Running definitely helps with my core and back also. The thing about running is that you have to make sure you don't hurt anything else. I prefer trail running much more because of the lower impact, but it's also convenient when I can go out my front door and do 2-3 miles in before it gets dark.I started walking 2.5 miles 3 days a wk, then upped that to a lw on my back with a 20 or 25lb plate strapped to it. Then running. I suffered shin splints for longest time when I started running. I just ran 5k the other day. Strange but my calves/ankles/feet hurt for days, then I run again and pain again. I'm over weight, but this is the first fall my lower back didn't go out. Has to be connected to the running, so I don't want to stop.