title: Prolonged constant load cycling exercise is associated with reduced gross efficiency and increased muscle oxygen uptake.
abstract: This study investigated the effects of prolonged constant load cycling exercise on cycling efficiency and local muscle oxygen uptake responses. Fourteen well-trained cyclists each completed a 2-h steady-state cycling bout at 60% of their maximal minute power output to assess changes in gross cycling efficiency (GE) and muscle oxygen uptake (mVO2) at time points 5, 30, 60, 90, and 120 min. Near-infrared spatially resolved spectroscopy (NIRS) was used to continually monitor tissue oxygenation of the Vastus Lateralis muscle, with arterial occlusions (OCC) applied to assess mVO2. The half-recovery time of oxygenated hemoglobin (HbO2) was also assessed pre and post the 2-h cycling exercise by measuring the hyperemic response following a 5-min OCC. GE significantly declined during the 2-h cycling bout (18.4 ± 1.6 to 17.4 ± 1.4%; P < 0.01). Conversely, mVO2increased, being significantly higher after 90 and 120 min than at min 5 (+0.04 mlO2/min/100 g; P = 0.03). The half-recovery time for HbO2was increased comparing pre and post the 2-h cycling exercise (+7.1 ± 19s), albeit not significantly (d: 0.48; P = 0.27). This study demonstrates that GE decreases during prolonged constant load cycling exercise and provides evidence of an increased mVO2, suggestive of progressive mitochondrial or contractile inefficiency.
authors.affiliation: Endurance Research Group, School of Sport and Exercise Sciences, University of Kent, Kent, UK.
authors.forename: J G
authors.initials: JG
authors.lastname: Hopker
authors.affiliation: Endurance Research Group, School of Sport and Exercise Sciences, University of Kent, Kent, UK.
authors.forename: C
authors.initials: C
authors.lastname: O'Grady
authors.affiliation: Endurance Research Group, School of Sport and Exercise Sciences, University of Kent, Kent, UK.|CAPS UMR1093, INSERM, Univ. Bourgogne-Franche Comté, F-21000 Dijon, France.
authors.forename: B
authors.initials: B
authors.lastname: Pageaux
mesh_terms: D000293:Adolescent; D000328:Adult; D001642:Bicycling / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism; D010101:Oxygen Consumption; D052097:Quadriceps Muscle / Q000378:metabolism*; D019265:Spectroscopy, Near-Infrared; D055815:Young Adult
keywords: Cycling efficiency; endurance performance; lactate threshold; maximal oxygen uptake; muscle efficiency