Your ability to recover would be more positively impacted by a caloric surplus and lots of sleep.
I might be talking out of my ass because I only recently have been reading/studying your books, but I can give you my 2 cents on why he thinks this from my limited perspective.
The train of thought must have arrived from the use "active recovery" for endurance athletes. In my experience, endurance athletes only do active recovery rides to recover from intense rides to "flush out the legs" and to enjoy themselves. As you mentioned, the metabolic system is completely different. Heavy weight lifting will not produce the sacroplasmic waste as say running for 30 minutes. The prevailing logic from this concludes "active recovery" is not necessary for heavy weight lifting. Furthermore, it is slightly detrimental if you're trying to gain weight.
Correct me if I'm wrong.
P.S.
I just started taking classes to get my degree in physiology, but from the impression I have now the only benefits is the anatomy, nutrition and the basic purpose for any given subject. None of it really helps for training. I don’t know what SBS is sometimes and what’s not in the academic world.
Your ability to recover would be more positively impacted by a caloric surplus and lots of sleep.
I don't know much about heart rates, but if you're in such bad shape that you think going outside is a workout then yes you need to do some.
How do you get your heart rate into the 130's just by walking around outside?
I can't back it up with anymore more than my own anecdote and some loose interpretations from the literature, so take this with a grain of salt, but:
1) The "concurrent training effect" between strength and endurance adaptations only tends to show up with large volumes of endurance work. So you get that "can I train for a marathon" crowd that still wants to squat every day of the week, or your bodybuilder types that want to do 3 hours of cardio a day going into a show, and I can imagine that they'd end up with problems.
Talking about going for an easy jog or sitting on the bike for 20-30 minutes a few days a week? That I'm not so sure about.
2) There's some sketchy evidence from the Kaatsu guys (yeah, I know) showing that there may be something to combining small amounts of strength-endurance or even aerobic kinds of work with straight-up heavy loading. Whether it's a combo of increased sarcoplasmic crap, or vascularization, or both (there's hints it may be both), I don't know.
Who's this beneficial for? Good question. We already know that getting blood pumping into a worked muscle, and getting that muscle warm and moving in general, does good things, provided said exercise isn't adding extra stress to the system. It could be as simple as that.
3) Speaking only for myself, I can note that I feel a ton better when I keep a tiny bit of cardio in my weekly routine (the above 20-30 minutes, 2-3 times a week). It makes my legs feel (subjectively) better, and I notice a difference in the gym as far as recovery between sets and such, compared to doing none at all. Maybe I could do the same thing by dropping rests between sets, but just going on experience, it seems to be a chicken-egg relationship there - it's easier to cut rest times if I'm already fit, and cutting rest times increases fitness in itself.
Could be placebo effect, sure. But in comparison to how I felt when I did *no* cardio at all, it's a night and day difference whatever the cause.
Now I can fully admit that I'm not coming from the same place as most guys on here - I've done my bulking and fattening, and I don't really have that need to add massive amounts of body weight anymore. I also remember what it was like being skinny and when I "couldn't put on weight", and at that point doing cardio was the last thing I was concerned with.
To those guys, I'm solidly with you - they probably don't have any need for any extra cardio. For a recovering fat-ass such as myself with more injuries than I care to count, it helps; even if that help is pure placebo, I'll take it. So in that sense I don't really disagree with you. I just think LI cardio *in reasonable amounts* can be slotted in for some people without destroying strength gains.
I'd think this would be much more relevant to the classic endomorph types, or even the skinny guys that are progressing nicely but have added a bit too much fat in the process.
That's quite a reasonable analysis, and I'd agree.
Please don't set me on fire for this, but isn't that the rationale behind using kettlebell swings to complement barbell training? The swing is a great movement: explosive and repetitive without banging the joints the way something like jogging would ("aerobics without the indignity of jogging"). Some powerlifters have labeled it "the expensive pull-through", but I think just as many or more have successfully incorporated the KB swing to improve cardiovascular capacity and to get some blood flowing through the glutes/hams/quads/adductors to promote recovery. (I also like KB windmills or armbars for increasing shoulder resilience.)