Title: Creatine and Exercise Performance

Key words: skeletal muscle, glycine, arginine, ergogenic aid, high intensity exercise, performance enhancement

Date: Aug 2000

Category: 12.Sports

Type: Article

Author: Dr M Draper

 

Creatine and Exercise Performance

Introduction

Creatine is crucial for energy flow within skeletal muscle. It can be synthesised from glycine, arginine and a suitable methylated group such as methionine1. For a 70kg man, a non-vegetarian diet (that includes meat or fish) contributes about 1gm of creatine per day of the 2gms that is required to replace that lost mainly as creatinine from the kidney. Vegetarians synthetise their creatine in kidney, liver and pancreas and have lower levels in their muscles. The total creatine pool (Cr.tot) of 120 gms is 95% located in skeletal muscle (24-40 micromol/gm). Around 30% is in free form (Cr.f) and 70% as phosphocreatine (Cr.phos). Creatine levels are not affected by short term training or gender.

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?

Creatine Monohydrate 20 gms daily (4 x 5gms ie approx 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 122mmol/kg).(4 ) and there is unpublished data that lower intakes (3gms/day) for 14 and 30days can increase levels to 132 and 142 mmol/kg respectively. If the availability of Cr.phos is a performance limiting factor for intense, fatiguing short lasting activity then these raised levels should improve performance (a true ergogenic aid). Krieder5 postulates 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 onset of muscle fatigue and quicker recovery.

Does creatine supplementation improve performance?

The answer, initially, would appear to be "Yes" from various laboratory studies reviewed by Williams6. For example, Balsom7 showed higher pedalling frequency in ten 6 second periods when subjects who had taken placebo were compared with creatine subjects. However, a critical review by Mujika and Padilla8 concluded that the laboratory studies usually had untrained subjects. The limited scientific data concerning highly trained athletes performing single competition-like tasks also 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.

CREATINE REFERENCES;

  1. Reeds PJ.Creatine and creatinine metabolism’.in Waterlow JC, Stephen JML Eds , Nitrogen Metabolism in Man. Applied Science Publishers, London, 1981; pp263-269.
  2. Newsholme E, Leech T, Duester GKeep on Running1994; pp93-97. Wiley & Sons ISBN 0-471-94314-2.
  3. Saltin B, pp 387-412 in Taylor AW et al Eds Biochemistry of Exercise VII Human Kinetics , Illinois. 1990
  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 MHNutritional ergogenics in athleticsJournal 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 aid for sports performance in highly trained athletes: a critical review Int. J Sports Med. 1997; 18:7, 491-6.
  9. Hopkins WG et al . Design and analysis of research on sports performance enhancementMed.Sci.Sports Exerc. 1999; 31:3, 472-85.
  10. Silber ML Scientific facts behind creatine monohydrate as sport nutrition supplementJ. Sports Med.Phys. Fitness 1999; 39:3, 179-88.