Context - - - - as it applies to me. When I am strength training in the gym for general conditioning, it is multiple reps and sets somewhere around 80% 1 max rep. If I fail to complete the last couple of reps in the last set, failure will depend on the fatigue I have going into the workout and number of sets.

Strength training to support sprinting is a different calculus.

Sprinting on the bike and training for sprinting on the bike is about max efforts after a prescribed warmup with long recovery periods between intervals.

With respect to 2x20 threshold efforts with 15 minutes RBI, performance on the second effort would be about my initial fatigue going into the workout, consistence of diet and carb fueling during the warmup and first effort and then carb intake for the second effort.

I just returned by Mallorca Spain last night where I did a mountainous route that featured 5 climbs over 25 miles with 2700 feet of climbing. The start of the course is a lead in to a 6.5 % grade. One descends and then starts another longer easy grade followed by a steep descent and then a climb to the top. I had to climb back up the hill I descended at the start of the ride on the return. My goal was to perform as well on the last climb as I did on the first.

I did the harder climbs at threshold, medium grades at SST and false flats and other stuff at VT1/ high zone 2. And of course, sometimes I would just coast along or ride recovery.

I had a solid breakfast start and I packed a lot of carbs to eat on the ride. I forced myself to eat the carbs during the ride and I stayed ahead of the game. The last climb was no problem, I performed well and beat a couple of Germans in some fun cat 6 racing up the final climb and I felt great at the end and did a practice time trial the next day.

None of the riding I did during the mountain ride or TT ride the next day was to failure per se nor did my power fall apart at the end. But I know myself and my capability and I eat a lot.

Finally, with respect to some intervals, yes, they should be done at maximum to get benefit, such as a set of 15 second max power intervals. And yes, the max power intervals will take longer from which to recover. And yes, max power sprint intervals are beneficial and improve not only sprint power but aerobic capacity and yes they require a lot of carbs. YMMV.