This is the "crisscross" or OU workout. See here for a basic guide http://home.trainingpeaks.com/blog/article/3-top-indoor-cycling-workouts-under-1-hour
There are a number of reasons why it's excellent:
- It's at threshold. There is no getting away from the fact that if you want to improve your power you need to spend time in this zone. The standard workout for this is "2x20" or variant that requires you to hold threshold power steady for an extended period of time. When done on a turbo I find these pretty mind numbing. This workout is more fun since it breaks the long interval down into more manageable "very hard"/"slightly less hard" chunks. In terms of the end result the average power/training benefit will be the same.
- It's very time efficient. In terms of training stress/minute or calories burned/minute it's amongst the highest. Because the first part is slightly under threshold you can get away with a short warmup (or even skip warmup altogether and do the first 2 minutes as a fast ramp up to threshold. The first 5-6 minutes will feel very tough but by the end of the first interval you should feel normal). Also if pushed for time you can cut recovery, the description recommends 4 minutes, I find 3 is more than enough.
- It's good race preparation. The article mentions one, working in a small race group, but that's not the only example there are others. In the real world any course will have some bits that are tougher than others. The best way to pace these once they start requiring 20 minutes or so+ of effort is go a bit harder on the hard bits and a bit easier on the less hard bits. In the case of TTs the reason for this is basic physics, for long climbs its better not to change gear every time the gradient shifts since this wastes power.Also starting slightly under threshold is not a bad idea for events 20 minutes and up. You are unlikely to win them during the first 60 seconds but may lose them if you go off too hard and have nothing left for the hard bits/end.
- It's good mental training. Since it's more like real life its possible to imagine doing a real ride. If there is a particular course, e.g, a 10TT then you can set the O/U to correspond to its contours.
- Also the U sectors will feel, comparatively, easy. This helps with pacing as you can push harder for a bit if you know you will have a bit of a "rest" shortly. Having this in mind is also handy for the inevitable occasion when you pop during a threshold effort. If you can fall back to an effort that's still comparatively high then you finish better than if you crash right down to your endurance pace. You can see this happen on long climbs when some riders apparently drop off but then claw back and rejoin.
- It's hugely adaptable. You make lots of tweaks to keep the sessions varied/interesting and/or extend the area being changed. Just some e.g.s
- > Make the U lower (around top of Temp) and the O higher (well above threshold).This really will feel like being in a tiny group trying to get to the finish ahead of the pelaton.
- > Make U high sweetspot and O low threshold and increase the length of each work interval and reduce/eliminate rest. Eventually it's possible to do a full 60 minutes this way, I have found this to be the "easiest" way to do a sol one hour at close to FTP.
- > Make some of the Os much higher than the others and imagine you are in a race. The first could be first is trying to get a gap with a couple of others then hold it. The last is the final effort to hit the finish first.
- You can use the different sections to work on other things as well. E.g. varying cadence. One set can be done by keeping cadence constant and increasing resistance. The next vice versa. Or start the first section at 50rpm then increase 5 rpm each time until you max out. Or try getting the extra power for the Os through a specific muscle group, e.g. push harder with your glutes or concentrate on "scraping the mud of your soles" a la Some combinations may feel more comfortable than others, which ones may surprise you. Even if not just doing this will make the time pass quicker.
The first set of 3 was done increasing power by increasing cadence, then a second set of 2 keeping cadence more constant and varying resistance (which felt easier). Interestingly the HR for each set shows how each U has a bit of recovery following it being pushed up by the O. Quite apart from anything else this gives a handy check of my current FTP guesstimate.