AUTHOR=George Mitchell A. , McLay Kaitlin M. , Doyle-Baker Patricia K. , Reimer Raylene A. , Murias Juan M. 

TITLE=Fitness Level and Not Aging per se, Determines the Oxygen Uptake Kinetics Response

JOURNAL=Frontiers in Physiology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2018.00277

DOI=10.3389/fphys.2018.00277

ISSN=1664-042X

ABSTRACT=<p>Although aging has been associated to slower <inline-formula><mml:math id="M1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover accent="true"><mml:mtext>V</mml:mtext><mml:mo>˙</mml:mo></mml:mover></mml:math></inline-formula>O<sub>2</sub> kinetics, some evidence indicates that fitness status and not aging <italic>per se</italic> might modulate this response. The main goal of this study was to examine the <inline-formula><mml:math id="M2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover accent="true"><mml:mtext>V</mml:mtext><mml:mo>˙</mml:mo></mml:mover></mml:math></inline-formula>O<sub>2</sub>, deoxygenated hemoglobin+myoglobin (deoxy-[Hb+Mb]) kinetics, and the NIRS-derived vascular reperfusion responses in older compared to young men of different training levels (i.e., inactive, recreationally active, and endurance trained). Ten young inactive [YI; 26 ± 5 yrs.; peak <inline-formula><mml:math id="M3" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover accent="true"><mml:mtext>V</mml:mtext><mml:mo>˙</mml:mo></mml:mover></mml:math></inline-formula>O<sub>2</sub> (<inline-formula><mml:math id="M4" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover accent="true"><mml:mtext>V</mml:mtext><mml:mo>˙</mml:mo></mml:mover></mml:math></inline-formula>O<sub>2peak</sub>), 2.96 ± 0.55 L·min<sup>−1</sup>], 10 young recreationally active (YR; 26 ± 6 yrs.; 3.92 ± 0.33 L·min<sup>−1</sup>), 10 young endurance trained (YT; 30 ± 4 yrs.; 4.42 ± 0.32 L·min<sup>−1</sup>), 7 older inactive (OI; 69 ± 4 yrs.; 2.50 ± 0.31 L·min<sup>−1</sup>), 10 older recreationally active (OR; 69 ± 5 yrs.; 2.71 ± 0.42 L·min<sup>−1</sup>), and 10 older endurance trained (OT; 66 ± 3 yrs.; 3.20 ± 0.35 L·min<sup>−1</sup>) men completed transitions of moderate intensity cycling exercise (MODS) to determine <inline-formula><mml:math id="M5" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover accent="true"><mml:mtext>V</mml:mtext><mml:mo>˙</mml:mo></mml:mover></mml:math></inline-formula>O<sub>2</sub> and deoxy-[Hb+Mb] kinetics, and the deoxy-[Hb+Mb]/<inline-formula><mml:math id="M6" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover accent="true"><mml:mtext>V</mml:mtext><mml:mo>˙</mml:mo></mml:mover></mml:math></inline-formula>O<sub>2</sub> ratio. The time constant of <inline-formula><mml:math id="M7" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover accent="true"><mml:mtext>V</mml:mtext><mml:mo>˙</mml:mo></mml:mover></mml:math></inline-formula>O<sub>2</sub> (τ<inline-formula><mml:math id="M8" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover accent="true"><mml:mtext>V</mml:mtext><mml:mo>˙</mml:mo></mml:mover></mml:math></inline-formula>O<sub>2</sub>) was greater in YI (38.8 ± 10.4 s) and OI (44.1 ± 10.8 s) compared with YR (26.8 ± 7.5 s) and OR (26.6 ± 6.5 s), as well as compared to YT (14.8 ± 3.4 s), and OT (17.7 ± 2.7 s) (<italic>p</italic> &lt; 0.05). τ<inline-formula><mml:math id="M9" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover accent="true"><mml:mtext>V</mml:mtext><mml:mo>˙</mml:mo></mml:mover></mml:math></inline-formula>O<sub>2</sub> was greater in YR and OR compared with YT and OT (<italic>p</italic> &lt; 0.05). The deoxy-[Hb+Mb]/<inline-formula><mml:math id="M10" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover accent="true"><mml:mtext>V</mml:mtext><mml:mo>˙</mml:mo></mml:mover></mml:math></inline-formula>O<sub>2</sub> ratio was greater in YI (1.23 ± 0.05) and OI (1.29 ± 0.08) compared with YR (1.11 ± 0.03) and OR (1.13 ± 0.06), as well as compared to YT (1.01 ± 0.03), and OT (1.06 ± 0.03) (<italic>p</italic> &lt; 0.05). Similarly, the deoxy-[Hb+Mb]/ <inline-formula><mml:math id="M11" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover accent="true"><mml:mtext>V</mml:mtext><mml:mo>˙</mml:mo></mml:mover></mml:math></inline-formula>O<sub>2</sub> ratio was greater in YR and OR compared with YT and OT (<italic>p</italic> &lt; 0.05). There was a main effect of training (<italic>p</italic> = 0.033), whereby inactive (<italic>p</italic> = 0.018) and recreationally active men (<italic>p</italic> = 0.031) had significantly poorer vascular reperfusion than endurance trained men regardless of age. This study demonstrated not only that age-related slowing of <inline-formula><mml:math id="M12" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover accent="true"><mml:mtext>V</mml:mtext><mml:mo>˙</mml:mo></mml:mover></mml:math></inline-formula>O<sub>2</sub> kinetics can be eliminated in endurance trained individuals, but also that inactive lifestyle negatively impacts the <inline-formula><mml:math id="M13" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover accent="true"><mml:mtext>V</mml:mtext><mml:mo>˙</mml:mo></mml:mover></mml:math></inline-formula>O<sub>2</sub> kinetics response of young healthy individuals.</p>