What Was Muscle, Anyway? - What I First Realized Through Rehabilitation Wednesday, September 23, 2026 - Autumnal Equinox Day R8, Day 27 of My Hospital Stay

Today, while doing my rehabilitation exercises, I suddenly found myself thinking:

"What was muscle, anyway?"

I have always liked going to the gym.  
I also liked strength training.

I would read the instructions written on the machines and follow them.  
I would count the repetitions.  
I would think, "I managed to do this much today."

I never had a personal trainer.  
I had never seriously studied muscles from a scientific perspective, either.

Still, I believed that exercise was good for my body, and I genuinely enjoyed it.

But after fracturing my left upper arm and beginning rehabilitation, the way I think about muscles has gradually started to change.

At first, I could barely move my shoulder.

Because rehabilitation did not begin until about a month after the fracture, the tissues around my shoulder had become quite stiff.

But over the past few days, things have changed considerably.

I can raise my arm upward.  
I can extend it to the side.  
I can bring it above my head.

Movements that seemed impossible at first have gradually become possible.

The pain has also decreased considerably.

Of course, I still have some discomfort.

The movement that is still particularly difficult is external rotation.

With my elbow kept against my body, I move my forearm outward.

That movement still does not go very far.

The muscles around my shoulder are still quite stiff, too.

My rehabilitation therapists are designing exercises based on the condition of my muscles, incorporating external rotation and extension.

Sometimes I use a strength-training machine.

When I do, the therapist slowly counts, "One, two, three..."

I exercise for ten counts and then rest.

Sometimes I go to fifteen and then rest.

That is when the therapist told me:

"Muscles should not be overworked. Rest is important, too."

That made me stop and think.

I see.

So muscles are not something you simply make stronger by doing as many repetitions as possible.

What had I actually been doing at the gym all those years?

What exactly is a muscle?

In my registered sales clerk studies, I have learned the terms skeletal muscle, smooth muscle, and cardiac muscle.

Skeletal muscles are muscles that we move voluntarily.  
Smooth muscles are found in organs such as the stomach and intestines.  
Cardiac muscle is the muscle that makes the heart beat.

I know these terms.

But if someone had asked me, "What exactly is a muscle?" I would have realized that I knew very little.

Muscles are made of proteins.

But they are not simply lumps of protein.

There are muscle fibers, and within them are even more detailed structures. Proteins such as actin and myosin work together to make the muscle contract.

When we do strength training, muscles do not simply become stronger because "we used them."

They receive a load, rest, use nutrients, and adapt to the stress.

Only now am I beginning to truly understand this.

And it is not just my shoulder.

I also have pain in my knee.

For about two years, my left knee had sometimes hurt on the inner side when I did breaststroke.

When I had an X-ray at Bethel Hospital, there was no abnormality in the bones.

Later, an MRI at Dogo Onsen Hospital showed a small tear in the meniscus.

For now, surgery has not been recommended. I have been doing therapeutic exercises such as bending and straightening my knee and raising my leg.

Walking is not a problem.  
Going up and down stairs is also fine.

However, it hurts when I squat down to pick something up.

It hurts quite a lot when I bend my knee deeply, as when sitting in the Japanese seiza position.

Tomorrow, I will go to the Japanese Red Cross Hospital for my approximately three-month follow-up examination for my left upper arm fracture.

The main examination will be an X-ray of my shoulder, but I also plan to tell the doctor about my knee:

"I have no trouble walking or going up and down stairs, but the inner side of my knee hurts quite a lot when I squat down or bend it deeply, as when sitting in seiza."

The meniscus is not the only structure involved.

Around the knee are ligaments, tendons, muscles, and many other tissues.

The knee, too, does not move because of just one part.

Thinking about this makes me wonder if the same may be true of my fracture.

On June 18, I was riding an electric tricycle and reached out to press a pedestrian crossing button without getting off.

I fell.

I fractured my left upper arm.

I know that a great deal of force was placed on my left arm.

But I do not really know what happened inside my body at that moment, where the force traveled, or how it was distributed.

The bone in my shoulder was fractured.

But perhaps the force also affected other parts of my body.

Of course, I still do not know whether my current knee pain was caused by the fall or whether it was something that already existed before the accident.

So tomorrow, I plan to ask the doctor.

If this accident had never happened, I probably would never have thought this deeply about muscles.

"I like strength training."

That was about it.

I used the machines, counted repetitions, worked up a sweat, and thought that was enough.

But now I find myself wondering:

What exactly is a muscle?  
How does a muscle produce force?  
Why does it need rest?  
How do muscles, bones, tendons, and ligaments work together to move the body?

Suddenly, all of this has become a mystery to me.

There is still so much I do not know.

But perhaps realizing that I did not know something is also the beginning of learning.

Today, I feel that I have moved just a little way from being

"someone who has always done strength training"

to being

"someone who has begun to wonder, What exactly is a muscle?"

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