Abstract
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% below and 10% 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 4 mM, 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% below and 10% 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 significantly 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 the decrease of perceived exertion can be involved in this process
caffeine; anaerobic threshold; endurance; lactate; perceived exertion
Braz J Med Biol Res, April 1998, Volume 31(4) 581-585 (Short Communication)
Effects of caffeine on time to exhaustion in exercise performed below and above the anaerobic threshold
B.S. Denadai and M.L.D.R. Denadai
Departamento de Educação Física, Instituto de Biociências, Universidade Estadual Paulista, Rio Claro, SP, Brasil
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References
Abstract
Correspondence and Footnotes
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% below and 10% 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 4 mM, 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% below and 10% 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 significantly 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 the decrease of perceived exertion can be involved in this process.
Key words: caffeine, anaerobic threshold, endurance, lactate, perceived exertion
The possible ergogenic effects of caffeine (CAF) on exercise performance have served as the basis for a large number of studies. However, there are still controversies about the conditions under which caffeine is capable of modifying performance, as well as concerning its possible mechanisms of action due to the absence of standardization among the various experimental procedures. Furthermore, the action of caffeine depends on the type, intensity and duration of exercise, nutritional and training status, the dose of caffeine, environmental conditions, and individual variations (1,2).
Specifically concerning exercise intensity, Jacobson and Kulling (3) have suggested that caffeine may be capable of increasing the time of endurance only when the effort is performed at intensities that allow individuals to exercise for more than one hour. Normally, exercises that can be performed beyond this period of time show intensities below the anaerobic threshold (AT) (4), suggesting that caffeine may modify performance only in exercises below this intensity. Most studies analyzing the effects of caffeine on time of endurance used relative loads to maximum oxygen consumption (%VO2max) (5,6), while there are no studies with exercise intensities relative to the AT. Since AT can present values between 35% and 90% of VO2max (7), it is not possible to affirm that, in studies in which the ergogenic effect of caffeine was found or not, subjects were below or above AT, respectively. Thus, the objective of the present study was to determine the effects of caffeine (5 mg/kg) on the time of endurance and rate of perceived exertion during exercise performed below and above AT.
Eight males (age: 20.4 ± 2.3 years; height: 172 ± 8.3 cm; weight: 75.4 ± 9.4 kg), non-regular consumers of caffeine, gave their written consent to participate in the study. All volunteers were classified as untrained individuals, i.e., individuals not engaged in regular physical activity or sport.
Anaerobic threshold was defined as the intensity (watts; W) corresponding to a lactate concentration of 4 mM and was determined using a progressive test conducted on an electromagnetically braked cycle ergometer. The initial workload was 25 W and the intensity was increased by 25 W every 5 min until exhaustion. At the end of each stage, 25 µl of blood was collected from the ear lobe, into microcentrifuge tubes containing 50 µl NaF (1%). The intensity at 4 mM lactate concentration was calculated by linear interpolation (8).
Following AT testing, the subjects reported to the laboratory on four occasions for treatments that were randomized for each subject. Each subject completed the four experimental treatments within a 3-4-week period. Subjects maintained their normal dietary habits and were asked not to drink coffee or caffeine-containing drinks for 24 h before each experiment. On the basis of AT measurement, the subjects were asked to cycle until exhaustion at two different intensities: approximately 10% below and 10% above AT. The test was stopped when subjects could no longer maintain pedalling at 50 rpm. Each intensity was performed twice in a double-blind randomized order with the subject ingesting either CAF (150 ml of hot water containing 5 g of decaffeinated coffee and caffeine (5 mg/kg)) or a placebo (PLA; 150 ml of hot water containing 5 g of decaffeinated coffee) 60 min prior to the test. Possible discrimination between CAF and PLA was eliminated by addition of an artificial sweetener to the beverages (9).
Venous blood was sampled from a venous catheter in a forearm vein immediately before each trial (0 min), after 10 min of exercise, and immediately after exercise, and subsequently analyzed for serum free fatty acids (FFA) (10), glucose (11) and caffeine (12). Lactate was measured by an electrochemical method (YSI 2300 STAT). During the experimental trial, rating of perceived exertion (RPE) and heart rate (Polar Vantage XL) were recorded every 5 min. RPE was assessed by the Borg scale (13). Time to exhaustion was also measured during each trial.
Results are reported as means ± SD. Plasma caffeine and time to exhaustion were analyzed by the Student t-test and other data were analyzed using repeated measures two-way ANOVA for time and treatment effects. Whenever necessary, the means were compared by the Tukey test. Statistical significance was set at P
Description
Caffeine improves endurance performance below the anaerobic threshold in untrained individuals.