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VOLUME 2 ISSUE 2 Journal of International Society of Swimming Coaching
Although a muscle fiber’s CP supply could theoretically be depleted within 6 to 10 seconds of intense
exercise, you will notice, in Table 3, that there is still some CP remaining even when athletes are
severely fatigued. The muscles apparently defend themselves against complete depletion by slowing
their rate of creatine phosphate use after the first few seconds of exercise.
Luckily, the splitting of creatine and phosphate is not the only way the muscles have of releasing
energy and regenerating ATP. Other metabolic processes, i.e. anaerobic glycolysis and aerobic
glycolysis are also able to perform this function, and, in so doing, prevent the complete depletion of
creatine phosphate.
It is a fallacy that all the creatine phosphate in a muscle must be used up before anaerobic glycolysis
and aerobic glycolysis begin regenerating ATP. Actually the latter two metabolic processes begin
contributing ATP to the effort immediately at the start of exercise. They are slower reacting,
however, and require more time to reach their peak rate of ATP regeneration (5 to 6 seconds for
anaerobic glycolysis and 1 to 3 minutes for aerobic glycolysis). Consequently, the splitting of creatine
phosphate is the major source of ATP regeneration from the first few seconds of exercise until the
other two metabolic processes get “up to speed”. When that happens, the working muscles’
dependence on creatine phosphate will be reduced, allowing some to remain stored in them for later
use. However, when the rate of creatine phosphate splitting is reduced and anaerobic and aerobic
glycolysis become the major sources for regenerating ATP, exercise will need to proceed at a reduced
pace where these slower metabolic processes can keep up with the energy demand. Nevertheless,
this is advantageous to the athlete because rapid ATP regeneration would stop if creatine phosphate
was completely depleted.
Thus, creatine phosphate declines in two stages during exercise, a fast stage at the start of exercise,
followed by a slower phase until the end of exercise. The two phases of CP decline are illustrated by
the graph in figure 5. The rapidity of the initial drop and the severity of the final drop are both
increased when the intensity of work is increased. Athletes can reduce the rate of creatine phosphate
use, by slowing their effort (pacing) in the early stages of a competition so aerobic and anaerobic
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