Scenario: The sound of an alarm wakes you up at 6:30 a.m. to start your day. Upon waking up, you decide to go for a jog at the local park, but you are restricted to 30 minutes because of a work meeting scheduled for 8:30 at the office. After exercising, you sit down to pour your favorite cereal and eat breakfast, before driving to work for 20 minutes. You arrive in time for your meeting, which lasts longer than expected, ending around 10. Once the meeting is over, you return to your office to catch up on emails and tasks before going to lunch meeting with a few co-workers. While at lunch, you and your co-workers share personal stories and work-related updates for about an hour before returning to the office to finish up tasks and additional meetings prior to leaving work at 4:30 p.m. After leaving work, you drive back home to cook dinner leftovers before watching television until bedtime around 10 p.m. A similar but different routine repeats the following day - but why is this important even though you exercised?!
The 24-hour day entails four distinct behaviors called the 24-hour activity cycle. These behaviors are sleep, sedentary behavior, light physical activity, and moderate to vigorous physical activity. Current physical activity guidelines recommend that adults engage in at least 150 minutes per week of moderate physical activity, at least 75 minutes per week of vigorous physical activity or some combination of both. Sedentary behavior recommendations suggest adults “sit less and move more” due to a paucity of evidence during the development of the 2018 Physical Activity Guidelines for Americans. Finally, the National Sleep Foundation recommends that adults sleep at least seven hours a day. Thus, accurately measuring all these behaviors and meeting their recommendations pose a challenge.
All of behaviors of the 24-hour activity cycle are individually and independently associated with health. Ample evidence suggests that more time spent in moderate to vigorous physical activity and less time in sedentary behavior reduces the risk of a wide range of negative health outcomes such as hypertension, diabetes, cancer, cardiovascular disease, stroke, and a shorter mortality. By contrast, more time spent in sedentary behavior and less time in moderate to vigorous physical activity increases the risk of these negative health outcomes. Finally, current evidence also suggests a short sleep duration (less than seven hours per day) also poses similar negative health consequences as sedentary behavior. As such, growing evidence has now suggested that the combined effects of all these behaviors may be greater than their individual effects.
Time spent in one of these complex behaviors will offset time spent in the remaining behaviors. Meeting the aerobic physical activity recommendations or exercising for an hour each day, constitutes only about two percent of a 24-hour day. The remaining 98% of our day and behaviors (sleep, sedentary behavior and light physical activity) should be considered. Meta-analytical evidence suggests even if an individual meets the aerobic physical activity recommendations and engages in high levels of sedentary time throughout the day, the risk of mortality remains high. Previous research has also shown that even physical activity-focused programs do not yield meaningful reductions in sedentary time as an individual can be physically active (e.g. exercise 30 min/day) and yet spend the rest of the day sedentary. Thus, focusing efforts on a single behavior limits efficacy and may lead to spurious conclusions for our health.
To help inform a paradigm shift in this area future progress should be established in different areas. Research investigation should consider examining efforts to determine appropriate levels of sleep, sedentary behavior, light physical activity, and moderate to vigorous physical activity (or in certain combinations) to establish optimal 24-hour day recommendations. The fitness and medical community may also benefit in this area by exploring innovative tactics to understand time spent beyond their client’s exercise session to design a healthy 24-hour day.
More information about the 24-hour activity cycle can be found in three distinct continuing education courses.
Benjamin D. Boudreaux, Ph.D. is a postdoctoral fellow at Columbia University Irving Medical Center. His research area of emphasis lies at the intersection of exercise science and physical activity epidemiology. His primary research interests includes examining the relationship between the 24-Hour Activity Cycle in the prevention or treatment of cardiovascular disease and other human health outcomes. He has extensive experience with consumer wearable devices in different populations for validation purposes or as a tool to alter physical activity and sedentary behaviors. Beyond research, Dr. Boudreaux devotes his service efforts towards the disability and Type 1 Diabetes communities such as running the 2023 TCS NYC Marathon for Type 1 Diabetes awareness and presenting or publishing about the importance of physical activity and exercise in the autism community.