I jogged 3 miles in 30 minutes (my usual workout) and decided to tack on another 3 miles at 4.1 mph just to burn some extra calories because I felt like I had a lot of energy left. Well, the first 2 additional went fine but starting into the last mile I felt a bit hypoglycemic, I guess. I got a bit shaky and lightheaded and ended up stopping at 5.6 miles instead of 6.

The thing is that I've done 5 miles in a workout like that before, and even if I haven't done it recently it bothers me that I can't do 6, given the low level of intensity for the second half of the workout. I mean, people run 26-mile marathons. I realize I'm not ready for that, but I always assumed I could at least walk as much again as I jogged.

Since this isn't a muscle fatigue issue I am wondering if it's a question of building endurance as though it were a muscle fatigue issue, or if it's as simple as buying some Gatorade and sipping a bit in the second half of my workout.