Maggie's Farm

It depends on so many variables. If you are under 35-50 and have stayed active You don't need a lot more. If you are hiking in 100+ temps, like the Grand Canyon rim to rim, you will need both endurance training and acclimation time. If you are not physically active you will need endurance training and lots of time to be ready for anything really challenging. If you go ultra-light your effort will be considerably less for the same hike.

Expect to not meet your goal. That could mean a 3-5 day hike ends in the 2nd day or it could merely mean that your 20 mile a day goal is cut in half but you finish the hike. If you haven't hiked a serious hike, i.e. multi-day 10-15 miles a day or a one day 15-20 mile hike probably you are in for a surprise.

At the top of the Bright Angel Trail in Grand Canyon is a short story about a young women who was an Olympic marathon runner who decided to hike down the trail to the river and back (less than marathon distance). She died on the trail from dehydration. What that story illustrates is that in addition to conditioning you need experience/knowledge.

Here is a suggestion I follow when hiking in hot weather. I carry powdered Gatorade and twice a day I mix up a quart of it and drink it as I hike. Any electrolyte drink mix will work.

Another trick for difficult hikes is don't fill your stomach. Eat granola bars or whatever you choose to snack on every 2 hours or so but don't eat a "meal". If you have considerable experience hiking and know your limitations disregard this because through hikers eat like two teenage boys. But if you are not accustomed to hiking a full stomach will grind you to a stop or worse. Pace yourself.

I stop to rest for ten minutes every hour. I typically don't even feel like stopping but I do it anyway. Over 8 hours it makes a big difference in maintaining your energy level.