Inclusion criteria were met by 21 papers covering 33 trials3. Thirty of these showed a performance improvement with a mean improvement of 3.2 ± 4.3 % with caffeine consumption. The review concluded that overall caffeine ingestion can be an effective ergogenic aid for endurance athletes when consumed in moderate quantities (3-6mg/kg body weight), before and/or during exercise3. However, abstaining from caffeine for at least 7 days before an event optimised caffeine’s ergogenic effect on performance during the event3.
In 2011, a study examining caffeine withdrawal and high-intensity endurance cycling performance also suggested that an intake of caffeine of 3mg/kg body significantly improved exercise performance irrespective of whether a 4-day withdrawal period was imposed on habitual caffeine users4. Further research published in 2012 concluded that a caffeine intake of 3mg/kg body weight appears to improve cycling performance; although doubling this (to 6mg/kg body weight) did not confer additional performance improvement in well-trained athletes5.
Additionally, a 2013 study considered the potentially enhancing effects of caffeine versus coffee, concluding that caffeine consumed in coffee (5mg/kg body weight) and as a supplement (5mg/kg body weight) one hour prior to exercise can improve endurance exercise performance6.
A 2016 review concluded that there is an indication that the use of coffee (as opposed to caffeine alone) as an ergogenic aid can improve performance in endurance cycling and running7. The authors suggested that coffee providing 3-8.1 mg/kg of caffeine may be used as a safe alternative to anhydrous caffeine to improve endurance performance7. Further results from a 2017 study of male runners suggest that 60 minutes after ingesting 0.09 g/kg of caffeinated coffee, one-mile race performance was enhanced by 1.9% and 1.3% compared with a placebo and decaffeinated coffee respectively, in trained male runners8.
A 2017 meta-analysis suggested that caffeine had a suppressive effect on ratings of perceived exertion, and had no effect on measures of heart rate, respiratory exchange ratio or V̇O29. The authors suggested that whilst the positive effects of caffeine supplementation on sustained high-intensity exercise performance are well accepted, the mechanisms to explain that response remain unresolved9.
A further 2020 study (27 men, 19 women) investigated the effect of habitual caffeine intake on 5km cycling time-trial performance following the ingestion of caffeinated coffee. 16 participants were classified as high-caffeine users and 30 as low. Ingesting caffeinated coffee improved 5km cycling time-trial performance in both high and low caffeine users by a similar magnitude. The authors concluded that regular caffeine consumption did not alter the impact of coffee ingestion on performance prior to a 5km cycling time trial10.
Additionally, a 2020 systematic review considered overall effects of caffeine supplementation and exercise performance. The author’s findings supported previous work that suggests there are ergogenic effects of caffeine on muscle endurance, muscle strength, anaerobic power and aerobic endurance. They concluded that the effect of caffeine is generally greater in aerobic exercise compared with anaerobic exercise11.
A small number of studies have considered a potential ergogenic effect of low and very low intakes of caffeine taken late in prolonged exercise. A low intake of caffeine (~200 mg) has been shown to improve vigilance, alertness and mood, and improve cognitive processes during and following strenuous exercise, however there is a lack of research on its potential effects on high intensity sprint and burst activities. As the response to caffeine consumption is variable, athletes need to determine whether the ingestion of lower amounts of caffeine before and/or during training and competitions is ergogenic on an individual basis12.
Summary of meta-analyses
Does caffeine affect men and women differently?
To date, most studies that have shown positive effects of caffeine supplementation on sports performance have been carried out in men. However, differences in terms of body size, composition, and hormones might cause different outcomes on performance for the same dosage of caffeine intake for women.
A 2019 systematic review concluded that whilst some investigations had not found differences between sexes in terms of caffeine supplementation on aerobic performance or the fatigue index, other studies suggested that the ergogenicity of caffeine for anaerobic performance (e.g. producing more power and improving sprint performance) was higher in men than women38.
Further work supporting the suggestion that caffeine may have a similar effect in men and women with regards to aerobic performance, investigated the effect of coffee on 5km cycling time trial performance. The authors concluded that ingesting coffee providing 3mg/kg of caffeine increased salivary caffeine levels and improved 5km cycling time trial performance in men and women by a similar magnitude39.
Caffeine and muscle pain
In 2009, a research paper reported on the effects caffeine had on muscle pain during 30 minutes of high-intensity cycling. Caffeine ingestion (5mg/kg body weight) was statistically significant in reducing the reported intensity of muscle pain and the effect was larger in the group of habitually low caffeine consumers13.
A 2011 study examined the effect of caffeine on leg pain and rating of perceived exertion during repeated bouts of high intensity exercise. Data revealed no effect of caffeine on leg pain or perceived exertion although caffeine intake improved multiple measures of performance. The authors concluded that it was plausible to suggest that subjects were able to perform better with similar levels of pain and exertion with 5mg/kg of caffeine compared to a placebo14.
