How Does Sleep Affect Your Fitness?

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Since I’m just overcome a few days’ lacks of sleep and stopped training due to rushing for coursework, I think it’s a great opportunity to let me really look into what ‘rest’ really means for building muscle.

As everyone says that sleep is important, but in fact, sometimes we tend to just leave it behind. And sometimes I really can’t resist the urge to complete everything before going to bed.

In this post, let us dive into everything about sleep and investigate to what extent sleep could affect our fitness journey.

What Happen If We Did Not Get Enough Sleep?

First of all, let’s get the general idea of why the professionals say it’s bad to not get enough sleep.

Of course, lack of sleep can cause a lot of problems, but since this blog is specifically about fitness, let’s be laser-focus–the effect of sleep on fitness.

The sleep that we refer to is the ‘deep sleep phase’ a.k.a the non-REM sleep. Which can’t be replaced with the casual afternoon nap. After all, a deep sleep brings a specific effect a nap can’t do. It does the repairing job that our body is unable to finish during the awake time. Thus affecting the things mentioned below:

Training performance

Well, let’s look at the external factors first. Your performance and progression in the gym if lack sleep.

Ever notice that when the time we know we did not get enough sleep the day before, chances are we get a sluggish feeling when we go to the gym that day (not just a normal ‘sluggishness’, but worst than that).

Here are two scenarios, first, you had a training session the day before, in this case, the sluggishness occurs because your body can’t get enough recovery from the training day before. That is a sign your body tells you to get some rest.

The other scenario is that although you did not have a training session day before, you just feel sluggishness than those days that you did your regular training. That is because your body did not get enough energy to replenish up to your normal energy level.

In both cases, the best solution is to skip one gym day and get some rest anyway. Just remember that you always can return to gym after. However, if you really wanted to have a session, that’s fine, you still can get a great workout, but not as effective compared with the day after a good rest.

I won’t go to the gym if I did not sleep well that day. Because I know that the workout that I will be going through not only will be shi**y, I obtain no benefit in the long term.


The point is actually highly related to the last point, the recovery that occurs after a training session.

As I said, the true process of muscle growth is outside the gym, therefore, really, sometimes we need to look at the whole process rather than just look at how much time we spend in the gym. Even if gaining muscle is currently not your goal, remember that any type of workout still required recovery.

In my previous post about ‘why we need a deload week?‘, I’ve explained the supercompensation phase in the process of recovery after training. That is the moment our body gets to adapt to a higher level of challenge therefore you are able to improve your performance in the next session.

Notice how a good rest actually helps us to have better performance in the gym? In fact, rest time is actually part of the training process in the fitness journey. When we get sufficient rest and continue improving, we’ll get to progress towards a better level from the starting point.

Metabolism and Appetite

There are a few factors that affect our metabolism, surprisingly, it is not just about how much we eat and how active we are.

From the diagram, it is surprising that most of the energy that we used is not on exercise, but just these basic functions used to regulate the body every day.

For sleep, the part that is affected is the BMR part. Perhaps not much on the fixed factor such as gender, age and muscle to fat ratio, but much more on the hormone. An individual that has well-functioning hormones will have a higher metabolism and not easy to gain fat.

Talking about hormones, it is actually playing an important role in our appetite.

Having not enough sleep perhaps isn’t directly affecting our appetite, but what it actually affects is insulin sensitivity–which leads to excessive glucose consumption.

What is the effect of high insulin resistance? Your appetite. The study shows that a group of people that sleep under the average sleeping hour (less than 6 hours) tend to consume more calories than those that sleep enough.

Body Composition

This seems impossible, but let’s look at a study at 2015. The experiment investigate a group of people that did not sleep for one night. Their muscle had detected a sign of protein breakdown, and some fat accumulation had occurred within that day.

This is so subtle that no one even notices after one day of sleep deprivation. Of course, not many weight changes are seen, because once the muscle break down, what that replacing it is the fat.

Scary, right? Afraid not, this is just one day, the good news is that our body is always trying to recover from past damage, I believe that once that person returns to their regular sleep routine, the damage can be reverted pretty soon.

But if one had a lack of sleep in a long term, this is a thing that we need to be worried about..

So how important it really is? Compared with training and diet?

“I know sleep is important, but I don’t think it is as important as training and diet?”

“Is it okay to sacrifice my sleeping time because I just skipped a workout?”

There is the question I always ask. Because what we always think about fitness is just diet and exercise, ironically, sleep isn’t accounting for more in these places.

More of the time, people tend to get guilty of skipping a workout or cheating on a diet, but we never get guilty if we did not get enough sleep the day before.

Therefore, let’s debunked the level of importance between three of these: sleep vs diet vs training.

Of course, as I say goal matters, therefore as always, I will make the comparison based on your goal and the effect.

Goal: Build muscle

-Training: 5 out of 5 (You can’t have significant muscle growth if you did not train hard)

-Diet: 3 out of 5 (As long as you eat enough and have sufficient nutrition, you can still build muscle)

-Sleep: 4 out of 5 (Recovery means progression)

Goal: Lose Fat

-Training: 3 out of 5 (The training here is to have more energy expense and retain muscle)

-Diet: 5 out of 5 (Caloric deficit is the key to losing weight)

-Sleeping: 4 out of 5 (You won’t lose much fat if you lack sleep, most of them will be muscle loss)

Goal: Maintaining Health

-Training: 3 out of 5 (Workout helps maintain your current fitness level)

-Diet: 4 out of 5 (As long as you did not overeat, you are good to go)

-Sleeping: 5 out of 5 (Sleeps regulates most of the hormones in your body)

The Winner?

Let’s face the fact, there are no more or less important between three of these. Because the amount of sleep is as important as diet and training is, perhaps not less important. Three of these co-exist with each other.

Of course, it isn’t mean everything will go wrong if we did not get enough sleep for just a while. Same as training and dieting, consistency is the key, and I believe that you will soon notice some positive improvement after integrating good sleep habits as a part of your fitness journey.

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2 responses to “How Does Sleep Affect Your Fitness?”

  1. Fitsyness Avatar


    1. Alyssa Avatar

      Thank you 🙂

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