"Cardio" is sort-of a misnomer because all exertion raises heart rate. However, it is a shorthand that people use for forms of exercise which do not use heavy weights.
Let's keep it simple. To put an activity in the cardio category, you have to be continuously sweaty and short of breath (but not out of breath - that is anaerobic HIIT exercise) for about an hour. I ignore heart rate, but many people keep track of it. Thus walking, hiking, comfortable swimming, biking to the beach, are not exertion in any sense. They are just "living life" - the rewards of fitness. You know it's exertion (aka "exercise", as opposed to recreation) if you'd rather avoid it, if it sucks to be doing it, and if you want a nap after.
1. So-called "fat burning" cardio. Another misnomer because this doesn't burn fat worth a darn (nor does any form of one-hour exercise). This refers to around 60 minutes of aerobic exercise at a pace short of sprinting but with the maximum pace you can maintain for an hour. This is endurance exercise which does not stress the heart very much but puts it to good use. Running, elliptical, stairmaster, speedy biking, treadmill, speedy swimming are all typical "fat-burner" exercises. I mix them up without breaks to avoid boredom.
2. HIIT cardio. This is true cardiac fitness training. Often, it refers to exercise with 10-60-second wind sprints (or even more for some people) of maximum anaerobic effort relieved by slower but comparably-lengthed intervals. If you can do those intervals for 10 minutes without a full break before the next round, I am mighty impressed. I can't. I can only do about 3 reps of intervals without needing a minute break to lean on something while trying not to barf. HIIT cardio might help you survive your first heart attack because it increases heart vasculature. Regular bouts of HIIT will raise your level of performance on the "fat-burners" too. For HIIT, I use speed rope, combat bike, sometimes Stair machine or ski machine. Could just do running sprints outdoors.
3. Calisthenics. An hour of mixed calisthenics with no rest breaks is "general conditioning." It combines aerobic cardio, some bursts of anaerobic cardio, some explosive movements, and full-body muscle use (but not strength building). Typical cali routines include burpees, step-ups, pushups, running in place, planks, dips, ball slams, box jumps, mountain climbers, kettlebell swings, squats with light weights, lunges, roll-ups, heavy ropes, band walks, jumping jacks. Some activities like martial arts or playing sports contain calisthenic-like mixes. However, bear in mind that athletes use calisthenics to train to perform their best in the sports themselves. Sports are fun, not physical training.
At my gym, the almost too-crowded morning (5, 6, and 7 AM) before-work classes are free with membership and combine calis with pure cardio. General conditioning. All ages, all shapes, but very challenging and exhausting for me. Truly, moving weights is less stressful in a way because weight-moving is horribly intense, but not continuous. You don't need a gym for calis. They do not require much equipment and are fun to do outdoors, like the army does.
Readers know that we feel that calisthenics are the ideal general conditioning sorts of activities, but that an overall fitness-building program has to include the triad of strength training with weights, calis, and a mix of the two "cardio" types. Nb: do not undertake a 5-6 day/week challenging fitness program without a stress test and physical, and a decent nutrition plan. Also, work up the intensity gradually, over a few months, but doing some of it almost daily. Starting from baseline, it takes one or two years of 5-6 days/week to get into decent condition for most people over age 35. Progress is slow, very hard, very unpleasant, and requires stick-to-itiveness, so it's not for most people and I don't blame them.
I don't blame them because most of the world aspires to life free of heavy lifting, so why would anybody do it voluntarily? The secret is that this stuff is great for energy, mental attitude and mental discipline, and a positive attitude towards life. I was thinking this weekend about how fitness has become part of the basic rhythm and architecture of my life with Mrs. BD. It's been an interesting addition, and another thing we do together.
