Background: Near-Infrared Spectroscopy (NIRS) is a widely used technique allowing the non-invasive measurement of skeletal muscle microvascular and mitochondrial function. However, the association between NIRS technology measurements and mitochondrial function analyzed from muscle biopsy by high-resolution respirometry is not clear. Methods: Healthy adults (n=20; 10 females; age 25.3±4.6 years) participated in the study. A NIRS device was used to measure muscle oxygenation during a 5-min brachial occlusion. Muscle oxygen consumption (mVO 2 ) and the change in tissue saturation index (TSI) from baseline to the end of occlusion (ΔTSI Base-Min) were calculated. Muscle biopsy from the vastus lateralis was collected on a separate day to assess complex I mediated mitochondrial respiration. Results: mVO 2 (from 0.021 to 0.070 mlO 2 /min/100g), ΔTSI Base-Min (from 25.2 to 50.2 %) and complex I mediated mitochondrial respiration (from 9.7 to 57.3 pmol·mg ⁻¹ ·s ⁻¹ ) showed wide interindividual variation. Complex I mediated mitochondrial respiration was correlated negatively with mVO 2 (r=-0.64, p=0.002) and ΔTSI Base-Min (r=-0.80, p=0.0003). In multivariate linear regression analysis (Enter-method), complex I mediated respiration was the only variable significantly associated with mVO 2 and ΔTSI Base-Min when sex, body fat percentage and peak oxygen uptake (VO 2 peak) during cycle ergometer test were included in the analysis as confounding factors (Standardized Coefficients ß=-0.431, p=0.017 and ß=-0.691, p=0.0006, respectively). Conclusions: Our findings suggest that during 5-min occlusion, higher mitochondrial respiratory capacity is associated with lower mVO 2 utilization. Lower oxygen utilization during occlusion may indicate a more efficient use of oxygen by mitochondria and better preserved energy metabolism.
Jeskanen et al. (Tue,) studied this question.