My max HR this Fall at end of several 5K races with hard finish and sprint is around 185. I ran a 5K race on Saturday at an avg pace of 6:29 with temp. at 40 degrees. My avg HR during race was 162. I have raced ten 5Ks and 10Ks this year and my avg HR has been between 169 - 172 including a race a few weeks ago with exact same temperature and conditions. My avg pace was 6:30 and HR avg was 170. My avg pace during all these races has been between 6:29 and 6:37. Yesterday was my fastest yet lowest HR avg by a lot.
My second mile was flat and I was running this at 162 HR avg. at 6:35 pace. Mile 3 I ran at 6:24 pace and my avg was 168 and I was picking up the pace the last half mile big time. My half marathon a couple months ago my avg HR was 165. Something is not right. My training has not changed other than taking some supplement with C0Q10, acetyl-Lcarnitine, and alpha lipoic acid starting last week. There is no way this supplement could have this effect. Is there any explanation for this HR differenc?