Why? I run every other day for longer distances (10k or so) and imagine that the benefits of running for 10k are greater than 5k twice. I notice that my heart rate tends to be higher toward the end of a longer run - presumably because my muscles are more fatigued. Pushing to fatigue (but not so much as to lose running form) seems to be the best way to get muscles to adapt.

So I stand by what I've said: I think that in the beginning it's very important to establish a habit, and for that, running every day a little is better that running once a lot, and then never running again for a long time (because the "habit" didn't stick). I've also found that running every day works better for establishing the habit than "once a week" or whatever, since it's easier to be tempted to shuffle the day around and in the end not do anything.

I think that if you're considering whether you should run 5k every day or 10k every other day, you probably don't have an issue with actually getting out there, in which case this is a whole other debate, and I have nothing to add to it seeing how I'd have a hard time running a 10k.

Also, if you've got some other motivation source (say you absolutely want to run a marathon, or whatever) and you don't need a "hack" or to "trick yourself into liking running", this debate doesn't really concern you since it's about a problem you don't have.

There are also pros and cons of shorter and longer distances. Ideally you are running faster on shorter runs and a bit slower on longer runs. Getting in HITs occasionally will improve your long speed and help prevent injury. It is also a great thing to do on days you only have 10 minutes.

You can also ask “Why?” about this assumption.

I personally view cardio as just a means to improve my cardiovascular system, not muscles. So I just do boring steady-state (where I can easily rap out a song or sing Bob Dylan's lyrics).

If I want increased mitochondria and the size of the muscle cells, then nothing beats an even more efficient method of strength training. Just 5 minutes of work (1 minute per set) of lifting a heavy weight for 5 times. But even here there's concept of RPE where you don't accumulate as much fatigue as you might think.

I first did strength training and my resting heart beat dropped from 75 to 60 after about 8 months. After that I started doing steady-state cardio of 30 minutes on rest days and it's now at 55 after 3 years.

You can easily take a 5km run and increase the effectiveness: go faster.

Fitness runners always fixate on distance. No speed, power or agility training.

I am not saying there is a need for speed, power, agility training as well, but I think it is achieving different things than long, slower runs.

It’s the same way I managed to start exercising, with extremely low-effort, easy and short exercises. I now do app-selected exercises that challenge me, but I never before was able to stick to those, doing "too easy" exercises was what helped me manage to actually get into a routine.

Much of the health benefit from running is also available from briskly walking a couple of miles on a regular basis. Higher intensity training builds cardiovascular capacity, but the health benefits happen at intensity levels that don't really do that.

https://www.active.com/health/articles/why-too-much-running-...

You should see the anorexic-looking treadmill runners at my gym who have no muscle type IIB. I bet they already have cardiomyopathies / hypertrophies and will regret their extremist, extremely-unwise lifestyles when their joints need to be replaced in 20 years.