Plasma ammonia concentrations and the slow component of oxygen uptake kinetics during cycle ergometry.

The purposes of this study were to 1) compare the patterns of responses for plasma ammonia concentration ([NH3]) during moderate- vs. heavy-intensity cycle ergometry, and 2) examine the relationship between the V O2 slow component (V O 2SC) and plasma [NH3]. Thirteen healthy, untrained men (mean +/- SEM age = 24.8 +/- 0.6 years) performed a total of eight constant power output exercises (7 minutes in duration) at two different intensities (moderate, 60% gas exchange threshold [GET] = 60% of the gas exchange threshold; and heavy, Delta 50% = 50% of the difference between GET and V O2 max). Blood was collected from an antecubital vein before the exercise, during the last 3 minutes of the 6-minute warm-up, and during each minute of the 7-minute constant power output workbout. The time course of changes in plasma [NH3] and V O2 during the two constant power output exercise intensities were assessed separately using 2 (intensity) x 7 (time) repeated-measures analyses of variance. For 60% GET, there were no significant differences in the mean normalized plasma [NH3] during the 7-minute workbout. For Delta 50%, there was a significant increase in the mean normalized plasma [NH3] during the 7-minute workbout. These findings suggest a potential relationship between exercise-induced hyperammonemia and the V O 2SC during heavy-intensity exercise.