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Physiological responses to caffeine during endurance running in habitual caffeine users
M A Tarnopolsky1, S A Atkinson, J D MacDougall
1Department of Pediatrics, Physical Education and Medicine, McMaster University, Hamilton, Ontario, Canada.
Medicine and Science in Sports and Exercise
|August 1, 1989
Summary
Caffeine increased free fatty acid (FFA) levels in endurance runners but did not improve performance. This study suggests caffeine may not offer ergogenic benefits for habitual consumers during prolonged running.
Area of Science:
- Exercise Physiology
- Nutritional Biochemistry
Background:
- Caffeine is known to enhance endurance performance, but the underlying mechanisms remain unclear.
- Potential factors include increased free fatty acid (FFA) oxidation and improved neuromuscular function.
Purpose of the Study:
- To investigate the metabolic and neuromuscular effects of caffeine in habitual caffeine-consuming endurance runners.
- To determine if caffeine administration impacts key physiological markers during prolonged exercise.
Main Methods:
- Six varsity runners completed a 90-minute treadmill run at 70% VO2max under controlled conditions.
- A randomized, crossover, double-blind study administered caffeine (6 mg.kg-1) or placebo.
- Plasma FFA, glucose, lactate, epinephrine, and norepinephrine levels were measured, alongside VO2, HR, RER, and neuromuscular function.
Main Results:
- Caffeine significantly increased plasma FFA levels before and during exercise (P < 0.05).
- No significant changes were observed in VO2, heart rate, respiratory exchange ratio, perceived exertion, or plasma glucose, lactate, epinephrine, and norepinephrine.
- Neuromuscular function, including maximal voluntary strength, peak twitch torque, and motor unit activation, remained unaltered.
Conclusions:
- Caffeine administration elevates plasma FFA in athletic, habitual consumers.
- However, these findings indicate no significant metabolic or neuromuscular adaptations that would provide an ergogenic benefit for endurance running.