Skeletal muscle ammonia production and repeated, intense exercise in humans

We investigated the impact of repeated, high-intensity exercise on NH3 metabolism using the single-leg knee extensor model. The muscle glycogen level would be lowered by the initial exercise and low glycogen may stimulate NH3 production independent of any other effects of previous exercise. Therefore a high muscle glycogen condition was included in the protocol so that the pre-exercise glycogen concentration would be at least at a normal resting level for the second exercise. The subjects (n = 6) used previous exercise and (or) diet to begin the exercise with either normal (87.0 +/- 14.4 mmol/kg wet weight) or high (176.8 +/- 22.9 mmol/kg wet weight) glycogen (C and HG, respectively) in the quadriceps. They exercised (Ex1) one leg to exhaustion (140% leg VO2 max), rested 1 h, repeated the exercise (Ex2), and then repeated the protocol with the opposite leg. The exercise durations of Ex1 and Ex2, respectively, for C were 2.82 +/- 0.51 and 2.47 +/- 0.47 min (p < 0.05) and for HG were 2.92 +/- 0.57 and 2.77 +/- 0.50 min. The NH3 efflux was reduced (p < 0.05) from Ex1 to Ex2 in both C (516 +/- 159 and 250 +/- 69 mumol, respectively) and HG (618 +/- 233 and 275 +/- 124 mumol, respectively). While NH3 efflux was virtually identical between C and HG in both Ex1 and Ex2, HG consistently had a greater arterial NH3 concentration (p < 0.05). The decreased efflux in Ex2 compared with Ex1 was not due to greater accumulation of muscle NH3.(ABSTRACT TRUNCATED AT 250 WORDS)