The nutritional biochemistry of creatine

Creatine is a naturally occurring compound that is synthezied endogenously and is present in a meat eaters diet. It is stored in abundance in skeletal muscle, where is exists in free and phosphorylated forms and plays a pivotal role in maintaining a high adenosine triphosphate:adenosine diphosphate ratio during intense contraction. Fatigue development during short-term maximal exercise has been associated with the inability of skeletal muscle to maintain this ratio, at least partly because of phosphocreatine depletion. Ingestion of creatine monohydrate in solution at a rate of 20 g/day for 5 to 6 days has been shown to increase muscle total creatine concentration by approximately 25 mmol/kg dry mass in man, but the variation between subjects is large. After this initial loading phase, muscle stores can be maintained by ingesting 2 g/day. A positive relationship has since been demonstrated between muscle creatine uptake and improvements in performance during repeated bouts of maximal exercise and rates of phosphocreatine resynthesis during recovery from maximal exercise. The mechanism by which improvements in maximal exercise performance are achieved following creatine ingestion possibly relates to an increase in phosphocreatine concentration, specifically in Type II muscle fibres, maintaining adenosine triphosphate resynthesis during exercise. Recently, muscle creatine accumulation has been shown to be substantially increased by combining creatine supplementation with carbohydrate ingestion, elevating muscle creatine concentration in all subjects close to the upper limit of 160 mmol/kg dm. Creatine supplementation should be viewed as a significant development in sports-related nutrition. (C) Elsevier Science Inc.