Circadian Rhythms and Physiological Performance: A Runner’s Perspective

Many of the biological processes within our bodies such as neurological activity and hormone production exhibit circadian rhythm. That is to say they cycle on a 24 hour basis. The synchronization of these biological clocks was thought to be under the master control of the “suprachiasmatic nucleus” located within the hypothalamus of the brain (physiological jargon with no importance regarding what I have to say). However, it has recently been shown that other tissues – including skeletal muscle – exhibit their own circadian rhythm patterns. These have the potential to be out of phase with the master controller, and may therefore regulate their own cycling.

What relevance does this have to running?

The findings of these investigations could have direct ramifications on both the quality of your training and your performance in races for multiple reasons:

Firstly, it has been demonstrated the strength and power of your muscles are higher during the late afternoon compared with the morning – you have probably experienced that yourself (I certainly notice when I run at 9a.m. on a Saturday). It is therefore suggested that training may be of better quality, and result in better improvements, if done during the hours of peak muscle performance i.e. 4-6p.m in most cases.

In terms of racing, it may be of advantage to attempt to alter the circadian rhythm of your skeletal muscles such that it is out of phase with your biological clock, aligning the time of peak performance with the starting time of your race. This may be achieved through altering eating patterns and activity scheduling, but for most normal folk this is probably a little impractical (and not without its risks: sleep deprivation etc.).

Somewhat more logically, you may alter the circadian rhythm of your muscles by altering the time at which you train. It has been noted that the greatest improvements in performance occur at the time of day in which the highest-intensity training is regularly performed. Therefore, by training at the specific time of day for the event you plan to perform in, you will increase the likelihood of running a personal best time. Recent studies show that although this link exists there are no adaptions to neural signaling suggesting that this change has arisen due to alteration of the circadian rhythms associated with our muscle cells.

Furthermore, the levels of glycogen within our muscle cells exhibit circadian rhythm. Glycogen is our cells’ method of storing glucose, our #1 source of energy, and its levels vary by as much as 200% during a 24hr period. In rats, it was shown that when glycogen levels were at their peak, the rodents could swim 60% further, demonstrating a direct link between physiological performance and circadian rhythms. Imagine if you could line up your peak level of stored glucose to the period of your target race: you’d be absolutely flying!

Unfortunately, the source of these circadian rhythms within the skeletal muscle cells is unknown. The link, however, definitely exists. If only I knew how to exploit this to its fullest…

James

Zhang X, Dube TJ, & Esser KA (2009). Working around the clock: circadian rhythms and skeletal muscle. Journal of applied physiology (Bethesda, Md. : 1985), 107 (5), 1647-54 PMID: 19696362

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