Not Time of Day for Training but Location Location Location

The question of time of day for training has been asked often. Better to train at night? better to train in the morning? Better for anaerobic? better for aerobic?

Indeed, one of my fave current studies has shown that the circadian clock is threaded right into the muscles - at least of mice

J Appl Physiol. 2009 Nov;107(5):1647-54. Epub 2009 Aug 20.

Working around the clock: circadian rhythms and skeletal muscle.

Zhang X, Dube TJ, Esser KA.

Center for Muscle Biology, Dept. of Physiology, Chandler College of Medicine, Univ. of Kentucky, 800 Rose St., Lexington, KY 40536, USA.

The study of the circadian molecular clock in skeletal muscle is in the very early stages. Initial research has demonstrated the presence of the molecular clock in skeletal muscle and that skeletal muscle of a clock-compromised mouse, Clock mutant, exhibits significant disruption in normal expression of many genes required for adult muscle structure and metabolism. In light of the growing association between the molecular clock, metabolism, and metabolic disease, it will also be important to understand the contribution of circadian factors to normal metabolism, metabolic responses to muscle training, and contribution of the molecular clock in muscle-to-muscle disease (e.g., insulin resistance). Consistent with the potential for the skeletal muscle molecular clock modulating skeletal muscle physiology, there are findings in the literature that there is significant time-of-day effects for strength and metabolism. Additionally, there is some recent evidence that temporal specificity is important for optimizing training for muscular performance. While these studies do not prove that the molecular clock in skeletal muscle is important, they are suggestive of a circadian contribution to skeletal muscle function. The application of well-established models of skeletal muscle research in function and metabolism with available genetic models of molecular clock disruption will allow for more mechanistic understanding of potential relationships.

So this all sounds like business as usual - a little dubious - but heh we still don't know about diurnal effects on training. One other contemporary study suggests well, we know more now than we thought we did, because we varied a usually stable/assumed variable in the study: location. And then lots of things shifted.

J Strength Cond Res. 2010 Jan;24(1):23-9.

Effects of 5 weeks of training at the same time of day on the diurnal variations of maximal muscle power performance.

Blonc S, Perrot S, Racinais S, Aussepe S, Hue O.

Laboratory ACTES, UFR STAPS-Université Antilles-Guyane, Campus de Fouillole, Pointe-à-Pitre, France. stephen.blonc@univ-ag.fr

The purpose of this study was to investigate whether maximal muscle power production in humans is influenced by the habitual time of training to provide recommendations for adapting training hours in the month preceding a competition. Sixteen participants performed maximal brief squat and countermovement jumps and short-term cycle sprints tests before and after 5 weeks of training. Subjects were randomly assigned to either a Morning-Trained Group (MTG, 7:00-9:00 hr) or an Evening-Trained Group (ETG, 17:00-19:00 hr). They trained and performed the evaluation tests in both the morning and evening in their naturally warm and moderately humid environment. The results indicated a significant increase in performance (approximately 5-6% for both tests) after training for both groups but failed to show any time-of-day effect on either performance or training benefit. These findings could be linked to the stabilization of performances throughout the day because of the passive warm-up effect of the environment. In summary, our data showed that anaerobic muscle power production could be performed at any time of day with the same benefit.

In other words, it seems that time of day makes no significant difference to results on a test.

THe authors provide a really nice review of about half a dozen key studies that have looked at time of day and training effect. So why didn't that happen here? Here's what the authors' postulate: weather, light, location. External rather than internal factors.

In our study, the lack of difference between morning and evening training could be explained in part by the moderately warm and humid environmental conditions, in which the natural light remains similar from 6:00 to 18:00 hours. Previous studies conducted in our laboratory in a moderately warm environment failed to show any daytime variations in anaerobic performance (^31,32). Moreover, this particular tropical environment changes little over the entire year, with few variations in temperature. The passive warm-up effect of this environment has been suggested to blunt the passive warm-up effect of time of day (³²). This may thus lead to specific physiologic adaptations to exercise (³) and certainly influences the circadian regulation of some neurohormonal metabolisms. It might have acted as a stabilizer, and the results of the good intraclass correlations for the CMJ as well as the good to very good test-retest correlations for all jumps support this point. Indeed, previous studies conducted in the same environment showed a stability in performance throughout the day, and the training benefit thus appears as strong at any time of day.

This is an important observation because, up to now, such stability has only been shown for short-term acute but not chronic exercise. Moreover, it is particularly interesting when improved maximal muscle power performance is sought because training should be carried out at the time of day when performance is highest and maximal (³⁰).

I love speculation in research papers! something that says we have this finding that's different from other people's and we're trying to figure out A. what the differences are between our set ups and B. why those differences might have an effect. Temperate vs Tropic. Long daylight vs not.

So even here to say "time of day doesn't matter" for training has to have a caveat attached - depending on WHERE and what time of year you may be training. And that's a cool result

Hope the above helps offer one more reason that hitting the tropics is a good idea for health and well-being.



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Citations:

Zhang, X., Dube, T., & Esser, K. (2009). Working around the clock: circadian rhythms and skeletal muscle Journal of Applied Physiology, 107 (5), 1647-1654 DOI: 10.1152/japplphysiol.00725.2009

Blonc S, Perrot S, Racinais S, Aussepe S, & Hue O (2010). Effects of 5 weeks of training at the same time of day on the diurnal variations of maximal muscle power performance. Journal of strength and conditioning research / National Strength & Conditioning Association, 24 (1), 23-9 PMID: 19966592