In my teens I was in great shape, raced BMX, road biked, ran, karate etc. Between 30 and 50 I got soft put on an extra 40 lbs etc. Two years ago I turned it all around, lost the weight, hit the gym, and cycling has ended up being my exercise of choice weather permiting. Most rides are about 25 miles at my max warp couple times a week. I usally get two spin classes and weight training in a typical week as well. I am in good shape for a 1958 model. Have been a couple group rides in the 35 mile range with rests and food breaks no worries. So tried a 50 mile ride, no breaks at what I figured was a pace that would just about drain me by the finish. 30 miles no problem but at 40 I hit the wall I had never experienced it. I ate a couple energy bars, drank the rest of the single water bottle and finshed the ride with out too much trouble a bit under 3 hours. Once home I was a zombie, no energy, couldnt think right just felt like crap. I ate carbs and protein, drank lots of water and ending up going to bed till the next morning. Took another whole day to feel normal again. Of course I knew I should have raised my miles a bit at a time ,drank and more ate earlier but I guess I need to get beat up to learn. I have concluded that I am in great shape for about an hour. Bright side is I now have another goal..true endurance.