What Causes Muscle Weakness?

Research indicates it might be cell “leakage” from overexertion.

Muscle fatigue can most easily be defined as a failure of your muscle to generate force. But the how and the why are harder to define.

The clearest explanation of the how and why muscles become weak came from Columbia University, whose study found that that the fatigue striking marathoners and heart patients alike comes from “leaky” muscle cells.

“Ordinarily, ebbs and flows of calcium in cells control muscle contractions. But when muscles grow tired, the investigators report, tiny channels in them start leaking calcium, and that weakens contractions. At the same time, the leaked calcium stimulates an enzyme that eats into muscle fibers, contributing to the muscle exhaustion,” Gina Kolata wrote in The New York Times.

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The popular theory, that muscles become tired because they release lactic acid, was debunked not long before the Columbia discovery. The finding actually came from research into ways to treat people with heart failure, a condition that has stricken nearly 5 million Americans.

The heart study made researchers wonder whether a class of drugs they developed, potentially for cardiac patients, would also work on skeletal muscle, according to Andrew Marks, MD, principal investigator of the cardiac study.

Eventually, to test the theory, mice were exercised to exhaustion, then given the new drugs. They could run 10 to 20 percent longer. Biopsies of expert cyclists’ muscle tissue later tested positive for the excessive calcium leaks, showing it also happened in humans and leading to the temping thought that a drug could be developed for athletes.

Such a drug, however, could actually circumvent a sign that an athlete is going into a danger zone and should cut back on the effort being made, Kolata wrote.

Deconditioning (sedentary lifestyle), aging, infections, pregnancy, chronic diseases, muscle damage through injury, medicine, and prolonged use of alcohol and smoking can all cause the various types of muscle weakness.

More uncommon causes include chronic fatigue syndrome, fibromyalgia, underactive thyroid, dehydration, conditions of muscle inflammation, cancers, and nerve conditions that damage muscles.

One other common reason for muscle fatigue is anxiety. “The way you breathe, the way you walk, and the way you think with anxiety can all cause muscle weakness or tiredness. It's a common but scary condition that is often evaluated by a doctor,” according to CalmClinic.

The reasons can include hyperventilation, reduced blood flow from anxiety, muscle tension, and a perceived weakness that comes from anxiety making you much more sensitive to your body.

That answers some of the how and why, but most of muscle fatigue comes from overexertion.

Healthy lifestyle changes that can help prevent overexertion include nutrition, which means maintaining a well-balanced diet of complex proteins, fruits, vegetables, and carbohydrates. You should eat a light meal or snack about two hours before working out, writes Marla Ranieri, PT, DPT, for the Hospital for Special Surgery. It is not recommended to work out on a full stomach or an empty stomach.

Hydration also is key, meaning drinking water throughout the day and using sports drinks during exercise to prevent dehydration, Ranieri says. (Too much hydration, however, can hinder performance.)

Improve your aerobic capacity, she adds. “As your respiratory muscles begin to fatigue, oxygen will be redirected from the muscles of your limbs to those of your diaphragm. One way to improve your endurance is to gradually increase your aerobic workouts with interval training.”

Using correct form during exercise, or paying attention to body mechanics, also is helpful in preventing muscle fatigue.
“The right strength and flexibility will help you achieve correct form during exercising. If you can’t perform an exercise with proper form, then you need to either decrease your weight or modify the exercise. Improper body mechanics decreases efficiency and in turn burns more energy than necessary,” Ranieri writes.

Finally, she adds, complete a warm up and cool down for 5 to 10 minutes each time you exercise. Allow rest between workout sessions and strength repetitions, and make sure the rest break is enough to breath easily between exercise sets.

“Listen to your body – fatigue is a sign that recovery has not taken place yet. If that is the case, then perform active recovery, which means participating in low impact, low intensity exercise such as walking, light swimming, or yoga. Do not return to higher intensity exercise until you feel fully recovered and recharged.”

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