title: Maintained peak leg and pulmonary VO2 despite substantial reduction in muscle mitochondrial capacity.
abstract: We recently reported the circulatory and muscle oxidative capacities of the arm after prolonged low-intensity skiing in the arctic (Boushel et al., 2014). In the present study, leg VO2 was measured by the Fick method during leg cycling while muscle mitochondrial capacity was examined on a biopsy of the vastus lateralis in healthy volunteers (7 male, 2 female) before and after 42 days of skiing at 60% HR max. Peak pulmonary VO2 (3.52 ± 0.18 L.min(-1) pre vs 3.52 ± 0.19 post) and VO2 across the leg (2.8 ± 0.4L.min(-1) pre vs 3.0 ± 0.2 post) were unchanged after the ski journey. Peak leg O2 delivery (3.6 ± 0.2 L.min(-1) pre vs 3.8 ± 0.4 post), O2 extraction (82 ± 1% pre vs 83 ± 1 post), and muscle capillaries per mm(2) (576 ± 17 pre vs 612 ± 28 post) were also unchanged; however, leg muscle mitochondrial OXPHOS capacity was reduced (90 ± 3 pmol.sec(-1) .mg(-1) pre vs 70 ± 2 post, P < 0.05) as was citrate synthase activity (40 ± 3 μmol.min(-1) .g(-1) pre vs 34 ± 3 vs P < 0.05). These findings indicate that peak muscle VO2 can be sustained with a substantial reduction in mitochondrial OXPHOS capacity. This is achieved at a similar O2 delivery and a higher relative ADP-stimulated mitochondrial respiration at a higher mitochondrial p50. These findings support the concept that muscle mitochondrial respiration is submaximal at VO2max , and that mitochondrial volume can be downregulated by chronic energy demand.
authors.affiliation: The Copenhagen Muscle Research Centre, Copenhagen, Denmark.|School of Kinesiology, University of British Columbia, Vancouver, BC, Canada.
authors.forename: R
authors.initials: R
authors.lastname: Boushel
authors.affiliation: Department of Visceral, Transplant and Thoracic Surgery, D. Swarovski Research Laboratory, Medical University of Innsbruck, Innsbruck, Austria.
authors.forename: E
authors.initials: E
authors.lastname: Gnaiger
authors.affiliation: Åstrand Laboratory, The Swedish School of Sport and Health Sciences, Stockholm, Sweden.
authors.forename: F J
authors.initials: FJ
authors.lastname: Larsen
authors.affiliation: The Copenhagen Muscle Research Centre, Copenhagen, Denmark.|X-Lab, Department of Biomedical Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: J W
authors.initials: JW
authors.lastname: Helge
authors.affiliation: The Copenhagen Muscle Research Centre, Copenhagen, Denmark.|Centre for Sports Medicine and Human Performance, Brunel University, London, Uxbridge, UK.
authors.forename: J
authors.initials: J
authors.lastname: González-Alonso
authors.affiliation: The Copenhagen Muscle Research Centre, Copenhagen, Denmark.|GENUD Toledo Research Group, Universidad de Castilla-La Mancha (UCLM), Spain.
authors.forename: I
authors.initials: I
authors.lastname: Ara
authors.affiliation: The Copenhagen Muscle Research Centre, Copenhagen, Denmark.
authors.forename: T
authors.initials: T
authors.lastname: Munch-Andersen
authors.affiliation: The Copenhagen Muscle Research Centre, Copenhagen, Denmark.|Biomedical Sciences, Health & Medical Sciences, University of Copenhagen & Clinical Biochemistry, Rigshospitalet, Copenhagen, Denmark.
authors.forename: G
authors.initials: G
authors.lastname: van Hall
authors.affiliation: The Copenhagen Muscle Research Centre, Copenhagen, Denmark.
authors.forename: H
authors.initials: H
authors.lastname: Søndergaard
authors.affiliation: The Copenhagen Muscle Research Centre, Copenhagen, Denmark.
authors.forename: B
authors.initials: B
authors.lastname: Saltin
authors.affiliation: The Copenhagen Muscle Research Centre, Copenhagen, Denmark.|Department of Physical Education, and Research Institute of Biomedical and Health Sciences (IUIBS), University of Las Palmas de Gran Canaria, Las Palmas, Spain.
authors.forename: J A L
authors.initials: JA
authors.lastname: Calbet
mesh_terms: D000328:Adult; D002196:Capillaries / Q000033:anatomy & histology; D019069:Cell Respiration; D002950:Citrate (si)-Synthase / Q000378:metabolism; D005080:Exercise Test; D005260:Female; D006801:Humans; D008168:Lung / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D008931:Mitochondria, Muscle / Q000502:physiology*; D053142:Mitochondrial Size; D010085:Oxidative Phosphorylation; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption; D052097:Quadriceps Muscle / Q000098:blood supply* / Q000166:cytology / Q000502:physiology*; D012039:Regional Blood Flow; D012865:Skiing / Q000502:physiology*
chemical_list: D002950:Citrate (si)-Synthase; D010100:Oxygen
keywords: VO
  2; blood flow; capillaries; fiber type; mitochondria; training