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Should We Exercise at a Particular Time of the Day, or at Our Convenience?

Is there a best time to work out, based on circadian rhythms?
(With response from
 Dr. Sheri Colberg, Ph.D., FACSM, Advisory Board Member)

Circadian rhythms are estimated 24 –hour biological cycles that function to prepare the organism for daily environmental changes. It is a molecular clock mechanism found in most cell types including skeletal muscles. Regulation of these circadian oscillations is controlled by a hierarchical system, with the central clock located within suprachiasmatic nucleus (SCN) located in hypothalamus. The SCN, which is also known as the central pacemaker, is synchronized to light and dark cycles, which also functions to coordinate many physiological processes through neuro humoral signals. The types of circadian time cues are zeitgeber, which is the photic or light time cue, and non – photic zeitgebers such as feeding time and physical activity time. These times have been shown to affect molecular rhythms and behavior. Studies have shown that altering metabolic, endocrine and homeostatic events can change the expression of circadian clock genes in the peripheral tissue with no change in SCN. This results in misalignment of the central and peripheral clocks, with associated disruption in organ and system circadian clock. Disturbances in the circadian rhythms have been shown to have harmful impacts on health, which may lead to metabolic syndrome.

The purpose of this review is to present various findings demonstrating that the molecular clock exists in skeletal muscle, and support the idea that exercise plays a role as a time cue for clocks in peripheral tissues. About 215 mRNA were expressed in a circadian pattern in the gastrocnemius muscle of wildtype C57BL6 mice. In a study, mice were allowed free access to a wheel, no access to a wheel, or access limited to a 6 hour time frame at the beginning or end of dark for a minimum of 16 days. Changes in the molecular clock in the SCN after 16 days was observed in the control mice, suggesting a phase shift. Also, PER: LUC amplitude was damped in the mice with wheel access scheduled early in the dark phase but unaffected with scheduled activity late in the dark phase or with free access to wheel running. This suggests that the timing of exercise may be critical for the maintenance of molecular rhythms in the SCN. Vasoactive intestinal polypeptide (VIP) knockout mouse is shown to have an unstable clock mechanism, but then found that scheduled exercise functioned to enhance the stability of both activity and heart rate rhythms.

Another study determined the significant differences in circadian rhythms measured by noninvasive wrist skin temperature rhythm monitoring among optimal, fair and poor percentage fat categorized in healthy non-diabetic young men. 59 subjects between the ages of 20-34 were recruited and studied for 60 days. They were grouped based on their BMI as healthy weight, overweight or obese and all were free from cardiovascular disease, diabetes, pulmonary disease and many diseases. Resting heart rate and blood pressure were measured, so was their body composition and a maximal graded exercise test performed. Their circadian rhythm parameters were measured by noninvasive wrist temperature rhythm monitoring and recording devices. Temperature amplitude and stability were determined for each subject.  The iButton was worn by subjects for 7 consecutive days inside the wrist of non-dominant hand. It was returned after 7 days and information transferred through adapter. Subjects recorded daily questions concerning sleep, frequency and timing of nutritional intake, alcohol use, and smoking, and removal times of wrist skin temperature monitor. The statistical analysis used was the ANOVA model. There was no association between body fat and peak wrist temperature during night time hours (r= -0.05; P= 0.79). The poor % fat group (109.10 ± 14.12) had significantly lower circadian temperature stability than the optimal % fat (166.52 ± 17.84) or fair % fat group (175.21 ± 23.96).

Another recent study was performed to determine the exact time one needs to work out, based on circadian rhythm, to obtain a better outcome. In this study it was found that the various times one exercises give different outcomes. For instance, when one exercises from 7 to 9am, their pain tolerance is higher but they will have poor flexibility since their body temperature is low and therefore more likely to sustain an injury. Exercising from 10 am to 12 p.m. is good for any skill based sports that require alertness and short term memory peaks. Meanwhile from 4 to 8 pm showed an overall performance peak since it coincides with the peak body temperature. Body temperature is normally high at that time since there is a higher lung capacity, blood flow to muscle and flexibility.

In conclusion the best time for one to work out is whenever is appropriate for and suits that person since many things affect the circadian rhythms.

Practice Pearls:

  • Circadian rhythms is a molecular clock mechanism found in most cell types including skeletal muscles.
  • Presence of a molecular clock is argued to be a necessary timekeeping mechanism to prepare the cell for daily changes in environmental conditions
  • The best time to work out is when it is convenient for one since every time frame has its advantages and disadvantages.

 

Comment from Dr. Sheri Colberg, Ph.D., FACSM, Advisory Board Member

It has been suggested that many different things affect circadian oscillations, and in people with diabetes and in aging, some of these normal controls fail to work effectively.  For example, alterations in the release of melatonin, a critical hormone that regulates sleep and central nervous system balance, occur in both states (diabetes and aging) that lead to more imbalances.  Exercise of any type helps reset autonomic function, or the balance between sympathetic and parasympathetic branches of the autonomic nervous system.  For management of diabetes and successful aging both, being physically active on a regular basis is likely more important than the time of day that activity is undertaken.  

 

References:

Colino Stacey “What is the best time of the day to exercise? The answer is complicated”. US News 6 July 2016. Web. 14 July 2016.

Schroder, Elizabeth A., and Karyn A. Esser. “Circadian Rhythms, Skeletal Muscle Molecular Clocks and Exercise.” Exercise and sport sciences reviews 41.4 (2013): 10.1097/JES.0b013e3182a58a70. PMC. Web. 14 July 2016.

Tranel, Hannah R. et al. “Physical Activity, and Not Fat Mass Is a Primary Predictor of Circadian Parameters in Young Men.” Chronobiology international 32.6 (2015): 832–841. PMC. Web. 14 July 2016.