Muscle deoxygenation in the quadriceps during ramp incremental cycling: Deep vs. superficial heterogeneity

Abstract

Muscle deoxygenation (i.e., deoxy[Hb + Mb]) during exercise assesses the matching of oxygen delivery (Q̇O2) to oxygen utilization (V̇O2). Until now limitations in near-infrared spectroscopy (NIRS) technology did not permit discrimination of deoxy[Hb + Mb] between superficial and deep muscles. In humans, the deep quadriceps is more highly vascularized and oxidative than the superficial quadriceps. Using high-power time-resolved NIRS, we tested the hypothesis that deoxygenation of the deep quadriceps would be less than in superficial muscle during incremental cycling exercise in eight males. Pulmonary V̇O2 was measured and muscle deoxy[Hb + Mb] was determined in the superficial vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF-s) and the deep rectus femoris (RF-d). deoxy[Hb + Mb] in RF-d was significantly less than VL at 70% (67.2 ± 7.0 vs. 75.5 ± 10.7 μM) and 80% (71.4 ± 11.0 vs. 79.0 ± 15.4 μM) of peak work rate (WR(peak)), but greater than VL and VM at WR(peak) (87.7 ± 32.5 vs. 76.6 ± 17.5 and 75.1 ± 19.9 μM). RF-s was intermediate at WR(peak) (82.6 ± 18.7 μM). Total hemoglobin and myoglobin concentration and tissue oxygen saturation were significantly greater in RF-d than RF-s throughout exercise. The slope of deoxy[Hb + Mb] increase (proportional to Q̇O2/V̇O2) in VL and VM slowed markedly above 70% WR(peak), whereas it became greater in RF-d. This divergent deoxygenation pattern may be due to a greater population of slow-twitch muscle fibers in the RF-d muscle and the differential recruitment profiles and vascular and metabolic control properties of specific fiber populations within superficial and deeper muscle regions.

Metabolic and performance‐related consequences of exercising at and slightly above MLSS

“…Overall, these data corroborate previous evidence highlighting the diverse relative contribution of each of the muscles (or muscle portions) engaged in the exercise task to the whole‐body arteriovenous O 2 difference which arises from the heterogeneity in motor unit recruitment patterns, fiber‐type expression, and the resulting vascular dynamic controls that characterize the active muscles. What is interesting is that the greater muscle activity in the VL muscle (ie, greater EMG signal) during MLSS p+10 and subsequent time‐to‐exhaustion trials was not accompanied by an increase in the [HHb] signal (in contrast to the RF muscle).…”

“…The physiological mechanisms underlying these different patterns of behavior of the VL and RF muscles in regulating the delivery and utilization of O 2 are a current topic of debate . What is important in relation to the findings of the present study is that these behavior patterns might be reflective of the metabolic changes occurring when transitioning from the heavy‐to‐severe exercise intensity domain.…”

“…In relation to the physiological responses associated with the upper limit of sustainable exercise (ie, heavy‐to‐severe boundary), a growing amount of evidence has shown that, during ramp‐incremental cycling exercise to exhaustion, following a rather linear increase from the onset of exercise, the NIRS‐derived deoxygenated hemoglobin [HHb] signal of the vastus lateralis (VL) muscle displays a breakpoint ([HHb] BP ) that occurs at ~75%‐85% of V.O 2peak . This leads to a plateau‐like response in the [HHb] signal, with controlling mechanisms for this “apparent” upper limit still being a subject of debate . The [HHb] BP has been linked to a metabolic rate similar to MLSS and CP, and is also seen (albeit with a different profile) in the rectus femoris (RF) muscle .…”

Reproducibility of NIRS assessment of muscle oxidative capacity in smokers with and without COPD

“…While these features alone do not form the basis of quality control, they highlight that patient physical characteristics limiting reflected light from active muscle tissue are likely partly responsible for reducing reproducibility of k measurements. Alternative NIRS systems, such as high-power time-resolved (TRS) NIRS, allow deeper penetration into muscle during rest and exercise (Okushima et al, 2015), and therefore may increase the reliability of ${\mathrm{normalm}\dot{\mathrm{V}}\mathrm{normalO}}_{\mathrm{2}}$ recovery kinetic assessment in these patients.…”

Heterogeneity of blood flow and metabolism during exercise in patients with chronic obstructive pulmonary disease

“…Indeed, the study by Kalliokoski et al (2000) in healthy individuals showed differences in heterogeneity of Q among the quadriceps muscle regions that was characterized by a decrease in the heterogeneity of Q in those exercising muscles in which Q was the highest (vastus intermedius and vastus medialis) as compared to those muscles with the lowest Q (vastus lateralis and rectus femoris) during exercise. More recently, it was shown that superficial and deep muscle NIRS readings are different in healthy individuals at rest and during exercise (Okushima et al, 2015).…”