When is the best time of day to exercise?

From Diabetes in Control 14th July 2016
Is there a best time to work out, based on circadian rhythms?

Circadian rhythms are estimated 24 –hour biological cycles that function to prepare the organism for daily environmental changes. There is a molecular clock mechanism found in most cell types including skeletal muscles.  Disturbances in the circadian rhythms have been shown to have harmful impacts on health, which may lead to metabolic syndrome.
Experiments in mice suggest that the timing of exercise may be critical for the maintenance of molecular rhythms.  Scheduled exercise functioned to enhance the stability of both activity and heart rate rhythms.
Another study determined the significant differences in circadian rhythms  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.

Subjects recorded daily questions concerning sleep, frequency and timing of nutritional intake, alcohol use, and smoking, and removal times of wrist skin temperature monitor.

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 have poorer flexibility  since their body temperature is low and therefore more likely to sustain an injury. (My comment: so not great for yoga or running but maybe better for walking, meditiation or  weight training?)

Exercising from 10 am to 12 p.m. is good for any skill based sports that require alertness and short term memory peaks.  (Anyone for tennis?)

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. (So good for a run and yoga and indeed most sports and activity)
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.