Caffeine

Effect of caffeine ingestion on muscular strength and endurance: a meta-analysis.
Warren GL, Park ND, Maresca RD, McKibans KI, Millard-Stafford ML.
Med Sci Sports Exerc. 2010 Jul;42(7):1375-87.

 Our objective was to perform a systematic review and meta-analysis of the research literature assessing the effect of caffeine ingestion on maximal voluntary contraction (MVC) strength and muscular endurance. Thirty-four relevant studies between 1939 and 2008 were included in the meta-analyses of caffeine’s effects on MVC strength (n = 27 studies) and muscular endurance (n = 23 studies). Effect sizes (ES) were calculated as the standardized mean difference and meta-analyses were completed using a random-effects model. Overall, caffeine ingestion was found to result in a small beneficial effect on MVC strength (overall ES = 0.19, P = 0.0003). However, caffeine appears to improve MVC strength primarily in the knee extensors (i.e., by approximately 7%, ES = 0.37) and not in other muscle groups such as the forearm or the knee flexors. In an attempt to offer a physiological mechanism behind caffeine’s ability to improve MVC strength, a meta-analysis was run on ES from nine studies that measured percent muscle activation during MVC in trials comparing caffeine versus placebo; the overall ES (0.67) was highly significant (P = 0.00008) and of moderate to large size, thus implicating an effect of caffeine on the CNS. Caffeine ingestion was also found to exert a small beneficial effect on muscular endurance (overall ES = 0.28, P = 0.00005). However, it appears caffeine improves muscular endurance only when it is assessed using open (i.e., by approximately 18%, ES = 0.37) and not fixed end point tests. Overall, caffeine ingestion improves MVC strength and muscular endurance. The effect on strength appears exclusively in the knee extensors, and the effect on muscular endurance appears only detectable with open end point tests. PMID: 20019636

  Caffeine-Not just a stimulant.
Glade MJ.
Nutrition. 2010 Oct;26(10):932-8.

 The beneficial effects of human caffeine consumption deserve clarification. A detailed literature review was conducted and summarized. A large body of scientific evidence describes the beneficial effects of human caffeine consumption on a number of physiologic systems. The consumption of moderate amounts of caffeine 1) increases energy availability, 2) increases daily energy expenditure, 3) decreases fatigue, 4) decreases the sense of effort associated with physical activity, 5) enhances physical performance, 6) enhances motor performance, 7) enhances cognitive performance, increases alertness, wakefulness, and feelings of “energy,” 9) decreases mental fatigue, 10) quickens reactions, 11) increases the accuracy of reactions, 12) increases the ability to concentrate and focus attention, 13) enhances short-term memory, 14) increases the ability to solve problems requiring reasoning, 15) increases the ability to make correct decisions, 16) enhances cognitive functioning capabilities and neuromuscular coordination, and 17) in otherwise healthy non-pregnant adults is safe. PMID: 20888549
Copyright © 2010 Elsevier Inc. All rights reserved

  Caffeine enhances upper body strength in resistance-trained women.
Goldstein E, Jacobs PL, Whitehurst M, Penhollow T, Antonio J.
J Int Soc Sports Nutr. 2010 May 14;7:18.

 Research has indicated that low-to-moderate dosages of caffeine supplementation are ergogenic for sustained endurance efforts as well as high-intensity exercise. The effects of caffeine supplementation on strength-power performance are equivocal, with some studies indicating a benefit and others demonstrating no change in performance. The majority of research that has examined the effects of caffeine supplementation on strength-power performance has been carried out in both trained and untrained men. Therefore, the purpose of this study was to determine the acute effects of caffeine supplementation on strength and muscular endurance in resistance-trained women. In a randomized manner, 15 women consumed caffeine (6 mg/kg) or placebo (PL) seven days apart. Sixty min following supplementation, participants performed a one-repetition maximum (1RM) barbell bench press test and repetitions to failure at 60% of 1RM. Heart rate (HR) and blood pressure (BP) were assessed at rest, 60 minutes post-consumption, and immediately following completion of repetitions to failure. Repeated measures ANOVA indicated a significantly greater bench press maximum with caffeine (p </= 0.05) (52.9 +/- 11.1 kg vs. 52.1 +/- 11.7 kg) with no significant differences between conditions in 60% 1RM repetitions (p = 0.81). Systolic blood pressure was significantly greater post-exercise, with caffeine (p < 0.05) (116.8 +/- 5.3 mmHg vs. 112.9 +/- 4.9 mmHg). These findings indicate a moderate dose of caffeine may be sufficient for enhancing strength performance in resistance-trained women. PMID: 20470411

  The effects of caffeine on ventilation and pulmonary function during exercise: an often-overlooked response.
Chapman RF, Mickleborough TD.
Phys Sportsmed. 2009 Dec;37(4):97-103.

 The effects of caffeine on exercise performance have been well documented, with most reviews focusing on the metabolic, hormonal, and/or central nervous system effects. However, caffeine’s effects on ventilation and pulmonary function are often overlooked. Studies have shown that caffeine is a strong ventilatory stimulant, increasing the sensitivity of the peripheral chemoreceptors in untrained subjects and increasing exercise ventilation at all workloads in highly trained endurance athletes. The consequences of increased exercise ventilation could hold either positive or negative effects for exercise performance. Anti-inflammatory and bronchoprotective effects of caffeine are great enough to consider its efficacy as a possible prophylactic antiasthma treatment. Although an upper urinary concentration limit exists for caffeine with international sports doping control agencies, caffeine’s universal accessibility in the marketplace has resulted in its daily use being increasingly more socially acceptable as an ergogenic substance for sport and exercise. PMID: 20048546

  Effect of caffeine on sport-specific endurance performance: a systematic review.
Ganio MS, Klau JF, Casa DJ, Armstrong LE, Maresh CM.
J Strength Cond Res. 2009 Jan;23(1):315-24.

 Endurance athletes often ingest caffeine because of its reported ergogenic properties. Although there are a vast number of studies quantifying caffeine’s effects, many research studies measure endurance performance using a time-to-exhaustion test (subjects exercise at a fixed intensity to volitional exhaustion). Time-to-exhaustion as a performance measure is not ideal because of the high degree of measurement variability between and within subjects. Also, we are unaware of any endurance sports in which individuals win by going a longer distance or for a longer amount of time than their competitors. Measuring performance with a time-trial test (set distance or time with best effort) has high reproducibility and is more applicable to sport. Therefore, the purpose of this review was to critically and objectively evaluate studies that have examined the effect of caffeine on time-trial endurance (>5 minutes) performance. A literature search revealed 21 studies with a total of 33 identifiable caffeine treatments that measured endurance performance with a time-trial component. Each study was objectively analyzed with the Physiotherapy Evidence Database (PEDro) scale. The mean PEDro rating was 9.3 out of 10, indicating a high quality of research in this topic area. The mean improvement in performance with caffeine ingestion was 3.2 +/- 4.3%; however, this improvement was highly variable between studies (-0.3 to 17.3%). The high degree of variability may be dependent on a number of factors including ingestion timing, ingestion mode/vehicle, and subject habituation. Further research should seek to identify individual factors that mediate the large range of improvements observed with caffeine ingestion. In conclusion, caffeine ingestion can be an effective ergogenic aid for endurance athletes when taken before and/or during exercise in moderate quantities (3-6 mg.kg body mass). Abstaining from caffeine at least 7 days before use will give the greatest chance of optimizing the ergogenic effect. PMID: 19077738