Here's one better. It's a type 2 diabetes study that compared exercise against metformin against a placebo. The conclusions were so overwhelmingly in favor of exercise that the study was stopped early.
Two of four subtasks that reflect complex cognitive speed (Stroop color/word interference and Concept Shifting Test) showed main and interaction effects with age of aerobic capacity in a hierarchical regression analysis, accounting for up to 5% of variance in parameter score after correction for age, sex, and intelligence main effects.
Still, that study is rather weak evidence. The benefits could be relegated to preventing decline in older people. Anecdotally, I do feel duller on days when I don't run; even if I didn't, I'd still exercise. It helps me relieve stress.
In terms of general benefits, most people would be better off if they exercised more, not less. I mean it's not like fit people wake up one day, look at a mirror and see a firm, toned body with six-pack abs then scream at the sky, "Nooooo! Why me?!"
...really? It seems stunningly obvious to me that exercise and a good diet is good for overall health and mental health. I think the burden of proof is on you here. Or are you just positing that exercise+diet has no impact on productivity, not health?
well, Ritalin, at least, is supposed to do different things to someone who has ADD than to someone who does not, (I mean, personally, I can sleep while taking the stuff) but for me, exercise and diet help, but not 1/10th as much as the drugs. (Note, my experience has been that exercise /and/ the drugs work much better than the drugs by themselves.)
I'm in a lazy state at the moment (where I have lived most of my life), but during periods where I exercised regularly I have had much more energy and drive.
It really is habit forming, though once you fall out it's hard to get back in. After all, being lazy is habit forming too, and once you've stopped accounting for gym time in your day it can be hard to start squeezing it back in.
I'll be the outlier: as far as I can tell exercise does absolutely nothing for me mentally. I've started exercising more in the last year to improve my health and appearance (to be honest, not in that order), and have gotten some positive results there, but I've noticed no short or long term change in my cognitive skills or ability to focus.
what ive found is a 0 sugar, 0 bread, very low-carb diet makes a huge difference in my ability to focus. as your no longer riding the daily ups and downs of the blood sugar roller coaster.
.. certainly not easy to kick sugar/bread/milk habit.
But, if you need a bit... it works for me. When I am hiking or skiing 3-4 times a week, I get a lot more done.