“If you give an athlete more petrol in the tank, they will go further. What we've done is to give them 50% to 60% more petrol,” said Dr. Hawley, professor and head of the exercise metabolism group at RMIT University (formerly the Royal Melbourne Institute of Technology) in Victoria, Australia.
“It has been incredibly hard for exercise physiologists to learn how to put more petrol back in the engine,” Dr. Hawley added. “This [dilemma] has occupied researchers for many decades. We [asked athletes to ingest] caffeine, which has no nutritional benefit, and the results were astounding.”
Dr. Hawley and colleagues led by David J. Pederson, MD, studied the effects of the co-ingestion of caffeine with carbyhydrate on rates of muscle glycogen resynthesis during the period of recovery after subjects exercised to exhaustion. The subjects in the randomized, double-blind, crossover study were seven highly trained competitive cyclists/triathletes, all of whom routinely cycled for >250 km/week (12-15 hours/week).
On the first evening of the study, all subjects came into the lab and cycled to exhaustion and then ate a low-carbohydrate meal. The next morning, they returned and rode until volitional fatigue. They then ingested either 4 g/kg bodyweight of carbohydrate as sports drinks, bars, or gels within 5 minutes of stopping exercise and again after 60, 120, and 180 minutes. A total of 8 mg/kg caffeine was given in two equal doses in a specially formulated sports drink made by GlaxoSmithKline Consumer Healthcare. The placebo was the same sports drink without caffeine, which looked and tasted identical to the caffeine-containing drink. Caffeine was given immediately after exercise and again after 2 hours of recovery. The researchers took muscle biopsies after 60 and 240 minutes of recovery. They took blood samples at 30, 60, 90, 120, 180, and 240 minutes of recovery.
Muscle glycogen levels were similar at exhaustion and increased by similar amounts after 1 hour of recovery for both interventions. However, after 4 hours of recovery the caffeine-containing drink resulted in
- higher glycogen accumulation (313 vs 234 μmol/kg, P <.001)
- 66% higher rate of resynthesis for the 4-hour recovery period (57.7 vs. 38.0 μmol/kg, P <.05), and
- significantly greater phosphorylation of CaM-kinase (CaMK), which is thought to speed transport of glucose into muscle cells
“One of the problems athletes face, particularly endurance athletes, is the need to replenish their fuels (mainly carbohydrates) quickly in between training sessions.
Translating research into practice
Athletes are likely to be most interested in how the dosage of caffeine used in the trial compares to that found in commonly available beverages. Dr. Hawley said that the dose would translate to ~560 mg of caffeine for a 70-kg subject. “A bottle of cola contains about 60 mg, cup of coffee about 100, so [the trial dosage] is equivalent to 5 or 6 cups of strong coffee.”
“We found that the amount of carbohydrate that could be stored by the muscles when ingested along with caffeine was about 60% higher than with carbohydrates alone. If you’ve got 60% more fuel there for your next day’s run, cycle ride, or soccer game, there is no question that you would be able to go farther or faster....The practical outcome of that is that an athlete training or competing the next day will have a better training session or race,” Dr. Hawley predicted.
The researchers believe that the effect is due to an increase in two key signaling proteins that affect glucose transport. The most important protein is the CaMK, which is associated with increased glucose transport into muscle.
“Caffeine has a wonderful effect on both short-term sprint performance and on endurance. It is a remarkable drug that affects both ends of the spectrum. Most other ergogenic aids work only on one particular activity or time course,” Dr. Hawley said. “If you put the carbohydrate with caffeine, you’ve probably got the best of both worlds. We are now thinking that the recommendations [that currently call for carbohydrates and caffeine before and during exercise] should be both before and after exertion.”
Reference
1. Pedersen DJ, Lessard SJ, Coffey VG, et al. High rates of muscle glycogen resynthesis after exhaustive exercise when carbohydrate is co-ingested with caffeine. [published online ahead of print May 8, 2008]. J Appl Physiol. 2008. http://jap.physiology.org/cgi/content/abstract/01121.2007v1?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&author1=pedersen&fulltext=caffeine&searchid=1&FIRSTINDEX=0&sortspec=relevance&resourcetype=HWCIT.
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