Intensity-dependent Alterations In Post-exercise Skeletal Muscle Oxygen Consumption Are Evident Using Near-infrared Spectroscopy

Near-infrared spectroscopy (NIRS) has emerged as a tool to non-invasively assess oxygen consumption in a specific muscle bed. However, it is unknown whether changes in oxygen consumption in response to different exercise intensities are detectable using NIRS. PURPOSE: Determine whether NIRS-derived oxygen consumption of the vastus lateralis (VL) is altered following whole-body maximal vs. submaximal exercise. METHODS: Ten healthy volunteers (21 ± 1 years old) participated in two visits to the lab. A NIRS device was placed on the belly of the VL muscle of the subject’s right leg. A pneumatic cuff capable of rapid inflation was placed on the same leg proximal to the tibiofemoral joint. Laying supine, the cuff was inflated to 300 mmHg 3x for 30 seconds. A physiological calibration was performed to correct for changes in blood volume. Differences in oxygenated and deoxygenated hemoglobin (Hbdiff) were collected continuously using NIRS. Desaturation slopes (% s-1) were calculated from analyses of Hbdiff signals to estimate skeletal muscle oxygen consumption, and the average of the three cuffs was reported. Participants then performed a progressive maximal exercise test on a cycle ergometer to exhaustion (MAX), and NIRS-derived oxygen consumption was assessed again 15 min after exercise. One week later, the protocol was repeated before and after a submaximal test at 60% VO2peak for the time to match the caloric expenditure of the maximal exercise test (SUBMAX). A repeated measures ANOVA (time * trial) was performed with statistical significance accepted at P ≤ 0.05. RESULTS: There was a significant interaction (P = 0.002), a significant main effect of time (P < 0.001), and a significant main effect of trial (P = 0.001). Oxygen consumption was increased after MAX (-0.129 ± 0.055 % s-1 vs. -0.493 ± 0.251 % s-1 pre- vs. post-exercise, respectively; P < 0.001) and SUBMAX (-0.126 ± 0.041 % s-1 vs. -0.311 ± 0.166 pre- vs. post-exercise; P = 0.001). While there were no pre-exercise differences in oxygen consumption (P = 0.709), post-exercise oxygen consumption was significantly greater following the MAX vs. SUBMAX trial (P = 0.001). CONCLUSION: NIRS can detect increases in local skeletal muscle oxygen consumption consistent with excess post-exercise oxygen consumption that reflects differences in exercise intensity. Supported by: Supported by Towson University (TU) School of Emerging Technology, TU College of Health Professions, and the Summer Undergraduate Research Institute.