Abstract
BackgroundThe purpose of this study was to examine the cardiovascular effects of two low-levels of caffeine ingestion in non habitual caffeine users at various submaximal and maximal exercise intensities.MethodsNine male subjects (19–25 yr; 83.3 ± 3.1 kg; 184 ± 2 cm), underwent three testing sessions administered in a randomized and double-blind fashion. During each session, subjects were provided 4 oz of water and a gelatin capsule containing a placebo, 1.5 mg/kg caffeine, or 3.0 mg/kg caffeine. After thirty minutes of rest, a warm-up (30 Watts for 2 min) the pedal rate of 60 rpm was maintained at a steady-state output of 60 watts for five minutes; increased to 120 watts for five minutes and to 180 watts for five minutes. After a 2 min rest the workload was 180 watts for one minute and increased by 30 watts every minute until exhaustion. Heart rate (HR) was measured during the last 15-seconds of each minute of submaximal exercise. Systolic blood pressure (BP) was measured at rest and during each of the three sub-maximal steady state power outputs. Minute ventilation (VE), Tidal volume (VT), Breathing frequency (Bf), Rating of perceived exertion (RPE), Respiratory exchange ratio (RER), and Oxygen consumption (VO2) were measured at rest and during each minute of exercise.ResultsCaffeine at 1.5 and 3.0 mg/kg body weight significantly lowered (p < 0.05) HR during all three submaximal exercise intensities compared to placebo (range – 4 to 7 bpm lower) but not at rest or maximal exercise. BP was significantly higher (p < 0.05) at rest and after the 3 mg/kg caffeine vs placebo (116 ± 13 vs 123 ± 10 mm Hg). Neither dose of caffeine had any effect on BP during submaximal exercise. Caffeine had no effect on VE, VT, VO2, RPE, maximal power output or time to exhaustion.ConclusionIn non habitual caffeine users it appears that consuming a caffeine pill (1.5 & 3.0 mg/kg) at a dose comparable to 1–3 cups of coffee lowers heart rate during submaximal exercise but not at near maximal and maximal exercise. In addition, this caffeine dose also only appears to affect systolic blood pressure at rest but not during cycling exercise.
Highlights
Caffeine is the most widely used drug in the world and the use of caffeine or caffeine containing beverages is extremely common among all levels of athletes hoping to gain an ergogenic benefit
Neither dose of caffeine had any effect on blood pressure (BP) during submaximal exercise
There were no differences in the resting mean VE, VO2, VT, and Breathing frequency (Bf) between the three trials
Summary
Caffeine is the most widely used drug in the world and the use of caffeine or caffeine containing beverages is extremely common among all levels of athletes hoping to gain an ergogenic benefit. Caffeine is generally regarded to have ergogenic properties and its use is currently banned by the NCAA at dose which elicits a urinary concentration of 15 ug/ml; a dose which is far higher than needed to achieve performance benefits [2]. Much of the exercise research with caffeine has investigated potential mechanisms mediating performance. The inhibition of adenosine receptors including those in the central nervous system is considered by some to be a more likely mediator of caffeine's ergogenic properties [1,2,3]. Some have added to the debate suggesting that the inhibition of adenosine receptors including those in the central nervous system could be a more likely mediator of caffeine's ergogenic properties [13]. While not considered to have a role in performance enhancement, caffeine's cardiovascular effects have generated much interest. The purpose of this study was to examine the cardiovascular effects of two lowlevels of caffeine ingestion in non habitual caffeine users at various submaximal and maximal exercise intensities
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