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Effects of aging, sex, and physical training on cardiovascular responses to exercise.
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1992
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The relative contributions of decreases in maximal heart rate, stroke volume, and oxygen extraction and of changes in body weight and composition to the age‑related decline in maximal oxygen uptake (VO₂max) are unclear and may be influenced by sex and level of physical activity. The study investigates how aging, sex, and physical activity affect VO₂max by examining VO₂, cardiac output, and heart rate during exercise in younger and older sedentary and trained men and women. Researchers measured VO₂, cardiac output, and heart rate during submaximal and maximal treadmill exercise and evaluated body weight and fat‑free mass in healthy younger and older sedentary and endurance‑trained men and women. Older adults show a 40–41 % lower VO₂max when sedentary and 25–32 % lower when trained, largely due to reduced stroke volume (≈50 % of the decline) and lower maximal heart rate and oxygen extraction, with training mitigating age effects and normalization to fat‑free mass reducing but not eliminating differences; sex differences in trained subjects are linked to body composition.
BACKGROUND The relative contributions of decreases in maximal heart rate, stroke volume, and oxygen extraction and of changes in body weight and composition to the age-related decline in maximal oxygen uptake (VO2max) are unclear and may be influenced by sex and level of physical activity. METHODS AND RESULTS To investigate mechanisms by which aging, sex, and physical activity influence VO2max, we quantified VO2, cardiac output, and heart rate during submaximal and maximal treadmill exercise and assessed weight and fat-free mass in healthy younger and older sedentary and endurance exercise-trained men and women. For results expressed in milliliters per kilogram per minute, a three-to-four-decade greater age was associated with a 40-41% lower VO2max in sedentary subjects and a 25-32% lower VO2max in trained individuals (p less than 0.001). A smaller stroke volume accounted for nearly 50% of these age-related differences, and the remainder was explained by a lower maximal heart rate and reduced oxygen extraction (all p less than 0.001). Age-related effects on maximal heart rate and oxygen extraction were attenuated in trained subjects (p less than 0.05). After normalization of VO2max and maximal cardiac output to fat-free mass, age- and training-related differences were reduced by 24-47% but remained significant (p less than 0.05). For trained but not sedentary subjects, maximal cardiac output and stroke volume normalized to fat-free mass were greater in men than in women (p less than 0.05). CONCLUSIONS A lower stroke volume, heart rate, and arteriovenous oxygen difference at maximal exercise all contribute to the age-related decline in VO2max. Effects of age and training on VO2max, maximal cardiac output, and stroke volume cannot be fully explained by differences in body composition. In sedentary subjects, however, the sex difference in maximal cardiac output and stroke volume can be accounted for by the greater percentage of body fat in women than in men.