Caffeine and Exercise Performance 

Caffeine may be the most widely used stimulant in the world. It is found in a variety of plants, dietary sources (including coffee, tea, chocolate, cocoa, and colas), and non-prescription medications. The average caffeine consumption in the USA is approximately 2 cups of coffee per day (200 mg); 10% of the population ingests more than 1000 mg per day. Caffeine is a socially acceptable, legal drug consumed by all groups in society. 

Caffeine is often referred to as a nutritional ergogenic aid, but it has no nutritional value. Ingested caffeine is quickly absorbed from the stomach and peaks in the blood in 1-2 hours. Caffeine has the potential to affect all systems of the body, as it is absorbed by most tissue. The remaining caffeine is broken down in the liver and byproducts are excreted in urine. 

CAFFEINE AND ENDURANCE EXERCISE PERFORMANCE 

Laboratory studies from the 1970’s suggested that caffeine enhanced endurance performance by increasing the release of adrenaline into the blood stimulating the release of free fatty acids from fat tissue and/or skeletal muscle. The working muscles use this extra fat early in exercise, reducing the need to use muscle carbohydrate (glycogen). The “sparing” of muscle glycogen made more available later in exercise to delay fatigue. 

In the 1980’s, many studies found that caffeine did not alter exercise metabolism, and implied that it had no ergogenic effect, without actually measuring performance. A few reports did examine caffeine and performance during endurance exercise and generally found no ergogenic effect. By the end of the decade, it was suggested that caffeine did not alter metabolism during endurance exercise and may not be ergogenic. 

Recent work reported that ingestion of 3-9 mg of caffeine per kilogram (kg) of body weight one hour prior to exercise increased endurance running and cycling performance in the laboratory. To put this into perspective, 3 mg per kg body weight equals approximately one mug or 2 regular size cups of drip-percolated coffee; and 9 mg/kg = approximately 3 mugs of 5-6 regular size cups of coffee. These studies employed well-trained, elite or serious, recreational athletes. Studies with untrained individuals cannot be performed due to their inability to reliably exercise to exhaustion. 

The mechanism to explain these endurance improvements is unclear. Muscle glycogen is spared early during submaximal exercise following caffeine ingestion (5-9 mg/kg). It is unknown whether glycogen sparing occurs as a result of caffeine’s ability to increase fat availability for skeletal muscle use. Furthermore, there is no evidence supporting a metabolic component for enhancing performance at a low caffeine dose (3 mg/kg). Therefore, it appears that alterations in muscle metabolism alone cannot fully explain the ergogenic effect of caffeine during endurance exercise. 

CAFFEINE AND SHORT-TERM EXERCISE PERFORMANCE 

Research suggests that caffeine ingestion improves performance during short-term exercise lasting approximately 5 minutes at 90 to 100 percent of maximal oxygen uptake in the laboratory. This exercise intensity requires maximal provision of energy from both aerobic (oxygen requiring) and anaerobic (non-oxygen) sources. It is unknown if this finding applies to race situations. The reasons for the performance improvement may be a direct positive effect of caffeine on muscle anaerobic energy provision and contraction or a central nervous component related to the sensation of effort. Caffeine ingestion does not appear to improve sprint performance, but additional well-controlled laboratory and field studies are required to confirm this conclusion. Sprinting is defined as exercise that can be maintained from a few seconds to 90 seconds where most of the required energy is derived from anaerobic metabolism. 

Read more at: http://www.acsm.org/docs/current-comments/caffeineandexercise.pdf