2013 Volume 34 Pages 80-86
To investigate effects of aerobic exercise training on balance for oxygen delivery and utilization of exercising muscles, the relationship between muscle deoxygenation （HHb） and activation was examined in 3 different muscles of the quadriceps during cycling ramp exercise. Seven young aerobic-trained and seven untrained male adults pedaled at 60 rpm to exhaustion, with a work rate （WR） increase of 20 W/min. At the vastus lateralis （VL），rectus femoris （RF） and vastus medialis （VM），muscle deoxygenation and activity were measured by time-resolved near-infrared spectroscopy （NIRS） and surface electromyography （EMG），respectively. Muscle deoxygenation was corrected for adipose tissue thickness and normalized to the amplitude of the HHb response. Muscle deoxygenation and activation were then plotted as a percentage of maximal work rates （%WRmax）． The HHb responses for all three muscle groups showed sigmoid function, which were determined as the best fitting model. The RF muscle demonstrated a “right shift” of the HHb response compared to VL and VM throughout the majority of the ramp exercise. There existed no significant differences of the HHb response per se between the aerobic-trained and untrained subjects. However, the spatial heterogeneity of HHb responses per unit of muscle activity in different muscles of the quadriceps was greater in the trained subjects compared with the untrained subjects. These data suggest that greater oxygen delivery of the trained subjects might not have improved the regional balance for oxygen delivery and utilization in different muscles of the quadriceps during ramp-incremental exercise.
