HIIT is the only efficient form of pure cardio training, and cardio is 1/3 of fitness maintenance and development. "Cardio" means stressing the heart and oxygen delivery. That is, it strengthens cardiac muscle, increases cardiac vascularization, and ramps up pulmonary function.
HIIT (High-intensity interval training) comes in many forms. As usual, everybody has his opinion about it. The general format is 30-60-second full-out sprints followed by active recovery (slow) intervals at a 1:1 or 1:2 time ratio. For me, the !:2 works best. For example, when I do HIIT on the treadmill I do 60-second sprints followed by 2-minute slow walks but I probably should do 30-sec sprints with 60-sec walks. Trouble is that it takes several seconds to get anything up to max speed.
- Speed? Obviously the pace of a "sprint" depends on fitness level. All that matters is that you give it everything you've got. Pace will improve over weeks.
- Warm-up? A 5-10-minute warm up before an HIIT session is recommended. My habit is a 10-minute low-resistance elliptical before I do any exercise at all. Gets everything warmed-up without fatigue and reduces risk of cramps or sprains.
- How many HIIT reps? Generally 5-10 is the limit. Stop when the quality of the sprints deteriorate noticeably. I aim for 10, but it depends on the day.
- Jump right in to HIIT? No, not if over age 40. Crawl, walk, then run.
- Does a tough hour of calisthenics count as HIIT? Sort-of, but not entirely. Thing is, people usually do not do calisthenics at max pace. They pace themselves (as do I) to be able to complete the routine. 60 seconds of max intensity/speed of jumping jacks is very tough. 60 seconds of warm-up jumping jacks is not so tough.
- How often can you do HIIT? As often as you want, but you won't have time for your other exercises if you do them daily.
- Does HIIT build strength? Really only cardiac strength. Keeps the muscles working and functional, though.
- Are things like Soul Cycle HIIT? Yes, they are.
- Does HIIT build endurance? Yes, generally-speaking. While some different energy systems and muscle fibers are activated by different forms of activity, a good sprinting regimen builds endurance. That's why endurance/distance athletes use HIIT in their training programs. Marathoners today run sprints to train, as do distance swimmers and bikers.
- What forms? Almost anything. Probably ideal to vary it week to week. Swim, run, speed jump rope, combat bike, rower, ski erg - whatever you can speed up and slow down with. I see good jumpers do 15 minutes of HIIT - with all the jump rope variations and the speeds up and down. It's like a dance. I can not do 15 minutes of jump rope at any speed.
- Time? Say you do a ten-minute warm-up and then 20 minutes of HIIT. What to do afterwards to fill out your daily hour of exercise? Well, I do whatever I want to fit in. Some calisthenics like pushups, pullups, curls, goblet squats, lunges, etc. Stay busy. There is no end to things to do. An hour goes by fast.
- What about weight-loss and fat-burning? No exercise does much for that. That's nutritional. If you are fat, you eat too much, and it will slow you down. Too skinny? Grab a Big Mac with fries.
- What about "Long, slow"? "Long, slow" exercises like an hour of fast walk, jogging, swims, biking, etc are fine for maintaining endurance but do not count as cardio training because they do not raise the heart rate high enough. As I have said, I often do an hour of "long,slow" weekly, mixing it up between elliptical, stair machine, and treadmill or rower unless there is a multi-hour hill hike instead. My genius trainer approves of these things as a "recovery day," not as exertion. For fitness beginners, though, they can feel exertional.
