Relationship between Indicators Measured by 31P-magnetic Resonance Spectroscopy and Near-infrared Spectroscopy after Decreased Muscle and Vessel Function

The purpose of this study was to compare indicators of oxidative capacity obtained from 31P-magnetic resonance spectroscopy (31P-MRS) and near-infrared spectroscopy (NIRS) following a 21-day upper-limb cast immobilization. Eight healthy men (19.5±0.9 years, mean±SD) participated in this study. For all subjects, the non-dominant arm was immobilized for 3 weeks with a cast (IMM) and the dominant arm was measured as control (CON). We measured the following parameters for participants pre- and post-immobilization: forearm cross-sectional area (CSA) and maximal voluntary contraction (MVC) of the grip. The oxidative capacity was evaluated by the time constant for the recovery of muscle oxygen consumption (TcVo2mus) determined by NIRS and the time constant of PCr (TcPCr) by 31P-MRS. There was no significant change in forearm CSA. MVC, TcVo2mus, and TcPCr were significantly decreased 26.5%, 25.9% and 32.2%, respectively, post-immobilization. A positive correlation was found between pre- and post-immobilization in TcVo2mus and TcPCr. The TcVo2mus and TcPCr were decreased during the 3-week immobilization, and there was a positive correlation between TcVo2mus and TcPCr both pre- and post-immobilization. The result of this study indicates that NIRS determined oxidative capacity is useful in a clinical setup where muscle and vascular functions are compromised.