Although most of the ground that we tread can run, not all are equally fit for it. A tough soil (asphalt), too soft (grass) or other very unstable (sand) can increase the risk of injury. If you can choose the ground you run, choose well!
It is the hardest, and it is usually recommended to avoid it if you can choose another more pleasant land.
Besides, if you run favorite races, usually run on asphalt, so from time to time you will have to roll on this type of ground to get the body a bit accustomed and avoid surprises.
In some cases (always rated by a physio) it is recommended to run on asphalt if the runner has problems with his Achilles tendon.
In short: the asphalt, if you can avoid as “main” soil better, although you can always do some other weekly session on it. If you can only run on asphalt, you do not have to injure yourself, but prevention is better than cure. Take special care in all aspects of your training (wearing proper sneakers, taking care of running technique, avoiding overexposure.
The lawn is the surface that meets the absolute requirements for running. It is a soft surface (although not in excess) and in most cases reasonably homogeneous (without bumps), so whenever you can, it runs on lawns.
It is only contraindicated in cases where the runner is prone to plantar fasciitis (then a harder surface than the grass should be chosen).
Although the tartan track is built for running, it is not highly recommended to do long training sessions on top of it. The tartan is made to return much of the energy so that it can be used to run faster, so although it is not as hard as asphalt, it is still quite a lot.
It is useful for days of series in which you want to measure distances, or to train at times when there is no natural light. For the rest of sessions better discard it, because in addition to its hardness, running in tartan is always very monotonous and the iliotibial belt suffers more than usual for running in a curve (although the exterior streets minimize the effect).
The treadmill is the joker for all those, who do not have the right climate (in winter you will be warm and in cool summer in an interior). For those who enjoy that they are in the gym and want to combine bodybuilding + aerobics, and for those who do a little cardio but do not usually run more than twenty minutes each session.
While it is true that it is a hard surface, it is less than asphalt, so the belt is more favorable in this respect.
Another decisive point of the treadmill is that it can be programmed for a specific incline (ramps), which can be very useful if it is challenging to find inclined terrain in your environment. Also, if you do not have a heart rate monitor or a GPS, the tape can be a good data logger (calories, rhythm, distance) and if you have one, many of them can be synchronized with this type of machine to obtain extra training data.
As a negative, the tape is much more boring than the outside (so the training can be made much heavier), and you have to take a higher concentration, you can have some fall.
Depending on the terrain you must take more care or less for possible kinks or falls, and if the terrain requires, wear good trail shoes , but as a general rule is a suitable terrain, good to get out of the rut and run more close to nature. Running the countryside recharges the batteries and motivates you more.
Although the sand on the beach is very soft, it is also very unstable. It would be just as harmful to start running barefoot on a trampoline, even if it is a soft soil, with so much instability, is useless, only to increase the risk of injury.
Another thing is the sea (compact sand) that can be an excellent floor to run if you do not have much inclination and always with the shoes slipped.
Roads of gravel and tracks (forest)
They are also recommended soils as the lawn. Although at first glance they can give another sensation, they have some softness and offer to cushion so that our legs do not suffer as much. If they are not very broken, they help strengthen the legs, but it is better to run with one eye on the ground to see where they put their feet in case there are irregularities.