Weak Strength Is Also the Body's Doing

"My thigh just melted away." "I have no strength in it." "My leg feels like it might buckle on the stairs."

People often already have a guess ready: I must not have used it, so the muscle shrank. I need to start working it hard again.

That is true. A muscle that goes unused for a long time does shrink. But people say the same thing just days after an injury. Not nearly enough time has passed for the muscle to have shrunk, and yet the strength will not come.

There is one more thing to look at here.

There is more than one reason strength does not come

The most common reason is a muscle that has shrunk from disuse. Sometimes a nerve is compressed. Sometimes pain itself keeps someone from using it. Sometimes muscle mass has declined with age.

Among these several reasons, there is one called arthrogenic muscle inhibition. This is when the activity of the muscles around a joint decreases because of irritation from the joint itself.

When the inside of a joint is swollen or inflamed, the signal to the muscles that move that joint decreases. The muscle itself is fine, but less strength comes through.

Why would that happen? If a muscle over a swollen joint pulls with its usual full force, the joint gets damaged further. It can be understood as the body making the muscle pull less, to keep the joint from being hurt further.

It happens even without an injury

There is an experiment that confirmed this directly in people.

Researchers raised the pressure inside the knee joints of 17 healthy adults by injecting a clear saline solution. This was not an injury. There was no tear, no inflammation. Only saline was added.

And the strength in the front thigh muscle dropped.

Simply filling the joint with fluid was enough to cause that.

In this case, willpower alone does not bring it back

I often hear people say, "I try to put strength into it, but it just will not come."

In that same experiment, the pathway going down from the brain to the muscle was actually firing harder, not weaker. More was being sent from above, yet less strength was reaching the muscle.

The researchers found no evidence that the brain itself was involved, and concluded that inhibition occurring at the level of the spinal cord alone could account for a difference this large.

That means this happens below the level of consciousness. So in this case, strength does not come back simply by resolving to try harder.

Looking at people with major knee ligament injuries, as many as just over half still showed this state at six weeks after the injury, according to one report. Even after the pain has settled, strength can come back late.

So there is an order to it

At this point one question remains. Should you exercise, or should you rest?

Based on the research available so far, the answer runs like this. Rehabilitation exercise comes first. Results were better when electrical stimulation or cold therapy were added on top of that.

Still, what to add and when depends on the state of the joint. A joint that is still swollen and one that has settled down are different.

While the joint is still swollen, simply putting in more effort does not resolve much. Muscle inhibition during swelling even changes how a person bears weight on one leg. Piling more force on top does not help, because the body simply suppresses it again.

Same words, different starting point

Even the same complaint, "I have no strength," can mean something different happened in the body.

There is the case of a muscle shrunk from disuse. This progresses slowly over time, and the muscle itself has actually shrunk. This is the most common case.

There is the case that starts from the joint. Here, strength can drop within days, with no time for the muscle to have shrunk at all. The muscle is unchanged; it is the signal telling that muscle to work that has been suppressed.

The two can also overlap in the same person. This is often the case with a knee that has hurt for a long time.

When to get checked first

If, right after an injury, the knee swells sharply and cannot bear weight, if the joint feels like it is out of alignment, or if it becomes feverish and visibly red and swollen — checking what is happening inside the joint comes first.

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Many people put not being able to put strength into a limb down to laziness or weak will.

Of course, a muscle shrunk from disuse is the most common case. But there are also cases where the joint has made the body hold back on its own strength. It is not that the muscle is damaged — it is that the body is trying not to damage the joint further.

So it is better not to treat weak strength as the business of the muscle alone. The answer sometimes lies in the joint that muscle is attached to. This continues from what it means when someone is told a joint has worn down.

Written by Dr. Heo Ji-young (PhD in Korean Medicine Pathology, Kyung Hee University · former Research Professor of Herbology, Kyung Hee University)