mrchad9 wrote:I never run. For me the best thing is to do/practice whatever it is you are practicing for. Running definitely is not required.
Since I never run in the mountains I never run to get in shape for them. Try a stairmaster. Or ride a bike (I don't do that in the mountains either but find it more enjoyable than running).
I think Mrchad is right on when he says "...do/practice whatever it is you are practicing for.". With that said I realize most of us aren't able to get out and hike most days. Augmenting this with routine cardio and strength training is ideal. Doesn't have to be running though.
Personally I don't do much weight-bearing exercise now other than working on my core, but I do run, a lot. For me it makes a significant difference. Since you asked, I do a long run every weekend, with 25m+ 2 or 3 out of 4 weeks (with 16m minimum), but I run trail ultras at altitude, so I'm not recommending this. I think for most of us to maintain a reasonable level of fitness 20-30 minutes of cardio 4 or 5 days per week is fine, with longer times if using a bike. Those days you are able to get out and hike on the weekend could be your long day, or try to do a longer workout (gradually increasing from week to week time and/or distance to avoid injury) with a lower level of intensity one day of the week in order to increase your endurance.
There are many ways to keep in shape. Perhaps good advice would be to find a routine that works for you that you enjoy and stick with it. If you don't have training partners, setting goals or events to look forward to are good ways to maintain focus.