title: The Spatial Distribution of Absolute Skeletal Muscle Deoxygenation During Ramp-Incremental Exercise Is Not Influenced by Hypoxia.
abstract: Time-resolved near-infrared spectroscopy (TRS-NIRS) allows absolute quantitation of deoxygenated haemoglobin and myoglobin concentration ([HHb]) in skeletal muscle. We recently showed that the spatial distribution of peak [HHb] within the quadriceps during moderate-intensity cycling is reduced with progressive hypoxia and this is associated with impaired aerobic energy provision. We therefore aimed to determine whether reduced spatial distribution of skeletal muscle [HHb] was associated with impaired aerobic energy transfer during exhaustive ramp-incremental exercise in hypoxia. Seven healthy men performed ramp-incremental cycle exercise (20 W/min) to exhaustion at 3 fractional inspired O2 concentrations (FIO2): 0.21, 0.16, 0.12. Pulmonary O2 uptake ([Formula: see text]) was measured using a flow meter and gas analyser system. Lactate threshold (LT) was estimated non-invasively. Absolute muscle deoxygenation was quantified by multichannel TRS-NIRS from the rectus femoris and vastus lateralis (proximal and distal regions). [Formula: see text] and LT were progressively reduced (p<0.05) with hypoxia. There was a significant effect (p<0.05) of FIO2 on [HHb] at baseline, LT, and peak. However the spatial variance of [HHb] was not different between FIO2 conditions. Peak total Hb ([Hbtot]) was significantly reduced between FIO2 conditions (p<0.001). There was no association between reductions in the spatial distribution of skeletal muscle [HHb] and indices of aerobic energy transfer during ramp-incremental exercise in hypoxia. While regional [HHb] quantified by TRS-NIRS at exhaustion was greater in hypoxia, the spatial distribution of [HHb] was unaffected. Interestingly, peak [Hbtot] was reduced at the tolerable limit in hypoxia implying a vasodilatory reserve may exist in conditions with reduced FIO2.
authors.affiliation: Department of Internal Medicine and Cardiology, Leipzig University, Heart Center, Strümpellstraße 39, 04289, Leipzig, Germany. bows@med.uni-leipzig.de.
authors.forename: T Scott
authors.initials: TS
authors.lastname: Bowen
authors.affiliation: Applied Physiology Laboratory, Kobe Design University, Kobe, Japan.
authors.forename: Shunsaku
authors.initials: S
authors.lastname: Koga
authors.affiliation: Graduate School of Human Development and Environment, Laboratory for Applied Human Physiology, Kobe University, Kobe, Japan.
authors.forename: Tatsuro
authors.initials: T
authors.lastname: Amano
authors.affiliation: Graduate School of Human Development and Environment, Laboratory for Applied Human Physiology, Kobe University, Kobe, Japan.
authors.forename: Narihiko
authors.initials: N
authors.lastname: Kondo
authors.affiliation: Division of Respiratory and Critical Care Physiology and Medicine, Rehabilitation Clinical Trials Center, Los Angeles Biomedical Research Institute and Harbor-UCLA Medical Center, Torrance, CA, USA.|School of Biomedical Sciences, University of Leeds, Leeds, UK.
authors.forename: Harry B
authors.initials: HB
authors.lastname: Rossiter
mesh_terms: D000328:Adult; D015444:Exercise; D006454:Hemoglobins / Q000032:analysis; D006801:Humans; D000860:Hypoxia / Q000378:metabolism*; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption; D019265:Spectroscopy, Near-Infrared
chemical_list: D006454:Hemoglobins; D010100:Oxygen
keywords: HHb; Heterogeneity; NIRS; Near infrared-spectroscopy; Skeletal muscle