After a strenuous workout, or even after a long day of walking around, you’ll begin to notice that your muscles are aching and tired. This sensation can range from a slightly uncomfortable and tired feeling to complete exhaustion and incapacitation depending on how hard you push yourself. This phenomenon is called muscle fatigue, and in this article, we’re going to go into how muscles work and explain in detail, what causes muscle fatigue.
How Do Muscles Work?
Before we can go into detail about what causes muscle fatigue, we first need to establish how exactly muscles work.
Muscles, like the rest of our body, are composed of cells. Muscle cells work by sensing electrical impulses coming from the brain. When a cell receives that impulse, calcium is released from a cell component called the endoplasmic reticulum, and the muscle contracts.
Muscle contractions are responsible for any sort of physical activity we make, whether that’s picking up a glass of water or squatting hundreds of pounds.
What is Muscle Fatigue?
Muscle fatigue is when the muscles lose the ability to contract efficiently, and that can happen in a number of ways which we’ll discuss in further detail below.
Basically, if you work your body too hard your muscles can no longer support the activity. They enter a sort of “shut down”, forcing your body to rest to prevent serious damage.
Muscle fatigue is caused by strenuous activity, and it can occur via one of the two methods below:
As we mentioned above, your brain – a key part of the nervous system – is responsible for all forms of muscle contraction. If you overtax the nervous system, this can lead to muscle fatigue.
Nervous fatigue is the less common form of muscle fatigue, and it only occurs when you put an incredible amount of strain on your muscles.
Basically, the electrical impulses your brain sends to muscle cells often operate at far below peak capacity. For normal situations like just going about your day, the brain controls these impulses with ease.
The problem comes when you put an immense amount of stress on your muscles, and your nervous system is forced to send plenty of impulses to your muscle fibers. In this situation, your nervous system can get fatigued and cause your muscles to give out.
As mentioned above, this type of fatigue is rarely seen outside of extremely strenuous situations. Bodybuilders like Lazar Angelov or even athletes that put an incredible amount of stress on their muscles like sprinters or swimmers will occasionally run into this form of muscle fatigue when they push themselves too far.
Muscle fatigue from a nervous system issue is characterized by a suspicious lack of pain or discomfort. Your muscles just sort of “give up”, refusing to continue to work. This fatigue happens gradually during high periods of stress. The brain will be sending frequent and strong impulses, and these will gradually decrease in frequency and strength until the muscle gives out.
For the casual exerciser, the type of muscle fatigue that is far more common is Metabolic fatigue.
This type of fatigue is a lot more complicated and a lot more complicated to explain. Let’s get into it!
Metabolic fatigue occurs for one of two reasons:
- A lack of fuel within the muscle
- Accumulation of substances within the muscle
Either of these occurrences can cause metabolic muscle fatigue, and we’ll address them one at the time.
Lack of Fuel
To contract properly, muscles require substances known as substrates to be present in the cell. These substrates serve as a key component of muscle contraction. Your body as a whole is an efficient machine, and depriving it of the fuel it needs to function will cause it to stop. Your muscles are no exception to this rule, and they require a good source of energy as well as specific nutrients to function at peak performance.
Key nutrients for muscle performance are Adenosine Triphosphate (ATP), creatine phosphate, and glycogen. Below we’ll explain a little more about how these molecules function together to make a muscle contract. It will be easy to glean how a lack of them would result in serious metabolic muscle fatigue.
A muscle cell also called a muscle fiber, is composed of two main protein filaments: Actin and Myosin. Muscle contraction occurs when these fibers slide over one another, and for any movement in the body, you require energy.
ATP is the main source of energy for our body as a whole and is vitally important to keeping us alive and functioning. In muscle cells, ATP fixes to the myosin head and this event causes the myosin to contract over the actin. It’s easy to see how a lack of ATP could cause some serious issues!
Creatine phosphate conserves energy in order to help ATP rapidly regenerate within the cell. Slow regeneration leads to not enough ATP for a muscle to contract.
Glycogen is also an energy storage molecule. It stores glucose, which is one of the building blocks of ATP. Without glucose, you can’t have ATP. Simple as that!
Without these three molecules, your muscle will cease to function properly.
Accumulation of Matter Within the Muscle
The second way to cause metabolic fatigue is from the build-up of substances in the muscle. These substances are called metabolites and are the waste products of muscle metabolism.
As your muscles burn through energy and contract, there are leftover byproducts that aren’t used and can actually hamper the effectiveness of your muscle fibers.
There’s a wide range of byproducts that can produce this effect, and going into each one in detail is outside the scope of this article, but suffice it to say that these waste products interfere with the production of calcium ions, an important part of muscle contraction.
Without calcium ions, you can’t have muscle contraction. This is the second cause of metabolic fatigue.
Avoid Muscle Fatigue
Avoiding muscle fatigue is simple: avoid pushing your muscles too hard. Fatiguing muscles is an important part of muscle growth, as when you break muscle fibers down they rebuild a stronger version, but pushing yourself to the point of muscle failure over and over again can really put a strain on your body.
Take a day of rest in between strenuous workouts to let your muscles grow and refresh before your next workout. Avoid injury and build a better body with proper management of muscle fatigue.