The majority of my running takes place outside. On the road, on the pavement, on trails, on gravel pathways and through different terrains that use and build different muscle groups
It does seem weird that some people prefer running on treadmills than running the natural environment. Many seem to cite injury prevention, or soreness, as the reason they prefer the treadmill.
If I’m completely honest, I’m not sure if I consider treadmill running to be any substitute for turning the legs over outside. The artificial environment, not to mention the lack of different terrain types, lack of hills to develop strength and also lack of wind resistance, all make treadmill running less appealing to me. It’s not as much bang for your buck.
As for the injuries that treadmill runners claim to be avoiding, I’m sceptical. More likely injuries are caused by incorrect technique, poor choice of shoes and cushioning, rather than anything inherent to running on terrain.
Probably the best thing about doing your running outside is that you simply can’t switch ‘off’. If you run 5 kilometres away from your home, you’re going to have to somehow run or walk the 5ks back. It makes you work harder. And that makes you a better runner.