Balancing HR, watts & RPE to maximize 5x5 adaptation

Hello - I’m a 50-yr old cat 3 entering my 8th yr of structured training. This year i’m changing up my training plan, having done 10 weeks of neuromuscular work I’m on week 4 of 15 weeks of Trevor’s 5x5 twice-a-week program. My hope is this will raise my ceiling (which i seemed to bump up to mid-summer every year prior, only to get a second wind and my best numbers too late in September)

I’m having a difficult time balancing the goals as I understand them. I am targeting 90% of max HR and not going more than a beat over. I’m typically reaching this number during the 3rd interval; from there on out my wattage & RPE drop as i complete the final 2. No matter whether I start just below or up to 10% above FTP (+/- 270), i am reaching the 90% HR, backing off, only to ‘recover’ and rebound up to close to the wattage i started at.

I expect the suggestion will be too start at an easier wattage i can hold steady the entire duration. Doing so I’ll be at a 5-6 RPE which seems counterproductive (yes, i struggle going easy :-). I’ll also be noticeably under the 90% target HR for at least 3 if not 4 or 5 of the intervals. The later seems like it is not beneficial to the multiweek development.

Any insights or suggestions are greatly appreciated. Ultimately I want to do whatever is going to contribute to the greatest adaptation

I am also curious about this. I think that I am @jembow 's doppelganger. I’m 51 (race age), working on the 5x5s, and having a similar issue. I have not done any testing to measure my LTHR so I’m going off of the 90% max and it seems too easy for my HR.

I had a vacation/ rest week 2 wks back and have performed 4 more sessions since. I switched to ERG mode in an attempt to equalize the power across intervals.

I am doing these at 100% of prescribed power. Interestingly, I am now 10/20/30 watts lower starting off but still bumping up my HR max at some point in the 3rd interval. I having to back down the power 5-10% to keep under the HR zone. The RPE has stayed the same in ERG mode, initial 2 intervals are a 7-8 but once i hit the HR cap i drop to a 7 or 6.

Very strange to me that the lower initial power in ERG mode has not extended my ability to hold it later in the workout. 10 weeks left; hoping I’ll start to see some adaptation in the next few weeks

On A similar note, when doing certain such intervals like 4 or 5 minutes one can determine the maximal power for the interval from the power duration curve. So say your mean maximal power for 5 minutes was 250 watts, from a general training stress point of view what % of that should one anticipate doing a 5 minute repeated interval? Is there an optimal point since the power curve is not the same for every person that may have identical FTP/TP. Would it not be better to determine the amount or effort (power target) based upon the mean value from the power duration curve rather than FTP/TP/CP etc?