ABSTRACT
Energy for the contractile unit in the muscle fibre (the myofibrils) is obtained from the hydrolysis of adenosine triphosphate (ATP) to adenosine diphosphate (ADP) and phosphate. However, the amount of ATP in the muscle is limited: the total amount of ATP in the muscles of the sprinter would support the energy requirement for about 2 s. To continue running, ATP must be regenerated from ADP and phosphate; this occurs due to the oxidation of fuels. Thus ATP is produced in energy-yielding reactions and is utilised in energy-requiring processes: this constitutes the ATP/ADP cycle (fig 1). Although the precise chemical details of the use of ATP by muscle and its production in the mitochondria interest many biochemists and physiologists, it is the fuels whose metabolism provides energy for the synthesis of ATP that are of much more relevance to the scientifically interested athlete, the health scientist and the physician. The ATP/ADP energy currency cycle. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315025001/ca0a1b50-16e7-4532-9e85-fe2cd38f2327/content/fig65_1_C.jpg" xmlns:xlink="https://www.w3.org/1999/xlink"/>
