Which Is the Best Indicator of Muscle Oxygen Extraction During Exercise Using NIRS?: Evidence that HHb Is Not the Candidate

Abstract

Recently, deoxygenated hemoglobin (HHb) has been used as one of the most popular indicators of muscle O2 extraction during exercise in the field of exercise physiology. However, HHb may not sufficiently represent muscle O2 extraction, as total hemoglobin (tHb) is not stable during exercise. The purpose of this study was to measure various muscle oxygenation signals during cycle exercise and clarify which is the best indicator of muscle O2 extraction during exercise using NIRS. Ten healthy men performed 6-min cycle exercise at both moderate and heavy work rates. Oxygenated hemoglobin (O2-Hb), HHb, tHb, and muscle tissue oxygen saturation (SmO2) were measured with near-infrared spatial resolved spectroscopy from the vastus lateralis muscle. Skin blood flow (sBF) was also monitored at a site close to the NIRS probe. During moderate exercise, tHb, O2-Hb, and SmO2 displayed progressive increases until the end of exercise. In contrast, HHb remained stable during moderate work rate. sBF remained stable during moderate exercise but showed a progressive decrease at heavy work rate. These results provide evidence that HHb may not sufficiently represent muscle O2 extraction since tHb is not stable during exercise and HHb is insensitive to exercise-induced hyperaemia.

Test–retest reliability of skeletal muscle oxygenation measurements during submaximal cycling exercise in patients with chronic heart failure

“…However, it did not alter TSI either. Moreover, [HHb] was insensitive to exercise‐induced hyperaemia of skeletal muscle, as opposed to TSI (Kime et al ., ). The latter indicates insufficient capability of [HHb] to represent skeletal muscle fractional O 2 extraction because of insensitivity to increased O 2 delivery.…”

“…Because TSI is an absolute value, it may be viable for between-subject comparison and assessment of attainment of critical limits during exercise (Bowen et al, 2012). Furthermore, it may serve as a better estimate for muscle fractional O 2 extraction than does [HHb] (Kime et al, 2013). Therefore, the TSI is the main focus of this study.…”

“…the balance between O 2 delivery and utilization) in skeletal muscle employed both [HHb] and TSI as its proxy (Sperandio et al, 2009;Bowen et al, 2012). While there is an ongoing debate on which parameter serves this purpose best, no consensus exists on a preference of reporting either [HHb] or TSI (Jones et al, 2009;Quaresima & Ferrari, 2009;Kime et al, 2013;Koga et al, 2014). The main arguments concern the influence of superficial tissue layers (i.e.…”

“…One of the more recent innovations in NIRS development, namely spatially resolved spectroscopy (SRS), allows for the NIRS device to acquire absolute saturation of oxygen of the chromophores in the tissue (mainly haemoglobin and myoglobin). The oxygen saturation is designated as muscle tissue oxygen saturation (SmO 2 ), and dependent on the device, as tissue saturation index (TSI) or tissue oxygenation index (Buchheit et al, 2011;Bowen et al, 2012;Kime et al, 2013). The additional advantage of the determination of absolute oxygenation values introduces the potential of identifying physiological 'critical' limits in working skeletal muscle.…”

Skeletal muscle oxygen dynamics and peak aerobic capacity

“…In specific terms, the near-infrared spatial resolved spectroscopy technique measures relative change from rest in oxygenated hemoglobin (Hb)/myoglobin (Mb) (Oxy-Hb/Mb: an indicator of the balance between O2 supply and utilization), deoxygenated-Hb/Mb (Deoxy-Hb/ Mb: an indicator of the balance between O2 unloading in the muscle and blood outflow from the muscle), and total-Hb (Oxy-Hb/Mb plus Deoxy-Hb/Mb: indicator of blood volume) concentration and muscle O2 saturation (SmO2: oxy-Hb/Mb per total-Hb: an indicator of the balance between O2 supply and utilization, which is less sensitive to changes in blood volume than oxy-Hb/Mb). Muscle O2 extraction can be estimated by deoxy-Hb/Mb or SmO2 when total-Hb/Mb is stable 3,4) . However, every variable has not always been represented in previous studies using NIRS.…”