Table 2.

Summary of studies exploring the effects of caffeine between trained and untrained individuals

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

1 RM 1 repetition maximum

^aData were analyzed using the magnitude based inferences approach