Caffeine is a well-replicated performance-enhancing supplement, with these effects established at meta-analysis level; as such, further research exploring the straightforward ergogenic effects of caffeine is unlikely to alter practice. |
However, there are many unanswered questions with regard to the use of caffeine in sport which represent promising avenues to enhance our understanding and provide some nuance into the use of caffeine around exercise. |
These unanswered questions include whether the ergogenic effects of caffeine alter with sex, time of day, genotype, habitual use, and training status, and there is a need for a greater understanding of the effects of caffeine on performance anxiety and post-exercise recovery. |
1 Introduction
2 What Else Do We Need to Know About Caffeine in Sport?
2.1 What are the Wider, Non-direct Influences of Caffeine on Performance?
2.2 What are the Effects of Genotype on Caffeine Ergogenicity?
2.3 Does Time of Day Impact the Ergogenic Effects of Caffeine?
Reference | Sample | Chronotype assessment | Testing times of day | Caffeine dose | Performance metric | Main findings |
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Boyett et al.a [83] | 20 young men (also categorized as trained n = 7, and untrained n = 7) | Not performed | One caffeine and one placebo condition in the morning hours (between 06:00 and 10:00 h); one caffeine and one placebo condition in the evening hours (between 16:00 and 20:00 h) | 6 mg/kg | Isokinetic knee extension and 3-km cycling time trial | Isokinetic peak torque at angular velocity of 30 °/s was ‘possibly’ enhanced when ingesting caffeine in the evening as compared to evening placebo ingestion; for cycling time trial, ingesting caffeine in the morning ‘very likely’ enhanced performance as compared to morning placebo ingestion; ingesting caffeine in the evening ‘possibly’ enhanced performance as compared to evening placebo ingestion; ingesting caffeine in the morning ‘likely’ enhanced performance more than ingesting caffeine in the evening; when analyzed based on training status, ingesting caffeine in the morning ‘likely’ enhanced performance as compared to morning ingestion of placebo in trained individuals; the evening caffeine vs placebo comparison produced ‘unclear’ effects; ingesting caffeine in the morning and evening hours ‘likely’ enhanced performance as compared to placebo; in untrained individuals, ingesting caffeine in the morning or evening ‘likely’ improved performance as compared to morning and evening ingestion of placebo |
Lopes-Silva et al. [79] | 13 physically active young men | None of the participants belonged to any extreme type as determined by the Horne and Ösberg self- questionnaire | One caffeine and one placebo condition in the morning hours (between 08:00 h); one caffeine and one placebo condition in the evening hours (18:00 h) | 5 mg/kg | 10 × 6 s cycle sprints | No differences in total work between caffeine and placebo conditions |
Miller et al. [202] | 188 young male students | The study included morning, evening, and intermediate types as determined by the Horne and Ösberg self- questionnaire | Randomized to testing performed at 08:00, 11:00, 14:00, 17:00, 20:00, or 23:00 h | 1 and 3 mg/kg | Forearm flexor MVC | Increase in MVC strength occurred only in the morning hours and with 3 mg/kg of caffeine |
Mora-Rodríguez et al. [81] | 12 young resistance-trained men | Not performed | One caffeine and one placebo condition in the morning hours (10:00 h); one placebo condition in the evening hours (18:00 h) | 3 mg/kg | Squat and bench press with loads that elicited barbell displacement of 1.00 m/s and with loads amounting to 75% of 1 RM; knee extension and hand MVC; knee extension electrically evoked MVC | In the squat exercise when using loads that elicited barbell displacement of 1.00 m/s, ingesting caffeine in the morning and placebo in the evening enhanced barbell velocity as compared to morning ingestion of placebo; for the bench press, ingesting placebo in the evening enhanced barbell velocity as compared to morning ingestion of placebo and caffeine; in both the squat and bench press exercises with loads of 75% 1 RM, ingesting caffeine in the morning or placebo in the evening enhanced barbell velocity as compared to morning ingestion of placebo; for knee extension and hand MVC, no differences were observed between the conditions; ingesting caffeine in the morning enhanced electrically evoked knee extension MVC as compared to morning ingestion of placebo |
