It’s About Time
by Women’s Brain Health Initiative:
MOVING TO THE BEAT OF YOUR CIRCADIAN RHYTHM.
We’ve all experienced challenges of fitting exercise into our weekly routine, balancing work or school, household, and family responsibilities. But did you know that short bouts of just 10 minutes of exercise that add up to 150 minutes per week can have profound impacts on your health? Better yet, if you can time it with your natural body rhythm, known as your circadian rhythm, the health benefits are greater.
EXERCISING WITH YOUR CIRCADIAN RHYTHM
A circadian rhythm is a natural “internal clock” that is synchronized with light and dark cycles from sunlight. This internal clock affects several body systems, including hormone production, sleep and wake cycles, and body temperature.
YOUR CIRCADIAN RHYTHM IS SO IMPORTANT FOR BODY FUNCTIONING THAT EVIDENCE SHOWS DISRUPTION OF ITS NATURAL RHYTHM NEGATIVELY IMPACTS YOUR HEALTH IN SEVERAL WAYS INCLUDING DIMINISHING COGNITIVE PERFORMANCE, ALTERING METABOLISM, AND IS EVEN ASSOCIATED WITH DEPRESSION, DIABETES, OBESITY, ALZHEIMER’S DISEASE, AND CANCER.
Fortunately, research has shown that exercise, which is one of the Six Pillars of Brain Health that will help reduce risk of developing dementia, is a powerful non-pharmacologic way of resetting or realigning your circadian rhythm. In addition, synchronizing physical activities with your natural circadian rhythm may optimize the positive impacts of exercise on health and physical performance.
TYPE OF EXERCISE & TIMING
The type of exercise you engage in can determine the ideal time slot to optimize health benefits and keep your circadian rhythm happy. For instance, certain types of yoga are best performed early morning on a fasting stomach to stretch muscles, activate organs, and lubricate joints. In fact, there is a specific series of movements referred to as “sun salutations” that have been traditionally practiced shortly after sunrise for these reasons.
Andrea Roth, RYT 200, yoga instructor and Co-owner at Level Up Fitness Academy in the Greater Toronto Area explained: “Starting your day with a series of sun salutations can have a positive impact on your energy levels, your ability to regulate stress, and your overall clarity and focus.”
Toward the end of the day, when you are trying to wind down and prepare for restful sleep, “there is a slower-paced type of yoga known as Yin yoga that incorporates deep stretching and meditation,” said Roth.
When it comes to endurance exercise (like jogging and swimming), there is accumulating evidence that later in the afternoon or early evening may be best for building fitness (e.g., strength, power, and flexibility), in part because of how our bodies access energy systems suited for prolonged movement in these time slots.
Some evidence also suggests that our perception of exertion, that is, how hard we feel that we are working, is lower in the early afternoon.
This may be related to several circadian-regulated factors, like hormone release and mood. If you are thinking about working out for a little bit longer one day or wanting to try out a challenging set of movements, the early afternoon timeslot may allow you to push yourself harder without noticing it.
EXERCISE & SLEEP
Strenuous physical exertion late in the evening is shown to be detrimental to sleep, leading to poor muscle recovery during sleep and sleep deficits. As our body prepares for sleep, our body temperature naturally decreases, and production of the hormone melatonin increases. Exercise too late at night counteracts these circadian rhythms, making it harder for the body and brain to settle into a restful state.
Another factor to consider is that people generally consume water during and after exercise, as well as foods high in protein and carbohydrates after exercise. Food and drink stimulate the digestive system and can therefore disrupt sleep quality if consumed late at night. For this reason, it is recommended to have your last meal or snack at least an hour before going to bed.
FLUCTUATIONS IN EXERCISE PERFORMANCE BY TIME OF DAY
If your goal is to build strength or increase your muscular endurance, there is evidence to suggest that exercise performance peaks in the late afternoon (3 p.m.-6 p.m.), with circadian rhythms related to body temperature and gene expression potentially playing a role. Dr. Alireza Basti and colleagues looked at relationships between time of day, resting muscle tone, and exercise performance.
Published in BMJ Open Sport & Exercise Medicine in 2021, in this study a group of 19 participants completed two strength tests (i.e., hand strength test and counter-movement jump) and one aerobic endurance test (i.e., shuttle run test) at four times of day: 9 a.m., noon, 3 p.m., and 6 p.m., over four rounds.
Across the rounds, researchers found that both male and female participants performed significantly better in the late afternoon. Interestingly, the best performance for the aerobic endurance test was at 6 p.m. across the four rounds, even though participants reported that they were less motivated to complete tests later in the day.
Further research examined biomechanical characteristics of major muscle groups at different times of day, including muscle tone, and found that muscles were more responsive in the late afternoon, helping to explain differences in exercise performance.
These findings on timing may be helpful for exercise rehabilitation in clinical settings, where the goal is to restore muscle tone and function.
If muscles are more responsive to activation in the late afternoon, physiotherapy and rehabilitation during this time slot may be more effective, which could help individuals meet their therapy goals in a shorter time frame.
Daniel Roth, NSCA-certified strength and conditioning specialist and Head Trainer and Co-owner of Level Up Fitness Academy in the Greater Toronto Area works with a range of clients, including individuals with acute and long-term mobility challenges. According to Roth, “For individuals who are restricted in what they can do, be it from injury or other limitations, identifying the optimal window for muscle responsiveness could help to jump-start physical improvements.”
However, it is important to note that there is a difference between building physical capacity and testing that capacity in real-world situations. Roth explained: “Training during less optimal times is one way to ensure you can perform well no matter what situations or conditions you are faced with. Training during sub-optimal times can build physical – and mental – resilience.”
METABOLIC BENEFITS OF EXERCISE BY TIME OF DAY
Exercise at different times of the day also plays a part in circadian regulation of metabolism. Research by Dr. Shogo Sato and colleagues examined timing of exercise on energy metabolism in mice. In their 2019 article published in Cell Metabolism, Dr. Sato and colleagues demonstrated that energy metabolism (i.e., usage of various energy sources) differs during daytime exercise (i.e., circadian active phase) versus nighttime exercise (i.e., circadian rest phase).
Using a mouse model for their research, the authors observed that skeletal muscles that are responsible for movement were better at using carbohydrates and ketone bodies (lipids/fat produced by the liver) as energy sources during daytime exercise.
Muscles also metabolized lipids (fat) and amino acids (protein) at a higher rate when exercise was performed during the day when compared to night. Furthermore, these metabolic differences in energy usage based on time of day led to changes in systemic (whole body) metabolic homeostasis.
DR. SATO AND HIS CO-AUTHORS SUGGESTED THAT METABOLIC CHANGES FROM DAYTIME EXERCISE COULD BE ESPECIALLY HELPFUL FOR PEOPLE WITH METABOLIC DISEASES, LIKE DIABETES, OR FOR THOSE WHO ARE CLINICALLY OBESE AND TRYING TO LOSE WEIGHT. FUTURE STUDIES MAY CONSIDER DIFFERENCES IN METABOLIC REGULATION BASED ON EXERCISE TIMING TO DEVELOP BETTER PROTOCOLS AND “EXERCISE PRESCRIPTIONS” FOR PEOPLE WITH METABOLIC DISEASES.
Overall, it appears there are advantages in aligning the timing of exercise with your circadian rhythm, especially if you are working toward specific goals like better performance, muscle rehabilitation, and metabolic regulation. At the same time, when one considers the full range of health benefits from exercise, the best time to move is whenever you’re able to do it.