EFFECTS OF CAFFEINE ON BLOOD-PRESSURE, HEART-RATE, AND FOREARM BLOOD-FLOW DURING DYNAMIC LEG EXERCISE

This study examined the acute effects of caffeine on the cardiovascula r system during dynamic leg exercise. Ten trained, caffeine-naive cycl ists (7 women and 3 men) were studied at rest and during bicycle ergom etry before and after the ingestion of 6 mg/kg caffeine or 6 mg/kg fru ctose (placebo) with 250 ml of water. After consumption of caffeine or placebo, subjects either rested for 100 min (rest protocol) or rested for 45 min followed by 55 min of cycle ergometry at 65% of maximal ox ygen consumption (exercise protocol). Measurement of mean arterial pre ssure (MAP), forearm blood flow (FBF), heart rate, skin temperature, a nd rectal temperature and calculation of forearm vascular conductance (FVC) were made at baseline and at 20-min intervals. Plasma ANG II was measured at baseline and at 60 min postingestion in the two exercise protocols. Before exercise, caffeine increased both systolic blood pre ssure (17%) and MAP (11%) without affecting FBF or FVC. During dynamic exercise, caffeine attenuated the increase in FBF (53%) and FVC (50%) and accentuated exercise-induced increases in ANG II (44%). Systolic blood pressure and MAP were also higher during exercise plus caffeine; however, these increases were secondary to the effects of caffeine on resting blood pressure. No significant differences were observed in h eart rate, skin temperature, or rectal temperature. These findings ind icate that caffeine can alter the cardiovascular response to dynamic e xercise in a manner that may modify regional blood flow and conductanc e.