What Causes Muscular Fatigue?

Muscle fatigue is one of the most common complaints among athletes and fitness enthusiasts. Whether you're into cycling, running or bodybuilding, you know how it feels to have painful, sore muscles and low energy. From nutrient deficiencies and inadequate rest to overtraining, this condition can have a variety of causes. Sometimes, it may indicate a more serious problem that requires medical attention.

Make small changes to your diet and exercise routine to reduce muscle fatigue. (Image: wundervisuals/E+/GettyImages)

Tip

Muscle fatigue often results from overtraining and poor nutrition. Listen to your body in the gym and eat for your goals. Get plenty of rest so your muscles can recover from exercise.

What Is Muscle Fatigue?

Your muscles feel strong and energized when you start working out. After a few sets, fatigue sets in. Sometimes, it occurs after a day or two of intense training. You're feeling weak and tired, you can barely move around and everything hurts.

Most times, muscle fatigue is accompanied by pain and soreness. This condition can be defined as a temporary decrease in muscle power and force resulting from physical exertion, according to a 2017 review featured in the journal Experimental & Molecular Medicine. It usually develops after sustained or repetitive exercise, such as when you train the same muscle group two days in a row or push yourself too hard in the gym.

However, overtraining and sustained exercise are not the only causes of extreme fatigue. A poor night's sleep, dehydration, nutrient deficiencies and stress can contribute to this problem. Muscle fatigue can also be a symptom of certain disorders, such as fibromyalgia, Addison's disease or depression. These illnesses affect your body's ability to function optimally and recover from training.

Signs and Symptoms

Fatigue is just one of the many signs of muscle exhaustion. You may also experience pain and aches, overall weaknesses, trembling, soreness or chills. Localized swelling, decreased performance and poor recovery from training are common too.

Symptoms vary from one person to another depending on the cause of muscle fatigue. Overtraining, for example, may lead to delayed-onset muscle soreness (DOMS). This condition occurs about 24 to 48 hours after exercise, causing fatigue, dull muscle aches, inflammation and strength loss. The pain can be debilitating.

Unless your symptoms are severe, you should start to feel better within days. Foam rolling, stretching, massage and proper rest can help relieve muscle fatigue and accelerate healing. If your condition worsens or doesn't improve in a week or so, seek medical attention.

Lactic Acid and Muscle Metabolism

Until recently, lactic acid buildup was blamed for muscle soreness and fatigue. The latest research, though, has debunked this myth. When you work out hard or at high intensity, your body begins to produce lactic acid for fuel.

The conversion of glucose to lactic acid is called anaerobic glycolysis, or anaerobic glucose breakdown, and provides energy for 30 seconds to three minutes of high-intensity effort. During this process, lactate and hydrogen ions build up in muscle tissue, inhibiting muscular contractions. As a result, you may feel sore and fatigued later on.

According to Science Nordic, muscle soreness and stiffness can occur at both high and low concentrations of lactic acid. These symptoms result from a multitude of physiological reactions associated with exercise-induced microtrauma. So, lactic acid isn't the only culprit. In fact, this metabolic byproduct is an important source of fuel during exercise.

Overtraining and Muscle Exhaustion

Overtraining syndrome often leads to extreme fatigue, according to a 2017 review published in Sports Medicine. The hormonal changes that occur in your body when you work out too hard or for too long can interfere with the recovery process and affect your performance.

If you're spending long hours in the gym, your body doesn't have time to recover. At this point, every training session puts even greater stress on your muscles and joints. You may experience performance plateaus, slow post-workout recovery, general fatigue, low energy, poor sleep and even depression.

A 2016 research article published in the Open Access Journal of Sports Medicine suggests that overtraining syndrome can affect immune function and increase oxidative stress levels. In addition to muscle fatigue, it may cause high blood pressure, irritability, anxiety, loss of motivation, mood swings, poor mental focus and weight loss. Researchers point out that simple preventive measures, such as staying hydrated, eating a balanced diet and keeping a training log, can help prevent overtraining and its symptoms.

Does DOMS Cause Muscle Fatigue?

Another possible cause of muscle fatigue is DOMS, or delayed-onset muscle soreness, which often occurs after performing a workout you're not used to, according to a 2016 study featured in The Journal of Physiological Sciences. If you've just started to exercise or you're trying new workouts, you have a greater risk of developing this condition. Movements that involve eccentric muscle contractions are more likely to cause DOMS.

Its symptoms range from muscle fatigue and soreness to diminished physical performance. In fact, DOMS is a very mild form of rhabdomyolysis, a life-threatening condition. If you keep pushing yourself in the gym before the soreness has resolved, you'll cause further damage to your muscles. This may lead to full-blown rhabdomyolysis and affect kidney function.

As you see, too much exercise can be just as bad as no exercise at all. Spending more time in the gym doesn't guarantee faster gains or improved performance. On the contrary, it can fatigue your muscles and stall your progress. Any exercise routine you're not used to can cause DOMS, so try to gradually change workout intensity, duration and frequency.

