Unchanged Muscle Deoxygenation Heterogeneity During Bicycle Exercise After 6 Weeks of Endurance Training

Abstract

The purpose of this study was to examine the changes in muscle oxygen saturation (SmO₂) level and its heterogeneity after 6 weeks of endurance training using multi-channel near infrared spatially resolved spectroscopy (NIR_SRS). Nine healthy subjects participated in this study (Male = 6, Female = 3, age: 27 ± 5 years, height: 168.7 ± 7.4 cm, weight: 62.4 ± 12.4 kg). The subjects performed a 30 W ramp incremental bicycle exercise test until exhaustion before and after endurance training. The NIR_SRS probe was attached to the left vastus lateralis muscle along the direction of the long axis. The subjects performed bicycle exercise for 30 min/day, 3 days/week for 6 weeks. The work rate during training was set at $60\% \dot {\rm V}{\rm O}_{2{\rm{peak}}}$ and increased every $5\% \dot {\rm V}{\rm O}_{2{\rm{peak}}}$ when the subjects could maintain the work rate three times consecutively. After training,  .VO_2peak was significantly increased (Pre: 42.7 ± 9.9 ml/kg/min, Post: 52.3 ± 7.2 ml/kg/min, p < 0.001) and the mean SmO₂ within measurement sites at $\dot {\rm V}{\rm O}_{2{\rm{peak}}}$ was significantly decreased (Pre: 56.1 ± 1.1 %, Post: 53.3 ± 2.2 %, p < 0.05). Conversely, the heterogeneity of the SmO₂ during exercise was not changed by training. These results suggest that the functional heterogeneity of O₂ balance did not change due to endurance training, and the O₂ balance heterogeneity may not interfere with O₂ exchange in the activating muscle in healthy individuals.