AGE‐RELATED DECLINE IN MAXIMAL OXYGEN CAPACITY: CONSEQUENCES FOR PERFORMANCE OF EVERYDAY ACTIVITIES

Abstract

To the Editor: Routine activities of daily living in young and adult individuals only induce a minimal challenge on maximal capacity, but with increasing age, less physically demanding tasks require increasingly more of the maximal physical capacity. The latter may make it almost impossible for a significant proportion of old subjects to perform even light activities of daily living (ADLs). A minimum aerobic threshold for independent living appears to fluctuate between 13 and 15 mL oxygen/min per kg, which has been suggested as a minimum requirement for successfully coping with everyday tasks.1,2 Interestingly, men have higher muscle mass and aerobic capacity than women, which may explain why men perform better in ADLs than women and why women in general are functionally dependent for about 4 years longer than men.3 This difference between the sexes may render old women more vulnerable because their maximal functional capacity may fall below the threshold of successful independent living. This study determined maximal oxygen uptake and the relative effort assessed as oxygen consumption necessary to perform selected everyday activities such as stair climbing, dressing, walking, and vacuuming in different age cohorts of women. Nine young (aged 32.2±1.7), eight middle-aged (54.1±1.3), and eight old (77.4±1.8) Danish women participated in the study. They all reported normal level of physical activity for Danish women such as daily walking, bicycling, or gardening. Maximal aerobic capacity was measured as maximal oxygen uptake (VO2max) using a progressive, maximal test on a Cybex cycle ergometer. Oxygen, carbon dioxide, ventilation, and respiratory exchange ratio were continuously analyzed using an on-line system (Innovision AMIS 2001, INNOVISION, Odense, Denmark).4 Oxygen consumption during everyday activities was performed during walking at a self-selected speed, dressing, stair climbing, and vacuuming (Figure 1). After 6 minutes of repetitive movements, expired air was collected in Douglas bags and analyzed for oxygen and carbon dioxide on a Beckmann analyzer. Maximal oxygen uptake and oxygen consumption during stair climbing, walking, dressing, and vacuuming in the three age groups of healthy community-dwelling women. Significant differences were observed between all three groups in VO2max and VO2max relative to body weight. Relative effort expressed as the percentage of oxygen consumption (l/min) during an everyday activity in relation to VO2max (l/min) increased with age in all everyday activities. Significant differences were observed between all groups. Absolute values of oxygen (l/min) used in the different everyday activities revealed no significant differences between the groups. Elderly women experience oxygen consumption during everyday activities near their VO2max, whereas middle-aged and young subjects possess a more significant margin between these two parameters. VO2max is reported to decrease 5% to 15% after age 25.5 The present study revealed an even more significant decrease of 29% between the young and the middle-aged groups (∼14.5%/decade) and 27% between the middle-aged and the old groups (∼10.8%/decade) in this parameter. Furthermore, the old women in this study were active and lived independently, in spite of this, the VO2max per kg of body weight was perilously close to the critical threshold claimed to be between 13 and 15 mL or O2/min per kg.1,2 It is important to notice that these data are cross-sectional and may not only reflect a biological change in VO2max, but also cultural and lifestyle differences. In the present study, all women were able to perform the four different everyday activities, but the elderly women had to make significantly higher efforts. During performance of the different everyday activities, no significant changes were observed in oxygen uptake between any of the groups, indicating that the same amount of oxygen is demanded for the same everyday activity independent of age, and significant changes were found in all activities between all groups in the relative effort of performance, demonstrating that older women perform these four everyday activities closer to their maximal capacity than younger subjects. Even very old subjects are able to increase their VO2max through regular training, which will optimize physical function and independence.4,6,7 Furthermore, a high VO2max demonstrates decrease in the risk of developing lifestyle diseases such as diabetes mellitus, osteoporosis, hypertension, cardiovascular diseases, and depression and even increase psychological well-being.8 In conclusion, oxygen consumption during performance of everyday activities was similar in the different age groups of women. In contrast, a significant age-related decline in VO2max was noticed. This narrows the window during aging between demand and capacity of oxygen consumption that makes everyday tasks such as stair climbing, walking, dressing, and vacuuming difficult—and finally impossible—to perform.