travel and rhum

Hi,
Next year I want to start some hiking in the Bavarian alps. Nothing super fancy with climbing or anything, but I want to bring my ham radio equipment, so I guess I will have some weight in my backpack.

I'm a reasonable fit person but I have no idea how inclined paths and an a reasonable heavy backpack will affect the distances I can walk. And I want to avoid i have to be rescued. So I plan to do some walks around were I live to see how much distance I can walk with a backpack. This way my gf can just come and pick me up once I'm exhausted, and I don't have to call emergency services.

Now to my question, how does walking on flat ground compare to walking up a mountain?

Additional information, I have a friend who goes regularly on hikes and I plan to go with him the first few times, but I don't want to annoy him with being slow or breaking down.

I have sprained my ankles in the past and, as a result, they are weak. I want to hike The Narrows in Zion National Park, but am concerned I may resprain an ankle on a slick river rock. Should I just skip this hike? Or, with proper equipment such as ankle braces would I be OK?