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Open AccessArticle

Interpretation of Near-Infrared Spectroscopy (NIRS) Signals in Skeletal Muscle

Department of Kinesiology, University of Georgia, Athens, GA 30602, USA
Author to whom correspondence should be addressed.
J. Funct. Morphol. Kinesiol. 2019, 4(2), 28;
Received: 5 April 2019 / Revised: 21 May 2019 / Accepted: 23 May 2019 / Published: 26 May 2019
(This article belongs to the Section Musculoskeletal Disorders)
Near-infrared spectroscopy (NIRS) uses the relative absorption of light at 850 and 760 nm to determine skeletal muscle oxygen saturation. Previous studies have used the ratio of both signals to report muscle oxygen saturation. Purpose: The purpose of this pilot study is to assess the different approaches used to represent muscle oxygen saturation and to evaluate the pulsations of oxygenated hemoglobin/myoglobin (O2heme) and deoxygenated hemoglobin/myoglobin (Heme) signals. Method: Twelve participants, aged 20–29 years, were tested on the forearm flexor muscles using continuous-wave NIRS at rest. Measurements were taken during 2–3 min rest, physiological calibration (5 min ischemia), and reperfusion. Ten participants were included in the study analysis. Results: There was a significant difference in pulse size between O2heme and Heme signals at the three locations (p < 0.05). Resting oxygen saturation was 58.8% + 9.2%, 69.6% + 3.9%, and 89.2% + 6.9% when calibrated using O2heme, the tissue oxygenation/saturation index (TSI), and Heme, respectively. Conclusion: The difference in magnitude of O2heme and Heme pulses with each heartbeat might suggest different anatomical locations of these signals, for which calibrating with just one of the signals instead of the ratio of both is proposed. Calculations of physiological calibration must account for increased blood volume in the tissue because of the changes in blood volume, which appear to be primarily from the O2heme signal. Resting oxygen levels calibrated with Heme agree with theoretical oxygen saturation. View Full-Text
Keywords: near-infrared spectroscopy (NIRS); oxygen consumption; hemoglobin; myoglobin; skeletal muscle near-infrared spectroscopy (NIRS); oxygen consumption; hemoglobin; myoglobin; skeletal muscle
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MDPI and ACS Style

Sanni, A.A.; McCully, K.K. Interpretation of Near-Infrared Spectroscopy (NIRS) Signals in Skeletal Muscle. J. Funct. Morphol. Kinesiol. 2019, 4, 28.

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