Winding  Up Your Body's Clock

clock of circadian rhythm

Scheduled physical activity is found to help regulate and amplify the body's circadian rhythm. This suggests a way for curing defective circadian rhythms and a multitude of diseases that have been linked to malfunctioning circadian rhythms. 

Animals, including humans, utilize clocks called circadian rhythms to keep the body aligned with nature's daily night and day cycle. The circadian rhythm is controlled by the suprachiasmatic nucleus in the brain. The circadian rhythm is a daily cycle of behavioral and physiological functions regulated by fluctuating levels of hormones. Malfunctions in the circadian rhythm often develop in the elderly and a recent study found these malfunctions in the circadian rhythm may be to blame for a myriad of diseases including diabetes, cancer, cardiovascular disease and mood disorders [Arendt J (2010). Occup Med (Lond) 60, 10–20.]. A study published in the December 2012 Journal of Applied Physiology found that scheduled physical activity strengthens and regulates the circadian rhythm (Voluntary scheduled exercise alters diurnal rhythms of behavior, physiology and gene expression in wild-type and vasoactive intestinal peptide-deficient mice, 2012. Analyne M. Schroeder, et al.). 

In the study mice were given varying levels of access to a running wheel: no access, free access, late night access and early night access. By measuring ambulatory activity, body temperature, heart rate and circadian rhythm hormones the researchers found that having scheduled access had a strong control over their circadian rhythm. Even free access versus no access had an effect. Mice are naturally active at night. The figure below shows how varying access to running wheels affected their ambulatory activity.

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Ambulatory activity in wild-type mice as a function of time of day in response to no, free, early night and late night access to running wheels.

Even more interesting was the effect of the running wheel access variable in vasointestinal polypeptide (VIP) deficient mice. VIP deficiency leads to circadian rhythm loss of function. Late night running wheel access was able to restore many of circadian physiological and behavior cycles to those seen in the wild type (VIP normal) mice. One of the molecular clocks measured was PER2 and Luciferase, the ratio of which corresponds to different points in the circadian rhythm. The figure below compares this molecular clock with wild type mice.

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A measurement of PER2::Luc ratios in VIP deficient mice (VIP -/-) as a result of varying access to a running wheel. The dotted lines represent the levels seen in the wild-type mice.

What this study shows is that not only can exercise be important for therapy, but the time that exercise is performed is also important. For people who perform exercise on a daily basis, maintaining a standard workout schedule is beneficial because our bodies are "ready to go"at the workout time each day. Apparently, this readiness does not require our normal circadian rhythm machinery as evident by the VIP deficient mice's ability to get on a schedule. Further research is needed to show that scheduled physical activity can help elderly patients suffering from a loss of circadian rhythm function.

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