Caffeine, a widely-consumed stimulant, is known to boost alertness and create a variety of other physiological effects, including increasing heart rate and blood pressure. In the workplace, caffeine is thought by some to boost productivity and in sports, caffeine, which remains legal in athletic competitions, has been the subject of some investigation with regard to its potential for improving performance and decreasing recovery time.
Caffeine did not add to the detrimental effect of exercise-induced muscle damage, according to a Brazilian study published in the March 2010 "International Journal of Sports Physiology and Performance." In the study, 4.5 mg per kilogram body weight of caffeine was given to soccer players before a workout. Levels of the enzymes creatine kinase and lactate dehydrogenase, markers of levels of muscle metabolism were not significantly different after the workout, from the control group that did not receive caffeine. Additionally, levels of white blood cells, which indicate a stress response, were not elevated in the caffeine group.
Caffeine consumption improved both same day and next day athletic performance, according to an Australian study published in the December 2010 "Journal of Sports Medicine and Physical Fitness." Athletes consumed 6 mg per kilogram body weight of caffeine before exercise sessions consisting of five sets of six 20-meter sprints. Repeated sprint ability, reactive agility time, sleep and next day exercise performance were measured. The caffeine group showed improved repeated sprint ability on both days. The performance improvement on the second day indicated a recovery-enhancing effect of the caffeine. The researchers noted that reactive agility time and sleep were unaffected.
No benefits to nerve-fatigue recovery were found for caffeine, in a Norwegian study published in the January 2010 "European Journal of Applied Physiology." Study participants ingested 6 mg per kilogram body weight of caffeine prior to an exercise involving contraction of the calf muscles with seven maximal contractions for 25 seconds, with 5-second rests in between. Electromyograph readings of muscle function and maximal performance, as evaluated by the maximum degree of muscle contraction the participants were able to perform, were not significantly different between the caffeine and the control groups.
Single muscle fibers did not show any effect from caffeine in power output, fatigue time, calcium levels or relaxation time, in a United States study on frog muscle fiber, published in the May 2009 "American Journal of Regulatory, Integrative and Comparative Physiology." The researchers concluded that any sports performance effects of caffeine are not related to caffeine's effects on the muscle fibers.
Carbohydrate ingested with caffeine increases levels of glycogen -- the storage form of glucose -- according to an Australian study, published in the July 2008 "Journal of Applied Physiology." Volunteers consumed a meal that included 4 g carbohydrate per kilogram body weight and 8 mg caffeine per kilogram body weight after an exercise session of cycling to exhaustion. After 4 hours of recovery, the glycogen level of the carbohydrate-plus-caffeine group was 66 percent higher than the group that consumed a meal of carbohydrate with no caffeine.