What Causes Muscle Fatigue and How to Recover

When it comes to muscle fatigue, whether it’s through Crossfit, Olympic weightlifting, bodybuilding, powerlifting or any other sport, if there’s one thing that all athlete’s can agree on, it’s the fact that after a grueling training session their muscles will require a great deal of care and attention and will feel incredibly sore and painful.

Physical exercise and exertion of any kind is exhausting, yet some people still try to push themselves too far without allowing themselves adequate time to rest and recover properly. Without rest and recovery muscles cannot repair themselves and grow stronger, and progress will not be as efficient as it could.

When we begin training, our muscles feel powerful, strong, and energized, yet as time goes by and we do more and more exercise, the muscles begin to feel weaker and a great deal more tired.

muscle fatigue crossfit athlete lying on floor after WODSource: RX'd Photography
We’ve all been there!

But what causes muscle fatigue, and how can it be avoided?

In reality, there are a number of factors that contribute towards muscle fatigue, yet the good news is that there are also a number of things you can do to help make life that little bit easier when dealing with muscle fatigue and soreness as well.


A decreased capacity to perform a maximum voluntary muscle action or a series of repetitive muscle actions. A fatigued muscle is unable to continue working even when the type of activity is changed.

Muscle fatigue can manifest itself in a variety of different ways, yet if you ignore the signs and symptoms, or if you don’t know what you’re looking for in the first place, well, in that instance, muscle fatigue can be very detrimental indeed.


mat fraser crossfit games athlete 2016 weightliftingSource: RX'd Photography
CrossFit Games winner Mat Fraser has incredible mental toughness, but he also trains smart and competes intelligently


Many people believe that lactic acid is solely responsible for muscle soreness and fatigue, but in actual fact, this is not the case at all.

When we exercise, and after exercising, we often experience feelings of pain and soreness in our muscles, which bodybuilders refer to as DOMS. DOMS, or Delayed Onset Muscle Soreness, can vary in severity of pain, yet lactic acid is not solely responsible, though it does play a part.

Lactic acid is released as a by-product of physical exertion, where the body then breaks it down into lactate. When lactic acid becomes lactate, hydrogen ions are released into the body, allowing lactate to be used as energy. However, when the body has used all of the lactate it can handle, any remaining lactate will be stored in the muscles.

This leads to increased acidity levels in the muscles, which in turn causes muscle pain, soreness, spasms, and cramps.


 Another common cause of muscle fatigue and soreness, that people tend not to even consider, is a nutrient deficiency. In order for the muscles to function as they should, the body requires a number of essential minerals, vitamins, and electrolytes which it cannot produce naturally. Because of this, they need to come in the form of supplements and whole food sources and drinks.

Paleo diet nuts, veg peppersSource: BOXROX
Eat for optimal performance

If an athlete’s diet is lacking certain minerals and vitamins, they may unwillingly speed up the process of muscle fatigue during training. Potassium, calcium and magnesium for example are all very important when it comes to muscular health and function, yet if a person is deficient in even one of these minerals, their performance will suffer hugely as a result.

These minerals aid the following effects:

  • Assist with muscle function
  • Enhance circulation
  • Increase blood cell production
  • Keep acidity levels in the muscles under control
  • Prevent excessive build-ups of lactic acid within the muscles

TIP: If a person is deficient in any mineral or vitamin, supplements could prove extremely useful, as well as changes in their diet to add in the nutrients they are missing.


 Another common cause of muscle fatigue and soreness is anaerobic respiration. In order for muscles to function and contract, they require energy, or rather, the cells that are the fabric of the muscles need energy, which comes in the form of oxygen.

When there is plenty of oxygen available, cellular respiration processes are referred to as aerobic respiration, yet when oxygen levels are poor, the cells breathe anaerobically, resulting in increased levels of lactic acid being produced as a waste product.

Put simply, if you exercise at a high intensity, you will quickly use up your oxygen levels, which will result in your cells respiring anaerobically. This will cause lactic acid to build up, resulting in it being converted into lactate, consequently your muscles will become far more acidic.


One of the most common causes of muscle soreness and fatigue is when an individual fails to stretch and warm up before they begin any form of physical activity. If you suddenly decide to jump directly into a strenuous and physically exerting workout, this can shock the muscles as they have suddenly switched from resting to being worked incredibly hard.

It’s the equivalent of you waking up in the morning, getting straight out of bed, and entering a 10K marathon right away. By gently warming your muscles up and stretching them, you are giving them a warning of what they are about to be put through, and you are allowing them to begin functioning much more efficiently. Additionally, this will increase blood flow and oxygen levels.


muscle fatigue snatch liftSource: RX'd Photography
Train effectively, recover properly.


Rest days are incredibly important in regards to muscle fatigue and athletic performance, because when you are resting your muscles recover and repair themselves. As a rough rule, aim for 7 hours minimum of sleep a night. Most professional Crossfit athletes sleep between 8 – 10 hours.


Before exercise it is crucially important that you take the time to stretch your muscles and to warm up. As a general rule, dynamic stretches before a WOD are useful, and longer extended sessions of static stretches should be kept for the end of your training. These are a great way to improve your flexibility and cool down after an intensive workout.

We looked at how failing to do so can result in muscle fatigue, soreness, and even injury, so make sure that you tailor your warm up in a way that is suitable and relevant for the exercises that you are about to perform.

Check out our guide to the perfect warm up (link) for an in depth account of how to create the most effective warm up in relation to the type of work out you are about to do.


If your muscles are sore and fatigued after exercise, experts recommend applying an ice pack to the affected area for a while, switching to a hot pack, and alternating for a couple of hours. Make sure you don’t apply ice directly onto the skin, and leave it on for no longer than fifteen minutes.


Muscles require energy in order to function correctly, and they require energy and macronutrients such as protein, in order to repair themselves after strenuous activity.

If you are struggling to consume enough food after a training session, think of using a protein shake instead, as it is quick, easy, and will give you what you need. Supplements, however, are no substitute for good quality food, so make sure you consume plenty of fresh, wholesome, and healthy foods throughout the day.

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