Sports Fitness Training

Caffeine, a central nervous system stimulant, is one of the most widely used drugs in the world. This substance may improve alertness, concentration, reaction time, and energy levels. In addition, its effect on promoting lipolysis has been touted as a mechanism by which it acts as an endurance ergogenic aid.

Human Studies

One of the first studies conducted on the effects of caffeine and endurance was by Perkins and Williams in 1975 Resting heart rate, submaximal heart rate, maximal heart rate, and ratings of perceived exertion were tested in female subjects before and after a progressive workload to exhaustion on a cycle ergometer. The subjects ingested a placebo, or 4 mg, 7 mg, or 10 mg of caffeine in this double-blind study. There was no significant effect on exercise performance.

Another early study on caffeine was conducted by Costill et al. Nine competitive cyclists exercised until exhaustion on a cycle ergometer at 80% . One trial was conducted 1 hour after the ingestion of decaffeinated coffee and the other after the ingestion of coffee containing 330 mg of caffeine. The trial with caffeine resulted in a longer cycling time compared with the trial without caffeine . Fat oxidation was significantly higher with the use of caffeine and ratings of perceived exertion were significantly lower. The authors concluded that caffeine increased endurance by increasing lipolysis and exerting a positive influence on nerve impulse transmission.

Ivy et al also conducted a study on caffeine and its effects on endurance in the late 1970s. Nine trained cyclists were used in this study The subjects ingested 250 mg of caffeine 1 hour before a 2-hour bout of isokinetic cycling at 80 rpm. The subjects also ingested an additional 250 mg of caffeine at 15-minute intervals during the first 90 minutes of exercise. This significantly increased work production and VO2 by 7.4% and 7.3%, respectively Fat oxidation was also elevated by 31%, therefore, the increase in work production with the ingestion of caffeine was attributed to an enhanced rate of lipid catabolism.

In a recent study by Cohen et al seven competitive road racers performed three, 21-km races in the heat and humidity after randomly ingesting 0, 5, or 9 mg/kg of caffeine. The subjects were allowed to imbibe water at each 5-km interval. They found no improvement in race times for any of the caffeine doses when compared with a placebo.

A study by Wemple et al. also showed no improvements with the use of caffeine. Six subjects performed 3 hours of cycling at 60% . Also, maximal performance was tested at 85% following the 3-hour endurance trial. During exercise, the subjects ingested 35 mL of a carbohydrate electrolyte drink with or without 25 mg/dL of caffeine. At rest, the urinary volume was significantly greater during the caffeine trial (1843 mL) versus the placebo (0411 mL), but during exercise there was no difference in urinary volume (398 versus 490 mL for caffeine and placebo, respectively). Conclusively, this study showed no improvement in endurance performance; however, this study also showed that there is not a risk of dehydration with the ingestion of 25 mg/dL of caffeine.

Conversely, most studies conducted on the use of caffeine have shown positive results on endurance performance. Immediately before exercise, six endurance-trained males, who had previously competed in at least two marathons, ingested 10 mg/kg of caffeine or a placebo? The exercise consisted of running on a treadmill at 75% of their VO2max for 45 minutes, and then increasing the speed by two miles per hour until exhaustion. The caffeine trial resulted in a significant increase in the distance run when compared with the placebo 0.9% increase and control (2.1% increase).

Different dosages of caffeine (0, 5, 9, or 13 mg/kg) were also investigated in nine well-trained cyclists 8 Encapsulated caffeine was administered 1 hour before the subjects cycled at SO% VO2max until exhaustion. A significant increase in endurance performance was noted during all three trials when compared with the placebo but there was not a dose­related response. Also, there was an increase in free fatty acid and glycerol concentrations with the ingestion of caffeine.

The effects of caffeine were investigated at different levels of intensity. Eight untrained males cycled until exhaustion at 10% above or below anaerobic threshold after randomly receiving 5 mg/kg of caffeine or a placebo 60 minutes before exercise. There were no differences between trials when the subjects exercised at 10% above anaerobic threshold; however, ratings of perceived exertion were significantly lower (14.1 versus 16.6 for caffeine and placebo, respectively) and time to exhaustion was significantly higher during the caffeine trial at 10% below anaerobic threshold. This may be because the subjects were untrained.

A study was also conducted on the effects of caffeine in coffee or water. Nine fit, young adults performed five trials after ingesting a capsule of caffeine or placebo with water or coffee (decaffeinated coffee, decaffeinated coffee with caffeine added, or regular coffee). The dosage of caffeine was 4.45 mg/kg with 7.15 mL/kg of solution. After 1 hour of rest, the subjects ran at 85% until exhaustion. Plasma epinephrine was significantly increased with the ingestion of caffeine, and the increase was significantly greater with the capsules when compared with the coffee. Also, endurance performance was only increased during the caffeine capsule trial (7.5- to 10-min increase when compared with the other four trials). The authors speculated that coffee must have a component that moderates the actions of caffeine.

Bell and Jacobs conducted one of the most recent studies done on caffeine. In this field study; nine healthy male recreational runners completed six 3.2-km runs wearing 11 kg of gear (Canadian Forces Warrior Test) after ingesting 325 mg of caffeine and 75 mg of ephedrine. Heart rate was significantly higher in the caffeine and ephedrine trials, and supplementation significantly improved the subjects’ time when compared with a control and placebo trial .

The plethora of data clearly show that there are potential benefits of consuming caffeine before an endurance event. This central nervous system stimulator can increase the release of catecholamines and increase the use of free fatty acids for energy. Dosages as low as 330 mg 1 hour before exercise have been shown to increase an individual’s performance time.

Safety and Toxicity

Moderate to high doses of caffeine can result in nervousness, restlessness, insomnia, and tremors. Caffeine is also a diuretic, which might increase the risk of dehydration and heat-related illness. Caffeine can be addictive and result in severe headaches, fatigue, irritability, and gastrointestinal distress after withdrawal from the substance. In addition, individual differences in caffeine sensitivity may account for the lack of an ergogenic effect.

Also, regarding competitive sports, the International Olympic Committee only permits 12 µg/mL of caffeine in the urine. This is the equivalent of consuming 600 to 800 mg of caffeine within 30 minutes .