I am 43 years old. My LT heart rate was measured at about 170 two years ago. My maximum heart rate is about 193-5 depending on the day.
When I do high intensity workouts, say 3min intervals or hills intended to be just above LT, I notice the following pattern. I'll use intervals as an example, but a time trial on a hill would involve the same pattern.
1. I don't make the intended heart rate in the first interval, but my power is fine.
2. I can do about 2 more intervals with my HR growing healthily to about 170-174 and recover OK.
3. I can do 1 or 2 more where my heart rate gets higher and higher. I might do an interval at 184 and one at 190. I may or may not recover into the aerobic/recovery zones from these. My power is fine. My perceived exertion is quite high, but not ridiculous.
It is as if my body's ability to regulate heart rate just goes away and it keeps creeping up. My perceived exertion is merely "very high" during these efforts -- once I get in this mode, I can ride for 10-15 minutes at 188-192 on big hills, which is certainly a long way from my LT!! My heart rate won't get back to normal for the rest of the workout.
I don't get a lot of other 43 year olds with this problem or read about it much. Most posts here seem concerned by their low maximum heart rates, I'm worried about having a high one that I visit regularly. I have had an EKG and apparently no one is rushing me to the hospital. Anyone ever heard of this?