic blood pressure measured every 30 min during a simulated night-shift with, and without, exercise prior to the beginning of the shift. (a) Consumption of two smaller (30 kJ/kg body mass) meals during the shift at 2200 and 0200 hours. (b) Consumption of one larger (60 kJ/kg body mass) meal during the shift at 2200 hours. The gray panel indicates time of exercise or rest. Black vertical lines indicate time of meal consumption.

Figure 3

Mean ± s.e. MAP measured every 30 min during a simulated night-shift with, and without, exercise prior to the beginning of the shift. (a) Consumption of two smaller (30 kJ/kg body mass) meals during the shift at 2200 and 0200 hours. (b) Consumption of one larger (60 kJ/kg body mass) meal during the shift at 2200 hours. The gray panel indicates time of exercise or rest. Black vertical lines indicate time of meal consumption. MAP, mean arterial pressure.

Figure 4

Mean ± s.e. heart rate measured every 30 min during a simulated night-shift with, and without, exercise prior to the beginning of the shift. (a) Consumption of two smaller (30 kJ/kg body mass) meals during the shift at 2200 and 0200 hours. (b) Consumption of one larger (60 kJ/kg body mass) meal during the shift at 2200 hours. The gray panel indicates time of exercise or rest. Black vertical lines indicate time of meal consumption.