The term "cardio" is commonly used in fitness these days. But what does it mean? And whatever happened to "aerobics"? The answers are a long story, or at least a long-ish post.
Back in 1968, Dr. Kenneth Cooper wrote the seminal book "Aerobics" and became known as the "Father of Aerobics." The book lists Cooper's top aerobic exercises as "running, swimming, cycling, walking, stationary running, handball, basketball and squash."
Today, these kinds of activities are typically called "cardio." So what's the difference?
"Cardio" of course refers to the heart, as in "cardiovascular" or "cardiogram" and is a Latinized version of the Greek kardia meaning "heart." (Hip kids also know that "cardio" can refer to intense make-out sessions.)
What about "cardio" workouts? One online definition reads:
Any type of aerobic exercise—treadmill, rower, stepper or stationary bike—which causes the heart to pump at 60% to 70% of its maximum rate; a [sic] optimal workout is thought to be > 20 minutes.
First of all, does anyone still use a "stepper"? Second, 60-70% seems quite arbitrary. And I have no idea why more than 20 minutes is an "optimal" cardio workout.
Anyway, these days people tend to call anything that raises the heart rate "cardio." But that makes it pretty meaningless. (This reminds me of the episode of "Chuck" where a drugged Ellie tells Captain Awesome, "If everything is awesome and nothing is unawesome then awesome by definition is just mediocre!" But I digress...) After all, lots of things can raise your heart rate: scary movies, too much caffeine, cats missing the litter box, etc.
Lifting weights would also have to be considered "cardio" as anyone who has ever done a heavy set of squats can confirm. And we wind up with "cardio" meaning nothing...or everything.
As previously mentioned, cardio refers to the heart. So what does "aerobic" refer to? The simple answer is: oxygen. Does that mean aerobics is anything that makes you breathe harder? Nope.
Your body has different "energy systems" for producing energy for activity. Keeping things simple (because this is a blog post, not a textbook), there are two kinds of energy production in the body: aerobic (with oxygen) and anaerobic (without oxygen). We spend the vast majority of our time producing energy aerobically. It's a very efficient and plentiful source of energy. Any activity you can keep up for a long time--walking or running, cycling, etc.--rely primarily on aerobically-produced energy.
Intense, power-oriented activities you can only keep up for a short time rely primarily on anaerobically-produced energy. This includes resistance training (like weightlifting), sprints (especially uphill), hitting things (a.k.a. "wapping"), etc. Note that it's the powerful movements that really tap the anaerobic system: throwing a punch or kick is anaerobic, while the movements in between can be fueled aerobically.
Now, there are generally two types of "cardio" bandied about: "steady-state" (or "low intensity") and "interval" (or "high intensity" or even "high intensity interval training" or "HIIT"). Steady-state cardio would include aerobic activities like walking, running, biking, or swimming relatively long distances at a fairly constant speed. These are the kinds of activities formerly known as "aerobics" (which made sense). It would also include "step aerobics" which is now known as "cardio step" because the activity level remains quite steady compared to the on-and-off (work-rest) nature of interval training. Same for "cardio kickboxing" which is not at all like real kickboxing. (The real deal is much more interval-y, even intra-round.)
Thus, "steady-state cardio" is better described as "aerobics" since it is driven by aerobic energy production.
Interval training typically relies extensively on anaerobic energy. HIIT always does (if you're doing it right). That doesn't mean there isn't an aerobic component as well, particularly during rest periods, but it's reasonable to not call HIIT "aerobics." So is it "cardio"? Only if you don't care about useful designations.
We can also throw something like metabolic resistance training (MRT) into the mix. There's no single definition for it, but it's generally doing multi-joint weightlifting exercises (e.g., squats, overhead press, etc.) without much rest between sets. So it's kind of like HIIT with resistance (barbell, dumbbell, kettlebell, resistance band, bodyweight, etc.) Definitely anaerobic in the work phases and aerobic during the rest periods (which are often "active" rest doing things like biking, rowing....you know, aerobics!).
And so we wind up with designations like:
- Aerobics: Cardio kickboxing, dance, zumba, cycling, running/walking (treadmill/outside), elliptical, rower, stair climbers or climbing stairs, jumping rope, step aerobics (which became "cardio step"), etc. I'd put interval training here, too--doing any of these things at low or medium intensity with regular rest periods.
- High Intensity Interval Training (HIIT): hill sprints, (real) kickboxing rounds, bike sprints, etc. Rest periods are kept short.
- Metabolic Resistance Training (MRT): High-ish intensity intervals using strength-building exercises (free weights, body-weight, machines, etc.) and very short rest periods.
If you want to use one general term for all of this, Alwyn Cosgrove uses the term "Energy System Development" (ESD) to cover developing the anaerobic and aerobic systems (and everything in between that we've skipped) as opposed to doing something like strength training--although it's anaerobic, we don't do it to develop anaerobic capacity, we do it to get stronger. MRT, on the other hand, can build strength but that's not it's primary purpose.
There you have it. Now I don't expect everyone to stop using "cardio" (just like people won't stop using "Tabatas" to describe workouts that are not max-effort) but at least you'll know how meaningless it is. Your friends might think calling some of your workouts "aerobics" is old-fashioned, but so are grammar, punctuation, and usage. Words have meaning.
Be seeing you.
-gary