Influence of caffeine on exercise performance in habitual caffeine users

Area of Science:

• Exercise Physiology
• Nutritional Biochemistry

Background:

• Habitual caffeine consumption (over 600 mg/day) may lead to tolerance, potentially diminishing its ergogenic effects during exercise.
• Understanding caffeine's impact on exercise performance in tolerant individuals is crucial for optimizing athletic strategies.

Purpose of the Study:

• To investigate the physiological effects of caffeine on exercise responses in women habituated to high caffeine intake.
• To determine if caffeine withdrawal enhances caffeine's ergogenic potential during prolonged endurance exercise.

Main Methods:

• Six women with high habitual caffeine intake completed three 1-hour running trials at 75% VO2 max.
• Trials included: placebo (PL), consuming caffeine with normal intake (CC), and consuming caffeine after 4-day withdrawal (CW).
• Caffeine dosage was 5 mg/kg body weight; physiological markers like oxygen uptake, R value, free fatty acids, lactate, norepinephrine, and dopamine were measured.

Main Results:

• Caffeine ingestion after withdrawal (CW) produced the most significant physiological effects.
• Exercise oxygen uptake was significantly elevated by 0.17 L/min in CW trials compared to PL and CC.
• Resting free fatty acid levels were highest in CW trials (1104 μEq/L), and post-exercise norepinephrine and dopamine were also elevated.

Conclusions:

• Habitual high caffeine users develop tolerance, reducing caffeine's effectiveness during prolonged exercise.
• A 4-day caffeine withdrawal period can significantly magnify caffeine's physiological effects and potential ergogenic benefits for habitual users.
• These findings suggest strategic caffeine cycling may be beneficial for athletes accustomed to regular caffeine intake.