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Comment by levocardia | Hacker News Reader

Note that the comparator here is "exercise before bed compared with doing the same amount and intensity of exercise earlier in the day" -- NOT "exercise before bed compared with doing no exercise at all."

Actual RCT findings (e.g. [1]) find that exercise does induce beneficial changes in sleep, compared against not exercising at all.

[1] https://www.frontiersin.org/journals/psychiatry/articles/10....

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Purely anecdotal of course, but as a person that struggles to do sports consistently: for me, the thing you are saying this does not prove is absolutely correct. As far as my body is concerned, not doing any sports for months will get me way better sleep then when I do any amount of exercise after 6pm.

As a matter of fact, if I do exercise (cardio) that late, I can guarantee that I will not be able to fall asleep before 1-3 am. Even if I do it consistently for a few weeks.

Obviously just an observation of my own body. But it's the reason why I will no longer even attempt to do anything remotely like cardio post 4pm

I've found that this is true for not cardio workouts like climbing as well. It's truly unfortunate since that's typically when I have time, but staying awake until 2 isn't worth it.

Anecdotal support incoming: I work out twice a day, 15-20 minutes of lifting in the morning and 15-20 minutes of exercise bike in the afternoon. Have done for about the last 2 years. I also can't exercise after about 8 (I typically lay down for bed at midnight or so) or I'm up all night. I'm thinking that there might just be some sort of something in bodies where physical exertion induces a physical exertion mode to operate in that precludes sleep for a while. It kinda tracks in an evolutionary biology sort of way (despite that field being speculative an untestable): we didn't used to exercise. We used to exert ourselves when we needed to to stay alive and just sort of hang out and rest when we could get away with it. Having two modes, one that says "We're safe and comfortable and can lose consciousness for a few hours now" and another that says "Idk what we're doing but we're doing something and need to not fall asleep for a bit" has pretty obvious advantages compared to a system that allows you to take a nap in the middle of climbing a tree to avoid a predator.

More anecdotal data. I’m not a morning person by any stretch, but after decades of training on the evenings I switched to morning workouts where I wake up at 4am to get to the gym I’ve founf that I have less sleep interruptions, now I don’t if it it was due to all the water intake before or that now when I finally hit the bed I’m already exhausted.

often-enough after a meal, I feel an impulse to walk a little bit, and I do. I live in a 5-floor building with roof access, thus six total flights of stairs.

I find myself walking down from my middle floor level to the first floor, then to the top, and then the bottom, and the top again, often enough, after a meal.

My body contains 4.5 liters of blood and I sometimes imagine pumping it a few times through my system to help the rest of my body process the meal.

This is especially true if the meal was carby/sugary. Instead of lying there motionless and making my insulin do all the work of bringing my blood sugar back to normal, I imagine myself "pumping" the sugary blood through something that is happy enough to do something with the sugar (your/my muscles, as walking up 12 flights of stairs obviously accomplishes).

I am on the margins "athletic", but some days find myself at the end of a pretty sedentary day.

I _always_ am thrilled to have a single airpod in and listen to a book while meandering 12 flights of stairs, even if it's late, like, midnight. I've 100% done that a few times, and i find it helps me sleep well. Maybe the lack of exercise + insulin spike + no muscle activity usage of blood sugar would disrupt my sleep more than having pumped the sugary blood through muscles a few times.

I quite like this for me. I've lived in this building longer than I've made use of the convenience of walking up these flights of stairs. Some days I do 40+ flights of stairs!!! Even I am impressed. But doing them simply a few times a day, two or three trips. 12-18 flights at a time. Adds up quickly, obviously.

isn't it unhealthy to exercise after meals?

Depends a lot on the person and what they've just eaten and how they're exerting themselves.

Light to moderate activity to help keep glucose levels flat-ish is almost certainly a net positive.

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