Decisions are backed by the environment (in a broad sense), so it's important to understand (for the sake of effectiveness) which changes can be done to the environment, to stimulate taking such decision[s].
I'll say one thing - my dad is 70, doubtful he's ever had a gym routine. But, as he's gained wait, he's had interest in better diet, losing weight. He told me he'd consider exercise. So I took him to his nearby gym, wrote down two checklists (an "A" day, and "B" say) and showed him the exercises, how weights & machines work, got him familiar/comfortable/unafraid of it. I think a big "friction" is people thinking "I have no idea what I'd even do in the gym". So having a plan helps that. That was a few weeks ago, and he's been in the gym a couple times a week in the morning. Super proud of him - as you can imagine, getting my older stubborn dad to learn a new truck is a tough sell!
Well, you can change your own environment. This is personal, but what has worked has been one of:
* Have a gym close to work (i.e. 5 minute walk or less) and a corporate culture that lets you take 45-60 minute lunch breaks. Bonus - I find this makes my afternoons much more productive.
* Live 6+ cycle-able miles from work and ideally have a shower at work
* Be a student with a gym near your classes and an hour or two to kill between them
When one of these things is true I always manage to get a decent routine going. Without that I have always failed. Moving away from southern California to a place where I walk and cycle everywhere has helped.
Depending on the social structure, problems of individuals may have a socialized cost; if this is the case, also people who don't give a flying raccoon or not, do actually pay for that.
Pretty much this. All you can do for most people is to be an example to them in this regard, and politely suggest getting some physical activity to them every now and then, if it comes up naturally in conversation.
They're all adults, in this age of information they all the facts available for such decision.
You could say the same about getting people to save for retirement, but then we tried making 401k plans opt-out and participation increased. We can dramatically change behavior simply by changing the default.
Sometimes there are obvious ways to do this--check here if you don't want to be an organ donor, click this link if you don't want half this raise/starting salary to automatically go into your 401k--and sometimes it's a lot trickier, but it still seems worth investigating in those cases.
It's not obvious how to make exercising opt-out, but I'm skeptical of any claims that we can't non-coercively change behavior until we investigate it a lot and fail consistently.
Some companies provide on-site gyms. Some have secure bike parking + showers. Some provide free or subsidized membership to nearby gyms (if simply subsidized, it could be made opt-out). Even something as simple as providing standing desks could make a difference.
Sure, they're all adults, but their behavior is still shaped more by culture and environment than thoughtful, conscious decisions. Why do I give the government an interest-free loan instead of minimizing my withholding and put it into an interest-bearing account? I know I have the fiscal discipline to benefit from this, but it's weird and not default, so I don't.
Trivial inconveniences are incredibly effective in changing behaviors. In many cases, we can adjust those inconveniences.
I know we could do all that, and it would likely be met with some success.
The point is - should we? Why waste all those resources in subtly coercing, conditioning and deceiving responsible, adult people into wanting to have better lives? The situation will self-correct in a few decades all by itself, and there is too many of us on this planet anyway.
I have a colleague at work who is younger than me, almost morbidly obese. He is fully aware of it, he even cracks jokes about it. He is interested in reading all the theory in the world about anatomy, digestion, dieting, excercise, even chemistry, but he is too weak-willed to actually hop on that bike (which he bought last year, yet to my knowledge never used so far), or go for a walk. But he's already finished the new Mass Effect game and is up to speed with all the TV series out there. Every now and then, I suggest that he joins us when we go out on light bike trip, or swimming in nearby lake in summer, but he always makes one excuse or another.
Another colleague of mine is slightly older, and used to be almost as obese as the first one. About a year ago, he decided to start cycling to work, and also do some cycling in his free time. He changed a lot, is much more lean (or rather less "unlean", he still has ways to go), and by his own words, feels much better.
Both of them have made their choice, and are making it over and over again.
That said, I'm all for teaching kids good habits, they do not know any better, and it is our generation's task to impart wisdom (or something we consider wisdom, anyway) to the next one.
The company I work for has showers, a decent on site gym and secure and convinient bike parking. All of that does get used, but the bike parking is probably 1/10 of the number of car parking spots and there aren't more than a handful of people in the gym in the morning.
This is in Denmark, btw, probably one of the easiest countries to bike in.
I really don't know how to get people to start exercising.
Decisions are backed by the environment (in a broad sense), so it's important to understand (for the sake of effectiveness) which changes can be done to the environment, to stimulate taking such decision[s].