This is another one of those topics from other journals I meant to get to. When I was overtraining and undereating, I used High Intensity Interval Training to break myself. It made me extra hungry and puffy, plus injured. I always had some joint or tendon that was really angry about sprints or jumping, but I'd always force through it anyway, especially if it was on some dumb %$# written workout schedule I was following. It didn't matter if it was raining ice, or there was only pain where my foot should be, I'd get it done. I also don't think I grasped that real HIIT is all-out and it's SHORT. If you can keep doing the intervals for for 30-40 minutes, then it's not that intense, and if you can do another 5 miles of steady cardio afterward, then you're really in the muck, overdoing it for the sake of overdoing it. You don't get the benefit of true, brief, intense HIIT and you pay a huge price.
I had to just stop. For a long time after quitting the gym I stuck to walking and Pilates and light weights, no breathless crushing of myself. I needed to recover. After a year or so of eating enough, sleeping well, and not "killing it," I eased back into occasionally doing intervals. I liked tabata intervals - 20 seconds work, 10 seconds rest, and you're done in 4 minutes. Four. Not 20 minutes of hill sprints followed by a 5 mile run. I'd literally do 4 minutes of kettlebell swings and snatches, then put my toys away and be done. I get much better results with that because: nothing breaks, my appetite doesn't quadruple, and I still have energy to move, work, and play for the rest of my waking hours.
I think the full recovery, the satisfying meals, the quality sleep, and the total lack of any bodypart that hurts are HUGE. Done in that context, HIIT actually creates energy instead of taking it away from me. I feel buzzed and energized right afterward and for the rest of the day. I'm also leaner and more muscular looking doing HIIT regularly vs never doing it. I know, I know, leanness is all food, so I can't really explain this one, except that maybe I use the food a little differently when my body is conditioned in this way? Or maybe my appetite is more appropriate? Or hunger signals more identifieable? Nothing you do for 4 minutes (or 10, or 12) has a huge impact on total calorie burn, so it's not that. It's interesting though. And by "regularly," I mean I do super challenging, lung-buzzing, queasy HIIT maybe once every week or two, and a tamer but still very challenging version three times a week or so, usually with body weight, jump rope, or kettlebells. I don't run outdoors unless something is chasing me, and I haven't been on a cardio machine in about ten years. I'm also not combining HIIT with long, heavy, exhausting strength training sessions in the gym, another way it used to go wrong for me.
Anyway, just some musings. I'm active every day, but I keep all of my deliberate workouts in the 5-20 minute range with two days per week being very short or easy. This leaves me so much energy to move around and live life! Something I never had when I was working out intensely for an hour or more a day.