Mora-Rodríguez et al. [82] | 13 young resistance-trained men | Not performed | One caffeine and one placebo condition in the morning hours (08:00 h); one caffeine and one placebo condition in the evening hours (18:00 h) | 6 mg/kg | Squat and bench press with loads of 25, 50, 75, and 90% of 1 RM | In the squat exercise, ingesting placebo in the evening, caffeine in the morning, and caffeine in the evening hours enhanced barbell velocity with loads of 25, 50, and 75% of 1 RM as compared to ingesting placebo in the morning; no significant effects were observed in the squat exercise with 90% 1 RM and in the bench press exercise with any of the employed loads |
Pataky et al.a [60] | 25 young men and 13 young women | Not performed | 15 participants performed the placebo and caffeine testing sessions at 10:00 h or earlier, while 23 participants performed the placebo and caffeine testing sessions at time later than 10:00 h | 6 mg/kg and/or mouth rinsing with 25 ml of caffeine solution | Power output during a 3-km cycling time trial | In the group performing the testing session before 10:00 h, ingestion of caffeine, mouth rinsing with caffeine, and ingestion of caffeine plus mouth rinsing with caffeine ‘very likely,’ ‘likely’ and ‘most likely’ improved power output; mouth rinsing with caffeine ‘possibly’ had an ergolytic effect on power output in those exercising at times later than 10:00 h; placebo ingestion plus mouth rinsing with placebo and mouth rinsing with placebo ‘very likely’ had a greater effect in those exercising at 10:00 h or earlier; caffeine ingestion plus mouth rinsing with caffeine ‘likely’ improved greater in the participants exercising at 10:00 h or earlier as compared to those exercising at times later than 10:00 h |
Souissi et al. [84] | 12 young Judo athletes | None of the participants belonged to any extreme type as determined by the Horne and Ösberg self- questionnaire | One caffeine and one placebo condition in the morning hours (07:00 h); one caffeine and one placebo condition in the evening hours (17:00 h) | 5 mg/kg | 30-s lower-body Wingate test | Peak and mean power were increased only when caffeine was ingested in the morning |
2.4 Does Caffeine Ergogenicity Vary According to Training Status?
Reference | Sample | Caffeine dose | Performance metric | Main findings |
---|---|---|---|---|
Astorino et al. [97] | 8 endurance-trained and 8 ‘active’ young men | 5 mg/kg | 10-km cycling time trial | Caffeine ingestion reduced the time necessary to complete 10-km of cycling in endurance-trained but not in ‘active’ men |
Boyett et al.a [83] | 7 endurance-trained and 7 untrained young men | 6 mg/kg | Isokinetic knee extension and 3-km cycling time trial | For cycling time trial, the differences in responses to caffeine and placebo ingestion in the morning training sessions were ‘unclear’ between the groups; for the two evening conditions, following caffeine ingestion, untrained individuals ‘likely’ experienced greater reductions in time necessary to complete 3-km of cycling than trained individuals; for isokinetic peak torque, the comparisons were either ‘trivial’ or ‘unclear’ |
Brooks et al. [109] | 7 resistance-trained and 7 untrained young men | 5 mg/kg | Weight lifted and force produced in the 1 RM Smith machine squat | Caffeine ingestion improved 1 RM weight lifted in untrained but not in resistance-trained men; no between-group differences were observed for force production |
Collomp et al. [24] | 7 trained swimmers and 7 untrained swimmers (young men and women) | 250 mg | 1600-m swimming for the trained swimmers and 400-m for the untrained | Caffeine ingestion improved swimming velocity in trained but not in untrained participants |
O’Rourke et al. [108] | 15 young well-trained and 15 recreational runners (sex was not specified) | 5 mg/kg | 5-km running time trial | Caffeine ingestion reduced time necessary to complete 5-km of running in both well-trained and recreational runners |
Porterfield et al. [107] | 10 endurance-trained and 10 untrained young men | 5 mg/kg | Cycling time to exhaustion | Caffeine ingestion did not improve time to exhaustion either in endurance-trained or untrained men |
