Transcript Creatine
Creatine Supplementation What is Creatine? • Naturally occurring constituent found in food • Also synthesized in the kidneys, liver, and pancreas from amino acids arginine, glycine, and methionine. Where is Creatine Found? • Creatine is a naturally occurring amino acid found in the body (primarily muscle tissue) • The daily requirement of creatine is about 2-3 grams/day • About half of the daily needs are obtained from the diet (primarily meat and fish) • The remaining daily need for creatine is synthesized from the amino acids glycine, arginine, and methionine primarily in the liver Creatine Stores • Normal creatine content in muscle tissue is 120-140 mmol/kg dm (60% as PCr, 40% as Cr) • Dietary availability of creatine may result in higher or lower stores • Creatine supplementation can increase creatine stores to as much as 160 mmol/kg dm Forms of Creatine Supplements • • • • Creatine Monohydrate – Most Common Creatine Phosphate Creatine Citrate Creatine blended w/CHO, Proteins, AA, Caffeine – – – – Powders Tablets Gel Liquid Supplement Strategies • Load 20 g/day (4 equal doses 5g) - 5-7 days – Increase TCr stores approx. 20% (Grande) • Maintain 3-5 g/day (0.03 g/kg) • Others recommend 2-3g/day over longer load period (1mo.)- just as effective Factors Affecting Cr Loading Success • Cr w/ CHO (glucose) = Insulin Effect – Studies shown 60% greater increase in TCr stores over Cr only • Ingestion following exercise is best • Greatest increase occur in those with lowest initial levels • There are responders and non-responders (2030%) • Best response is in Type II muscle. • No differences between genders Documented Side Effects • • • • • Potential side effects are minor Gastrointestinal (GI) distress No renal or liver dysfunction No cramping in controlled studies Increased Body Mass (water retention in muscle cell due to osmotic changes) • Urinary Volume decrease during loading Creatine Enhancing Performance Function of Creatine • The body only has limited stores of ATP & ADP • When a Cr supplement is ingested, & enters the intestines, a majority of Cr is absorbed into the bloodstream. • Cr from bloodstream is taken up by skeletal and cardiac muscle through insulin-mediated active transport Function of Creatine (cont.) • After absorption, a portion of Cr combines with phosphate to form PCr • This storage of Cr and PCr allows rapid resynthesis of ATP to meet energy demands via the creatine kinase (CK) reaction • Theoretically, Cr supplementation will increase Cr and PCr stores, providing more PCr to be utilized in CK reactions History of Cr Supplementation • Soviets and Eastern block countries began using Cr as potential performance (1960’s & 70’s) • First real studies of Cr supplementation for performance enhancement began in 1990’s in US and GB • GB Olympic Champions Linford Christie (100m) and Sally Gunnell (400 hurdles) - 1992 Barcelona games Mechanisms of Performance Enhancement • Increased PCr concentrations in muscle should aid in rapid resynthesis of ATP via the Cr kinase reaction • Increases PCr diffusion between mitochondria and myosin heads. • Reduce muscle acidity by consuming H+ in process of ADP-ATP – Muscle can accumulate more lactic acid before reaching limiting muscle pH = Increase duration of high intensity exercise Mechanisms of Performance Enhancement • Causes osmotic changes in muscle cell which increases water content of cell – Stimulus for protein synthesis – Decreases rate of protein degradation • Facilitates calcium uptake by the sarcoplasmic reticulum which shortens relaxation time. Does IT Work? • High intensity, short duration activities lasting < 2 min especially repeated with short rest periods • Sprints, jumps, weight lifting, sprinting, etc. Does It Work? (cont.) • No effect in continuous aerobic activities • Effective in both genders • Effective in young and old. • Effectiveness is greatest in novice athletes.