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What Exactly Is Cardio?

Cardio is really a modern term that has grown to replace aerobic exercise. To avoid the stigma of the aerobic craze of the 70s people switched to cardio when discussing it relative to fitness and strength-training programs to disassociate with the aerobics-only phenomenon.
Cardio is short for cardiovascular exercise which means really any exercise that benefits the heart. This used to be mainly aerobic training but now research suggests that weight lifting also benefits the heart - this is an example of a phrase that became popular before science could really validate it.

Aerobic exercise is any sustainable activity that utilizes oxygen (ergo the burning of fat) for a primary source of fuel. Weight lifting that is intense and in short duration will primarily use stored glycogen and the ATP-CP pathway (intramuscular energetics with creatine phosphate that - adenosine triphosphate or ATP is broken to adenosine diphosphate and this releases energy. To rebuild ADP to ATP, the CP is split, lending the extra phosphate moelcule needed for ADP to become ATP and thereby fuel another reaction).

Now, this definition is muddied because you can have weight training i.e. longer sets that actually use oxygen and are therefore more aerobic (take circuit training, for example, when people aren't using a heavy load). You can also have what is traditionally thought of as cardio i.e. sprints that can be anaerobic depending on the rest. If the heart rate is allowed to lower between the intervals followed by maximum output then you are more in the anaerobic/glycolytic range. If you are only doing intervals but the heart does not drop substantially then you are going to be in more of a cardio range.

Basically, and this is a nutshell, oversimplifying because I've already gotten quite technical, there are primarily three systems that fuel energy. ALL energy systems are used to some extent, but various activity will use more of one or the other.

Anything lasting just a few seconds is going to be primarily anaerobic and use the ATP-CP system. This includes weight lifting, where the reps last a few seconds and are maximal bouts of output. Active rest occurs between the repetitions and then actual rest occurs between the sets. Shot-put, 50 yard-dash, weight lifting, olympic lifting, power-lifting are all examples of this.

Anything lasting a few minutes is primarily the glycolytic system where lactic acid is utilized to generate energy. This would be prolonged bouts such as sprints, longer weight lifting sets, etc. Basketball (run down court, then stay at the court = submaximal bout followed by active rest), and Soccer are examples of this.

Anything beyond that first few minutes must utilize oxygen turnover and therefore you are in the aerobic zone. This would be longer runs, rowing, hiking, etc.

Now, keep in mind there is no black and white with this - you still cross over into multiple systems. The reason why HIIT is more cardio than, say, a 20 minute weight training session, is that in HIIT on the slower intervals you are still performing work. Your heart rate drops somewhat but doesn't drop a lot and therefore is still elevated in its output - this means that oxygen must fuel the process. On the other hand, in typical weight training, you are resting between sets which allows adequate recovery for the heart rate to slow while the muscle energetics replenish themselves.
A long weight training session with short rest and a lot of supersets is going to be aerobic at the same time as being anaerobic during the sets - you are anaerobic to explosively move the weight but because you are not allowing your heart rate to drop significantly between bouts of work the entire workout becomes more aerboic.

Hope that helps - if you really want to dig into the details just search on ATP-CP or muscular energetics and you can get some good primers. Of course, then you might be forced to look into the Krebs Cycle and other pathways of metabolism and discover just why it is a gross oversimplification for people to say "this exercise burns muscle" or "if you exercise on an empty stomach your body is forced to burn fat"

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Comment by Jarom Thurston on September 5, 2008 at 2:41pm: Hey Mike....Stone Cold Steve Austin, huh...hahah...others say I look like Vin Diesel too...too funny. Anyway, to answer your question about what I eat on my ultra marathons....anything and everything really. It's a balancing act but really you just have to almost force yourself to eat and drink enough to keep safe. Because when you burn 500 - 1000 calories an hour and you are going for 10, 15, 24 or more hours in these races you can easily burn 10,000 - 30,000 calories. Yeah, crazy I know. Almost unthinkable, but it's nearly impossible to physically eat that much, especially when your appetite is gone and you feel nauseated which happens alot during Ultras. So what I do, and most ultra runners do, is carbo load like made the week before say a 100 mile run. Sometimes I'll gain 5-10 lbs right before a race because I know I'm going to burn it ALL UP. At the Badwater Race I weighed in exactly 10lbs lighter at the finish line then at the starting line 47 hours earlier...plus I ate and drank who know how much stuff...hahaha. So filling my body with loads of food and carbs and calories prior to a race is one way, the other is during the race. During a race I'll eat anything from P&B sandwiches to soup to ho-ho's...hahaha (seriously) you might crave anything. At Badwater I ate a lot of Tuna in oil...don't know why, but that's what my body was craving after 80 miles. Most of the ultras I run have aid stations planted every 5-10 miles, like The Bear 100 I'll be running this month from Logan to Bear Lake in the mountains. So every Aid station I'll be offered cereal bars, cookies, gummy bears, pretzels, salt capsuls, gatorade, water, coke, bananas, other fruit, soup or just straight beef or chicken broth, jerky, potatoes ...etc you get the picture! There's lots of other stuff like gues, gels and sports drinks that everyone experiments with. I like Hammer Nutrition's Perpetuem...it's a powder you mix with water for extreme endurance events...it's very bland and helps keep my stomach from getting too nauseated. Does that answer your question? See you next week.

Comment by Brenna on September 5, 2008 at 10:49am: haha, sorry don't mean to hijack this blog and turn it into a biosynthesis 101 discussion. Extensibly the ADP and ACP conversions explain why we need to balance certain types of foods and supplements with their associated activity? If I'm interpreting right, every breathing person is in an ATP mode, albeit different levels (the process of getting oxygen through breathing, walking to our car, etc. is a lowered form of cadio) when we increase the cardio by duration (such as low heart rate zone training for a duration lasting more than a few minutes) the process shifts to an ATP-CP mode, which the CP breaks down the ATP mode and shifing over to ADP? Resistance and interval cardio training will use the metabolic energy from ATP making it an ADP. Am I missing the mark?

Maybe it's a stretch, but does this explain why an imbalance of carbohydrates and proteins (such as fad diets) is so inefficent on the physical level? And why runners/bikers typically intake more carbohydrates than those who are weight lifters (and concequently why they require increased creatine or protein intake)?

Comment by Total Health & Fitness on September 4, 2008 at 9:16pm: Adenosine-5'-triphosphate (ATP) - ATP transports chemical energy within cells for metabolism

Adenosine diphosphate (ADP) - A nucleotide (Nucleotides are the structural units of RNA and DNA) consisting of adenine, ribose sugar, and two phosphate groups. Adenosine diphosphate (ADP) is formed by the removal of one phosphate from an ATP molecule by enzymes called ATPases. The formation of ADP from ATP releases usable metabolic energy. ADP is converted back to ATP by ATP synthases. Thus ADP is an important energy transfer molecule in cells.

Comment by Brenna on September 4, 2008 at 7:36pm: Interesting post. I love it, although I am still trying to digest the technical portion. I like to exercise both my body and my brain cells (okay, I'm a nerd). I'd be interested in clarification of acronyms or any lay sources you may have to do further research.

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