2.5 Does Caffeine Ergogenicity Vary According to Sex?
Reference | Sample | Caffeine dose | Performance metric | Main findings |
---|---|---|---|---|
Butts and Crowell [121] | 13 young men and 15 women | 300 mg | Cycling time to exhaustion | Caffeine ingestion did not improve time to exhaustion in both sexes |
Sabblah et al. [122] | 10 young men and 8 women | 5 mg/kg | Weight lifted in the squat and bench press 1 RM; repetitions to muscle failure with 40% 1 RM in the bench press | Caffeine ingestion enhanced weight lifted in the 1 RM bench press in men and women; no effects of caffeine were observed for 1 RM squat and 40% 1 RM in the bench press performance to muscle failure in both sexes |
Skinner et al. [120] | 16 young men and 11 women | 3 mg/kg | Cycling time to exhaustion | Caffeine ingestion improved time to exhaustion both in men and women |
Suvi et al. [123] | 13 young men and 10 women | 6 mg/kg | Walks until volitional exhaustion | Caffeine ingestion did not improve time to exhaustion in both sexes |
2.6 Does Habitual Caffeine Use Alter Its Ergogenic Effects?
Reference | Sample | Method of assessing habitual caffeine intake | Caffeine dose | Performance metric | Main findings |
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Beaumont et al. [129] | 18 habitually low caffeine users (< 75 mg/day) randomly ingested caffeine or placebo for 28 days | Semi-quantitative food frequency questionnaire (not reported if validated or not) | 3 mg/kg for 20 straight days | 60-min cycling followed by maximum work completed in 30 min | Habitual caffeine intake attenuated the effects of caffeine on exercise performance |
Bell and McLellan et al. [128] | 13 caffeine users (≥ 300 mg/day) and 8 non-users (< 50 mg/day) | Questionnaire (not reported if validated or not) | 5 mg/kg | Cycling time to exhaustion | The duration and the magnitude of the ergogenic effects of caffeine was greater in habitual non-users |
Dodd et al. [127] | 8 caffeine users (> 300 mg/day) and 8 non-users (≤ 25 mg/day) | Questionnaire (not reported if validated or not) | 3 and 5 mg/kg | Cycling time to exhaustion | No differences in responses to caffeine ingestion between habitual and non-habitual users in time to exhaustion |
Evans et al. [203] | 6 caffeine users (> 130 mg/day) and 10 non-users (< 40 mg/day) | Questionnaire (not reported if validated or not) | 200 mg | 10 × 40-m sprints | Caffeine ingestion attenuated sprint performance decrement only in non-habitual users |
Lara et al. [131] | 11 habitually low caffeine users (< 50 mg/day) randomly ingested caffeine or placebo for 20 days | A food frequency questionnaire (not reported if validated or not) | 3 mg/kg for 20 straight days | Cycling time to exhaustion and 15-s Wingate sprints | Habitual caffeine intake attenuated the effects of caffeine on exercise performance |
Glaister et al. [27] | 21 men with caffeine intake of 88 ± 87 mg/day | Questionnaire (not reported if validated or not) | 5 mg/kg | 12 × 30-m sprints | No correlation between habitual caffeine intake and improvements in performance following acute caffeine ingestion |
Gonçalves et al. [130] | 14 low caffeine users (58 mg/day), 12 moderate caffeine users (143 mg/day) and 14 high caffeine users (351 mg/day) | A validated food frequency questionnaire | 6 mg/kg | Cycle ergometer time trial | Time necessary to complete the time trial was reduced in all groups following acute caffeine ingestion with no effect of habitual caffeine intake |
Jordan et al. [204] | 8 caffeine users (> 300 mg/day) and 10 non-users (≤ 50 mg/day) | Questionnaire created by the authors | 6 mg/kg | 12 × 30-m sprints | Caffeine ingestion improved best sprint time with no effect of habitual caffeine intake |
Sabol et al. [132] | 6 caffeine users (> 100 mg/day) and 14 caffeine non-users (≤ 100 mg/day) | A validated food frequency questionnaire | 2, 4, and 6 mg/kg | Medicine ball throw and vertical jump | Caffeine ingestion improved medicine ball throw distance (only 6 mg/kg) and vertical jump height (all caffeine doses) with no effect of habitual caffeine intake |
Tarnopolsky and Cupido [205] | 6 caffeine users (> 500 mg/day) and 6 non-users (< 50 mg/day) | 4-day food records | 6 mg/kg | Ankle dorsiflexors MVC | No effect of habitual caffeine intake and no effect of caffeine ingestion on MVC |
Wiles et al. [206] | 18 men with different levels of habitual intake (exact values were not specified) | Questionnaire (not reported if validated or not) | 3 g of coffee (150–200 mg of caffeine) | 1500-m running time trial | Caffeine ingestion reduced time necessary to complete 1500-m running; based on the rank order of habitual caffeine ingestion there was no effect of habitual caffeine intake (however, this study lacked a proper statistical analysis of the differences between individuals with varying amounts of habitual caffeine intake) |
