We like to think of exercise as a pretty simple concept usually - just get moving, hard enough to break a sweat, frequently enough to make the habit stick and long enough to accumulate 150 minutes per week in order to send injury/illness/disease into retreat! The best part is, by and large, this is true. However, the part that doesn't usually make the headlines might be the most fascinating....that exercise instantly changes the state of our body, even deeper than the tissue level.....all the way to each and every one of our approximately 37 trillion individual cells.
With that in mind and since the "state" of our cells is constantly adapting and changing to keep us ready for whatever situation we might enter into, it stands to reason that we can get different responses (output) from the same exercise (input) depending on when we do the work. This is super important, because it opens the door to even greater refinement in exercise dosing and therefore precision use of it; which is exactly what a recent "Atlas of Exercise Metabolism" starts to decode.
A team of experts from around the globe studied how exercise had a differing influence on two of the most obvious "states": activation (e.g. early daytime for humans or the opposite for nocturnal critters), when we burn mostly sugar supplied by our food and used by our muscles to do work and the second "state", rest & recovery (typically night) when we tap into sugar storage (in our liver) and start to convert fat to fuel when our sleep storage runs out......essentially running the daytime process in reverse.
They uncovered two particularly key points worth knowing about:
First - exercise indeed has different impacts at different times: In the morning our bodies are typically getting ready for work and food. Since we rely more on fat metabolism for fuel until we eat, if the goal is to burn body fat, exercise at this time of day may be preferable as was shown in the study. Fat used from sources in/around the liver however, did better when the body was ramping down from activity (such as early evening). On the other hand, if the goal is to normalize the body's ability to efficiently burn blood sugar (such as in cases of pre-diabetes) exercising later in the day (or after a meal) when our muscles are more full can be effective as was shown in this earlier work. We can also catch the muscles on the upswing (early AM) as they are naturally ready for work and get great benefits. This list goes on and on but the take home message is - we can turn a good thing into a great thing if we match our input (exercise) with the natural day/night rhythms already at work.
Second - exercise also seemed to "realign" the circadian rhythm at the cellular level. Although not exactly a "clock", each and every cell has timed functions that follow a roughly 24 hour cycle. In certain diseases these cycles get thrown off. It turns out that exercise, similar to winding an analog wristwatch, helped the body realign these rhythms. This was especially true for exercise during the early active hours, which means exercise early in the day might have the greatest impact here for most people.
What does this mean for us?
Well, maybe nothing at all. The simple rule still holds - exercise is such powerful stuff that doing enough of it is a good thing in most cases no matter what time you do it - so first and foremost "just get it in". But for some, the 30-50% who have the habit already and may want to squeeze even better results from the effort, aligning goals with physiological clocks and rhythms may make it easier to achieve them.
Timing may not be "everything" but it is clearly "something". We hope you can make some time to wind up your cellular clocks!
Have a great weekend,