Spencer is VO2 max repeats. Your VO2 max is said to be anywhere between 115% to 125% of FTP, so if you were doing the prescribed 120% it may be slightly below your true VO2 max. This would account for the VO2 max efforts feeling “doable”. In that case, just up the percentage a bit for those workouts. If you’re a punchy rider/racer and your fitness is aimed at crits or XCO, you should feel right at home with these workouts. “All” you have to do is hang on for 3 mins and then you get plenty of rest.
In contrast, Lamarck is a different energy system and mindset. Working at longer duration at FTP/threshold with minimal rest can be challenging for a punchy rider/racer. This is where I struggle as well as an XCO racer, but someone that does TTs would feel right at home. Also, if you go into Lamarck on fatigued legs it’s only more difficult. The way I’ve gotten through these threshold efforts is allowing one 20 second back pedal per interval. I tell myself I can backpedal at the 5 min mark for a quick rest. It gives my mind a mental out “should” I need it. Then my goal is to try not to use/need that back pedal. Then I tell myself if I used no backpedals in any previous intervals, I am allowed 2 backpedals in the final interval. Once the final interval comes along I normally don’t need any backpedals, but knowing they are available is all the mental game I need.
Exactly, you finished it and were pushed to your limit. With an IF of 0.92 for the workout (Lamarck) that sounds about right and you nailed the workout’s intention. Nice work and on to the next beating!