No Stupid Questions

All the people saying "yes" are incorrect. Running on pavement and running on trails exert different strains on the body, but not less. The tendency in road runners is to end up with tibial stress fractures, and in trail runners it is metatarsal stress fractures, but the injury rates are similar. Trail running requires stronger stabilizer muscles (primarily gluteus medius) to maintain knee health in the long term, but this is a problem for both as well.

Use good shoes, strength train your gluteus medius and calves, do most of your miles at an easy pace, and you'll be running for decades, regardless of your chosen surface. You might even change it up and do both!

(My credentials are that i am an ultramarathoner and have run half a dozen races between 26.2 and 50 miles, on pavement and trail, and i have been coached by a professional ultra runner for several seasons.)

Yes it’s absolute shit for your body. There is good reason why dedicated running tracks use a rubber like substance. Running in the woods is also a good alternative. Just not the rock hard surface of urban infrastructure.

There was a mini scandal at the Atlanta Olympics because they made the track surface very hard, to suit sprinters and long-jumpers (in the hope of new records, in sports where the US is strong) and it meant that some of the runners who usually do the 5k and the 10k (track) struggled to compete in both events. (The sprinters, of course, were not covering enough distance to care.)

I managed to track down a decent reference for it, which also addresses your question in some detail: The Hard and Soft of It

The Atlanta Olympic Track was built as hard and fast as rules would allow. I know because I circled the thing 49 times in the 1996 Trials before I dropped out of the 10,000-meter finals with one lap to go. Those Games weren't for me, and the concrete-hard track aggravated a case of plantar fasciitis that kept me from running more than a block for about a month after that.

On the surface, others had better luck: Michael Johnson and his golden slippers set world records later that summer in the 200 and 400; the former endures nearly a decade later. However, after Haile Gebrselassie won the 10,000 meters, he withdrew from the 5,000 meters, complaining of severe blisters on the bottom of his feet caused in part by the hard track.

But comparing trail to road is a bit more complicated. Trails can be pretty hard and also, not as smooth and even as (some) roads, and asphalt is different from concrete. The linked article has some good discussion of different surfaces.

Yes but you don't really start to notice the shock absorption difference and the joint pain until you're in your thirties or forties.

I'm close to 50, been running for decades, and still pull over 2k miles annually. Almost all that on asphalt. Haven't experienced any joint problems yet. I credit three things for that. First, modern running shoes are designed to soften the impact, and recently they have gotten ridiculously soft. The extreme cases give you 50mm (about 2 inches) of soft foam under your feet, but even more normal running shoes have advanced foam and bouncy elements in the outsole to soften the impact. Second, proper running form is not rocket science, and most people fall into a decent running form naturally. This form is the most gentle on the joints. And finally, if you are serious enough about running to go the distance where hard surfaces could be a problem, you are already likely to supplement your running with strength training, which further helps to protect your joints.

I'm an athlete and a biomechanics student who studies this sort of thing. Technically, if you do the physics, yes, pavement is harder than dirt. Will your body actually notice that difference given the forces that you experience from an easy run in modern shoes? Not likely. For a few hours a day, day in and day out over decades, then yes you will. But if you run a few miles once or twice a week, no, you probably won't see a huge difference. (And most trails frequented by runners are packed dirt that is not much softer than pavement. Getting onto shift and squishy loam tails isn't feasible for everyone.)

I used to get shin splints so now I only jog on jello

Yes. I ran on asfalt and my shins started to hurt a lot. Friend's an athlete and told me why it is. Started running on gravel and was fine.

I guess it also depends on how hard your dirt is.

Just jog on the beach with no shoes so you get those cool spread out toes

Yes.

Yes, this should be true.

Not a medical person, just common sense.

Definitely. Decomposed granite (that orange gravelly stuff) or dirt is much better for your joints and shins than running on cement.

I'm seeing that this matters for running but how about walking?

I think the influence of your weight, technique and muscles is much more prominent.