400 runner here, forgive my lack of knowledge on distance running, but I have a question pertaining to long run intensity. I do 2-3 "long" runs a week for basic aerobic conditioning and recovery. Intervals and the weight room make up the meat of my training as I'm a sprinter, but what is a good HR percentage to shoot for on challenging distance runs and recovery distance runs. I've been around 85% by the end of the challenging runs and mid to low 70% on the recovery. Too high? Too low? Thanks, again kind of out of my "comfort zone" on this subject