title: Kinetics of pulmonary VO2 and femoral artery blood flow and their relationship during repeated bouts of heavy exercise.
abstract: The mechanism that alters the pulmonary VO2 response to heavy-intensity exercise following prior heavy exercise has been frequently ascribed to an improvement in pre-exercise blood flow (BF) or O(2) delivery. Interventions to improve O(2) delivery have rarely resulted in a similar enhancement of VO2. However, the actual limb blood flow and VO2 dynamics in the second bout of repeated exercise remain equivocal. Seven healthy female subjects (21-32 years) performed consecutive 6-min (separated by 6 min of 10 W exercise) bilateral knee extension (KE) exercise in a semisupine position at a work rate halfway between the lactate threshold (LT) and VO2peak. Femoral artery blood flow (FBF) was measured by Doppler ultrasound simultaneously with breath-by-breath VO2 each protocol being repeated at least four times for precise kinetic characterization. The effective time-constant (tau') of the VO2 response was reduced following prior exercise (bout 1: 61.0 +/-10.5 vs. bout 2: 51.6+/-9.0 s; mean +/- SD; P<0.05), which was a result of a reduced slow component (bout 1: 16.0+/-8.0 vs. bout 2: 12.5+/-6.7 %; P<0.05) and an unchanged 'primary' tau. FBF was consistently faster than VO2. However, there was no bout-effect on tau' FBF (bout 1: 28.2+/-12.0 vs. bout 2: 34.2+/-8.5 s). The relationship between the exercise-associated VO2 (i.e., deltaVO2) and Delta FBF was similar between bouts, with a tendency (N.S: P>0.05) for deltaVO2/deltaFBF to be increased during the transition to bout 2 rather than decreased, as hypothesized. The return of VO2 kinetics toward first order, therefore, was associated with an 'appropriate', not enhanced, BF to the working muscles. Whether a relative prior-hyperemia in bout 2 enables a more homogeneous intramuscular distribution of BF and/or metabolic response is unclear, however, these data are consistent with events more proximal to the exercise muscle in mediating the VO2 response during repeated heavy-intensity KE exercise.
authors.affiliation: Department of Exercise Science and Physiology, School of Health Sciences, Prefectural University of Hiroshima, 1-1-71, Ujina-higashi, Minami-ku, Hiroshima, 734-8558, Japan.
authors.forename: Masako
authors.initials: M
authors.lastname: Endo
authors.forename: Yoko
authors.initials: Y
authors.lastname: Okada
authors.forename: Harry B
authors.initials: HB
authors.lastname: Rossiter
authors.forename: Anna
authors.initials: A
authors.lastname: Ooue
authors.forename: Akira
authors.initials: A
authors.lastname: Miura
authors.forename: Shunsaku
authors.initials: S
authors.lastname: Koga
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Fukuba
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005260:Female; D005263:Femoral Artery / Q000502:physiology*; D006339:Heart Rate; D006801:Humans; D007700:Kinetics; D010100:Oxygen / Q000502:physiology; D010101:Oxygen Consumption; D012123:Pulmonary Ventilation / Q000502:physiology*; D013997:Time Factors
chemical_list: D010100:Oxygen