Non-Invasive Muscle Metabolism Assessment with Near-Infrared Spectroscopy and Electrical Muscle Stimulation

Abstract

Background: Muscle biopsy, the gold standard for assessing muscle aerobic capacity, is an invasive procedure. Noninvasive alternatives, such as 31-phosphorus magnetic resonance spectroscopy (31P-MRS) and near-infrared spectroscopy (NIRS), provide valuable insights, with NIRS providing superior time resolution and ease of use compared with 31P-MRS. Objectives: This study aimed to evaluate muscle metabolism using a 6 s muscle contraction phase with electrical muscle stimulation (EMS) and to assess the impact of EMS on exercise performance under hyperbaric conditions with elevated oxygen pressure. Methods: This study included nine male participants (21 ± 2 years) who underwent 5 min of EMS on the forearm flexor muscle group, with muscle oxygen dynamics assessed using NIRS. For statistical analysis, the mean values between groups were assessed using paired t-tests, and associations were evaluated using Pearson’s correlation coefficient. Results: Spontaneous blood flow interruption during EMS-induced muscle activity indicated the potential for assessing muscle metabolism without disrupting external blood flow. A significant negative correlation was observed between oxygen consumption and changes in oxygenated hemoglobin levels during muscle activity under hyperbaric conditions. Conclusions: This study demonstrates that skeletal muscle metabolism can be measured using a brief 6 s quantitative EMS. Furthermore, hyperbaric exercise appears to enhance aerobic capacity by increasing the rate and availability of oxygen consumption during exercise.