Time of Day and Training Status Both Impact the Efficacy of Caffeine for Short Duration Cycling Performance

Abstract

This project was designed to assess the effects of time of day and training status on the benefits of caffeine supplementation for cycling performance. Twenty male subjects (Age, 25 years; Peak oxygen consumption, 57 mL·kg−1·min−1) were divided into tertiles based on training levels, with top and bottom tertiles designated as ‘trained’ (n = 7) and ‘untrained’ (n = 7). Subjects completed two familiarization trials and four experimental trials consisting of a computer-simulated 3-km cycling time trial (TT). The trials were performed in randomized order for each combination of time of day (morning and evening) and treatment (6mg/kg of caffeine or placebo). Magnitude-based inferences were used to evaluate all treatment effects. For all subjects, caffeine enhanced TT performance in the morning (2.3% ± 1.7%, ‘very likely’) and evening (1.4% ± 1.1%, ‘likely’). Both untrained and trained subjects improved performance with caffeine supplementation in the morning (5.5% ± 4.3%, ‘likely’; 1.0% ± 1.7%, ‘likely’, respectively), but only untrained subjects rode faster in the evening (2.9% ± 2.6%, ‘likely’). Altogether, our observations indicate that trained athletes are more likely to derive ergogenic effects from caffeine in the morning than the evening. Further, untrained individuals appear to receive larger gains from caffeine in the evening than their trained counterparts.

Systematic Review of the use of “Magnitude-Based Inference” in Sports Science and Medicine

“…At these sample sizes, the Type I error rate for the "possible" threshold is 22% to 45% and for the "likely" threshold is 12% to 22% (Fig 3A and 3B). Consistent with these calculations, we noticed numerous studies in which effects associated with large p-values (for H o =0)-often in the 0.2 to 0.3 range-were declared "likely" or higher by MBI [36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52]. See Fig 4 for "Although parametric analysis was unable to demonstrate significant differences, magnitude-based inferences indicated that the change in 1-RM squat showed a likely benefit from PA on increasing lower body strength and a very likely benefit for increasing lean body mass (LBM)."…”

Caffeine and Bicarbonate for Speed. A Meta-Analysis of Legal Supplements Potential for Improving Intense Endurance Exercise Performance

“…We terminated our study search in April 2016 but the field of ergogenic supplements continues to evolve. Recently, studies has been published showing no effect on intense endurance performance from both bicarbonate (Callahan et al, 2016) and nitrate (Callahan et al, 2016) supplementation whereas caffeine has resulted in both unchanged (Cordingley et al, 2016) and improved performance (Boyett et al, 2016). A number of the included studies in the current meta-analysis also reported negative findings, so to what extent an actual publication bias toward positive results exits remains unknown.…”

Are the Current Guidelines on Caffeine Use in Sport Optimal for Everyone? Inter-individual Variation in Caffeine Ergogenicity, and a Move Towards Personalised Sports Nutrition

“…These include smoking [ 63 , 64 ], dietary vegetable intake [ 65 ], oral contraceptive use [ 66 , 67 ], pregnancy [ 68 ], menstrual cycle stage [ 69 ], training status [ 44 , 45 ], and hormone replacement therapy [ 70 ]. Other non-genetic, but controllable, factors affecting caffeine ergogenicity are related to the nature of caffeine ingestion, including caffeine dose [ 71 ], source [ 72 – 74 ], age [ 75 ], timing [ 76 ], time of day [ 76 , 77 ], and training status [ 78 , 79 ].…”