Have you ever wondered why your muscles feel sore and tired after a workout? Or why you can’t seem to lift as heavy after a few sets? The reason behind these phenomena is muscle fatigue.
Muscle fatigue is something we all experience. It refers to a decrease in strength and performance of a muscle after prolonged use. But what’s actually happening inside your body when your muscles feel fatigued? Let’s dive into the science behind muscle fatigue.
What Muscle Fatigue Feels Like
You know that feeling when your muscles start to burn during your workout? When every rep feels like a struggle and you can’t even lift a light weight anymore? That’s muscle fatigue setting in.
Here are some common signs that your muscles are fatigued:
- Decreased strength – You’re unable to lift as heavy of a weight or do as many reps as you could earlier.
- Muscle shaking – Your muscles visibly shake or tremble when trying to perform an exercise.
- Achy muscles – Your muscles feel sore or pain during and after exercise.
- Burning sensation – You get that “burning” feeling in your muscles when exercising.
- Reduced muscle control – Your movements are unstable or shaky because your muscles don’t have their normal level of control.
So in simple terms, muscle fatigue means your muscles are tired and unable to generate their peak level of force. Keep pushing them when fatigued, and you risk overtraining and injury.
Why Do Your Muscles Get Fatigued?
To understand muscle fatigue, we first need to understand how muscles work.
Your muscles are made up of small fibers called myofibrils. Inside these fibers are even smaller strands called myofilaments. The two main myofilaments are:
- Actin – Thinner filaments that make up the structure of muscle fibers.
- Myosin – Thicker filaments that bind to actin and allow muscles to contract.
Muscle contractions happen when actin and myosin filaments slide over one another, pulling the two ends of the muscle fiber closer together and shortening it.
This process requires energy in the form of ATP (adenosine triphosphate). ATP provides fuel for actin and myosin to interact and produce movement.
Here’s the key point – your muscles only store a limited amount of ATP. During exercise, ATP is broken down to provide energy for muscle contractions. But ATP gets used up faster than your body can reproduce it.
Once ATP runs low, your muscles cannot keep contracting with as much force. That’s what causes the burning sensation and decreased strength – your muscles are tapped out on their immediate energy source.
Now let’s look at a few specific ways ATP gets depleted, contributing to fatigue:
Lactic Acid Buildup
When ATP is in short supply, your body switches to anaerobic glycolysis to keep producing energy. This breakdown of glucose creates lactic acid as a byproduct.
Too much lactic acid interferes with muscle contraction. It also causes that “burning” feeling during intense exercise. Clearing out excess lactic acid is one reason you may feel soreness hours or days after working out.
Calcium Imbalance
Calcium is essential for muscle contractions. It allows actin and myosin to interact and pull the muscle fibers inward.
But high-intensity exercise causes calcium to leak out of its storage sacs (sarcoplasmic reticulum) inside muscle cells. This makes less calcium available for contracting the muscle.
Nervous System Fatigue
Your central nervous system controls muscle contraction via signals between the brain and motor neurons.
During exercise, nerve signals have to increase to recruit more muscle fibers. But firing at high frequencies causes neurotransmitters to get depleted.
Without enough neurotransmitters, the signal from your brain telling your muscles to contract becomes weaker. This reduces strength and coordination.
Other Factors Contributing to Muscle Fatigue
Aside from ATP depletion, lactic acid buildup, calcium leakage, and nervous system fatigue, here are some other causes of muscle fatigue:
- Dehydration – Water loss reduces blood volume, making it harder to deliver oxygen and nutrients to working muscles.
- Electrolyte imbalance – Sweating causes critical electrolytes like sodium and potassium to drop. Proper electrolyte levels are essential for muscle contractions.
- Muscle damage – Intense exercise can damage muscle proteins and cell membranes, disturbing contraction mechanisms. Soreness and weakness persist until muscles fully repair.
- Overtraining – High training volume and insufficient recovery leads to prolonged fatigue. Your body can’t adapt quickly enough if constantly overworked.
- Poor nutrition – Inadequate carbohydrate intake makes it harder to replenish ATP. Low protein intake impairs muscle repair. Both scenarios worsen fatigue.
- Insufficient sleep – Muscles need sleep to fully recover. Skimping on Zzz’s prevents muscles from bouncing back to full strength capacity after each workout.
Tips to Delay Muscle Fatigue
Now that you understand why your muscles fatigue, here are some evidence-based ways to stave it off during your workouts:
- Consume carbs and moderate protein before exercise – This helps ensure you have sufficient ATP and amino acids to fuel your muscles. Time nutrients 1-4 hours pre-workout.
- Stay hydrated – Sip water or sports drinks during exercise to maintain blood volume. Watch that you don’t overdrink and dilute electrolytes.
- Breathe properly – Don’t hold your breath during exertion. Inhale during less intense phases and exhale during intense efforts. Oxygen is your muscles’ lifeblood.
- Pace yourself – Can’t go all-out every set or sprint the entire time. Let your muscles catch their breath periodically to clear metabolites.
- Vary intensity – Alternate heavy and light sets or intervals of higher and lower speed/resistance. This allows muscles time to partially recover within a workout.
- Get adequate sleep – Strive for 7-9 hours per night for optimal restoration. Muscles repair best when you’re sleeping.
- Avoid overtraining – Balance hard training days with easier days and take regular rest days. Listen when your body feels excessively fatigued.
- Correct nutrition deficiencies – See a sports dietitian or physician if you suspect poor diet is worsening fatigue. Optimize calories, carbs, protein, vitamins, minerals, etc.
The Importance of Recovery
Muscle fatigue during exercise is normal. What’s key is giving your muscles the proper rest and nutrition they need to fully recover afterward.
Recovery allows your muscles to:
- Restore ATP, electrolytes, glycogen, and other nutrients
- Repair any microscopic tears and damage
- Ramp up protein synthesis to reinforce muscle fibers
- Adapt to become stronger and more fatigue-resistant
Adequate rest, proper nutrition, hydration, sleep, and stress management optimize recovery. This allows you to come back feeling refreshed and energetic for your next workout.
Conclusion
Muscle fatigue is the result of ATP depletion, byproducts like lactic acid, calcium leakage, and nervous system fatigue reducing your muscles’ ability to contract. While some degree of fatigue is expected during training, allowing sufficient recovery helps restore muscular performance so you can keep getting stronger over time. Use the tips in this article to put off fatigue and train hardconsistently.
