Caffeine After Workouts Refuels Muscle

Finish your workout, eat some pasta, then wash it down with five or six cups of strong coffee, new research from Australian researchers says.

Glycogen, muscles' fuel source during exercise, is replenished more rapidly when athletes consume both carbohydrate and caffeine following exhaustive exercise, new research from the online edition of the Journal of Applied Physiology shows.

Athletes who ingested caffeine with carbohydrate had 66% more glycogen in their muscles four hours after finishing intense, glycogen-depleting exercise, compared to when they consumed carbohydrate alone, according to the study.

Caffeine Helps Carbohydrate Processing

It is known that consuming carbohydrate and caffeine before and during exercise improves athletic performances. But this is the first study that shows caffeine, combined with carbohydrates following exercise, can help refuel the muscle faster.

"If you have 66% more fuel for the next day's training or competition, there is absolutely no question you will go farther or faster," said Dr. Hawley, the study's senior author. Caffeine is present in common foods and beverages, including coffee, tea, chocolate and cola drinks.

Cyclists Take Part

The study was conducted on seven top endurance cyclists in four sessions. The participants first rode a stationary cycle until exhaustion, and then consumed a low-carbohydrate dinner before going home. This exercise bout was designed to reduce the athletes' muscle glycogen stores prior to the experimental trial the next day.

The athletes did not eat again until they returned to the lab the next day for the second session when they again cycled until exhaustion. They then ingested a drink that contained carbohydrate alone or carbohydrate plus caffeine and rested in the laboratory for four hours.

During this post-exercise rest time, the researchers took several muscle biopsies and multiple blood samples to measure the amount of glycogen being replenished in the muscle, along with the concentrations of glucose-regulating metabolites and hormones in the blood, including glucose and insulin.

The entire two-session process was repeated 7-10 days later. The only difference was that this time, the athletes drank the beverage that they had not consumed in the previous trial. (That is, if they drank the carbohydrate alone in the first trial, they drank the carbohydrate plus caffeine in the second trial, and vice versa.)

The drinks looked, smelled and tasted the same and both contained the same amount of carbohydrate. Neither the researchers nor the cyclists knew which regimen they were receiving, making it a double-blind, placebo-controlled experiment.

Glucose and Insulin Levels Benefit

The researchers found the following:

* one hour after exercise, muscle glycogen levels had replenished to the same extent whether or not the athlete had the drink containing carbohydrate and caffeine or carbohydrate only
* four hours after exercise, the drink containing caffeine resulted in 66% higher glycogen levels compared to the carbohydrate-only drink
* throughout the four-hour recovery period, the caffeinated drink resulted in higher levels of blood glucose and plasma insulin
* several signaling proteins believed to play a role in glucose transport into the muscle were elevated to a greater extent after the athletes ingested the carbohydrate-plus-caffeine drink, compared to the carbohydrate-only drink

Dr. Hawley said it is not yet clear how caffeine aids in facilitating glucose uptake from the blood into the muscles. However, the higher circulating blood glucose and plasma insulin levels were likely to be a factor.

In addition, caffeine may increase the activity of several signaling enzymes, including the calcium-dependent protein kinase and protein kinase B (also called Akt), which have roles in muscle glucose uptake during and after exercise.

Image: Ethan Lofton, Creative Commons License