title: Reduction of V̇O2 slow component by priming exercise: novel mechanistic insights from time-resolved near-infrared spectroscopy.
abstract: Novel time-resolved near-infrared spectroscopy (TR-NIRS), with adipose tissue thickness correction, was used to test the hypotheses that heavy priming exercise reduces the V̇O2 slow component (V̇O2SC) (1) by elevating microvascular [Hb] volume at multiple sites within the quadriceps femoris (2) rather than reducing the heterogeneity of muscle deoxygenation kinetics. Twelve subjects completed two 6-min bouts of heavy work rate exercise, separated by 6 min of unloaded cycling. Priming exercise induced faster overall V̇O2 kinetics consequent to a substantial reduction in the V̇O2SC (0.27 ± 0.12 vs. 0.11 ± 0.09 L·min(-1), P < 0.05) with an unchanged primary V̇O2 time constant. An increased baseline for the primed bout [total (Hb + Mb)] (197.5 ± 21.6 vs. 210.7 ± 22.5 μmol L(-1), P < 0.01), reflecting increased microvascular [Hb] volume, correlated significantly with the V̇O2SC reduction. At multiple sites within the quadriceps femoris, priming exercise reduced the baseline and slowed the increase in [deoxy (Hb + Mb)]. Changes in the intersite coefficient of variation in the time delay and time constant of [deoxy (Hb + Mb)] during the second bout were not correlated with the V̇O2SC reduction. These results support a mechanistic link between priming exercise-induced increase in muscle [Hb] volume and the reduced V̇O2SC that serves to speed overall V̇O2 kinetics. However, reduction in the heterogeneity of muscle deoxygenation kinetics does not appear to be an obligatory feature of the priming response.
authors.affiliation: Environmental Physiology Laboratory, Prefectural University of Kumamoto, Kumamoto, Japan Graduate School of Health and Sports Science, Doshisha University, Kyoto, Japan yfukuoka@mail.doshisha.ac.jp.
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Fukuoka
authors.affiliation: Departments of Anatomy and Physiology and Kinesiology, Kansas State University, Manhattan, Kansas.
authors.forename: David C
authors.initials: DC
authors.lastname: Poole
authors.affiliation: Departments of Anatomy and Physiology and Kinesiology, Kansas State University, Manhattan, Kansas.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Barstow
authors.affiliation: Graduate School of Cultural Studies and Human Science, Kobe University, Kobe, Japan.
authors.forename: Narihiko
authors.initials: N
authors.lastname: Kondo
authors.affiliation: Faculty of Engineering, Osaka Institute of Technology, Osaka, Japan.
authors.forename: Masato
authors.initials: M
authors.lastname: Nishiwaki
authors.affiliation: Applied Physiology Laboratory, Kobe Design University, Kobe, Japan.
authors.forename: Dai
authors.initials: D
authors.lastname: Okushima
authors.affiliation: Applied Physiology Laboratory, Kobe Design University, Kobe, Japan.
authors.forename: Shunsaku
authors.initials: S
authors.lastname: Koga
keywords: Heavy exercise; hemoglobin concentration; muscle O2 diffusing capacity; muscle microcirculation