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

Malek, MH, Housh, TJ, Crouch, LD, Johnson, GO, Hendrix, CR, Beck, TW, Mielke, M, Schmidt, RJ, and Housh, DJ. Plasma ammonia concentrations and the slow component of oxygen uptake kinetics during cycle ergometry. J Strength Cond Res 22(6): 2018-2026, 2008-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 V̇o₂ slow component (V̇o_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, Δ50% = 50% of the difference between GET and V̇o₂max). 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 [NH ₃] and V̇o₂ during the two constant power output exercise intensities were assessed separately using 2 (intensity) × 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 Δ50%, 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 hyperammo-nemia and the V̇o_2SC during heavy-intensity exercise.