title: Limitations to oxygen transport and utilization during sprint exercise in humans: evidence for a functional reserve in muscle O2 diffusing capacity.
abstract: To determine the contribution of convective and diffusive limitations to V̇(O2peak) during exercise in humans, oxygen transport and haemodynamics were measured in 11 men (22 ± 2 years) during incremental (IE) and 30 s all-out cycling sprints (Wingate test, WgT), in normoxia (Nx, P(IO2): 143 mmHg) and hypoxia (Hyp, P(IO2): 73 mmHg). Carboxyhaemoglobin (COHb) was increased to 6-7% before both WgTs to left-shift the oxyhaemoglobin dissociation curve. Leg V̇(O2) was measured by the Fick method and leg blood flow (BF) with thermodilution, and muscle O2 diffusing capacity (D(MO2)) was calculated. In the WgT mean power output, leg BF, leg O2 delivery and leg V̇(O2) were 7, 5, 28 and 23% lower in Hyp than Nx (P < 0.05); however, peak WgT D(MO2) was higher in Hyp (51.5 ± 9.7) than Nx (20.5 ± 3.0 ml min(-1) mmHg(-1), P < 0.05). Despite a similar P(aO2) (33.3 ± 2.4 and 34.1 ± 3.3 mmHg), mean capillary P(O2) (16.7 ± 1.2 and 17.1 ± 1.6 mmHg), and peak perfusion during IE and WgT in Hyp, D(MO2) and leg V̇(O2) were 12 and 14% higher, respectively, during WgT than IE in Hyp (both P < 0.05). D(MO2) was insensitive to COHb (COHb: 0.7 vs. 7%, in IE Hyp and WgT Hyp). At exhaustion, the Y equilibration index was well above 1.0 in both conditions, reflecting greater convective than diffusive limitation to the O2 transfer in both Nx and Hyp. In conclusion, muscle V̇(O2) during sprint exercise is not limited by O2 delivery, O2 offloading from haemoglobin or structure-dependent diffusion constraints in the skeletal muscle. These findings reveal a remarkable functional reserve in muscle O2 diffusing capacity.
authors.affiliation: Department of Physical Education, University of Las Palmas de Gran Canaria, Campus Universitario de Tafira s/n, Las Palmas de Gran Canaria, Canary Islands, 35017, Spain.|Research Institute of Biomedical and Health Sciences (IUIBS), University of Las Palmas de Gran Canaria, 35016 Las Palmas de Gran Canaria, Canary Islands, Spain.
authors.forename: José A L
authors.initials: JA
authors.lastname: Calbet
authors.affiliation: Department of Physical Education, University of Las Palmas de Gran Canaria, Campus Universitario de Tafira s/n, Las Palmas de Gran Canaria, Canary Islands, 35017, Spain.|Research Institute of Biomedical and Health Sciences (IUIBS), University of Las Palmas de Gran Canaria, 35016 Las Palmas de Gran Canaria, Canary Islands, Spain.
authors.forename: José
authors.initials: J
authors.lastname: Losa-Reyna
authors.affiliation: Department of Physical Education, University of Las Palmas de Gran Canaria, Campus Universitario de Tafira s/n, Las Palmas de Gran Canaria, Canary Islands, 35017, Spain.|Research Institute of Biomedical and Health Sciences (IUIBS), University of Las Palmas de Gran Canaria, 35016 Las Palmas de Gran Canaria, Canary Islands, Spain.
authors.forename: Rafael
authors.initials: R
authors.lastname: Torres-Peralta
authors.affiliation: Center for Integrative Human Physiology, Institute of Physiology, University of Zürich, Zürich, Switzerland.
authors.forename: Peter
authors.initials: P
authors.lastname: Rasmussen
authors.affiliation: Department of Physical Education, University of Las Palmas de Gran Canaria, Campus Universitario de Tafira s/n, Las Palmas de Gran Canaria, Canary Islands, 35017, Spain.|Research Institute of Biomedical and Health Sciences (IUIBS), University of Las Palmas de Gran Canaria, 35016 Las Palmas de Gran Canaria, Canary Islands, Spain.
authors.forename: Jesús Gustavo
authors.initials: JG
authors.lastname: Ponce-González
authors.affiliation: School of Kinesiology, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: A William
authors.initials: AW
authors.lastname: Sheel
authors.affiliation: Department of Physical Education, University of Las Palmas de Gran Canaria, Campus Universitario de Tafira s/n, Las Palmas de Gran Canaria, Canary Islands, 35017, Spain.
authors.forename: Jaime
authors.initials: J
authors.lastname: de la Calle-Herrero
authors.affiliation: Department of Physical Education, University of Las Palmas de Gran Canaria, Campus Universitario de Tafira s/n, Las Palmas de Gran Canaria, Canary Islands, 35017, Spain.|Research Institute of Biomedical and Health Sciences (IUIBS), University of Las Palmas de Gran Canaria, 35016 Las Palmas de Gran Canaria, Canary Islands, Spain.
authors.forename: Amelia
authors.initials: A
authors.lastname: Guadalupe-Grau
authors.affiliation: Department of Physical Education, University of Las Palmas de Gran Canaria, Campus Universitario de Tafira s/n, Las Palmas de Gran Canaria, Canary Islands, 35017, Spain.|Research Institute of Biomedical and Health Sciences (IUIBS), University of Las Palmas de Gran Canaria, 35016 Las Palmas de Gran Canaria, Canary Islands, Spain.
authors.forename: David
authors.initials: D
authors.lastname: Morales-Alamo
authors.affiliation: Department of Physical Education, University of Las Palmas de Gran Canaria, Campus Universitario de Tafira s/n, Las Palmas de Gran Canaria, Canary Islands, 35017, Spain.
authors.forename: Teresa
authors.initials: T
authors.lastname: Fuentes
authors.affiliation: Department of Physical Education, University of Las Palmas de Gran Canaria, Campus Universitario de Tafira s/n, Las Palmas de Gran Canaria, Canary Islands, 35017, Spain.
authors.forename: Lorena
authors.initials: L
authors.lastname: Rodríguez-García
authors.affiliation: Center for Integrative Human Physiology, Institute of Physiology, University of Zürich, Zürich, Switzerland.
authors.forename: Christoph
authors.initials: C
authors.lastname: Siebenmann
authors.affiliation: School of Kinesiology, University of British Columbia, Vancouver, British Columbia, Canada.|Åstrand Laboratory, Swedish School of Sport and Health Sciences, Stockholm, Sweden.
authors.forename: Robert
authors.initials: R
authors.lastname: Boushel
authors.affiliation: Center for Integrative Human Physiology, Institute of Physiology, University of Zürich, Zürich, Switzerland.
authors.forename: Carsten
authors.initials: C
authors.lastname: Lundby
mesh_terms: D000328:Adult; D002302:Cardiac Output; D015444:Exercise / Q000502:physiology*; D005221:Fatigue / Q000503:physiopathology; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology; D007866:Leg / Q000098:blood supply; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D010101:Oxygen Consumption / Q000502:physiology*; D012039:Regional Blood Flow; D055815:Young Adult