Its all that Zwifting that Whorty does that has helped him get his HR up

That and he is getting fitter. Carl, like AAAC says always a good idea to keep an eye on HR going down steadily following an all out effort even at your youthful age.
Mine is 10-15bpm more from zwifting than it ever was on bkool recently peaking at 187 on a Zwift training plan.. I think its because i tend to do longer fast paced endurance rides than shorter races. And that may be one of reasons why Carl has improved so much too? Of course, it could equally happen on the right TR training plan.
Mid october:
your peak 5 second heart rate was 181 BPM
- your peak 10 second heart rate was 181 BPM
- your peak 1 minute heart rate was 176 BPM
- your peak 5 minute heart rate was 170 BPM
- your peak 10 minute heart rate was 169 BPM
- your peak 20 minute heart rate was 166 BPM
- your peak 60 minute heart rate was 150 BPM