Blood Pressure Responses To Exercise At Different Times Of Day

Elevated resting blood pressure (BP), or hypertension, is a risk factor for cardiovascular disease (CVD). Exaggerated exercise BP (EEBP) is an elevated BP at submaximal and maximal exercise and is associated with increased CVD morbidity and mortality. Due to BP’s circadian rhythm and varying chronotypes in the population, it is unknown if exercise performed at certain times of the day will elicit higher BP responses, thus complicating the identification of EEBPs. PURPOSE: To determine how exercise BPs change throughout the day in normotensive adults. METHODS: 31 healthy adults [male = 16, mean age ± standard deviation = 23 ± 4 years] completed a modified Bruce treadmill protocol at 3 different times of day: morning (M, 0700-0900 h), afternoon (A, 1300-1500 h), evening (E, 1800-2000 h). Systolic BP (SBP) was measured pre-exercise (standing prior to test start), and during the last minute of each stage using an automated device. Submaximal SBP was determined from stage 4 of the test; peak SBP was the highest SBP recorded. ΔSBP was calculated as peak SBP-pre-exercise SBP. Participants completed a Morning-Eveningness Questionnaire (MEQ) to determine chronotype. Pearson correlations were used to determine the relationship between MEQ score and ΔSBP during M and E tests. Submaximal, peak and ΔSBP were compared between test times with one-way repeated measures analysis of variance or non-parametric Friedman tests with significance set at P < 0.05. RESULTS: Submaximal SBP (P = 0.295), peak SBP (P = 0.087) and ΔSBP (P = 0.546) were similar across time points. Submaximal SBPs (median, interquartile range) were M:154,140-174 mmHg; A:154, 143-171 mmHg; E:159, 146-174 mmHg. Submaximal EEBP was defined as SBP ≥ 170 mmHg; 15 participants had EEBP during at least one test, 5 had an EEBP during all tests. MEQ scores were correlated with ΔSBP during E test suggesting individuals that were more evening types had a smaller increase in exercise SBP compared to more morning or intermediate types (r = 0.363, P = 0.045); M ΔSBP and MEQ score were not correlated (r = 0.034, P = 0.854). CONCLUSION: Time of day had no effect on BP response to exercise. Given the clinical value of EEBP, it is notable that 48% of our normotensive sample had EEBP during at least one test. Determining the relationship between chronotype and exercise BPs throughout the day is warranted.