Caffeine is the most readily available ergogenic aid; it is present in coffee, soft drinks, over the counter stimulants, analgesics, sports nutrition and chocolate.
Caffeine is also present in many sports drinks and in 2004 caffeine was removed from WADAs list of banned substances. Caffeine is a stimulant that is 99% bioavailable (the proportion of a nutrient that is absorbed from the diet and used) after oral consumption. It is metabolized by the liver and readily crosses most bodily membranes (e.g. blood-brain barrier).
The potential benefits of caffeine are the stimulation of the central nervous system (CNS). Caffeine has been associated with relaxation of smooth muscle (like in the gut) and greater utilization of free fatty acids (this is important for fat adapted athletes). Another benefit of caffeine is the lower rate of perceived exertion (RPE). Tarnopolsky (2008) identified that the ergogenic effects of caffeine, during endurance exercise, are facilitated somewhat by heightened contractile force and somewhat by a decrease in perceived exertion. So your muscles can contract with greater force but it feels easier than without the caffeine.
Now here’s the science: Costill et al (1978) attributed the lowered RPE to an increase in lipid (fat) oxidation, which would spare glycogen stores. Van Soeren and Graham (1998) also found an increase in plasma free fatty acids following caffeine ingestion, but suggested that the reduction in RPE during exercise was due to changes in the central nervous system (CNS). Rogers and Dinges (2005) suggested that caffeine is responsible for the blockage of CNS adenosine receptors and as it is able to cross the blood brain barrier, it is able to have a direct effect on the CNS. Adenosine moderates CNS neurotransmission, decreases catecholamine release (adrenaline and nor adrenaline) and inhibits lipolysis (the breakdown of fats by hydrolysis to release fatty acids). As caffeine blocks adenosine receptors, it inhibits the effects of adenosine. The effects of caffeine are therefore synonymous with adrenaline and nor adrenaline: increased heart rate and blood pressure, increased respiratory rate, bronchial dilation and relaxation of pulmonary smooth muscle, and increased alertness and neurocognitive performance (Bell et al, 2002).
The beneficial effects of caffeine are well documented for aerobic exercise, but less well documented in anaerobic exercise. Paton et al (2001) investigated the effects of caffeine on repeated 20m sprints, but did not show any benefit compared to the control group. Astorino et al (2011)investigated the effect of caffeine intake on pain perception during high-intensity exercise and found caffeine had no effect on leg pain or RPE.However, Woolf (2008) investigated caffeine (5 mg/kg body weight) against a placebo during anaerobic exercise and found that athletes who had taken caffeine were able to lift a greater weight during the chest press, and achieve a greater peak power during the Wingate test. These varied results indicate that greater research is required to fully assess the impact of caffeine on anaerobic exercise.
The adverse effects of caffeine include heightened anxiety, tachycardia, insomnia, increased core temperature and irritability. Caffeine overdose/toxicity can cause seizures and arrhythmias and withdrawal symptoms are likely to be seen after cessation following repeated use (Keisler and Armsey, 2006).
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