Timing, consistency of activity linked to better fitness

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 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 Karyn Esser, Ph.D., senior author and professor and chair of the UF College of Medicine's Department of Physiology and Aging. "The circadian mechanisms that generate daily rhythms in our system are important for our well-being."

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 included:

• Higher-amplitude activity and rest cycles. This reflects greater activity during the active part of the day relative to the rest period. Which was associated with better cardiorespiratory fitness and walking efficiency.

• Earlier daily peak activity, defined as the time of day when individuals were most active, 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.

This study suggests a link between earlier, consistent activity and better health, however it doesn't prove that following such a schedule will improve health and fitness.

Still, the findings open intriguing possibilities for personalized medicine. Circadian rhythms vary from person to person. Health strategies should 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. We're moving toward a future where understanding and respecting our individual rhythms can help guide medical care and daily living.