The effects of caffeine on graded exercise performance in caffeine naive versus habituated subjects
Tóm tắt
The physiological effects of caffeine on subjects habituated to caffeine is relatively unstudied compared to those of caffeine naive subjects during graded exercise. Thus, the purpose of this investigation was to determine the effects of caffeine on maximal oxygen consumption (VO2max) and the anaerobic threshold in these two populations. Seventeen moderately trained males were classified according to caffeine usage: (1) caffeine consumption 25 mg·day−1 or less (CN) (n=8) or (2) caffeine consumption above 300 mg·day−1 (CH) (n=9). The subjects were tested post-absorptive on the same cycle ergometer on three occasions with 7 days separating the tests. One hour before each test the subject ingested either a gelatin capsule (C); 3 mg·kg−1 body weight of caffeine (C3); or 5 mg·kg−1 body weight of caffeine (C5). The subject then performed an incrementalVO2max test beginning at 50 W and the work rate was increased 30 W every 2 min until the subject could not maintain the power output. Serial venous blood samples were drawn over 30 s at the end of each stage. The CN group significantly increased resting heart rate (f
c) and expired ventilation volume (V
E) after C3 and C5 andVO2 after C5. No significant differences were found for exerciseV
E,VO2, respiratory excharge ratio,f
c or time to exhaustion. There were no significant differences (P < 0.05) in the lactate threshold or the ventilatory threshold between treatment in either group. The CH subjects showed a significant increase (P<0.05) in resting plasma free fatty acid (FFA) concentration only during the C3 and C5 treatments. Plasma FFA levels were significantly increased (P < 0.05) at all times during C3 and C5 treatment in the CN subjects when compared to the control values. These data indicate that caffeine has no effect onVO2max or the anaerobic threshold seen during incremental, graded exercise. However, resting metabolism and ventilation, and both resting and exercise plasma FFA are increased in CN subjects.
Tài liệu tham khảo
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