Physiology isn't rocket science. It's harder.
Hi Steve,
More rambling: I latched onto this discussion out of curiosity too, just thinking out loud & hoping for guidance. Pavel was kind enough to start a new thread called "Super Fiber." There is such a thing: "The 'super fiber' is the IIA targeted with proper power endurance training. JMO" In my book, one of Pavel's opinions counts for ten of other people's "facts."
My thinking on the heart: 1st way cardio is: easy, slow, jogging, monotony, sustainable, LSD, aerobic, below threshold. 2nd way cardio is: hard, fast, sprinting, unsustainable, burst, intervals, anaerobic, smokers, above threshold. These categories are real, however you frame them.
By logical extension, 3rd way cardio should be something even harder than 2nd way. That's not possible. Once you're collapsed in the dirt, gasping for air, that's it. The one special category I can think of is rowing and hardstyle swings. The biomechanical breathing and Valsalva maneuver is supposed to strengthen the heart in a unique way.
Gallagher makes a category mistake. What he means by 3rd way isn't "even harder." It's something like "cardio with external resistance." Weights, rowing, wrestling opponent. But anything you do has to fall into one of the first two categories. The 5 & 10 minute snatch tests are 2nd way. But for you swings with 12 kg are so light that the effort is sustainable; 1st way. If I go for a brisk walk with a roll of quarters in each hand, that's also 1st way. The heart just beats fast or slow, and using weights is beside the point. There is no level even faster than fast. So that's why this discussion can't really be about the heart.
Gallagher uses the example of Mark Coleman and other MMA guys as the sort of superheroes this 3rd way training can produce. My outsider's understanding is that the training has evolved toward Easy Strength guidelines. Minimal, focused strength and cardio sessions that leave the athlete energy for practice. My source is Joel Jameison's site.
It sounds like you and I are both into GPP. Being able to carry a sofa, chase a bus, fight if necessary. I'm using the ETK standards as a proxy for well-rounded fitness, you're using GS competition. That's a whole 'nuther discussion.
The SAID principle is something of a chalkboard eraser that just wipes the slate clean anytime you start getting sciencey. Like Suzanne Vega sang, "Shove me in the shallow water before I get to deep." If you have exactly one clearly defined goal, such as rowing or GS competition, you can almost forget the science and just copy what has worked for other people. GS training for GS competition. If instead you are really into GPP, then it gets interesting. Either way, I'm incompetent to offer advice.
My only take-home from this thread is that swings are any amazing versatile exercise with carryover to deadlifting and running. I'm going to stick with biomechanical/bracing/Valsalva power breathing. Possibly I might grow myself a super hybrid warrior butt by going heavy & high volume.
Steve, thanks for starting up such a cool thread and good luck in competition and life!