2.7 How Should Caffeine be Utilized Within Repeated Competitive Bouts?
2.8 Does Caffeine Modify Training Adaptations?
2.9 How Should Caffeine be Consumed?
2.10 What is the Optimal Dose of Caffeine?
Reference | Sample | Caffeine dose | Performance metric | Main findings |
---|---|---|---|---|
Anderson et al. [119] | 8 young female rowers | 6 and 9 mg/kg | 2000-m rowing time; average power output | ↓ in rowing time only with 9 mg/kg; ↔ between caffeine and placebo for average power output |
Arazi et al. [207] | 10 teenage female karate athletes | 2 and 5 mg/kg | Weight lifted in 1 RM leg press; maximum number of repetitions with 60% of 1 RM; vertical jump height; power during ‘Running-based Anaerobic Sprint Test’ | ↔ between the caffeine doses and placebo in any of the analyzed outcomes |
Astorino et al. [172] | 15 young active men | 2 and 5 mg/kg | Isokinetic knee extension and knee flexion peak torque, average torque, total work, and average power | ↑ in peak knee flexion torque only with 5 mg/kg; ↑ in knee extension and knee flexion total work only with 5 mg/kg; ↑ in knee extension and knee flexion average power only with 5 mg/kg |
Bruce et al. [208] | 8 male rowers | 6 and 9 mg/kg | 2000-m rowing time | ↓ in rowing time with both caffeine doses; ↔ between caffeine and placebo for average power output |
Bugyi [209] | 25 young untrained men | 84, 162, 250 mg | Maximum isotonic hand contractions | ↔ between any of the caffeine doses and placebo |
Cohen et al. [210] | 7 young men and women; the sample comprised competitive road racers | 5 and 9 mg/kg | 21-km road race time trial | ↔ between any of the caffeine doses and placebo |
Del Coso et al. [211] | 12 young active women and men | 1 and 3 mg/kg | Power output in a half-squat and bench press exercises with loads ranging from 10 to 100% 1 RM | ↑ in power output during the half-squat only with 3 mg/kg; ↑ in power output during the bench press only with 3 mg/kg (for some loads, 3 mg/kg was more effective than placebo; for others, only the 3 mg/kg vs 1 mg/kg comparison was significant) |
Desbrow et al. [212] | 9 well-trained young male cyclists | 1.5 and 3 mg/kg | Cycling time trial | ↔ between any of the caffeine doses and placebo |
Desbrow et al. [171] | 16 well-trained young male cyclists | 3 and 6 mg/kg | 1-h cycling time trial | ↓ in cycling time with both caffeine doses |
Dodd et al. [127] | 17 recreationally trained young men | 3 and 5 mg/kg | Cycling time to exhaustion | ↔ between any of the caffeine doses and placebo |
Ellis et al. [213] | 15 youth soccer players | 1, 2, and 3 mg/kg | 20-m sprint time, arrowhead agility change of direction; countermovement jump height, peak power, average power, peak velocity, and peak force; Yo–Yo test distance | ↔ between any of the caffeine doses and placebo for 20-m sprint time; ↓ in right change of direction time with all three caffeine doses; ↓ in left change of direction time only with 2 mg/kg of caffeine; ↑ in vertical jump height only with 3 mg/kg; ↑ in peak and mean power as well as peak velocity and force with all three caffeine doses; ↔ between any of the caffeine doses and placebo for Yo–Yo distance |
Glaister et al. [178] | 17 young male sport science students | 2, 4, 6, 8, and 10 mg/kg | Repeated sprint peak power, mean power, and time to peak power | ↔ between any of the caffeine doses and placebo |
Graham and Spriet [170] | 8 well-trained young male distance runners | 3, 6, and 9 mg/kg | Running to exhaustion | ↑ in total running time only with 3 and 6 mg/kg |
Guest et al. [58] | 101 male athletes from various sports | 2 and 4 mg/kg | 10-km cycling time trial | ↓ in cycling time with both caffeine doses |
