I don’t know your max HR but if it’s anything close to 180, if you are only getting to 136 hr, then you aren’t doing anything even close to vO2 max and you need to be working way harder. VO2 work should be very difficult.
I’m not a cycling coach… but i’ll talk anyways… I did the below and i really liked the results… my 5’ tests increased by 8% comparing before and after. YMMV and perhaps you what you really need to do is develop a larger base and higher volume so that your FTP will go up first but idk… since we are talking about how vO2 should feel harder, here is how you could make vO2 harder and likely more beneficial:
here is a 3 week vO2 block based on a 3-day per week block periodization scheme that i recommend: (block periodization is recommended here because you seem to have a high aerobic capacity relative to FTP and is more likely .)
do your VO2 interval work as RPE based maximal efforts at high 100-110 RPM cadence. cadence is more important than watts and you should feel as you are working as hard as you can but don’t blow yourself to pieces. you need to be able to repeat your maximal efforts.
the point of this type of vO2 interval is to start out hard to immediately drive yourself into a state of maximal oxygen consumption, so you should be going maximal right from the start, and let your watts decay but don’t let your cadence decay.
taper for a week of endurance/recovery only then do a maximal effort 5’ test on day 6, rest on day 7…
day 1 short recovery ride to refresh legs after rest day,
day 2 do thorough warmup then do 2-3x6’ maximal efforts with 4-6’ easy spin rest between intervals
day 3: do thorough warmup then do 3-4x5’ maximal efforts with 4-7’ easy spin rest between intervals
day 4: start an easy ride, if you feel okay then do optional vO2’s: 4-5x4’ maximal efforts with 4-8’ easy spin rest between intervals
day 5: long endurance ride, (do your usual duration)
day 6: long endurance ride, (do your usual duration)
day 7: rest
day 1: recovery ride with 5-10x1’ low power/high cadence spin-outs sprinkled in
day 2: recovery ride all easy and keep it short
day 3: do thorough warmup then do 4-5x4’ maximal vO2 efforts with 4-6’ easy spin rest between intervals
day 4: do thorough warmup then do 5-7x3’ maximal vO2 efforts with 3-6’ easy spin rest between intervals
day 5: do thorough warmup then do 7-10x2’ maximal vO2 efforts with 3-6’ easy spin rest between intervals
day 6: go ride how you feel. if you’re completely dead, don’t ride, if you are tired, recovery, if you are still fresh, then go hard… but no one is really fresh after this.
day 7: rest
taper for a week of endurance/recovery only then do an opener workout on day 5 and the same maximal effort 5’ test on day 6, rest on day 7…