Changes in stamina can so affect an outdoor plan that before you know it, you'll find that instead of enjoying another great trip, you're in danger of being unable to complete it. A steeper hill than normal may require more frequent stops to recover than you had anticipated. A heavily packed backpack may become a poor trade for a few hours of good hunting. And the return trip to your vehicle, which at the beginning of the day seemed to be about the same distance as your incoming trip, can be a real source of trouble as the day wears on. Start with a more honest baseline First identify your…