Acute caffeine ingestion’s increase of voluntarily chosen resistance-training load after limited sleep
Journal Title (Medline/Pubmed accepted abbreviation):Int. J. Sport Nutr. Exerc. Metab.
Page Numbers : 157-164
Summary of Background and Research Design
Background:Sleep deprivation is very common and is often compensated for by consuming caffeine.
Hypothesis:Caffeine will increase the workload chosen by athletes and the effect will be greater when the athletes are sleep-deprived. Testosterone and cortisol concentrations will also be effected by caffeine consumption and sleep deprivation.
Subjects: 16 professional European rugby players, age 20.9 ± 0.9 y. Most athletes did not consume caffeine on a regular basis; those that did consumed 120 mg/day or less.
Experimental design: randomized, double-blind, placebo-controlled, cross-over trial
Treatments : Caffeine (4 mg/kg body weight) or placebo (lactose) in gelatin capsules (187 lb. man = 85 kg, 340 mg caffeine; there is about 100 mg caffeine in a strong cup of coffee).
Protocol : Before any of the trials, the athletes were evaluated for 1 repetition maxima (1RM) for back squat, bench press, and bent barbell row. They then were asked to arrive at the testing facility twice after a full-night’s sleep (8+ hours) and twice in a mildly sleep-deprived state (6 hrs or less). They arrived at 9:30 am after eating breakfast. Upon arrival, the participants ingested one of the treatments. Exactly 1 hour later, a warm-up was performed. They cycled on a stationary bicycle for 5 min and then performed the 3 weight training exercises with a light weight. They then performed 4 sets for back squats, bench press, and bent rows at 85% their previously determined 1RM in a circuit fashion. They performed as many repetitions as they could before failure. Workload was calculated as total repetitions × load lifted. The sum of these 3 values was defined as the “total workload”. Testosterone and cortisol were measured in saliva samples collected immediately before ingestion of the supplement, before the workout, and after the workout.
Summary of Research Findings
- On average, caffeine increased the workload performed for back squat (p = 0.01), bench press (p = 0.04), bent row (p = 0.02), and total workout (p = 0.003) for athletes that were not sleep-deprived.
- Caffeine ingestion also increased the workload for all of the exercises and the total workout in the sleep-deprived state (p < 0.002 for all exercises).
- Sleep deprivation was associated was a significant decrease in performance when caffeine consumption was not a factor.
- Total workload was equal between the non-sleep-deprived, placebo state and the sleep-deprived, caffeine state.
- The participants were divided into 2 discrete groups: “responders” (n = 8) and “non-responders” (n = 8). The responders performed significantly better with caffeine and the non-responders did not perform better with caffeine.
- Caffeine stimulated an increase in testosterone in both sleep-deprived and non-sleep-deprived states. The workout stimulated testosterone production, the most in the non-sleep-deprived state and the least in the sleep-deprived placebo state.
- Cortisol, a stress hormone, was significantly higher in the sleep-deprived condition. Exercise promoted an increase in cortisol in all groups, the highest increase being in the sleep-deprived, caffeine group.
Key practice applications
Performance was greater with caffeine in both the non-sleep-deprived state and the sleep-deprived state. Although a high, acute dose of caffeine compensated for sleep deprivation at a single workout when looking at performance, this tactic may not be effective when used routinely due to adaptation of caffeine tolerance and negative effects on the body such as increased cortisol concentrations in the blood (i.e. stress). Additionally, circulating hormones (i.e. testosterone and cortisol) are not in their maximal state for anabolic activity and gains will probably not be as great.
It is unknown why
the lack of sleep caused a decrease in performance; it is because of physical inabilities, lack of motivation, and/or lack of expectation (amount of sleep could
not be blinded)?
It would have been interesting if the authors followed up with the participants to see how exercising in a sleep-deprived state affected their physical health, mental capabilities, sleep requirements, and exercise capacity for the rest of the day and several days following the workout. Working out while tired can increase risk of being injured or getting sick.
Some athletes reported regularly consuming caffeine. It would have been interesting if the authors compared the “responders” and “non-responders” with normal caffeine intake. Perhaps caffeine ingestion led a caffeine tolerance.