Apologies for the long post, but this has been driving me mad.
I have been having issues with intermittent blunting of heart rate response for a few years.
First off, I’m a 47yo guy. Max HR is about 196. Resting is about 50. Lactate threshold is about 175bpm. FTP is around 305w. I ride about 8 hours a week, a mixture of indoor, outdoor road, and MTB. I’ve been riding at a similar level since my teens. I suffer from postural hypotension with syncope. Full cardiology investigation last year revealed nothing major.
A typical outdoor ride might be 3 hours, 160bpm average, 188 max, 250NP and 210 average power. Indoor, I tend to reach higher max HR, often low 190s with maybe an average power of 260w for an hour. I don’t sleep much, c6hrs a night, but that’s been the case for a long time.
Occasionally, I have a ride where my HR will not go above about 165bpm. I will be breathing hard, and the watts are there, maybe a sustained climb at say 350w for several minutes. the HR goes into low 160s and then just won’t budge. Lactic acid builds in the legs and I have to back off. I’m just unable to hold the power for any length of time. I might try a shorter effort of say 450-500w and the same happens. I can finish a 3 hour ride with an average of 140bpm, max of say 168 and literally 0% of the ride in zone 4, in spite of hitting steep hills as hard as I can, or trying to ride at FTP for longer periods. This even happened at reasonable altitude, around 3000m . These rides are just horrible. I can often tell in the first half hour whether it’s one of those days and I frequently bail.
(By “occasionally”, it could be anything from once a fortnight to every ride for two weeks, then ok for a couple of weeks etc. It’s not every ride (or i’d just conclude my max HR was much lower) but neither is it like once a month.)
The frustration is being unable to predict when it’s going to happen. Sometimes it will happen after a heavy week, so i think maybe it’s fatigue. Another time, it’ll happen after several days, or a full week off, so maybe not. Sometimes i might have had alcohol the night before or a bad night’s sleep, but then other times that hasn’t been the case. It seems to happen equally in the afternoon and evening as in the morning. I haven’t been able to connect it to diet or fluid or caffeine intake. It seems to happen just as much when relaxed and having fun (MTB) as indoors after a difficult day at work.
From what I’ve read, all these negative factors ought to cause an increased HR relative to power and RPE. I’m getting the reverse. For say an 8/10 effort, maybe 280w for 10 minutes, my HR stays way too low, doesn’t feed the muscles, and I have to curtail the effort.
This has often happened on the day of races and other important rides.
Can anyone suggest reasons why, on occasion, my HR just won’t respond to the demands from my muscles? What might i be overlooking?
Thanks in advance.