I think you're not hiking enough to support mountain climbing. There is no substitute - exercise at home helps, but the only thing that keeps me hiking is hiking - pretty much every day I am walking the dog, every weekend I am hiking some trail.

Stair steppers, yoga, and things that work the body help. Go hiking more.
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"In the beginner's mind there are many possibilities. In the expert's mind there are few." Shunryu Suzuki

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