Near infrared spectroscopy (NIRS) is a new biomedical monitoring technology with the advantage of
in vivo, portability and real time [
1,
13−
17]. It provides noninvasive measurements of the concentration changes of oxygenated hemoglobin (Δ[HbO
2]) and deoxygenated hemoglobin (Δ[Hb]), based on the absorption spectrum of main chromophores in tissue [
18−
20]. Coupled with the optical window (700 ~ 900 nm), infrared light penetrate in several centimeters deep below skin surface [
19,
21]. It was reported by Jöbsis that NIRS could be used to monitor oxygenated hemoglobin and deoxygenated hemoglobin concentration changes in the muscle and other tissues, then the NIR light path following a ‘banana-shaped’ curve into the tissue was simulated and the distance between the light source and the detector was calculated [
3]. For the need to evaluate muscle oxidation in sports, portable NIR spectroscopy was developed and validated. In previous NIRS research, oxygenated hemoglobin of local muscle was reported to have some relationship with maximal oxygen consumption (VO
2max) and BLa, however, the comparison between muscle oxygenation parameters monitored by NIRS was not paid enough attention to and the information obtained was not fully exploited. In this study, concentration change of muscle oxygenated hemoglobin, deoxygenated hemoglobin, total hemoglobin (HbT) and hemoglobin oxygenation index (HbD) were defined as Δ[HbO
2], Δ[Hb], Δ[HbO
2 + Hb] and Δ[HbO
2-Hb] correspondingly. The physiological changes of four parameters during the incremental test were discussed and the relationship of inflection points between HbD and BLa was demonstrated. Four parameters of muscle oxygenation and BLa concentration were simultaneously recorded and investigated to ensure they can reflect the physiological function timely and accurately.