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The influence of exercise intensity on pulmonary oxygen uptake kinetics in young and late middle-aged adults
AJP: Regulatory, Integrative and Comparative Physiology
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It is unclear whether pulmonary oxygen uptake (VO2) kinetics demonstrate linear, first order behaviour during supra gas exchange threshold exercise. Resolution of this issue is pertinent to the elucidation of the factors regulating VO2 kinetics, with oxygen availability and utilisation proposed as p...
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It is unclear whether pulmonary oxygen uptake (VO2) kinetics demonstrate linear, first order behaviour during supra gas exchange threshold exercise. Resolution of this issue is pertinent to the elucidation of the factors regulating VO2 kinetics, with oxygen availability and utilisation proposed as putative mediators. To re-examine this issue with the advantage of a relatively large sample size, fifty young (24±4 yrs) and fifteen late middle-aged (54±3 yrs) participants completed repeated bouts of moderate and heavy exercise. Pulmonary gas exchange, heart rate (HR) and cardiac output ("Q") variables were measured throughout. The phase II τ was slower during heavy exercise in both young (Mod: 22±9; Hvy: 29±9s; P≤0.001) and middle-aged (Mod: 22±9; Hvy: 30±8s; P≤0.001) individuals. The HR τ was slower during heavy exercise in young (Mod: 33±10; Hvy: 44±15s; P≤0.05) and middle-aged (Mod: 30±12; Hvy: 50±20s; P≤0.05) participants, and the "Q" τ showed a similar trend (Young - Mod: 21±13; Hvy: 28±16 s; Middle-aged - Mod: 32±13; Hvy: 40±15s; P≥0.05). There were no differences in primary component VO2 kinetics between age groups but the middle-aged group had a significantly reduced VO2 slow component amplitude in both absolute (Young: 0.25±0.09; Middle-aged: 0.11±0.06 l∙min-1; P≤0.05) and relative terms (Young: 15±10; Middle-aged: 9±4%; P≤0.05). Thus, VO2 kinetics do not demonstrate dynamic linearity during heavy intensity exercise. Speculatively, the slower phase II τ during heavy exercise might be attributable to reduced oxygen availability. Finally, the primary and slow components of VO2 kinetics appear to be differentially influenced by middle-age.
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