When you go for a run, you will initially burn your stored A…

When you go for a run, you will initially burn your stored ATP to produce movement.  However, this storage of ATP only lasts for a few moments.  Soon, you will be using ____48___ to re-phosphoralate ATP providing no measurable change to ATP concentrations.  After about 15 seconds, however, you will enter into __49__ respiration providing LOTS of ATP through the breakdown of glucose.  Some people, whom have lots of endurance, can run for a prolonged amount of time without causing muscle fatigue.  You might suspect that these individuals are genetically predisposed to this ability by having many __50__ muscle fibers.