Exercise systolic blood pressures are unaffected by time of day in healthy young adults

Blood pressure (BP) assessment during exercise testing has the capacity to identify exaggerated exercise BP (EEBP). BP has a circadian rhythm; therefore, exercise BPs may change throughout the day complicating EEBP identification. The purpose of this study was to determine the effect of time of day on exercise BP in healthy young adults. Thirty-one participants [48% female; 23(4) years] completed a modified Bruce treadmill protocol in the morning (M), afternoon (A), and evening (E). Submaximal (stage 4) and peak (highest value) systolic BP (SBP) were determined and ΔSBP was calculated (peak SBP-pre-exercise SBP). Repeated-measures tests were used to compare SBP data. EEBP was defined as a submaximal SBP ≥ 170 mmHg. Chronotype was assessed using the Morning-Eveningness Questionnaire (MEQ) and Pearson correlations were used to determine the relationship between MEQ score and ΔSBP during all tests. Significance was set at P < 0.05. Submaximal SBP (M:159(25); A:156(16); E:162(24) mmHg; P = 0.295), peak SBP (M:177(32); A:184(25); E:185(26) mmHg; P = 0.087) and ΔSBP (M:62(29); A:67(23); 65(20) mmHg; P = 0.546) were similar across time points. Eight participants had an EEBP on at least two tests. MEQ scores were correlated with ΔSBP during the A test (r = 0.357, P = 0.049) and E test (r = 0.363, P = 0.045). In conclusion, time of day had no effect on SBP responses to exercise, but our correlational analysis suggests changes in SBP may differ between chronotypes depending on the time of day of exercise. Given the clinical value of EEBP, it is notable that 26% of our healthy young sample had EEBP.