title: Oxygen uptake, cardiac output and muscle deoxygenation at the onset of moderate and supramaximal exercise in humans.
abstract: VO₂, Q and muscular deoxyhaemoglobin (HHb) kinetics were determined in 14 healthy male subjects at the onset of constant-load cycling exercise performed at 80% of the ventilatory threshold (80%(VT)) and at 120% of VO₂max (120%(Wmax)). An innovative approach was applied to calculate the time constant (τ₂) of the primary phase of VO₂ and Q kinetics at 120%(Wmax). Data were linearly interpolated after a semilogarithmic transformation of the difference between required/steady state and measured values. Furthermore, VO₂, Q and HHb data were fitted with traditional exponential models. τ₂ of VO₂ kinetics was longer (62.5 ± 20.9 s) at 120%(Wmax) than at 80%(VT) (27.8 ± 10.4 s). The τ₂ of Q kinetics was unaffected by exercise intensity and, at 120% of VO₂max, it was significantly faster (τ₂ = 35.7 ± 28.4 s) than that of VO₂ response. The time delay of HHb kinetics was shorter (4.3 ± 1.7 s) at 120%(Wmax) than at 80%(VT) (8.5 ± 2.6 s) suggesting a larger mismatch between O₂ uptake and delivery at 120%(Wmax). These results suggest that VO₂ at the onset of exercise is not regulated/limited by muscle's O₂ utilisation and that a slower adaptation of capillary perfusion may cause the deceleration of VO₂ kinetics observed during supramaximal exercise.
authors.affiliation: Department of Neurological, Neuropsychological, Morphological and Motor Sciences, School of Exercise and Sport Sciences, University of Verona, Via Felice Casorati, 43, 37131 Verona, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Adami
authors.forename: S
authors.initials: S
authors.lastname: Pogliaghi
authors.forename: G
authors.initials: G
authors.lastname: De Roia
authors.forename: C
authors.initials: C
authors.lastname: Capelli
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D000328:Adult; D002302:Cardiac Output / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000502:physiology; D010100:Oxygen / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology; D011659:Pulmonary Gas Exchange / Q000502:physiology; D055815:Young Adult
chemical_list: D006454:Hemoglobins; C100003:deoxyhemoglobin; D010100:Oxygen