In vivo quantitative near-infrared spectroscopy in skeletal muscle during incremental isometric handgrip exercise

The aim of this study was to investigate the performance of in vivo quantitative near-infrared spectroscopy (NIRS) in skeletal muscle at various workloads. NIRS was used for the quantitative measurement of O-2 consumption (m (V) over dot O-2) in the human flexor digitorum superficialis muscle at rest and during rhythmic isometric handgrip exercise in a broad range of work intensities (10-90% MVC=maximum voluntary contraction force). Six subjects were tested on three separate days. No significant differences were found in m(V) over dot O-2 measured over different days with the exception of the highest workload. The within-subject variability for each workload measured over the three measurements days ranged from 15.7 to 25.6% and did not increase at the high workloads. The m (V) over dot O-2 was 0.14 +/- 0.01 mlO(2) min(-1) 100 g(-1) at rest and increased roughly 19 times to 2.68 +/- 0.58 mlO(2) min(-1) 100 g(-1) at 72% MVC. se results show that local muscle oxygen consumption at rest as well as during The exercise at a broad range of work intensities can be measured reliably by NIRS, applied to a uniform selected subject population. This is of great importance as direct local measurement of m (V) over dot O-2 during exercise is not possible with the conventional techniques. The method is robust enough to measure over separate days and at various workloads and can therefore contribute to a better understanding of human physiology in both the normal and pathological state of the muscle.