Beware of Low-Carb Diets

There's a reason why high-protein diets and sports supplements are so popular among athletes. A diet rich in micronutrients and macronutrients can speed up recovery and enhance physical performance.

According to a 2018 article published in the journal Nutrients, eating carbs after exercise may help prevent fatigue and improve recovery time. Exercise, especially high-intensity workouts, depletes muscle glycogen stores, which in turn, can trigger fatigue. Researchers point out that ingesting 0.8 to 1.2 grams of carbs per kilogram of body weight per hour after training helps replenish glycogen stores and wards off fatigue.

Fresh fruit, rice, whole grains and other high-carb foods have their place in a balanced diet. After ingestion, carbs are converted to glucose and used as a source of fuel or stored as glycogen in the liver and muscles. If your diet is low in carbs, your glycogen levels will drop. This can result in poor recovery, decreased physical performance and fatigue.

Vitamin and Mineral Deficiencies

What you eat has a direct impact on muscle function and overall health. Certain nutrient deficiencies can keep you from performing at your peak. A 2015 study published in the journal Clinical Interventions in Aging found that adequate vitamin D intake may help prevent muscle fatigue and improve exercise performance. Researchers have also linked this nutrient to greater muscle power and strength, reduced injury risk and improved bone health.

Another nutrient that plays a key role in physical performance is magnesium. This mineral regulates muscle contraction and plays a vital role in energy production. It also activates vitamin D, which further enhances its beneficial effects on muscle function. As Medical News Today notes, magnesium deficiency may cause fatigue, weakness and muscle cramps.

Make sure your diet is rich in calcium. Low levels of this nutrient have been linked to muscle spasms and cramps, fatigue, numbness and tingling in the limbs, chest pain and other symptoms. In the long run, calcium deficiency may increase your risk of bone fractures and osteoporosis.

How to Relieve Muscle Fatigue

Now that you know what causes muscle fatigue, you may wonder how to prevent and relieve this symptom. From dietary changes to massage and adequate rest, there are a couple of things you can do when dealing with sore, fatigued muscles. Athletes, for example, often take ice baths to recover faster from training and reduce soreness. Also known as cold-water immersion, this method appears to be beneficial for muscle recovery.

Consider using a foam roller to massage your muscles and help them recover faster. According to a 2015 laboratory-controlled study published in the Journal of Athletic Training, foam rolling may reduce DOMS and relieve muscle fatigue. Subjects who used this technique for 20 minutes after exercise reported less muscle tenderness and pain along with improvements in power and sprint speed.

Therapeutic massage can help too. In 2018, the journal Frontiers in Physiology published a meta-analysis assessing the effectiveness of several recovery techniques on perceived fatigue, DOMS, inflammation and other factors that influence physical performance. Massage has been found to be more effective at reducing muscle fatigue, soreness and inflammation than contrast water therapy, cold water immersion, cryostimulation and other methods. Surprisingly, stretching has been found to trigger and worsen delayed onset muscle soreness.

Eat a Balanced Diet

Nutrition and exercise are equally important. Sports supplements and recovery techniques may help with fatigue, but cannot replace a balanced diet. Eat plenty of foods rich in protein, magnesium, calcium, vitamin D, antioxidants and other nutrients.

Magnesium, for example, occurs naturally in both animal and plant foods, including spinach, edamame, Swiss chard, citrus fruits, quinoa, wheat germ, oat bran, Brazil nuts, peanut butter, salmon, mackerel and tofu. Collard greens, kale, spinach, fatty fish and soybeans are all excellent sources of calcium, while beef liver, salmon, tuna, egg yolks and cheese pack large amounts of vitamin D.

Fill up on fruits, vegetables, nuts and seeds to boost your antioxidant intake. According to Antioxidants in Sports Nutrition, exercise raises free radical levels in the body, which in turn, contributes to muscle fatigue. Antioxidant supplements may improve workout performance by scavenging oxidative stress. You can get these nutrients in your diet by eating berries, citrus fruits, cruciferous veggies, leafy greens, carrots, grapes and other antioxidant-rich foods.

Get More Sleep

The National Sleep Foundation states that athletes who get plenty of shut-eye have greater energy and stamina as well as faster reaction times. A 2018 review published in the journal Nature and Science of Sleep confirms that sleep and physical performance are strongly connected and that adequate rest is one of the most effective recovery strategies for athletes.

Whether you want to prevent muscle fatigue, last longer in the gym or perform better at your sport of choice, make sleep a priority. Maintain a regular bedtime routine and try to get at least eight hours of sleep per night. Refrain from surfing the web on your smart phone or watching TV before bedtime. Electronic devices emit blue light that affects the body's circadian rhythm and inhibit melatonin production.

Take a warm bath or drink a cup of herbal tea to relax at night. The harder your workout, the more rest you'll need. Not even the best diet or exercise routine can replace a good night's sleep.

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