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1 Kinesiology and Anatomy & Physiology, Kansas State University, Manhattan, United States
2 ISS Inc., Champaign, Illinois, United States
* To whom correspondence should be addressed. E-mail: tbarsto{at}ksu.edu.
The aim of this study was to examine the effects of assuming constant reduced scattering coefficient (µ's) on the muscle oxygenation response to incremental exercise and its recovery kinetics. Fifteen subjects (age: 24 ± 5 yrs) underwent incremental cycling exercise. Frequency-domain NIRS was used to estimate deoxyhemoglobin ([HHb]), oxyhemoglobin ([HbO2]), total hemoglobin concentration (THb) and tissue O2 saturation (StO2), incorporating both continuous measurements of µ's and assuming constant µ's. When measuring µ's we observed significant changes (
) in NIRS variables at peak work rate [HHb] (15.0 ± 7.8 µM), [HbO2] (-4.8 ± 5.8 µM), THb (10.9 ± 8.4 µM) and StO2 (-11.8 ± 4.1 %). Assuming constant µ's resulted in greater 's (P < 0.01 vs. measured µ's) in the NIRS variables at peak work rate, where [HHb] (24.5 ± 15.6 µM), [HbO2] (-9.7 ± 8.2 µM), THb (14.8 ± 8.7 µM) and StO2 (-18.7 ± 8.4 %). Regarding the recovery kinetics, the large 95% confidence intervals (CI) for the difference between those determine measuring µ's and assuming constant µ's suggested poor agreement between methods. For the mean response time (MRT), which describes the overall kinetics, the 95% CI's were: MRT-[HHb] = 26.7 s; MRT-[HbO2] = 11.8 s and MRT- StO2 = 11.8 s. In conclusion, µ's changed from light to peak exercise. Further, assuming a constant µ's led to an overestimation of the changes in NIRS variables during exercise and distortion of the recovery kinetics.
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