How Repeatable Is the Ergogenic Effect of Caffeine? Limited Reproducibility of Acute Caffeine (3 mg.kg−1) Ingestion on Muscular Strength, Power, and Muscular Endurance

Abstract

This study aimed to determine the effect of 3 mg.kg−1 acute caffeine ingestion on muscular strength, power and strength endurance and the repeatability of potential ergogenic effects across multiple trials. Twenty-two university standard male rugby union players (20 ± 2 years) completed the study. Using a double-blind, randomized, and counterbalanced within-subject experimental design. Participants completed six experimental trials (three caffeine and three placebo) where force time characteristic of the Isometric Mid-Thigh Pull (IMTP), Countermovement Jump (CMJ) and Drop Jumps (DJ) were assessed followed by assessments of Chest Press (CP), Shoulder Press (SP), Squats (SQ), and Deadlifts (DL) Repetitions Until Failure (RTF at 70% 1 RM). ANOVA indicated that caffeine improved both the CMJ and DJ (p < 0.044) and increased RTF in all RTF assessments (p < 0.002). When individual caffeine trials were compared to corresponding placebo trials, effect sizes ranged from trivial-large favoring caffeine irrespective of a main effect of treatment being identified in the ANOVA. These results demonstrate for the first time that the performance enhancing effects of caffeine may not be repeatable between days, where our data uniquely indicates that this is in part attributable to between sessions variation in caffeine’s ergogenic potential.

Effects of Acute Ingestion of Caffeine Capsules on Muscle Strength and Muscle Endurance: A Systematic Review and Meta-Analysis

“…Upon reading the full text, 349 studies were excluded for the following reasons: (1) they investigated irrelevant outcomes ( n = 256); (2) the caffeine ingestion group was combined with other interventions ( n = 72); (3) they were animal studies ( n = 17); and (4) they reported long-term interventions ( n = 4). Finally, 14 studies [ 6 , 11 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 ] met the inclusion criteria.…”

“…Table 1 presents the characteristics of caffeine ingestion and participants. Of the 14 studies, 11 studies involved only males [ 11 , 27 , 28 , 29 , 31 , 32 , 33 , 34 , 35 , 37 , 38 ] and 3 studies involved only females [ 6 , 30 , 36 ]. Eight studies provided data for muscle strength [ 6 , 27 , 28 , 30 , 33 , 34 , 36 , 38 ], which was tested using one repetition maximum (1 RM).…”

“…Eight studies provided data for muscle strength [ 6 , 27 , 28 , 30 , 33 , 34 , 36 , 38 ], which was tested using one repetition maximum (1 RM). In addition, 13 studies provided data for muscle endurance [ 6 , 11 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 ], which was measured using the maximum number of repetitions achieved at a fixed load. The dose of caffeine ingestion ranged from 2 to 11 mg/kg BW, and the timing of caffeine ingestion was 45 min or 60 min.…”

“…The dose of caffeine ingestion ranged from 2 to 11 mg/kg BW, and the timing of caffeine ingestion was 45 min or 60 min. In terms of the intensity of muscle endurance tests, three studies involved low-intensity muscle endurance tests (<60% 1 RM) [ 6 , 30 , 34 ], seven studies involved moderate-intensity muscle endurance tests (60−85% 1 RM) [ 11 , 28 , 31 , 33 , 35 , 36 , 38 ], and three studies involved high-intensity muscle endurance tests (≥85% 1 RM) [ 29 , 31 , 32 ].…”

“…Southward et al [ 10 ] further verified the notable impact of caffeine ingestion on muscle endurance. This effect can be attributed to the mechanism where caffeine triggers the release of norepinephrine, acetylcholine, dopamine, and serotonin by binding to adenosine receptors A1 and A2A [ 11 ]. This, in turn, enhances muscle tone [ 12 ] and diminishes the suppressive influence of adenosine on neurotransmission, excitation, and nociception [ 13 ].…”