Effects of caffeine on time to exhaustion in exercise performed below and above the anaerobic threshold

Controversy still exists concerning the potential ergogenic benefit of caffeine (CAF) for exercise performance. The purpose of this study was to compare the effects of CAF ingestion on endurance performance during exercise on a bicycle ergometer at two different intensities, i.e., approximately 10 percent below and 10 percent above the anaerobic threshold (AT). Eight untrained males, non-regular consumers of CAF, participated in this study. AT, defined as the intensity (watts) corresponding to a lactate concentration of 4mM, was determined during an incremental exercise test from rest to exhaustion on an electrically braked cycle ergometer. On the basis of these measurements, the subjects were asked to cycle until exhaustion at two different intensities, i.e., approximately 10 percent below and 10 percent above AT. Each intensity was performed twice in a double-blind randomized order by ingesting either CAF (5 mg/kg) or a placebo (PLA) 60 min prior to the test. Venous blood was analyzed for free fatty acid, glucose, and lactate, before, during, and immediately after exercise. Rating of perceived exertion and time to exhaustion were also measured during each trial. There were no differences in free fatty acids or lactate levels between CAF and PLA during and immediately after exercise for either intensity. Immediately after exercise glucose increased in the CAF trial at both intensities. Rating of perceived exertion was singificantly lower (CAF = 14.1 + 2.5 vs PLA = 16.6 + 2.4) and time to exhaustion was significantly higher (CAF = 46.54 + 8.05 min vs PLA = 32.42 + 14.81 min) during exercise below AT with CAF. However, there was no effect of CAF treatment on rating of perceived exertion (CAF = 18.0 + 2.7 vs PLA = 17.6 + 2.3) and time to exhaustion (CAF = 18.45 + 7.28 min vs PLA = 19.17 + 4.37 min) during exercise above AT. We conclude that in untrained subjects caffeine can improve endurance performance during prolonged exercise performed below AT and that decrease of perceived exertion can be involved in this process.

Vagal and sympathetic control of heart rate during exercise by sedentary and exercise-trained rats

1. The present investigation was undertaken to study the vagal and sympathetic effects of an acute bout of exercise on ten sedentary (S) and nine trained (T) rats. The exercise training was performed 5 times a week for 13 weeks on a motor treadmill, at 1.0 mph, 15% grade for 60 min. 2. Heart rate (HR) was recorded at rest and during exercise, 15% grade at 0.5, 0.8 and 1.0 mph, for 3 min per stage. Vagal and sympathetic effects were studied after the administration of methylatropine (3 mg/kg) and propranolol (4 mg/kg). 3. Exercise training significantly attenuated cardiac acceleration at 0.8 (441 +/- 8 vs 486 +/- 9 bpm in S, P < 0.05) and 1.0 mph (466 +/- 12 vs 508 +/- 6 bpm in S, P < 0.05). The vagal effect was significantly increased in the T group at 0.8 (72 +/- 5 vs 32 +/- 10 bpm in S, P < 0.05) and 1.0 mph (46 +/- 8 vs 15 +/- 7 bpm in S, P < 0.05). The sympathetic effect was significantly decreased in the T group at 0.8 (73 +/- 9 vs 112 +/- 9 bpm in S, P < 0.05) and 1.0 mph (96 +/- 11 vs 125 +/- 7 bpm in S, P < 0.05). The intrinsic HR behavior was not different between groups.(ABSTRACT TRUNCATED AT 250 WORDS)