Nonlinear relationships between mitochondrial stimuli, muscle oxygen consumption, and muscle oxygen supply during dynamic handgrip exercise

 

Masako Fujioka¹, Ryotaro Kime¹, Shunsaku Koga², Takuya Osawa¹, Kousuke Shimomura¹, Takuya Osada¹, Norio Murase¹, and Toshihito Katsumura¹

¹Department of Sports Medicine for Health Promotion, Tokyo Medical University, Tokyo 160-8402, Japan; ²Applied Physiology Laboratory, Kobe Design University, Kobe 651-2196, Japan

 

The purpose of this study was to evaluate the relationships between mitochondrial stimuli, muscle oxygen consumption (m-VO₂), and O₂ supply at various exercise intensities.  Nine healthy male subjects performed incremental dynamic handgrip exercise until exhaustion.  The workload was increased by 5% maximum voluntary contraction (MVC) every minute, starting at 10% MVC.  Phosphocreatine (PCr) during exercise was evaluated using 31-phosphorus magnetic resonance spectroscopy.  The diffusive m-VO₂ and the muscle oxygenation difference (m-O_2diff) were monitored by near-infrared continuous wave spectroscopy.  The increase of the m-O_2diff level indicates that muscle O₂ demand predominated over O₂ supply during exercise.  The PCr level subsequently decreased with higher workloads.  The diffusive m-VO₂ above 10% MVC significantly increased from the resting (p<0.05), and was constant at higher workloads.  The m-O_2diff above 25% MVC was significantly greater from the resting (p<0.05).  In conclusion, although PCr, one type of mitochondrial stimuli, gradually decreased, diffusive m-VO₂ was constant at higher workloads.  As muscle deoxygenation gradually increased at higher workloads, muscle O₂ supply may have been inadequate during the dynamic handgrip exercise.

 

Key words: muscle O₂ dynamics, near-infrared spectroscopy, handgrip exercise