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GAINESVILLE, Fla. � Some people spring into action at dawn, while others prefer a slower start to their day. Whether you rise with a grin or a groan, scientists say your internal clock � known as the circadian rhythm � might influence that behavior and much more.

These biological clocks regulate not only sleep-wake cycles but also a wide range of daily physiological and metabolic functions. A growing body of research suggests that circadian rhythms are fundamental contributors to health and resilience.

Now, a new University of Florida Health study, funded by the National Institute on Aging, or NIA, shows that the timing and consistency of your daily activity might be associated with improved cardiorespiratory fitness and walking efficiency � two key indicators of healthy aging.

The NIA is a part of the National Institutes of Health.

The study found that older adults with earlier and more consistent daily activity patterns had better heart and lung fitness compared with those with later or more irregular schedules.

“While we’ve long known that being active supports healthy aging, this study reveals that when you’re active may also matter,� said , senior author and professor and chair of the ’s . “The circadian mechanisms that generate daily rhythms in our system are important for our well-being.�

Published in April in Medicine & Science in Sports and Exercise, the does not prove causation, Esser emphasized. While the results are promising, more research is needed to determine whether adjusting activity timing can lead to health improvements and whether these findings extend to younger populations, she said.

Researchers enrolled about 800 independent older adults in the study with an average age of 76. Participants wore wrist devices that continuously monitored activity for seven days. They then underwent cardiopulmonary exercise testing to obtain a comprehensive assessment of their heart and lung health.

Key findings include:

• Higher-amplitude activity and rest cycles â€� this reflects greater activity during the active part of the day relative to the rest period â€� were associated with better cardiorespiratory fitness and walking efficiency.
• Earlier daily peak activity â€� defined as the time of day when individuals were most active â€� was linked to improved cardiorespiratory fitness and walking efficiency.
• Greater consistency in daily activity patterns, such as having the peak activity occur at the same time each day, was also associated with better outcomes.

Activity includes all daily movement � walking, gardening, cleaning or shopping � not just formal exercise.

The body’s internal clock helps align physiological functions, such as hormone release, blood pressure and core temperature, to the natural cycle of day and night. Disruptions to this rhythm, such as those experienced during jet lag or shift work, can have negative consequences for sleep, mood and physical functioning.

Esser emphasized that although her study suggests a link between earlier, consistent activity and better health, it doesn’t prove that following such a schedule will improve health and fitness.

Still, the findings open intriguing possibilities for personalized medicine, she said. Because circadian rhythms vary from person to person, future health strategies could include tailoring activity and treatment schedules to an individual’s internal clock.

“Each of us has a chronotype � a biological tendency to be more alert in the morning or evening � and that variation may play a significant role in our health,� Esser said. “We’re moving toward a future where understanding and respecting our individual rhythms can help guide medical care and daily living.�

Scientists use an easy shorthand to describe whether someone is a morning or an evening person. An early riser is a “lark,� the name taken from the bird whose song is often heard around dawn. The late risers are “owls,� named, of course, after the bird that hunts at night and sleeps in the day.

In case anyone is wondering, Esser is a lark.

“The morning chronotype, that’s me,� she said. Lest anyone think all scientists share this trait, Esser notes, “I have a number of colleagues who are truly owls and don’t like mornings at all.