For the vast majority of my runs I experience tachycardia in the range of 240
bpm to 250
bpm. I am 31 years old and should have a maximum HR of ~185. My resting HR is 45 bpm.
Some background:
Run 1: 5 miles, Max HR 247, Average HR 208, 34F, pace 7:54.
Run 2: 3.7 miles, MAX HR 253, Average HR 200 (it leveled off at 160 BPM after I stopped at the 2.5 mile point) 45F
Run 3: 5 miles, Max HR 210, Average HR 165, leveled off at 165 during first six minutes, without me having to stop. 37F.