These natural surfaces also tend to slope, and this also creates a dangerous off-center force on the ankles and feet. Over time, running on uneven surfaces can result in tendonitis, inflammation of joints and tendons and even fractures.
To prevent injuries while running, the American Podiatric Medical Association recommends wearing running shoes that provide stability, support and cushioning based upon your foot type. Shoes should be designed to absorb the shock of hitting the surface while running. Replace your running shoes about every 350-550 miles. It is also wise to increase your running gradually, and follow the 10% Rule when training.
This doesn't necessarily mean you shouldn't run on the beach or on trails. Softer surfaces can be great for reducing stress and impact. Running on smooth, soft surfaces, such as trails, running tracks, dirt roads, smooth fields and sand is often a better option for many people. It is far less stressful than concrete and other pavement, but you need to pay attention to the variability in the trerain to have the safest experience.
When running on softer, natural surfaces, experts advise that you build up slowly, pay attention to the surface (watch for holes, rocks and other uneven ares), and use the right sort of footwear to minimize your risk of injury.
And no matter where you run, you should pay attention to the running surface, because changes in the terrain can occur at any time in any place.
The American Podiatric Medical Association
The American Academy of Podiatric Sports Medicine