Adaptation of the Slow Component of VO₂ Following 6 wk of High or Low Intensity Exercise Training
Eighteen untrained males [age: 23 +/- 0.6 yr (SEM)] were randomized into high intensity (HIT: above lactate threshold, LT), moderate intensity (LIT: below the LT) or no training (NT) groups. Subjects trained on a cycle ergometer 4 days.wk-1 for 6 wk with the power output held constant. Maximal cycle ergometry was performed before and after the training period to determine changes in power output and oxygen consumption (VO2) at the LT and peak exertion. Before training and after 1, 2, 4, and 6 wk, subjects performed high constant-load (HCL) cycling bouts to quantify training adaptations in the SC. Training was designed to keep total work equivalent between the HIT and LIT groups. Increases in power output and VO2 at LT and peak exercise after 6 wk were noted in the HIT and LIT groups in comparison to NT group (p<0.05). No differences were noted between HIT and LIT. Two-way repeated measures ANOVA revealed a significant trial*group interaction for adaptation in the SC (p<0.001). After 1wk of training, a significant reduction in the SC was noted for HIT [mean+/-SEM]: (pre-training (PT): 703 +/- 61 ml.min-1; 1 wk: 396 +/- 60 ml.min-1) (- 44% from PT). Further adaptation for the HIT was also noted at 4 wk: 202 +/- 45 ml.min-1 (-71% from PT). For LIT, a significant reduction was noted at 2 wk (PT: 588+/-76 ml.min-1; 2 wk: 374 +/- 50ml.min-1) (-36% from PT). Further adaptation for LIT group was noted at 6 wk (252 +/- 38 ml.min-1) (- 57% from PT). Adaptation in SC was not noted at any interval for NT. Temporal changes in blood lactate (r = 0.40) and ventilation (r = 0.72) were significantly correlated with the changes for SC over the 6 wk training period (p<0.05). In conclusion, it was demonstrated that training at supra-LT and sub-LT intensities produces similar improvement in VO2 and power output at peak exercise and in the LT, when total work output is controlled. However, training at supra-LT intensity promotes larger and faster adaptations in the SC than training at the sub-LT levels.