The energy thing, I have (like most people) a cruise-control instinct telling me roughly how hard I can push for the distance I'm running. But I do find it difficult to keep right on that edge. I'm able to do it when it counts, but it's mentally tiring. Outside of races, and depending on general fatigue, even dumb tempo runs can be a struggle.
But overall, it's not that I lack the energy reserves. It's the energy burning capacity that maxes out. The legs are burning, but the limiting factor is the overall general feeling of fatigue and discomfort, lungs struggling to suck in enough air, etc. I always took it for granted that this was the norm. I'm kinda weirded out that your legs would be the thing holding you back. But I think it may just be that I'm getting old at this point.
I wonder, in fact sometimes I think that maybe I don't know how to run
I mean how do you know you gave 100% of what you could give in a long race (10k, half, marathon)?
So far I encountered two type of races
1) I target a time, I follow the right tempo but at some point I somehow feel it's becoming too hard and that I may not reach it, usually I go a bit slower and finish the race suffering and below my target but not by far (my first half 1h43 instead of 1h40, my first marathon 3h39 instead of 3h30, 38mn20 instead of sub 38 at my last 10k etc...)
The reason that makes it hard are often due to a lack of experience in the distance at first and a lack of energy (didn't eat enough before/while my first half/marathon), or when it's too hot (my last 10k, one glass of water at 5k clearly wasn't enough for the race)
2) I target a time, I follow the pace and by the last quarter of the race I feel confident that I should reach it and even be able to beat it, I might then accelerate progressively
Funnily enough it happened at my 2nd 10k (45 -> 43.38), my 3rd and 4th half and my second marathon.
But I don't know how much is due to better preparation, and how much just to my race pace improving as time pass on and I continue to train regularly
Except for 10k (which at this point I almost consider as a "sprint") I also feel like I could have continue for a few more k at the pace I ran.
Like what should be the state you're supposed to finish in exactly in order to know you gave 100%?
I imagine it's closer to 2) than 1), but the fact I'm not exhausted by the end make me think that maybe my target time is maybe too high and I should have go for a more ambitous target?
Anyway I imagine it's a rather thin line between the two anyway and that reaching the "perfect" equilibrium is something is very hard to manage
Age might play its part too, I might as well get as more benefit from my age as I can