Journal Article Reduction of V-O2 slow component by priming exercise: novel mechanistic insights from time-resolved near-infrared spectroscopy

Fukuoka, Yoshiyuki  ,  Poole, David C.  ,  Barstow, Thomas J.  ,  Kondo, Narihiko  ,  Nishiwaki, Masato  ,  Okushima, Dai  ,  Koga, Shunsaku

3 ( 6 )  , p.e12432 , 2015-06 , Wiley
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 (V˙O2) slow component (V˙O2SC) (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 (V˙O2) kinetics consequent to a substantial reduction in the (V˙O2SC)(0.27 ± 0.12 vs. 0.11 ± 0.09 L·min(-1), P < 0.05) with an unchanged primary (V˙O2) 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 (V˙O2SC) 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 (V˙O2SC) reduction. These results support a mechanistic link between priming exercise-induced increase in muscle [Hb] volume and the reduced (V˙O2SC) that serves to speed overall (V˙O2) kinetics. However, reduction in the heterogeneity of muscle deoxygenation kinetics does not appear to be an obligatory feature of the priming response.

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