The purpose of this investigation was to quantify the acute pressor response to caffeine at rest and during exercise, and to compare responses for different reportings of caffeine consumption and sensitivity. Eight young men with high use (HU) consumption patterns (<600 mg/day) and eight with low use (LU) patterns (<90 mg/day) participated. Caffeine (C) (4.5 mg/kg fat free mass) and placebo (P) were administered, double-blind and counterbalanced. Systolic (SBP), diastolic blood pressure (DBP) and heart rate (HR) were monitored during baseline, 40 minutes of absorption and graded treadmill walking. Oxygen consumption (V02) and rating of perceived exertion (RPE) were monitored during exercise. No significant differences were found for the responses to C between HU and LU nor between sensitive and not sensitive groups. Following a 12 hour abstinence, caffeine significantly increase SBP and DBP at absorption compared to P (11/9 mm Hg). The increase was additive with exercise for SBP but not DBP. Caffeine significantly increased VO2 compared to P. No significant differences were found for HR nor RPE between C and P trials. The present data indicate chronic caffeine consumption does not build tolerance to the acute pressor response to caffeine ingestion, the resting pressor response is additive with the pressor response to exercise for SBP, and individual perceptions of caffeine sensitivity are not accurate predictors of pressor responses. / School of Physical Education

The effect of caffeine consumption on blood pressure has been widely studied. Robertson et al. (J Clin Invest 67: 1111-1117, 1981) cited findings of tolerance to humoral and hemodynamic effects from caffeine within four days when caffeine is consumed with each meal. These findings of tolerance have not been verified. The purpose of this study was to determine the effect of caffeine intake pattern on the development of tolerance to hemodynamic effects of caffeine. Fourteen volunteers were randomly assigned to two groups of seven. One group received 250 mg of caffeine in the morning only (MO), the other group received 250 mg of caffeine in the morning, afternoon, and evening (All Day-AD). Subjects underwent a seven day trial during which blood pressure (BP) and heart rate (HR) were assessed; morning beverage (250 mg of caffeine) was ingested and BP and HR assessments were obtained every 10 minutes for 50 minutes at rest, and after 10 minutes of cycling at 100 Watts. Afternoon and evening beverages were consumed which contained 250 mg caffeine each or placebo. No significant change in SBP, DBP, or HR from rest to 40 minutes post-caffeine absorption or between caffeine dosing pattern across trial days was found. A main effect was found for SBP post caffeine consumption (MO=5.4 vs. AD= 1.3). Mean values for DBP were stable across days 3-7 (M0=3.14-4.7 mmHg) but decreased from (3.86-.14 mmHg) from days 3 to 7 (AD). SBP revealed a significant interaction during exercise and across trial days. SBP and HR for the morning only group was higher than the all day caffeine consumption group across days. However DBP was lower across days for the morning only vs. the all day intake pattern. Therefore, caffeine dosing pattern does not appear to have an effect on tolerance to the hemodynamic effects of caffeine at rest or during exercise. / School of Physical Education