Progressive effect of endurance training on VO2 kinetics at the onset of submaximal exercise

The rates of increase in O-2 uptake (Vover dotO(2)) after step changes in work rate from 25 W to 60% of pretraining peak Vover dotO(2) (Vover dotO(2 peak)) were measured at various times during an endurance training program (2 h/ day at 60% pretraining Vover dotO(2 peak) peak). Seven untrained males [23 +/- 1 (SE) yr] performed a series of repeated step changes in work rate before training (PRE) and after 4 days (4D), 9 days (9D), and 30 days (30D) of training. Vover dotO(2) kinetic responses were determined from breath-by-breath data averaged across four repetitions and analyzed using a two-component exponential model. Mean response time (time taken to reach 63% of steady-state Vover dotO(2)) was faster (P < 0.01) than PRE (38.1 +/- 2.6 s) at both 4D (34.9 +/- 2.4 s) and 9D (32.5 +/- 1.8 s) and was faster (P < 0.01) at 30D than at all other times (28.3 +/- 1.0 s). Blood lactate concentrations (after 6 min of cycling) were also lower at 4D and 9D than PRE (P < 0.01) and were lower at 30D than at all other times (P < 0.01). Vover dotO(2 peak) was unchanged from PRE (3.52 +/- 0.20 l/min) at 8D (3.55 +/- 0.20 l/min) but was increased (P < 0.01) at 30D (3.89 +/- 0.18 l/ min). Muscle oxidative capacity (maximal citrate synthase activity) was not significantly increased until 30D (P < 0.01). It is concluded that at least part of the acceleration of whole body Vover dotO(2) kinetics with endurance training is a rapid phenomenon, occurring before changes in Vover dotO(2 peak) and/or muscle oxidative potential.