I have a reoccurring problem when runs up to 10k are easy peasy comfortable and no pain-around a 4:40 pace. But as soon as I try to go upwards of 15+ks I always pull up afterwards with a very sore left knee.

When I last ran a half I couldn’t run for another 2 months...

I have broken the tibia of this leg many years ago so not sure if this is relegated but interested in anyone’s thoughts on why this is happening and what I can do?

Is it that my form is breaking down as I get tired, or just a build up over the additional ks that leads to the pain?