I think you'll find the fat burn zone is around 120. 170 is...

I think you'll find the fat burn zone is around 120. 170 is reaching most people's max safe cardio rate.
From memory it's 220 or 230 minus your age should be the top safe rate and for cardio you want to be at about 80% of that.
Anyway, the fat-burning zone is a bit misunderstood, you'll burn more fat working in the upper range than spending a while in the "fat-burning" zone due to higher calorie burn (regardless of how many were from stored fat) and the after-burn metabolic lift.

- Just hoping to keep you alive since you seem to be a fellow sufferer of this frustrating long-term prospect of a stock.