I referred to it in my other comment in this thread, but if you really want to boost your range, look into MAF (maximum aerobic fitness).
The general principle is that you stay in the metabolic range where you're primarily burning fat reserves rather than using glycogen. The body typically has sufficient reserves for about 30 minutes of maximum glycogen use. The faster you run, the more glycogen you're using compared to fat, and so the quicker you'll run out and hit the wall.
A lot of people don't get on with MAF because it forces you to stop running and walk a lot in the early stages (essentially, you have a target HR of 180-age and if your HR is above that, you switch to walking), and even when your body does adapt and you can keep running all the time, you have to run much, much slower than you think you're capable of and that you probably want to be running at. But, over time you'll find your body gets more efficient and your speed at the target HR goes up over time. But to translate it into normal terminologoy, it's like you're always training in zone 2, although for most people 180-age is lower than the calculated top of zone 2.
An anecdotal result is that I used to be exhausted at the end of a 5km because I was running as fast as I could. Within a few weeks of switching to MAF training, I was routinely doing 10km-15km without really feeling tired and within a month I'd accidentally done a half marathon (very slowly, of course) after getting lost and being stuck on the wrong side of the river for 4km longer than I planned, and then an extra 3km the other side. I was tired at the end of that, but I also never would have believed I was even capable of that distance a month earlier.
The general principle is that you stay in the metabolic range where you're primarily burning fat reserves rather than using glycogen. The body typically has sufficient reserves for about 30 minutes of maximum glycogen use. The faster you run, the more glycogen you're using compared to fat, and so the quicker you'll run out and hit the wall.
A lot of people don't get on with MAF because it forces you to stop running and walk a lot in the early stages (essentially, you have a target HR of 180-age and if your HR is above that, you switch to walking), and even when your body does adapt and you can keep running all the time, you have to run much, much slower than you think you're capable of and that you probably want to be running at. But, over time you'll find your body gets more efficient and your speed at the target HR goes up over time. But to translate it into normal terminologoy, it's like you're always training in zone 2, although for most people 180-age is lower than the calculated top of zone 2.
An anecdotal result is that I used to be exhausted at the end of a 5km because I was running as fast as I could. Within a few weeks of switching to MAF training, I was routinely doing 10km-15km without really feeling tired and within a month I'd accidentally done a half marathon (very slowly, of course) after getting lost and being stuck on the wrong side of the river for 4km longer than I planned, and then an extra 3km the other side. I was tired at the end of that, but I also never would have believed I was even capable of that distance a month earlier.