Your HR looked to go higher later on just before the main road on the descent. I thought your maximum HR was higher than that as well but your probably still a bit tired which lowers the max you can get to. We really need a bigger lead into the hill as well.
Yeah, it never felt like I was maxed out HR wise, didn't feel like my heart was pumping too hard, but my lungs ached a bit and it was more just that my calf muscles couldn't stand it any more, so I think i need to build up my tolerance to lactic (or my mental toughness on that)...! You're right, it's a pretty hardcore start to the run to basically just hit a wall straight off!