There are many reports of running being good for mental health (though the jury is a little out on how effective it is in comparison to medication for depression - running seems to be about equivalent to medication for mild depression). Speaking personally, I know that my mental health is always better if I'm able to run. But how does running help me specifically as a writer?
I feel that running improves my life as a writer in a number of ways, not just on the mental health side.
I stand to write, usually (see "Are you sitting comfortably?"). "Sitting is the new smoking" but also because I run, I try not to let my hip-flexors and glutes get lazy by sitting down all day. Not only that, but my core muscles are engaged in standing and this helps both with running and in preventing back issues. Several friends have said to me that they wouldn't be able to stand to write because their back is bad. I think that their back might not be great because they sit all day, but we always agree to differ! It also needs a sensible approach - it would be hard for anyone to go from sitting all day to standing all day!
But, even standing to write doesn't count as either aerobic activity nor especially as anything that protects bone-density. Current guidelines suggest doing at least 150 minutes of aerobic activity per week to protect cardiovascular health. Getting up, walking downstairs and writing all day, doesn't cut it! When I went out to work, I was very active - cycling to work; running at lunchtime etc. - but once I left and started working from home, I needed to build exercise into my day. Running was the natural option for me. I do recognise it isn't for everyone!
I don't consciously think about writing when I'm out running, at least, not most of the time. I'm focused on other things, like listening to the birds or watching where I'm running, or fastening the gates behind me properly if I'm trail-running. But if I've had a knotty problem or not been sure about a scene or a plot-issue, going out for a run generally lets my head have enough space that it can work on it without me realising.
I'm an outdoors person and a country person. I couldn't bear to live in a city again. I don't care if it's raining, snowing, sunny, cloudy... I love to be outside. That said, I find it really hard to write outside as I get too distracted. Since I live rurally, it's easy to get out into the countryside to run, which gives me enough connection to the world that staying inside to write for the rest of the day is fine.
4. Keeping me going when things are tough
Although I love running, some days are really difficult. Sometimes I can't run because of injury, sometimes runs are just horrible. But injuries or bad runs teach me how to deal with set-backs and to keep going. If I'm injured, I have to work round it and protect my body until I am fit enough to run again. Likewise, if I have a set-back in my writing - a rejection, or a tricky plot-issue to sort out or whatever - I need to look at it differently and find a way to maintain my enthusiasm and improve my skills. I may take a course on writing, or do things to make me look at the work differently - draw, work on character notes, do mind-maps... anything that keeps me ticking over and prepared, ready for being able to tackle the work again.
If I'm having a bad run, I have to remind myself, "It doesn't matter how slowly you go, just keep putting one foot in front of the other. Run, jog, walk, crawl... just keep going." And this is great advice for when writing isn't going well. It doesn't matter how slowly it's going, just keep putting one word next to another. You can't edit a blank page. If I can only manage 100 words in a day, so be it. It's 100 words better than zero.
5. Last but not least, mental health
I have "black dog days" though I would mostly say my mental health isn't too bad. I can recognise when my black dog is starting to pad after me and I have a number of coping mechanisms that I've honed over the years to try and fend him off. They don't always work, admittedly, but I think they head him off at the pass more often than not. One of the main mechanisms is being active and being in touch with nature and running ticks both of those boxes. Most runs make me feel good. Sometimes they make me feel good while I'm actually doing them, which is a bonus, but even a horrible run makes me feel good afterwards - I did it; I ran a mile (or 3 or 5 or 10). Even if the feel-good aspect is nothing more than "Thank God I've stopped doing that; that was hellish" I still feel good!
All in all, I believe that running helps me to write. It keeps me fit, it gives my brain space to think, it keeps me in touch with nature, it teaches me resilience and it helps my mental health.
What about everyone else? What helps you?