Fant en liten studie her med referanse...
Creatine, as most PP readers will know, is manufactured routinely by the liver and kidneys and may be found in significant quantities in muscle, nerve and sperm cells. Within the muscles, it is used in the form of creatine phosphate, a high octane chemical which assists in supplying the energy indirectly needed to perform muscle contractions. This process of muscles being powered is performed by adenosine triphosphate (ATP), which is created inside muscle cells from carbohydrates,fats and proteins in the presence of oxygen, being broken down to adenosine diphosphate(ADP) during exercise. However, since ATP is generated slowly, creatine phosphate acts as a reserve source of immediately available energy by giving its phosphate to ADP creating ATP quickly in order to make the muscles work.
Numerous studies, many of them reported in PP, show that oral creatine monohydrate supplementation can produce performance-enhancing effects during anaerobic bouts of repeated exercise. This, of course, is good news for sprinters and weight lifters,but what about endurance athletes, who surge during a race to break the field or kick for the line at the end - can creatine supplementation help them? Recently, Dr Martin Engelhardt from the Orthopoadische Universitatsklinik in Frankfurt formulated a cycle ergometer experiment comparing endurance/ power endurance exercise in athletes without creatine supplementation against those with low-dose supplementation.
Twelve regional class triathletes aged between 22 and 27 were selected to take part in the test. Each athlete underwent a preliminary incremental cycle ergometer testto determine their 3 mmol.L-1 blood lactate intensity. Once established, this intensitywas used as the aerobic exercise intensity for the experiment.
The testing began with each athlete performing their aerobic exercise on the cyclefor 30 minutes, followed by two bouts of high-intensity interval training, which involved cycling hard for 15 secs and then 45 secs at their aerobic exercise intensity,10 times before two minutes rest and systematically repeating the interval session.After this, the subjects were 'rewarded' with another 30 minutes of cycling at their specific aerobic exercise intensity (a total of one hour and 20 minutes cycling!).The test results were then kept from the athletes, and the following day they were administered 6 grams of creatine daily (to be taken in two 3g doses) for a period of five days before returning to repeat the test. You've probably noticed that the creatine loading dose only amounted to 30g over the five days, whereas in many other studies of creatine supplementation the normal dose is 100g (four doses of 5g dailyfor five days).
Blood samples were taken throughout the testing to monitor creatine, creatinine (the degradation product of creatine), glucose and lactate levels, whereas urine samples(for measurement of creatine and creatinine urine levels) heart rate and oxygen uptakewere measured both before and after the aerobic exercises.
And the results? As you would expect, after creatine supplementation analysis ofthe blood and urine samples showed significant increases in the serum creatine concentration in the blood and serum creatinine levels in the urine. Fifty per cent of the athletes in the first test couldn't complete the entire second 30 min bout of endurance exercise,whereas after taking creatine each of the athletes who had struggled in the firsttest managed to increase their ride time by four minutes, although this increase didn't reach any statistical significance. However, after creatine supplementation,the researchers report that the total number of interval reps increased significantly and that 75 per cent of the athletes improved their performance (nobody did the reverse).Lactate concentrations showed no changes in the endurance test and interval training following supplementation. Blood glucose levels, however, decreased significantly between baseline levels and minutes 25-50 before creatine but did not decrease significantly during the same periods after supplementation.
After analysing the results, the researchers concluded that, at lower doses, ie, 6g daily for five days, creatine supplementation appears to have an effective impact on endurance athletes if they are required to sprint during an aerobic bout (as may happen when, for instance, you find yourself up against a couple of Kenyans during a 10K race). This conclusion is supported by the 18 per cent increase in interval performance after supplementation that was found in the study.
The problem is that the test wasn't performed as a double-blind trial, so both the athletes and the testers knew exactly when each athlete was taking creatine. Thus, sceptics could argue that it was the psychological or placebo effect that enabled the athletes to perform much better during the second test because they believedthe creatine was going to help them. That objection apart, it is interesting that such a comparatively low dose of creatine compared to normal practice seems to have had such a significant effect. One possible explanation is that an individual's creatine 'pool' is positively related to lean body mass; the more muscle, the larger the natural creatine stores. Thus an athlete with a slight frame would need less creatine supplementation than a bulkier athlete.
(Engelhardt, M. at al (1998). 'Creatine supplementation in endurance sports' Medicine and Science in Sports & Exercise, 30 (7): pp 1123-1129)
Jamie Mcloughlin
