At 150% FTP, I would assume these intervals are very short. I’d suggest starting with 3 sets of 4x1 minute (@ 290-300W) with a minute recovery between intervals and 5 minutes recovery between sets and perhaps work your way towards 5 sets of 5x1 minute. I wouldn’t suggest “full gas” rather start conservative and progress slowly over the weeks. High intensity intervals put a lot of stress on the body and have the potential to cause soreness/injury if not eased into. I prefer completing these intervals on the trainer in “erg” mode as this allows me to track progress easily. I usually stay in the saddle and keep the cadence consistent on the shorter stuff as that is my preference. On a 3x20m, I will mildly fluctuate cadence. Try to fine tune your intervals to mimic your goal rides/races. Good luck!
I might think of this as energy system training rather than hill climb training.
I coach a number of athletes in a very flat area who are also forced to train indoors, a lot.
I do a lot of low cadence work, 50-70c, on flat terrain. Mostly seated but do include some standing work as well mixed in the sessions at certain times.
If you are training for hills that are this duration then you are doing the right thing.
If you are training for longer efforts and bigger climbs elsewhere, I would recommend looking at increased duration intervals, higher muscle tension work to simulate the effort of a longer climb.
Along the lines of what @steveneal is saying - what are your goals? Is it racing, general fitness, etc.? This will dictate your approach. The adaptations you seek will depend heavily on the stimulus you provide. That is, if you hit each interval full gas with plenty of rest between each effort, you can expect the stimulus to be more anaerobic in nature. On the other hand, if you do each effort at, say, 100% of FTP with shorter rest between each rep, the stimulus will be more aerobic.
My goal is mostly general fitness the racing series I was doing died with COVID. There is a place north of me that has some short punchy rolling hills that I like to go to. I also use my trainer to do 3x3’s and 5x5’s. Just been trying to mix it up some so that I am not doing all my intervals inside.
In this situation, selecting the terrain that would allow you to most consistently complete your intervals at your target power is key. If you have short punchy rolling hills, perhaps shorter intervals are in order. If you want to do longer sustain intervals, perhaps a longer climb or uninterrupted stretch of road you be better. Match the terrain to your needs.
davesans
I would first look at the demands of your events if you ride any? If not look at specific demands of your group ride as well as any goal you may have like increasing max power output or increasing your Vlamax whcih is your high glygotic power. Then use the bridge and % FTP power to create the intervals. Longer the interval, reduce power and shorter the interval stive for the higher or even highest power. Anorher strategy you can use is to do over unders ar hard starts. Realizing it sounds liek the bridge is about 1M you could to 15sec over at 150+%FTP, then 15sec at 110% and back and forth. Or, you could do a max 10-15sec effort standing, then settle into highest power you can generate for remainder. Look for decrease in power decay over the course of 3-6 weeks. Often doing this type of anaerobic and max power work will natually have power decay as you move thru the intervals, look at the % of power decay over the intervals in a given period of trining. have fun and train smart.