Methods and systems are disclosed for determining an anaerobic threshold and/oran oxygen consumption rate in a human or animal subject. The methods include exposinga tissue of the subject to illumination radiation, collecting emitted radiationfrom the tissue, the emitted radiation including a portion of the illuminationradiation reflected or transmitted from the tissue, processing the emittedradiation to form a spectrum of the tissue, and determining, based on the spectrumof the tissue, the anaerobic threshold and/or the oxygen consumption rate ofthe subject.
