Near-infrared spectroscopy (NIRS), coupled with rapid venous (VO) and arterial occlusions (AO) can be used to non-invasively estimate resting local skeletal muscle blood flow (mBF) and oxygen consumption (mVO2), respectively. However, the day-to-day reliability of mBF and mVO2 responses to stressors such as incremental dynamic exercise has not been established. Purpose: To determine the reliability of NIRS derived mBF and mVO2 response from incremental dynamic exercise. Methods: Measurements of mBF and mVO2 were collected in the vastus lateralis of twelve healthy, physically active adults [7 m and 5 f; 25 y (SD 6)] over 3 non-consecutive visits within 10 days. After 10 mins rest, participants performed 3 mins of rhythmic isotonic knee extension (1 extension/4 s) at 5, 10, 15, 20, 25, and 30% of maximal voluntary contraction (MVC), prior to 4 VOs and then 2 AOs. Results: mBF and mVO2 proportionally increased with intensity (0.55 to 7.68 ml·min-1·100 ml-1 and 0.05 to 1.86 mlO2·min-1·100 g-1, respectively) up to 25% MVC where it began to plateau at 30% MVC. Moreover, a mBF/mVO2 mVOratio of ~5 was consistent for all exercise stages. The intra-class coefficient (ICC) for mBF indicated high to very high reliability for 10-30% MVC (0.82-0.9). There was very high reliability for mVO2 across all exercise stages (ICC 0.91-0.96). Conclusion: NIRS can reliably assess muscle blood flow and oxygen consumption responses to low-moderate exercise, meriting potential applications in clinical diagnosis and therapeutic assessment.
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