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Comment by cdrini | Hacker News Reader

Clarification since a number of the comments are reading this as "strength training makes your brain stronger". This study looked at _motor_ neurons, not neurons in your brain. Motor neurons are the neurons between your spinal cord and muscle cells, responsible for transferring the signal from your brain to contract/relax your muscles.

I think it was already known that working out muscles increases the innervation (the resolution of how many neurons are attached to a muscle) of the muscles, which is the mechanism for increased motor control that eg pianists have. I think this study is shedding more light on process, and providing stronger empirical evidence for that exact mechanism. Very exciting that this might be used to help people recover from nerve damage/spinal cord injury!

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Worth pointing out: we have some evidence that high-intensity interval training actually does make your brain stronger, through an unrelated mechanism.

HIIT exercise causes muscles to produce lactate, which crosses the blood–brain barrier and induces the expression of brain-derived neurotrophic factor. BDNF is critical to grow and repair neurons, and we can upregulate it significantly by sprinting hard a few times a week. That's good news for those of us with only a few hours a week to work out!

Not sure if you get the same benefits from lifting? I haven't researched this in a while so my sources might be behind the cutting edge.

https://pmc.ncbi.nlm.nih.gov/articles/PMC6246624/

https://pmc.ncbi.nlm.nih.gov/articles/PMC6435829/

Great points, and thank you for sharing references as well! I was later thinking that I should have also mentioned that "it likely is good for your brain, just not because of the processes in this study". Maybe if I exercised more I would've remembered! :D

I have a unique related problem. My left leg calf muscle is almost an inch smaller than my right calf muscle. I just noticed it this year. Felt so weird. Why would there be imbalance in calf muscle growth to such an extreme degree. Then I tried to do a single leg calf raise on the left leg and couldn't do it. I still can't do it after 6-7 months. I must admit I am not training the left calf muscle at all, just the usual running and some sporadic squats.

This could have something to do with motor neurons not firing or something I don't know. I went to a physical therapist who suggested some calf and toe stretches and it seemed ridiculous to me. Like why would I exercise a muscle or a bunch of bones that is not functioning as expected, wouldn't that exacerbate the problem ? He didn't give a convincing answer but this paper makes me think he was spot on.

Isolating and exercising the calf muscles could probably help fire those neurons I don't know.I should do some more study on this. It's not debilitating now but I don't know what will be the impact on my balance 20-30 years from now. I am 47.

I have the same thing, the PT is right. Activating your big toe kicks off a chain of biomechanics up to your hip muscles (glutes) and will correct your gait and muscles that are not firing if you work on it consciously. I still deal with it when I forget the problem went away and sit in my computer chair all day leaning on one side not using my other calf.

Awareness is key and conscious work will activate it over time.

Do you spend a lot of time driving an automatic transmission? After putting 150,000 miles on my car, I'm kind of surprised I don't have more asymmetry in my legs.

asymmetry is fine but not able to do a left calf raise is a problem. I do drive an automatic yes.

More likely you favor one leg when exercising, which is common and needs to be adjusted for. Asymmetric atrophy creates a feedback loop which exacerbates the atrophy.

Maybe totally unrelated, but I had a PT say people that run or walk on the side of a road experience these kinds of asymmetries.

The side of many roads is graded slightly to drain, and if you have a habit of always walking on, say, the right in N. America to go with traffic, you're consistently training asymmetrically without realizing it.

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