Intense interval training enhances human skeletal muscle oxygen uptake in the initial phase of dynamic exercise at high but not at low intensities.

The present study tested the hypothesis that intense interval training enhances human skeletal muscle blood flow and oxygen uptake (VO2) at the onset of dynamic exercise. We also investigated whether possible training effects were dependent on exercise intensity. Six habitually active males carried out 7 weeks of intermittent-exercise one-legged knee-extensor training at an intensity corresponding to approximately 150% of peak thigh VO2 on three to five occasions per week. After the training period, cardiovascular and metabolic measurements were performed during knee-extensor exercise with the trained leg (TL) and the control leg (CL) for 10 min at intensities of 10 and 30 W, and also for 4 min at 50 W. Femoral venous blood flow was higher (P < 0.05) in TL than CL from 75 to 180 s at 30 W ( approximately 75 s: 3.43 +/- 0.20 versus 2.99 +/- 0.18 l min(-1)) and from 40 to 210 s at 50 W ( approximately 75 s: 5.03 +/- 0.41 versus 4.13 +/- 0.33 l min(-1)). Mean arterial pressure was not different between legs. Thus, thigh vascular conductance was higher (P < 0.05) in TL than CL from 35 to 270 s at 30 W and from 150 to 240 s at 50 W. Femoral arterial-venous (a-v) O2 difference was higher (P < 0.05) in TL than CL from 20 to 70 s at 30 W, but not different between TL and CL at 50 W. Thigh VO2 was higher (P < 0.05) in TL than CL from 20 to 110 s at 30 W ( approximately 45 s: 0.38 +/- 0.04 versus 0.30 +/- 0.03 l min(-1)), and from 45 to 240 s at 50 W ( approximately 45 s: 0.64 +/- 0.06 versus 0.44 +/- 0.08 l min(-1)). No differences were observed between TL and CL during exercise at 10 W. The present data demonstrate that intense interval training elevates muscle oxygen uptake, blood flow and vascular conductance in the initial phase of exercise at high, but not at low, intensities.