Reduced physical activity during the day is widely seen as a harbinger of mortality in older people.
In a new study, researchers found fragmentation of physical activity—spreading daily activity across more episodes of brief activity—may be an earlier indicator of death risk.
The research was conducted by scientists at the Johns Hopkins Bloomberg School of Public Health.
Adults age 65 and older are one of the fastest-growing segments of the U.S. population.
They are also increasingly sedentary, and prior studies have shown that less physical activity among older adults is a predictor of more illness and premature death.
But in recent years, scientists have begun to explore activity fragmentation as a complementary and potentially more sensitive marker of overall health and functioning among older adults.
The current study used physical activity data collected using wearable monitors in 548 well-functioning older adults.
Of the 548 participants studied, 487 were alive at the end of 2017, and 61 were deceased.
The living participants engaged in an average of 5.7 hours of activity per day, compared to 4.7 hours for those who later died.
The team found that for this group of people there was no link between overall daily activity levels and greater mortality risk.
However, there was an association between mortality risk and more fragmented physical activity.
The researchers found that for each 10% higher activity fragmentation there was a 49% increase in the risk of mortality.
They defined activity fragmentation as the probability of transitioning from an active state to a sedentary state for each participant, so shorter average activity periods meant higher fragmentation.
They also found the percent of activity spent in bouts of less than five minutes appeared to be another good marker of mortality risk.
Each additional 10% of active time spent in such short bouts was linked to a 28% increase in the chance of mortality.
The findings show fragmentation of physical activity may be an early indicator of increased mortality risk.
The team notes too that although time spent exercising, such as brisk walking, is often examined as a marker for mortality risk, most physical activity for older adults comes from the ordinary, lighter-intensity activity routinely performed throughout the day, such as doing laundry, preparing meals, gardening, and even getting the mail.
The researchers are continuing to study activity fragmentation as a potential indicator of health decline, including cognitive decline and dementia.
The lead author of the study is Amal Wanigatunga, Ph.D., assistant scientist in the Bloomberg School’s Department of Epidemiology.
The study is published in JAMA Network Open.
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