Pushing Harder Makes the Body Shrink Back

A day when you finish all the kimchi-making at once usually leaves you in good spirits. You have used your body from morning to evening, and the result is right there to see.

But that same day marks, for some people, the start of the body building itself back up, and for others, the start of a long stretch of suffering. This happens even when the number of cabbage heads salted and the time spent are the same.

The Body Braces for the Same Task After Being Slightly Worn Down

With some kinds of exercise, while the muscle damage from a first bout is recovering, the body adapts. So when the same exercise is done again, the damage is smaller. This is called the repeated bout effect.

So a task that was hard the first time becomes easier the next. The body has not suddenly grown stronger. It has prepared itself specifically for that task.

When the same arm exercise was done twice with an interval in between, the muscle was less damaged the second time. A single prior experience is enough to bring this about.

The Body's Response Does Not Rise by Much

This property has a name. It is called hormesis. A stimulus at a low level raises the body's capacity to adapt, and above a certain level, that same kind of stimulus instead suppresses that capacity. This is a property confirmed repeatedly across many substances and conditions in pharmacology and toxicology.

Two things need to be seen together here.

First, the degree to which the body's response rises is not large. Pooling the data, even the cases where each study measured the largest rise in response were generally only 30 to 60% higher than doing nothing at all.

Second, above that, the direction reverses. Putting in a little more does not yield proportionally more — past a certain line, it crosses over into suppression. What you gain increases little by little, but the moment you cross the line, you begin instead to lose.

That Line Is Not Fixed in One Place

Rebuilding what has been worn down takes time. If the same stimulus comes in again before that work is finished, the body cannot move toward building itself back up stronger.

So what sets the line is not the size of the stimulus alone. That line also shifts depending on how long it takes the body to restore itself.

As people age, this time changes. A review of how aging muscle restores itself after the same kind of damage notes that the process starts later, drags on longer, and proceeds less smoothly. Soreness and reduced strength are usually at their worst somewhere between 12 hours and two days after the activity.

So an amount that used to serve as conditioning may now be an amount that piles the next stimulus onto a site not yet finished rebuilding. This happens even when the same person is doing the same task. The line has shifted.

And this line does not shift only from year to year. After a few nights of poor sleep, or after a bout of serious illness, the body can react differently today to an amount that was fine as recently as yesterday.

What the Body Does After Being Pushed

Once restoration starts falling behind, the body stops building that muscle up further. It makes the muscle hurt and weakens its output, forcing you to use it less. And for however many days it is used less, that muscle shrinks again.

Push once more from here, and the same thing repeats. But even if fear leads you to give it up entirely, the body does the same thing. To the degree you scale back, the line is pulled further inward, and the next time you do the same task, it becomes a larger stimulus than before.

Pushing too hard and giving up entirely meet at the same place. They point in opposite directions, but both pull the line inward.

There is a follow-up to the arm exercise study mentioned earlier. When the same thing was done with older men, the degree of change from the first bout itself was smaller than in younger participants, and the protection gained from the second bout was smaller as well. The researchers did not settle on a single reason. One explanation they offered was that the stimulus from the first bout was too small. When the incoming stimulus is small, the adaptation that follows is small too.

Where to Look First

There are two things that need to come before any talk of resetting the amount.

When the chest feels pressed or tight during exertion. When heaviness in the center of the chest, or an ache radiating into the arm, appears during exertion and settles within a few minutes of rest. Because it settles with rest, it is easy to dismiss — but the fact that it settles is itself one of the signs.

When soreness after an intense burst of activity is unusual and urine turns dark. If it takes on the color of cola or strong black tea, checking that same day is the right order. Even if the color is normal, if the soreness is more severe than the usual ache and strength does not come back, that alone is reason enough to get it checked.

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I see no small number of people who have run into trouble through exercise. I understand the impulse to push through in one go. You have taken a long time to get this far, and you want to make sure of it this time.

But whether doing it harder actually makes it more certain has to be asked separately. The same amount calls forth adaptation in one body and makes another body shrink back. The answer to that is not written during the activity itself, but in the days that follow.

A stimulus repeated within a manageable range is what builds adaptation. That range and its degree differ from person to person. Push hard, and the line pulls inward; give it up entirely, and it pulls inward as well. This is the same principle as the question of whether a stronger medicine is a better medicine.

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