Muscle oxygen saturation measured using "cyclic NIR signals" during exercise.

A new approach to measure muscle oxygen saturation (SmO(2)) using near infrared spectroscopy (NIRS) has been proposed in this paper. This approach exploits the cyclic NIRS signals seen during exercise which are often regarded as "movement artefacts". This new measure, which we term the "cyclic SmO(2)", has the potential to be less affected by the myoglobin which is traditionally believed to be indistinguishable from haemoglobin using NIRS techniques. The cyclic SmO(2) also has fewer assumptions than the conventional SmO(2) measured using time, phase and spatially resolved spectroscopy methods. In a cycling exercise study, NIRS measurements were made over the Vastus lateralis muscle of 11 subjects. In a light exercise protocol, the group mean of the conventional SmO(2) was 51.7 +/- 4.3% and that of the cyclic SmO(2) was 56.0 +/- 3.9%. It was immediately followed by a hard exercise protocol and the group mean of the conventional SmO(2) was reduced to 42.6 +/- 6.1% and that of the cyclic SmO(2) to 48.5 +/- 5.6%. The reduction agrees with the general expectation. The cyclic SmO(2) is a promising new measure of muscle oxygenation.