Aging women show nonlinear declines in fitness, activity levels

Jul 23 2012

By MedWire Reporters

Physical activity levels and cardiorespiratory fitness in women do not decline in a linear manner with age, research shows.

After age 60 years, fitness levels in women declined rapidly, whereas physical activity levels were highest in 50-year-old women and plateaued at age 60, report investigators.

"The menopause transition seems to be a critical period to initialize and promote physical activity, especially for sedentary women, because the accelerated decline in both activity and fitness starts around this time," say Xuemei Sui (University of South Carolina, Columbia, USA) and colleagues.

In a sample of 1467 women participating in the Aerobics Center Longitudinal Study, the researchers assessed the aging trajectory of self-reported physical activity, objectively measured cardiorespiratory fitness, and body mass index (BMI).

Approximately half of the women reported meeting the recommended levels of physical activity, defined as 500 or more metabolic equivalent (MET)-minutes per week. The median length of follow up was 6.6 years.

Overall, the associations between age and physical activity, fitness, and BMI differed.

There was a positive curvilinear association between BMI and age, whereas physical activity levels and cardiorespiratory fitness increased with age but declined at age 50 and 45 years, respectively. Regarding fitness, the decline was steep after age 45 years and further accelerated after age 60 years.

These findings showing a decline around the time of perimenopause identifies a "critical time window" for the promotion of physical activity in women, write Sui and colleagues in the British Journal of Sports Medicine.

For BMI, the increase slowed after 60 years of age. The researchers also examined the change in BMI with baseline activity and fitness levels; women who did not meet the physical activity recommendations at baseline had a higher BMI throughout adulthood compared with those who were active.

Similarly, women who were fit at baseline had a lower BMI throughout adulthood compared with their unfit counterparts.

The group points out that it might seem counterintuitive that activity levels increase for women in their 30s, 40s, and 50s, but BMI also increases during this period. They note that other than energy expenditure, there are many factors regulate bodyweight, among them estrogen, energy intake, and loss of muscle mass.

Although the aging-related decline in cardiorespiratory fitness cannot be avoided, regular physical activity remains its primary determinant, write Sui et al.

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