**Background:** I'm reasonably fit, I run and cycle fairly regularly (at least 10k run total a week and 40k cycle) as well as some weightlifting (3x a week, currently running GSLP). My running schedule usually consists of: - 5K race once a week (parkrun). - 5-10k endurance 'jog' (very comfortable pace). - 40mins interval/hill-repeats. This weekend I did a 14k run for the first time **at a comfortable jogging pace**. I have done 6-7 10k runs in the last 6 months but had got some energy gels and wanted to push to a higher number with a view to doing a half-marathon next year. My 5k race pace is 5:10min/km and my 10k relaxed pace is 6:20min/km I also recently invested in a heart-rate monitor (HRM) from Wahoo fitness (I have also checked its data against another HRM to confirm my findings). I used it on this run and knowing my maximum measured heart rate (from interval training) as 200... [![WTF][1]][1] **Surely something is wrong? I could have happily continued running for at least another 5k.** --------------------------------- ###Question: Would continuing to train at this intensity on my endurance runs eventually lead to a reduction in AvgHR? Also, ###Is this a sensible HR graph for a half-marathon? ###Are the heart rate zones about right? If not, how could I work them out? ###Should I re-evaluate what is a "comfortable pace"? [1]: https://i.sstatic.net/ASKKg.jpg