by Matt Weik, BS, CSCS, CPT, CSN
Muscle fatigue is something we are all too familiar with. Unfortunately, not everyone understands it fully. Sure, it can come about from intense workouts, but there are other (more serious) reasons you may suffer from muscle fatigue.
Muscle weakness can occur for various reasons, from infections to chronic conditions like diabetes or anemia. It’s more than just fatigue when your muscles struggle to contract or move effectively.
While some cases might develop gradually, a sudden loss of strength should never be ignored.
In this article, we will dive deeper and explore common causes of muscle fatigue and weakness and why consulting a doctor is important for understanding and managing this condition.
Disclaimer: This article is for informational purposes only and is not meant to treat or diagnose any condition. It is recommended that you speak with your doctor before starting any exercise program, changing your daily nutrition, or adding any supplements to your regimen.
What is Muscle Fatigue?
When muscles get tired during exercise, they can’t perform as well as when they are fresh. Anyone who trains is fully aware of that fact.
This can happen in different ways during workouts, though, such as lifting lighter weights, doing fewer repetitions, or finding it more challenging to keep up your usual running or cycling pace.
It’s important to distinguish between two types of muscle fatigue.
You experience muscle fatigue at its core when the same muscles are used repeatedly in a short time, like when your bench press gets weaker with each set or when your running pace slows during a 5k.
When fatigue builds up over days or affects different muscle groups, it’s usually a different story.
Studies about caffeine’s effects on performance have shown that this type of tiredness typically comes from the central nervous system.
7 Causes of Muscle Fatigue
Below are some of the major causes of muscle fatigue:
1. Lack of use
Muscle fatigue and weakness often come from deconditioning, a result of an inactive lifestyle where unused muscles lose bulk and strength as fibers are partially replaced with fat. This leads to quicker fatigue during activities that once felt effortless.
The positive thing is that the condition is reversible through regular, sensible exercise, which may take longer as we age.
Muscle power peaks in our 20s and 30s, but building strength is possible at any age.
While powerful bursts like sprinting decline earlier, endurance for activities like marathon running remains strong past 40. Staying fit is always beneficial, though older individuals may need guidance from trainers or physiotherapists to prevent injuries and build strength safely.
2. Autoimmune, Neuromuscular, and Neurological Diseases
Autoimmune, neuromuscular, and neurological diseases can lead to muscle weakness. Let’s take a deeper dive into some conditions:
- Guillain-Barré Syndrome (GBS): An autoimmune disorder leading to progressive muscle weakness.
- Graves’ Disease: Overproduction of thyroid hormones causes muscle weakness and, in severe cases, paralysis.
- Amyotrophic Lateral Sclerosis (ALS): Affects nerves controlling muscles, leading to muscle weakness and voluntary movement loss.
- Bell’s Palsy: Causes temporary facial muscle paralysis due to facial nerve damage or irritation.
- Cerebral Palsy: A developmental disorder causing muscular weakness due to oxygen deprivation during brain development.
- Muscular Dystrophies: A group of genetic disorders leading to progressive muscle weakness, difficulty walking, and respiratory issues.
- Cervical Spondylosis: Nerve root compression in the neck causes pain, numbness, and muscle weakness.
- Lambert-Eaton Myasthenic Syndrome: Autoimmune disease causing muscle weakness and fatigue.
- Myasthenia Gravis: Interrupts nerve-muscle communication, resulting in muscle weakness and atrophy.
- Multiple Sclerosis (MS): Degeneration of myelin sheath affects muscle strength, often more severe on the dominant side.
3. Aging
As we age, muscles naturally lose strength and bulk, becoming weaker. While this is often accepted as a part of growing older, it can be frustrating when simple tasks become challenging.
However, exercise remains beneficial at any age. A careful, safe routine can still improve muscle power and strength.
It’s important to note that recovery times are slower with age, and balance can be compromised, making bones more susceptible to breaks. Muscle weakness is a key factor in frailty, which isn’t limited to the elderly.
Staying active through exercise is crucial to prevent this, even in younger individuals.
4. Infections
When muscles feel weak and tired, it’s often due to an infection or illness that causes inflammation in the tissue. Although muscle strength usually returns to normal, severe instances, such as during a bad flu, may cause lingering muscle fatigue for weeks.
5. Electrolytes disorder
Electrolytes are essential for the proper function of muscles, nerves, heart, and brain. Common electrolytes include:
- Calcium
- Potassium
- Sodium
- Magnesium
Imbalanced electrolyte levels can lead to muscle fatigue. Some electrolyte-related disorders include hypokalemia and hyperkalemic periodic paralysis.
Risk factors for electrolyte imbalances include:
- Use of antibiotics or immunosuppressants
- Fluid loss due to sweating, vomiting, or diarrhea
- Chemotherapy
- Difficulty maintaining a healthy diet
6. Sleep disorder
Sleep disruptions affect your muscle strength and overall energy levels. Common causes include insomnia, ongoing anxiety, depression, and constant pain. Medical conditions like restless legs syndrome also impact sleep quality.
External factors like irregular work shifts or caring for children can make it challenging to get adequate rest. These disruptions can interfere with your body’s natural sleep cycle, affecting overall health and energy levels.
7. Medication
Some medications may lead to muscle fatigue as a side effect.
If you are facing this issue, it is crucial to speak with your doctor before altering any medication. Do not discontinue prescribed medications without professional advice.
