Evaluation of Muscle Oxygenation during Exercise by NIRS in Normal Subjects—Significance of the NIRS Threshold—

The purposes of the study were to indentify values for TOI threshold and deoxy‑hemoglobin threshold as well as TOI slope using a new NIRS measurement in the vastus lateralis muscle during exer‑ cise and to evaluate the clinical significances in the NIRS variables. To check the reproducibility of NIRS parameters ten healthy males participated in preliminary two tests with a separate 1‑week interval. Another fifteen healthy males participated in the study. Mean values of TOI slope and wattage at TOI threshold did not differ significantly in two tests. The mean values of TOI slope was −0.115 0.07%/watt and the mean wattage of HHb threshold TOI threshold and THI peak were 194 40 watt 188 36 watt and 135 35 watt respectively. Post‑hoc testing showed that the workloads at the NIRS threshold were significantly greater than at VT LT and THI peak. The workload at TOI threshold was significantly correlated with those at VT peak THI and peak watt but not with those at BMI and LT. These results suggest that NIRS threshold reflects the capacity for oxygen exchange in muscles thus affecting exercise performance in healthy subjects. (J Jpn Coll Angiol 2007 47: 21-27)