title: Muscle O2 extraction reserve during intense cycling is site-specific.
abstract: The present study compared peak muscle deoxygenation ([HHb]peak) responses at three quadriceps sites during occlusion (OCC), ramp incremental (RI), severe- (SVR) and moderate-intensity (MOD) exercise. Seven healthy men (25 ± 4 yr) each completed a stationary cycling RI (20 W/min) test to determine [HHb]peak [at distal and proximal vastus lateralis (VLD and VLP) and rectus femoris (RF)], peak V̇O2 (V̇O(2peak)), gas exchange threshold (GET), and peak work rate (WR(peak)). Subjects also completed MOD (WR = 80% GET) and SVR exercise (WR corresponding to 120% V̇O(2peak)) with absolute [HHb] (quantified by multichannel, time-resolved near-infrared spectroscopy) and pulmonary VO2 (V̇O(2p)) monitored continuously. Additionally, [HHb] and total hemoglobin ([Hb]tot) were monitored at rest and during subsequent OCC (250 mmHg). Site-specific adipose tissue thickness was assessed (B-mode ultrasound), and its relationship with resting [Hb]tot was used to correct absolute [HHb]. For VLD and RF, [HHb]peak was higher (P < 0.05) during OCC (VLD = 111 ± 38, RF = 114 ± 26 μM) than RI (VLD 64 ± 14, RF = 85 ± 20) and SVR (VLD = 63 ± 13, RF = 81 ± 18). [HHb]peak was similar (P > 0.05) across these conditions at the VLP (OCC = 67 ± 17, RI = 69 ± 17, SVR = 63 ± 17 μM). [HHb] peaked and then decreased prior to exercise cessation during SVR at all three muscle sites. [HHb]peak during MOD was consistently lower than other conditions at all sites. A "[HHb] reserve" exists during intense cycling at the VLD and RF, likely implying either sufficient blood flow to meet oxidative demands or insufficient diffusion time for complete equilibration. In VLP this [HHb] reserve was absent, suggesting that a critical PO2 may be challenged during intense cycling.
authors.affiliation: Kobe Design University, Kobe, Hyogo, Japan; The University of Western Ontario, London, Ontario, Canada; and.
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Spencer
authors.affiliation: Kobe University, Kobe, Hyogo, Japan.
authors.forename: Tatsuro
authors.initials: T
authors.lastname: Amano
authors.affiliation: Kobe University, Kobe, Hyogo, Japan.
authors.forename: Narihiko
authors.initials: N
authors.lastname: Kondo
authors.affiliation: The University of Western Ontario, London, Ontario, Canada; and.
authors.forename: John M
authors.initials: JM
authors.lastname: Kowalchuk
authors.affiliation: Kobe Design University, Kobe, Hyogo, Japan; s-koga@kobe-du.ac.jp.
authors.forename: Shunsaku
authors.initials: S
authors.lastname: Koga
mesh_terms: D000328:Adult; D001642:Bicycling; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D008297:Male; D009119:Muscle Contraction; D018763:Muscle Fatigue; D053580:Muscle Strength; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption; D010807:Physical Endurance; D052097:Quadriceps Muscle / Q000378:metabolism*; D019265:Spectroscopy, Near-Infrared; D013997:Time Factors; D055815:Young Adult
chemical_list: D006454:Hemoglobins; D010100:Oxygen
keywords: incremental exercise; muscle deoxygenation; near-infrared spectroscopy