I've been running for almost every day for a little over a year now for high school XC and on and off before that. I started looking at heart rate on runs and they all averaged above 160bpm, even on easy days. I'm trying to run at 130-135bpm but can barely do it, going around 12 minute pace, and I haven't made any progress in about a week. Before I started going slow, I was running 8 miles in an hour (7:30 pace) with high heart rate and raced a 3 mile in 18:32, so I'm not super slow already. I also have a resting heart rate of around 48bpm. I know that the common response would be that I'm not fit, but I feel like I am. I just don't know what to do because I don't think I can last running this slow for so long.