Where does running on asphalt fit on a continuum between packed dirt and concrete?

Anyone who runs always hears that one should never run on concrete, always run on dirt trails if possible, to ease the harsh impact on the joints.

But every once in a while I hear someone say “Well, at least he’s running on asphalt. It sure beats running on the sidewalk.”

So how bad is asphalt, compared to concrete? They both seem hard and they support traffic equally, but… I imagine that if I whacked a hammer on blacktop, I might get a loud “thunk” and leave a dent, while on concrete it would definitely ring more and probably not do a thing to the finish. There’s a difference in the surfaces.

But is that difference significant at all to a runner’s joints? Is there any kind of springiness that might help?

I remember when I ran in high school when it was hot, the asphalt had a definite give to it that the concrete did not. Not sure if that makes a whole lot of difference, but it might pile up.

I think the appropriate material property we’re looking at is stiffness.

Concrete’s stiffness starts at about 30 GPa.

Road asphalt, from what I’ve been able to dig up online, comes in at maybe a fifth of that, at room temperature.

That means at, for any given force (your foot hitting the ground for example), asphalt is going to “give” about 5 times as much.

According to Runners’ World, a list of surfaces in order of preference for your joints with grass as the highest:

Grass
Trails
Packed dirt
Cinders
Synthetic track
Treadmill
Asphalt
Sand
Concrete
Snow

Snow has less give than Concrete?:confused:

When considering joint health, maybe they are thinking about the likelihood of a slip & fall as a result of jogging on snow.

Of course by that standard, they should also consider the much higher chance that you’ll be creamed by some asshole in a Ford 2008 Earth Destroyer talking on his cell phone when jogging on asphalt.

Running in fresh snow is a rare treat.

It’s so cool to run along hearing crunch crunch crunch crunch as you go.

I imagine that the danger is more because the snow hides defects in the surface you are running on. You might not see a tree root that you will end up twisting your ankle on.

Thanks for the answers! It’s kind of neat to see that they did a “1-10” list, kind of like the mineral hardness scale that has talc at one end and diamond at the other.

But if they didn’t like snow, then wouldn’t they also not like grass, for the same reason? I never run on grass because I can’t see all the ankle-twisting ruts.

Packed snow, though, can be slippery, and the surface will be bumpy so that every time you put your foot down it will force your ankle to bend at a different angle. Sooner or later it could find an angle that your ankle doesn’t like.

The list was kind of “generally speaking” - when they talked about grass they were talking about, say, golf course grass. Snow can be slippery, turn to mud, etc.

I think YamatoTwinkie is correct to want to consider hardness, but also think it is only relevant if it is less than or somewhere near the hardness of other links in the system including the shoes, the socks, and the flesh under the foot bones. Clearly, these softer things are going to deform visibly, even if getting a good look at it is difficult. If you don’t leave footprints embedded into a surface, it can’t be giving enough to matter.

Most grass in florida has craploads of hidden defects, too. Of the three non-maintained-specifically-for-running surfaces I’d typically experience in town in Florida, impact-wise, I’d pick Asphalt, followed by a tie between concrete and grass, since the chance for twisting your leg on a hole is always there on grass.