Any three exercises, three sets to failure.
My goal with the Bloody Nine (or B9 as my friend now has me calling it) was to inculcate a basic, progressive / training-level fitness routine that could fit into any day, no matter what.
A few weeks in, my biggest problem is motivation, but I'm working on that — I've made at least 3x week, usually 4-5, and I'm on a four-day stretch now, so that's hopeful. But I feel like its full potential is lying in the daily application, so my goal for the next chunk of time will be to stick that landing.
Even so, I'm really pleased with it. I'm not good at planned/regular practice; my nature is to just kind of shuffle through things all the time, practicing what I can when I can. This means it's really easy to throw me off of streaks, though (especially since life tosses me many curveballs). The B9 has several important benefits that count for maintaining it, and account for why I've been doing as well as I have with it, slip-ups aside:
* It's fast — 20m or less, depending on how fast your exercise is (see below for slow exercise note). That means it can get done in those little "oh hey I'm ready a little early" slices of time, or before bed after you've already given up on getting anything else done for the day — it's just, like, 10-15m, yo. Even on some otherwise terrible days, I've managed to make it happen because of that.
* It can accommodate ANY terrain: bedrooms, hotels, campsites; you could even do it bedridden. (I did do it for a couple days when I was stuck on the couch with a pulled back-muscle.) And working around any injury is not a problem. (Though exercises that don't strain the lower back are…tricky to think of. I did it, though!) It's just a matter of which 3 exercises you pick that day. …I was initially worried that having to make that many decisions every day would wear me out, btw, but it's actually easy and more of a fun logic puzzle than anything. And the endless variety makes it a LOT easier to swallow, boredom-wise.
* It succeeds as a training-level workout because of the lack of rep-counts, and I think this makes it a better stress-buster/mental-supportive workout, too. Rather than boredly counting, I deliberately try to lose count [NOTE: I do this by reciting the Troll Counting from Discworld: “One, two, many, many, many…”] and just focus on doing perfect-form reps until my body tells me it's time to stop. It's super relaxing, I don't have to write down *anything*, and I can feel myself getting better at things like squats, even with just the 3-4x/week version.
* It's also dirt simple to extend, if you wanna. Pick four exercises. Wham. Probably takes 5 more minutes. Or just keep doing sets-to-failure, after three — hell, maybe try to lose count of that too. :) I'm sure I'll be interested in adding more, once I get more used to the habit.
* Last thing: slow exercises are wonderful for use in the B9. I initially reserved them for when I was injured or feeling shitty, but I was wrong, wrong, wrong to do so — especially as a student of taiji! Sure, my sifu would make me silk-reel until my legs gave out during class, but somehow the thought of doing it in sets as like, part of a HIIT workout, never occurred to me. But lord, it's brutal and amazing! Silk-reeling three times to failure inside a quarter-hour is one *heckapants* workout.
(A small taiji side-note, too: When you ask about "conditioning exercises" at a traditional Chinese school, they look at you funny and tell you to keep working on your forms. Until you drop. And then doing them again. "Kungfu makes you fit enough to do kungfu. Nothing else will." is something I heard repeatedly. I've latched onto this and now I often make "repeat this taiji move until you can't" part of my B9. If you know some 'fu, incorporating it can be both fun and useful af!)