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Perhaps this is why physical exercise appears to reduce the risk of Alzheimer’s disease[1]. Our lymphatic system relies on muscle contractions to move lymph. So, increasing exercise results in increased lymph flow, which might then clear more amyloid-beta from our brain.

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7113559/

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It’s funny, as someone who suffers bouts of Insomnia, I still exercise everyday, often kettle bell training with heavy bells which is pretty good cardio too.

What I’ve noticed is that I almost feel like I’ve had a full nights sleep after a workout. Before it, I feel groggy.

It’d anecdotal but it doesn’t just seem like it’s me who experiences this. I wonder if it’s the result of some type of “drainage”.

I have the same experience. I got four hours last night, but I worked out this morning. I feel almost normal.

You're definitely instilling a state on your body that's more normal. Being sleepy does make someone more prone to errors and injuries, though, so I wouldn't count on it as a substitute long term. Anecdote: I've also had a walk around the block help me sleep. Particularly if the house or bed is too hot to sleep.

Fascinating! As someone not familiar with how the lymph system operates, do you care to explain how muscle contractions outside the brain cause the lymph system in the brain to expel waste? I understood the blood-brain barrier sort of insulated the brain from a lot of this kind of thing.

Lymph is fascinating. It is your other circulatory system.

Capillaries are are so narrow they can only allow a single erythrocyte through at the same time. The pressure from your heart causes fluid leakage from the thin vessels. Lymph ducts/nodes help get this fluid back into your blood. Since the heart doesn't pump lymph, that helps move it through your body is actually your musculoskeletal system. That is to a certain degree true from your venous / return flow in your "normal" circulatory system, too. It's why your feet can swell if you're sitting down too much. I'd speculate that lymphatic flow efficiency has local and systemic elements that contribute to it (and so your leg muscles moving lymph help your overall lymphatic system health).

This didn't answer the question, like at all!

"I'd speculate that lymphatic flow efficiency has local and systemic elements that contribute to it (and so your leg muscles moving lymph help your overall lymphatic system health)."

Lymph system helps clear waste / ISF from the brain. Overall lymphatic circulation improvement from increased activity would intuitively improve lymphatic clearance from the brain. That would be true if there was direct lymphatic clearance or some indirectly / osmotic gradient driven process (I don't know which, or neither, is the case).

I'm no expert, but if the lymphatic system's flow is driven by the motion in its surroundings because the muscles and skeleton are in motion, maybe drainage just happens via gravity if motion continually alters momentum and gravity vectors? Genuinely curious too...

Am I remembering it incorrectly or did someone recently discover a mechanism for lymph to move through connective tissues (in particular, ligaments)?

Is it just about muscular contraction, or does any kind of motion have positive effect on the lymph system? Say a rollercoaster or jumping on trampoline.

I'm not sure anyone knows the answer to that in specific. In my experience, exercise is often followed by a nap and my inference is that clearing lymph from other tissues somehow encourages the body to also clear lymph from the brain, but I haven't actually found an explanation for how that works.

You might find this general overview of the body's lymphatic system interesting:

https://news.ycombinator.com/item?id=25427090

As noted by the article, it was only recently discovered that the central nervous system had lymphatic drainage (see [1]). I’m simply connecting the results of this mouse study with what we know about the lymphatic system, skeletal muscle, and the apparent benefit of exercise on Alzheimer’s disease risk, to form a hypothesis. I strongly suspect it’s true, but I cannot represent it as fact.

Edit: Here is a more direct answer to your question:

1) Increased localized pressure from contracting muscle pushes lymph away through a vessel.

2) Reduced localized pressure from relaxing muscle allows new lymph to refill the evacuated vessel portion.

3) Lymphatic vessels have valves that keep all this flow moving in the same direction.

4) Given that the lymphatic system is connected to the central nervous system, increased muscular contraction could increase drainage of the brain.

[1] https://www.nature.com/articles/nature14432

I was actually wondering today if hot/cold cycling the head could increase lymphatic drainage and increase cerebrospinal fluid cycling.

Cold shower, hot shower, cold shower etc on the head... Will I become mega mind?

It is pretty common to jump into a cold bath after spending time in a sauna

Regardless of actual health effects, it feels fantastic!

Yes it does but not sure if recommended for people with heart problems. But yes, hot cold cycles reset the nervous system and yes, it feels great afterwards. The worst I find is the initial moment before plunging in cold water and the more I hesitatie the harder it gets

The main psychological benefit of taking only cold showers over the last five months is practice with starting an action I don’t want to do, because oooh there have been times when I was already cold and despite knowing I’d feel great afterwards, the present moment was scary.

I’ve been wondering the same. I think of inducing heat/cold similar to turning a rusty spigot. The first few turns are difficult but the more you do it the easier it gets.

But do spigots in other parts of your body get turned that are also rusty, so to speak?

I notice cold/hot showers help my body regulate my temperature better, generally.

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