Reliability of Muscle Blood Flow and Oxygen Consumption Response from Exercise Using Near-infrared Spectroscopy

Near-infrared spectroscopy (NIRS), coupled with rapid venous and arterial occlusions, can be used for the non-invasive estimation of resting local skeletal muscle blood flow (mBF) and oxygen consumption (math formula), respectively. However, the day-to-day reliability of mBF and math formula responses to stressors such as incremental dynamic exercise has not been established. The aim of this study was to determine the reliability of NIRS-derived mBF and math formula responses from incremental dynamic exercise. Measurements of mBF and math formula were collected in the vastus lateralis of 12 healthy, physically active adults [seven men and five women; 25 (SD 6) years old] during three non-consecutive visits within 10 days. After 10 min rest, participants performed 3 min of rhythmic isotonic knee extension (one extension every 4 s) at 5, 10, 15, 20, 25 and 30% of maximal voluntary contraction (MVC), before four venous occlusions and then two arterial occlusions. The mBF and math formula increased proportionally with intensity [from 0.55 to 7.68 ml min−1 (100 ml)−1 and from 0.05 to 1.86 ml O2 min−1 (100 g)−1, respectively] up to 25% MVC, where they began to plateau at 30% MVC. Moreover, an mBF/math formula muscle oxygen consumption ratio of ∼5 was consistent for all exercise stages. The intraclass correlation coefficient for mBF indicated high to very high reliability for 10–30% MVC (0.82–0.9). There was very high reliability for math formula across all exercise stages (intraclass correlation coefficient 0.91–0.96). In conclusion, NIRS can reliably assess muscle blood flow and oxygen consumption responses to low- to moderate-intensity exercise, meriting potential applications in clinical diagnosis and therapeutic assessment.