I'm a long time browser posting for the first time. I'm posting because I have some concern that my max heart rate has seemingly jumped up suddenly, and don't have any idea what could have caused it to do so.
As a background, I use a Garmin Forerunner 45 to records my runs and heart rate, and I have always found the heart rate measurements to be accurate. I have never noticed any wild spikes and the sensors seems to pick up slight fluctuations in heart rate caused by mild inclines.
My 10K PR was back in late August, when I recorded an average HR of 171bpm and a max HR of 180bpm to get a time of 39:26. I was working hard that day and felt close to my limit. I don't know what my actual max heart rate is, but 180bpm on that run was the highest figure I had ever recorded and I assumed it was close to my max. I only held the 180bpm figure for 20 seconds or so.
I don't believe my fitness has changed much since late August, but I have taken the previous two weeks off running after typically running a 10K 4-5 times a week over lockdown. The first week I took off running was because I was on a cycle tour where I did become significantly fatigued towards the end, and last week I went on a mild/moderate hike each day (lots of hours walking, but at a low HR).
Now having started running again, I've noticed that on each of the three 10K runs I've been on my heart rate has gone above 180bpm. On one day my heart rate even reached 185bpm, which isn't a figure I've ever recorded before. The times for the runs were 48 mins, 49 mins, and 45 mins respectively, so between 5-10 minutes off my PR. There was around 100m elevation gain on each of the runs, and the 180-185bpm figures were each recorded during the climbs, so I don't think there is something wrong with the watch. But I was surprised to see the HR figure so high. This is a course I regularly run, and usually expect so see my heart rate in the low 170s when pushing up the hill. but on none of the three runs did I feel like I was pushing that hard, so I'm quite concerned to see this sudden spike in max HR figure recorded on my runs.
Is my heart rate/body trying to tell me something? Should I be concerned based on the limited information available? Is this something commonly seen? Thank you all in advance for your help.