I’m a frequent zwifter, but quite undisciplined. Will pick a random workout or race when I have no time or inclination to exercise outdoors. No training plans or anything.
Zwift setup is a watt bike with chest heart rate monitor. Outdoors, running and biking, it’s a garmin vivoactive 3 with wrist heartrate . I’ve tried chest straps outdoors, not a fan.

I’ve found on Zwift, doing a high intensity block, say 30 seconds to a minute above ftp, my heartrate won’t hit its maximum until the end of that block, sometimes even continues to climb for a bit after.

Main question, is this real or is it likely a tech issue?

If it is real, can I train specifically to rectify this?

If my heart isn’t pumping blood and therefore oxygen to the muscles quick enough, am I likely to go anaerobic quickly and then suffer lactic acid build up?

I do have a fairly decent recovery rate, so it seems that I’m not moments from death, and also the tech picks that up fairly quickly.

Sounds normal? You wouldn’t expect to ring max HR on one min VO2max interval – maybe if you are quite young perhaps. If you’re stacking a series of them you will after a time, depending on recovery period.

Many variables – training programs will prescribe percentage increments over ftp for VO2 intervals, so obv there is a massive difference between one min at 105% and 130%.

FWIW, my heart rate also takes a fairly long time to respond (can be a couple of minutes to get up to max HR from Z2 for instance). I’ve never been concerned about it but I’ve never attempted to “train by zone” using fairly short intervals…

Completely normal, it’s why power is a much better way to measure performance – heart rate is always a little delayed, and can be affected by caffeine, stress, lack of sleep etc.

Your recovery rate after an interval will improve as you train, so it’ll start to come down sooner after the interval, and faster once it start to come down.

Here’s one of my graphs from Saturdays 1.5hr threshold workout, the 1 min high bits are at 307w and 321w and the low 2 mins just under FTP at 265w (my FTP is 279w).

30s to 1 min to go from some sort of aerobic HR to max seems somewhere between normal and quite quick. this is just the lag between effort in your legs and the heart responding. entirely normal.

If I do a 1 minute very intense interval, say 150% of FTP, i would expect my HR to rise close to max but only hitting a peak at the very end or even slightly after the end of that interval.

I opened this thread as i have had difficulties with my HR not rising to meet the demand from my muscles (known as blunting) but my issue has been my HR staying below about 70% of max, even when doing say 150% of FTP up a 25% slope – i was having no reaction whatsoever. That made any hard effort impossible. 5-6 weeks of complete rest seems to have fixed it for now. (However, I am being investigating for various other heart issues and cardiologist doesn’t think it was just fatigue)

known as blunting

Our local coach has this, he had an ablation and whilst it cured his erratic heart beat, his heart no longer responds to increased efforts until after it’s too late (e.g. until after he’s been dropped). He has good and bad days, on bad days we accidentally drop him on the flat, on good days he can stay in the bunch on climbs unless it goes ballistic. It’s made quite a difference, he used to be so much stronger than me, but not anymore.

5-6 weeks of complete rest seems to have fixed it for now

If the problem was CNS fatigue, it’s very hard to diagnose and take a long time to recover from genuine over training, where you’ve fried your CNS properly.