Fuels for various athletic events and games

ATP in muscle can be assessed by the measurement of the maximal activities of key enzymes in extracts of human muscle (see Appendix 13.3). 

As intensity increases, the contributions of blood glucose and glycogen to ATP generation increase. Above about 50% of maximum power output, the rate of glycogen utilisation increases almost exponentially since some glycogen is converted to lactic acid at an increasing rate. 

Experiments cannot be performed on athletes during competitions, but athletes, non-athletes and patients can be studied in the laboratory. Estimates of the proportion of ATP generated from which fuels in various athletic events are based on such laboratory experiments and knowledge of exercise biochemistry and physiology. Some estimates are provided in Table 13.8. Quantitative information on the maximal capacity of some pathways for generating 

Only two fuels are used during the 100 m sprint - glycogen and phosphocreatine. The glycogen is converted exclusively to lactic acid. Both fuels contribute to the generation of ATP. The evidence for this observation is that the maximum activity of phos-phorylase, can generate about 3 units of ATP. However, the maximum rate at which ATP can be utilised is about 10 units (Hultman et al. 1990  

As the distance extends to 400 m, oxidation of some of the glycogen occurs, producing about 25% of the ATP generated in this event. Some of the oxygen required comes from oxymyoglobin that is present in the muscle (see below). 

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