I agree with Renee. I used to get the rubber at the end of a 200 also if I ran the first part too aggressively. Now with a concurrent program keeping my speed intact all year while adding some 400 specific work I can mash the last 110 of my 200 and negative split by about 4/10’s. I’m 51 running 22.74 FAT so I don’t believe age to be a limiting factor.