Jacobson and Edwards [214] | 36 recreationally active young men and women | 300 and 600 mg | Isokinetic knee extension and knee flexion peak torque | ↔ between any of the caffeine doses and placebo |
Jenkins et al. [178] | 13 male cyclists | 1, 2, and 3 mg/kg | Work performed during 15-min of cycling | ↑ in work performed only with 2 mg/kg |
Kovacs et al. [215] | 15 young well-trained triathletes or cyclists | 2.1, 3.2, and 4.5 mg/kg | 1 h cycling time trial | ↑ in cycling mean work output with 3.2, and 4.5 mg/kg enhanced performance as compared to placebo and 2.1 mg/kg of caffeine; ↑ in cycling mean work output with 2.1 as compared to placebo |
McLellan and Bell [216] | 13 young recreationally active men and women | 3, 5, 6.1, and 7 mg/kg | Running time to exhaustion | ↑ in total running time with all caffeine doses |
McNaughton [217] | 12 male team sports athletes | 5 and 10 mg/kg | Running time to exhaustion | ↑ in total running time only with 10 mg/kg |
Miller et al. [202] | 188 young male students | 1 and 3 mg/kg | Forearm flexor MVC | ↑ in MVC strength only with 3 mg/kg |
Pallarés et al. [173] | 13 young resistance-trained men | 3, 6, and 9 mg/kg | Barbell velocity in the bench press and squat with loads of 25, 50, 75, and 90% of 1 RM; peak power in a 4-s cycling sprint | ↑ in barbell velocity at 25% and 50% of 1 RM with all doses in the bench press and squat; ↑ in barbell velocity at 75% of 1 RM with 6 and 9 mg/kg in the bench press; ↑ in barbell velocity at 90% of 1 RM only with 9 mg/kg in the bench press; ↑ in barbell velocity at 75% of 1 RM with all three caffeine doses in the squat; ↑ in barbell velocity at 90% of 1 RM only with 6 and 9 mg/kg in the squat; ↑ in cycling peak power only with 9 mg/kg |
Pasman et al. [169] | 9 well-trained young cyclists | 5, 9, and 13 mg/kg | Cycling time to exhaustion | ↑ in total cycling time with all three caffeine doses |
Perkins and Williams [218] | 14 female young undergraduate students | 4, 7, and 10 mg/kg | Cycling time to exhaustion | ↔ between any of the caffeine doses and placebo |
Sabol et al. [132] | 20 young recreationally trained men | 2, 4, and 6 mg/kg | Medicine ball throw distance; vertical jump height | ↑ in medicine ball throw distance only with 6 mg/kg; ↑ in vertical jump height with all three caffeine doses |
Skinner et al. [219] | 10 young competitive male rowers | 2, 4, and 6 mg/kg | 2000-m rowing time; average power output | ↔ between any of the caffeine doses and placebo |
Stadheim et al. [220] | 8 young trained male cross-country skiers | 3 and 4.5 mg/kg | Cross-country, double poling ergometer time trial | ↑ in total distance covered with both doses of caffeine |
Tallis and Yavuz [174] | 10 young recreationally active men | 3 and 6 mg/kg | Concentric and eccentric knee extension and elbow flexor strength and total work | ↔ between the caffeine doses and placebo in the elbow flexors in any of the analyzed outcomes; ↑ in knee extension force only at high angular velocity with 6 mg/kg of caffeine; ↔ between any of the caffeine doses and placebo in average concentric, maximal and average eccentric strength of the knee extensors; ↔ between any of the caffeine doses and placebo in strength of the knee extensors during a repeated contractions protocol |
Trevino et al. [180] | 13 young recreationally active male | 5 and 10 mg/kg | Elbow flexor MVC and rate of torque development | ↔ between any of the caffeine doses and placebo |
Turley et al. [221] | 26 boys | 1, 3, and 5 mg/kg | Peak and average power during a 30-s Wingate test; handgrip MVC | ↑ in peak power only with 3 mg/kg of caffeine; ↑ in mean power only with 5 mg/kg of caffeine; ↑ in handgrip MVC only with 3 and 5 mg/kg of caffeine |