Maggie's Farm

Too bad they didn't include a link to the study so we could see the methodology.

Somewhat related: Weight lifting in old age does more than just keep your muscles strong.

Similarly, as a wise man once said:

“Has Easy ever worked as well as Hard? No. Next question.” -- Mark Rippetoe

Yep, things get hard, people move on. Or they look for excuses to give themselves permission to do easier things: "I need some unilateral work, so I'll do lunges instead of barbell squats." You don't need unilateral work, you need to do your barbell squats.

Maybe, but still, you don't need unilateral work, you need to do your barbell squats. :-)

Absolutely. One can't go all out all the time, because that would be silly. In general, mixing things up is good.

Here's my (extremely simplified) understanding of the way things work:

As you say, there are different metabolic pathways used by the body to move energy around. The key concept, I think, is that all these pathways are constantly in use, in proportions that are determined by the current level of activity. The advantage that HIIT has is that all those pathways are being used to their maximum, hence all are being trained and improved. At lower intensities, this is not the case, so HIIT gives you the best bang for the buck. As probably none of us here are professional athletes, we don't have the luxury of having hours and hours to devote to LSD training. And, of course, allowing for recovery is critical.

Having said that, you still have to train specifically for an event, whether that be a 100-mile bike ride, a 10K run, or an MMA bout. You need to train for your sport, but HIIT can give you a solid base of conditioning that is probably adequate for most physical activities that normal people will undertake.