Title: Testing Possible Ergogenic Aids
Key words: Methodology, creatine, ergogenic supplements, sport performance enhancement
Date: July 2000
Category: 12. Sports
Author: Dr M Draper
An ergogenic aid is an exogenous substance that, when ingested, improves the work output or performance. In sport, with closer scrutiny of pharmacological agents especially of stimulants, narcotics and anabolic steroids , attention has switched to nutritional ergogenic aids1. To highlight how the scientific methodology must be carefully conducted, so as not to be commercially exploited, this article will refer to creatine research.
Research scientists involved in exercise physiology and biochemistry discover a particular new mechanism. For instance, that creatine in the form of phosphocreatine is crucial for energy flow within skeletal muscle. The total creatine pool (Cr.tot) of 120 gms is 95% located in skeletal muscle (24-40 micromol/gm) and 30% is in free form (Cr.f) and 70% as phosphocreatine (Cr.phos). Creatine levels are not affected by short term training or gender and to obtain large dietary amounts, large amounts of protein would have to be consumed (1kg of beef yields 1gm of creatine). This could be detrimental to maintaining muscle glycogen stores. However, a synthetic form, creatine monohydate, enables larger doses to be ingested easily and legally. In a 100 metre sprint, it is estimated that 50% of the ATP is via Cr.phos and 50% from anaerobic glycogen breakdown (< 5% from aerobic glycogen)2. The Cr.phos derived ATP is most important for the first few seconds of muscle contraction and after 20 secs of exercise Cr.phos levels fall to aprox 20% of resting levels3. However regenesis allows repeated high intensity activity.
Is muscle creatine increased by oral supplementation?It is found that Creatine Monohydrate 20 gms daily (4 x 5gms ie aprox 0.3gms/kg body mass) for 5-6 days can raise the Cr.tot to 127-149 mmol/kg of dry muscle (controls < 122mmol/kg)4. If the availability of Cr.phos is a performance limiting factor for intense fatiguing, short lasting activity, could these raised levels improve performance as a true ergogenic aid? Krieder5 postulates that the ATP turnover from Cr.phos would be higher for repeated bouts of High-Intensity Exercise if the levels of Cr.tot and Cr.phos were initially higher and that Cr.phos resynthesis would also be increased. There may also be a delay in the onset of muscle fatigue and quicker recovery.
Does creatine supplementation improve performance?
The answer would initially appear to be "Yes", according to various laboratory studies reviewed by Williams6. For example, Balsom7 showed a higher pedalling frequency in ten 6 second periods when subjects who had ingested placebo were compared with those who had ingested creatine. However, a critical review by Mujika and Padilla8 concludes the laboratory studies usually had untrained subjects and that the limited scientific data concerning highly trained athletes performing single competition-like tasks indicates that this type of population does not benefit from creatine supplementation. A similiar criticism of the design and analysis of research on sport performance enhancement9 concludes that laboratory or field tests should not be extrapolated to elite athletes in competitive events. Perhaps the short term benefit seen in an experimental setting would not be borne out with longer term use when chronic supplementation may interfere with the normal homoeostatic mechanisms and down regulate the biosynthesis of endogenous creatine10.
The design of trials into ergogenic research must clearly identify the subjects (population sample) and only discuss the performance outcome for that particular group or sport. It is misleading however tempting to extrapolate to other subjects or to generalise from specific findings.
1. Williams MH et al. Creatine: the Power Supplement Champaign, Il. Human Kinetics. 1999
2. Newsholme E, Leech T, Duester GKeep on Running pp 93-97. Wiley & Sons 1994; ISBN 0-471-94314-2.
3. Saltin B,1990 pp 387-412 in Taylor AW et al Eds: Biochemistry of Exercise VII Human Kinetics , Illinois.
4. Greenhaff PL ,Bodin K , Soderlund K and Hultman E Effect of oral creatine supplementation on skeletal muscle phosphocreatine resynthesis. American Journal of Physiology, 1994 266 , E725-730.
5. Kreider RB, J. Exerc. Physiol. Online. 1998
6. Williams MH Nutritional ergogenics in athletics Journal of Sports Sciences 1995, 13: S63-S74.
7. Balsom PD et al.Creatine supplementation and dynamic high-intensity intermittent exercise Scand. J. Med. Sci. in Sports, 1993; 3: 143-149.
8. Mujika I & Padilla S Creatine supplementation as an ergonomic acid for sports performance in highly trained athletes: a critical review. Int. J Sports Med. 1997; 18:7, 491-6.
9. Hopkins WG et al .1999 Design and analysis of research on sports performance enhancement Med.Sci.Sports Exerc. 31:3, 472-85.
10. Silber ML 1999 Scientific facts behind creatine monohydrate as sport nutrition supplement J. Sports Med. Phys. Fitness 39:3, 179-88.