Timing is everything. Part 2: Exercise

Meyken Houppermans, PhD. CrossFit Level 3 Trainer.
Founder and Head Coach
The time a day at which you work out determines the degree to which your muscles adapt to your workout. Timing your workouts determines your training results. Workout according your muscle clock to maximize training results. Why is that?

Biological clock

As we explained in our article about Timing is everything (part 1: food): Our daily lives are structured by a 24-hour timeframe and by day and night. When the sun rises and it gets light, we wake up and start our day. When the sun goes down and it gets dark, we end our day and go to bed. At least most of us. Despite this pretty clear 24-hour structure, some of us are more energetic and productive in the morning, while others flourish at night,. This has everything to do with our biological clock.

Circadian rhythm

Our biological clock is the natural timing device that regulates our so-called circadian rhythms: natural physical, mental and emotional processes in our body in respond to light and dark (day and night). Circadian rhythms are also known as the sleep- wake cycle. Every cell, tissue, organ and muscle in our body has a biological clock, and all clocks are coordinated by acmaster clock in our brain that receives input from our eyes (light).

Circadian rhythms influence several processes in our bodycamong which hormone release, digestion and muscle’s metabolic response andenergy efficiency. Several factors such as a jet lag, evening shifts at work, bluelight from our phone and 24/7 light from buildings in our environment, can change circadian rhythms. These changes can have severe consequences: Sleepdisorders, obesity, diabetes type 2 and mental health issues and also less results from our workouts [1].

Muscle clock

Our circadian clock and oxygen in our body work together inside our muscle cells to produce energy. The degree of synchronization of their work depends on the time of day. The more synchronized they are, the more efficient muscle cells are in their ability to adapt to exercise and to use oxygen for energy. And that seems to be during our ‘normal’ waking hours.  

When we work out we consume oxygen fast. We also run out of oxygen fast, so we need another source of energy to keep going. That dip in oxygen triggers specific proteins in our body that signal muscles to switch to sugar for energy.  

Messing up the muscle clock, for example by working out at unusual times, prevents our capacity to induce sugar consumption and produce lactic acid. Adjusting our working to our ‘natural’ rhythm and to the time a day can improve muscle function. Furthermore, improving our muscle clock can also contribute to the treatment of diabetes, since in this disease muscles fail to consume glucose. [2] 

So in order to get the most out of a training session, adjust your planning to your natural rhythm: if you are a morning person you might want to workout in the morning, and if you are an evening person, a workout later during the day might be better. Timing is everything if you want to reap the benefits of your hard work.

Create your own health!©


[1] National Institute of General Medical Sciences. Circadian Rhythms. Retrieved 2020.

[2] Martin, Ryan & Esser, Karyn. (2022). Time for Exercise? Exercise and Its Influence on the Skeletal Muscle Clock. Journal of biological rhythms. 37. 7487304221122662. 10.1177/07487304221122662.; Peek CB, Levine DC, Cedernaes J, Taguchi A, Kobayashi Y, Tsai SJ, Bonar NA, McNulty MR, Ramsey KM, Bass J. Circadian Clock Interaction with HIF1α Mediates Oxygenic Metabolism and Anaerobic Glycolysis in Skeletal Muscle. Cell Metab. 2017 Jan 10;25(1):86-92. doi: 10.1016/j.cmet.2016.09.010. Epub 2016 Oct 20. PMID: 27773696; PMCID: PMC5226863.