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Oxygen-Uptake (VO₂) Kinetics and Functional Mobility Performance in Impaired Older Adults

¹ The Geriatric Research, Education and Clinical Center, Veterans Affairs Ann Arbor Health Care System, Michigan.
² Division of Geriatric Medicine, Department of Internal Medicine, The University of Michigan, Ann Arbor.
³ School of Kinesiology, University of Minnesota, Minneapolis.
⁴ Minneapolis Veterans Affairs Medical Center, Minnesota.

Background. Measures of maximal oxygen uptake (VO_2max) are limited in disabled older adults, and measures of submaximal oxygen uptake (VO₂) may better predict functional mobility limitations. These measures may include oxygen-uptake kinetics at the onset of submaximal exercise or during recovery. We sought to determine whether the lag in oxygen uptake at the beginning of exercise (oxygen deficit) and excess oxygen uptake above rest following exercise (excess postexercise oxygen consumption) (a) predict physical performance in impaired older adults with decreased aerobic function, and (b) predict physical performance better than peak VO₂.

Methods. Two groups of community-dwelling volunteers aged 65 or older were recruited according to their performance on a maximal graded exercise test. Using the Social Security Administration criterion of disability of a peak VO₂ 18 ml/kg/min, we compared the performance of an impaired aerobic capacity group at a peak VO₂ < 18 ml/kg/min (Impaired, n = 20, mean ± SEM age 82 ± 1 years) with an unimpaired group at Peak VO₂ > 18 (Unimpaired, n = 21, mean ± SEM age 76 ± 1 years).

Results. The mean ± SEM peak VO₂ was 58% lower in the Impaired (14 ± 1 ml/kg/min) than the Unimpaired (24 ± 1 ml/kg/min) adults. The time constant for oxygen deficit, tc_deficit, was more than twice as high in the Impaired than the Unimpaired (p <.05), and the time constant for excess postexercise oxygen consumption, tc_EPOC, tended to be higher in the Impaired than the Unimpaired (by 43%, p =.09). Measures of submaximal oxygen-uptake kinetics were as strong or more strongly predictive of functional mobility performance than peak VO₂ in both Unimpaired and Impaired older adults. The major predictor of functional performance for the Unimpaired was a measure of oxygen deficit accruing during exercise (tc_deficit), and for the Impaired, it was a measure of oxygen debt during recovery, tc_EPOC.

Conclusions. Measurement of submaximal oxygen-uptake kinetics may provide a more practical and relevant assessment of deconditioning in frail older adults, and may eventually supplant maximal (peak) oxygen uptake as a predictor of functional disability in older adults.