I recall reading this paper months ago, but forgot to blog about it. However, I saw a summary of this study on a crossfit-based blog yesterday. Here, I’ll elaborate on mechanism. To recap, exercise physiologists in Brazil aimed to study the effects of caffeine and time-of-day on strength-biased training (i.e. weightlifters and crossfitters). This seems logical since it is well known that caffeine improves endurance through increased activation of glucose- and fat-related metabolic pathways. However, the performance enhancing effect of caffeine is largely limited by tolerance; thus, someone like me who daily drinks 2 cups of strong coffee would benefit less than an aficionado of green tea. Further, a lab at the University of Kentucky has spent a decade studying changes in skeletal muscle structure and function across the day. In this study, the researchers compared (and normalized) muscle performance on back squat and bench press performed at maximum load and at 75% maximum load either in the morning (9 AM) or evening (7: 30 PM). A second group of athletes squatted and benched in the morning, but were given a HIGHLY caffeinated capsule (3 mg of caffeine for kg of body weight; assuming that the average crossfitter weighs 170 lbs [or 77 kg] that would be 231 mg of caffeine; the average cup of coffee offers 31 mg of caffeine for a person weighing 77 kg) to consume prior to training. Think of the capsule as consuming a pre-workout shake which are saturated with caffeine and taurine. Following consumption of this caffeine, the muscular performance of the athletes increased to levels seen in the group training at night who were not given caffeine. Here’s a summary of the results with respect to muscle performance.
In addition to examining motor output, the group also looked at changes in sympathetic tonus which dramatically increases during high intensity, strength-biased training due to the constant and rapid need for glucose (derived from the liver). Measures of sympathetic tonus included norepinephrine, epinephrine, cortisol, and testosterone. As expected, training, in general, increased sympathetic tonus. However, the greatest increases in sympathetic tonus from pre-workout levels were seen in the morning group given caffeine or the evening group (given placebo). Further, the extent of sympathetic tonus prior to training was already higher in the group squatting and benching in the evening compared with either morning group.
To recapitulate, a strength-biased athlete is likely to see the largest gains in pound for pound performance if they train in the evenings or after a pre-workout shake in the morning. However, I am skeptical about the long-term benefits of caffeine on strength-biased performance in those tolerant to it. At any rate, please note this study any of you who plan to compete in this year’s “Fittest on Earth” Open.
Mora-Rodríguez R, García Pallarés J, López-Samanes Á, Ortega JF, & Fernández-Elías VE (2012). Caffeine ingestion reverses the circadian rhythm effects on neuromuscular performance in highly resistance-trained men. PloS one, 7 (4) PMID: 22496767