Caffeine negates the effects of the controversial sports supplement, creatine, according to research carried out by scientists from the Katholieke Universiteit Leuven, in Belgium.
Creatine is used by athletes to increase lean body mass and improve performance in high-intensity, short-duration exercise, such as weightlifting, sprinting, and cycling. Caffeine is also recommended by some trainers as it intensifies muscle contractions, hides the discomfort of physical exertion, and even speeds up the use of the muscles short-term fuel stores, according to the American Physiological Society.
However the Belgian researchers have found that the combined effects of creatine and caffeine supplementation may be counterproductive to creatine's effect on muscle relaxation. The study is published in the February issue of the Journal of Applied Physiology.
Ten physical education students (nine men and one woman) who participated in the study, stopped their supplement and caffeine intake for the week leading up to the experiment. They were also asked to avoid changes in their level of physical activity and diet during the 25-week duration of the study.
A double blind experiment then required the subjects to perform the exercise test before and after creatine supplementation, short-term caffeine intake, creatine supplementation in the short term, acute caffeine intake, or a placebo.
The participants were randomly assigned to five experimental protocols, each lasting eight days. Three elements were measured during an experiment consisting of 30 intermittent contractions of quadriceps entailing two seconds of stimulation and two seconds of rest. Measurements included maximum torque, contraction time from 0.25 to 0.75 of Tmax, and relaxation time from 0.75 to 0.25 of max.
The team found that oral creatine supplementation shortened muscle relaxation time in humans: relation time was reduced by five per cent and was significantly shorter than after the placebo.They also noted that the intake of caffeine, combined with a daily creatine supplement, counteracted the beneficial effects of creatine intake on relaxation time and fatigue enhanced this inhibitory effect.
Another finding was that caffeine reduces the functional capacity of sacroplasmic reticulum calcium ATPase.
The creatine that is normally present in human muscle comes either from dietary intake (animal flesh) or is internally manufactured. The American Physiology Society claims that the purpose of creatine supplementation is to increase either total creatine stores or phosphocreatine (PCr) stores within muscle. Supplementation increases the rate of resynthesis of creatine phosphate following exercise.Various studies have shown increased muscle PCr levels after supplementing with 20-30g of creatine monohydrate daily.
Creatine supplementation has also been known to shorten relaxation time during intermittent maximal iosometric muscle contraction. This shortened time, along with a creatine loaded muscle, facilitates calcium absorption into the sarcoplasmic reticulum (the endoplasmic reticulum of skeletal and cardiac muscle). However, some believe that caffeine intake enhances calcium release from the sarcoplasmic reticulum.
The researchers concluded that sustained caffeine intake over a three-day period negates the benefits of creatine. They also suggested that the findings were indirect evidence that facilitation of muscle relaxation may be important to the ergogenic action of creatine supplementation as well as power production during sprint exercises.