Oxygen Uptake Kinetics of Older Humans are Slowed with Age but are Unaffected by Hyperoxia

<jats:title>SUMMARY</jats:title><jats:p>Cross‐sectional studies have compared the oxygen uptake (V<jats:sub>O2</jats:sub>) kinetics during the on‐transient of moderate intensity exercise in older and younger adults. The slower values in the older adults may have been due to an age‐related reduction in the capacity for O<jats:sub>2</jats:sub> transport or alternatively a reduced intramuscular oxidative capacity. We studied: (1) the effects of ageing on V<jats:sub>O2</jats:sub> kinetics in older adults on two occasions 9 years apart, and (2) the effect of hyperoxia on V<jats:sub>O2</jats:sub> kinetics at the second test time. After a 9 year period, follow‐up testing was undertaken on seven older adults (78 ± 5 years, mean ±<jats:sc>s.d.</jats:sc>). They each performed six repeats of 6 min bouts of constant‐load cycle exercise from loadless cycling to 80 % of their ventilatory threshold. They breathed one of two gas mixtures (euoxia: inspired O<jats:sub>2</jats:sub> fraction, <jats:italic>F</jats:italic><jats:sub>I,O2</jats:sub>, 0·21; hyperoxia: <jats:italic>F</jats:italic><jats:sub>I,O2</jats:sub>, 0·70) on different trials determined on a random basis. Breath‐by‐breath V<jats:sub>O2</jats:sub> data were time aligned and ensemble averaged. V<jats:sub>O2</jats:sub> kinetics, modelled with a single exponential from phase 2 onset (+20 s) to steady state and described by the exponential time constant ([tau]) were compared with data collected from the same adults 9 years earlier. One‐way repeated measures analysis of variance revealed that [tau] was slowed significantly with age (from 30 ± 8 to 46 ± 10 s), but was unaffected by hyperoxia (43 ± 15 s). We concluded that: (1) in older adults studied longitudinally over a 9 year period, the on‐transient V<jats:sub>O2</jats:sub> kinetics are slowed, in agreement with, but to a greater extent, than from cross‐sectional data; and (2) the phase 2 time constant ([tau]) for these older adults was not accelerated by hyperoxic breathing. Thus the expected hyperoxia‐induced increase in the capacity for O<jats:sub>2</jats:sub> transport was not associated with faster on‐transient V<jats:sub>O2</jats:sub> kinetics suggesting either that O<jats:sub>2</jats:sub> transport may not limit V<jats:sub>O2</jats:sub> kinetics during the 8th decade, or that O<jats:sub>2</jats:sub> transport was not improved with hyperoxia.</jats:p>