Hi,

It is an inter. topic. I think you will not be able to generalise it, because every person has its "own circadian rhythm" (inner day-night clock, early bird ...) which is entrainable very differently. Probably you should ask some specialists in the field of chronobiology.

Hi Robin, very thought-provoking question- thanks!

Like Kruno has mentioned, an endogenous central pacemaker of each organism internally sets precisely regulated signals for physiological and behavioural bodily activities. Light acts as both the main "time giver"  to this pacemaker, and also as masking factor, which can either increase or decrease behavioural activity. It has been known for some time that diurnal mammal animals show positive masking with the increased light (or its intensity), and negative masking with light/intensity is decreased. Alternatively, nocturnal animas display positive masking in response to darkness and negative masking after light exposure. One interesting pre-clinical research (reference below) studied effect of light in certain strains of rodents that display both diurnal and nocturnal chronotypes, while giving animals free access to an exercise wheel. The aim  was to understand different masking effects of light on animals with either diurnal or nocturnal chronotype, and their respective activity in response to the light. Researchers reported that both diurnal and nocturnal animals displayed stable masking by light, according to their respective chronotype: diurnal animals increased their activity in the presence of light, and nocturnal rodents decreased their wheel running activity. Hope this helps. Kind regards, Tatyana

Reference: Vivanco P, Rol MA, Madrid JA. Pacemaker phase control versus masking by light: setting the circadian chronotype in dual Octodon degus. Chronobiol Int. 2010;27(7):1365-79.

Thank you Kruno and Tatyana. The information was very informative. However I am more interested in the light itself. So if I am training at 05:30 AM inside a gym would it be better to train in dim light versus bright light....would that increase neural output, increase potentiation or strength?

Hi Robin, Sorry if I was not clear in my answer. This would depend on whether you are a 'diurnal' or a 'nocturnal' chronotype. If you are a 'diurnal' type, then the brighter the light the more intense excerdize activity is expected/increased neural output, etc.; if  you are a 'nocturnal' type- opposite effect (please refer to positive or negative masking above). Temperature of the exersize environment also expects to play a role.

I understand that you are interesting in publications on this topic, will search PubMed to see whether anything directly relevant to the human exercise- output based on chronotype was published. 

Kind regards, Tatyana 

Hi Robin, I found two related works on PubMed:

1.Knaier R, Meister S, Aeschbacher T, Gemperle D, Rossmeissl A, Cajochen C, Schmidt-Trucksäss A.Dose-response relationship between light exposure and cycling performance. Scand J Med Sci Sports. 2016 Jul;26(7):794-801. Main findings: "A medium or short duration (note: 60 minutes or less) of bright light (BL) exposure before and/or during time-trial does not enhance physical performance in athletes normalized for their individual chronotype. In contrast, a long duration (note: 120 minutes)  of exposure to BL is an effective tool to increase total work at least for the initial phase of a medium length time-trial."

2. Kantermann T, Forstner S, Halle M, Schlangen L, Roenneberg T, Schmidt-Trucksäss A. The stimulating effect of bright light on physical performance depends on internal time. PLoS One. 2012;7(7):e40655. Main findings: "The differences between total work levels in bright light (BL) and dim light (DL) were significantly higher if participants were tested at a respectively later time point after their individual mid-sleep (chronotype). ...timed BL exposure enhances physical performance with concomitant increase in individual strain, and is related not only to local (external) time, but also to an individual's internal time."

Hope this helps. Kind regards, Tatyana