title: Relationships between mechanical power, O(2) consumption, O(2) deficit and high-energy phosphates during calf exercise in humans.
abstract: Whole-body O(2) uptake ( VO(2)), O(2) deficit and the concentration of high-energy phosphates (determined by (31)P spectroscopy) in human calf muscle were measured during moderate aerobic square-wave exercise of increasing intensity in ten volunteers. Net VO(2) (above resting) increased linearly with mechanical power, yielding a delta efficiency of 13.1%. "Gross" O(2) deficit increased linearly with net VO(2). The fraction of phosphocreatine (PC) split at steady state increased linearly with the mechanical power and with the O(2) deficit. If the [PC] in resting muscle is known, the slope of the regression between PC split and O(2) deficit (in millimoles) yields the P/O(2) ratio. To calculate this, the O(2) deficit was corrected for the amount of O(2) derived from the body stores, as obtained from literature data. The value so obtained, for a resting [PC] of 30 mM was 5.9, consistent with canonical textbook values. Furthermore, the ratio of "true" O(2) deficit to steady-state VO(2) is a measure of the time constant of VO(2) kinetics at work onset at the muscle level: assuming a monoexponential time course without time delays it amounted to about 17 s, close to the value that can be expected in mammalian muscle at 37 degrees C.
authors.affiliation: Dipartimento di Scienze e Tecnologie Biomediche, Università degli Studi di Udine, P.le Kolbe 4, 33100, Udine, Italy. mfrancescato@mail.dstb.uniud.it
authors.forename: M P
authors.initials: MP
authors.lastname: Francescato
authors.forename: V
authors.initials: V
authors.lastname: Cettolo
authors.forename: P E
authors.initials: PE
authors.lastname: Di Prampero
mesh_terms: D000328:Adult; D004734:Energy Metabolism / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005260:Female; D006706:Homeostasis; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D007866:Leg; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008954:Models, Biological; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000378:metabolism / Q000502:physiology*; D010101:Oxygen Consumption / Q000502:physiology*; D010710:Phosphates / Q000378:metabolism*; D010725:Phosphocreatine / Q000378:metabolism; D011659:Pulmonary Gas Exchange
chemical_list: D010710:Phosphates; D010725:Phosphocreatine