Tissue oxygen saturation detection and related apparatus and methods

A narrow-band optical device for determining muscle oxygenation level, comprising:

• a wearable housing;
• an optical source array in the wearable housing including a plurality of narrow-band optical sources;
• a plurality of optical detectors in the wearable housing including at least three optical detectors arranged substantially in a linear arrangement on a same side of the optical source array, wherein the at least three optical detectors include a first optical detector of a first size disposed a first distance from the optical source array, a second optical detector of a second size larger than the first size disposed a second distance greater than the first distance from the optical source array, and a third optical detector disposed a third distance greater than the second distance from the optical source array,
• wherein the first optical detector, the second optical detector, and the third optical detector are configured to detect an optical signal emitted from the optical source array;
• and
• a processor coupled to outputs of the plurality of optical detectors and configured to process output signals from the plurality of optical detectors and determine the muscle oxygenation level.