SLOW COMPONENT OF O-2 UPTAKE DURING HEAVY EXERCISE - ADAPTATION TO ENDURANCE TRAINING

Seven untrained male subjects [age 25.6 +/- 1.5 (SE) yr, peak O-2 upta ke (VO2) 3.20 +/- 0.19 l/min] trained on a cycle ergometer 4 days/wk f or 6 wk, with the absolute training workload held constant for the dur ation of training. Before and at the end of each week of training, the subjects performed 20 min of constant-power exercise at a power desig ned to elicit a pronounced slow component of VO2 (end-exercise VO2 - V O2 at minute 3 of exercise) in the pretraining session. An additional 20-min exercise bout was performed after training at this same absolut e power output during which epinephrine (Epi) was infused at a rate of 100 ng . kg(-1) . min(-1) between minutes 10 and 20. After 2 wk of tr aining, significant decreases in VO2 slow component, end-exercise VO2, blood lactate ([La-] and glucose concentrations, plasma Epi ([Epi]) a nd norepinephrine concentrations, ventilation (VE), and heart rate (HR ) were observed (P < 0.05). Although the rapid attenuation of the got slow component coincided temporally with reductions in plasma [Epi], b lood [La-], and VE, the infusion of Epi after training significantly i ncreased plasma [Epi] (Delta 2.22 ng/ml), blood [La-] (Delta 2.4 mmol/ l) and VE (Delta 10.0 l/min) without any change in exercise VO2. We th erefore conclude that diminution of the VO2 slow component with traini ng is attributable to factors other than the reduction in plasma [Epi] , blood [La-] and VE.