Aerobic vs. Anaerobic Exercise - A Breakdown

To contextualise this post, I have been going to be a small, personal-trained directed gym for five months. Before this, exercise to me involved running around and huffing and getting sweaty. Anything that could achieve this was satisfactory. I had no goals other than ‘run really far and don’t stop and make it look effortless’. When I was in Year 4 I came fourth in Cross Country. I had been clinging to the hope that my past endurance capabilities were lying in wait for their chance to re-emerge and there I’d be: this vision of athleticism, who would not be defeated by cramps and breathlessness.



For reference, the gym that I go to works by starting off with 10 minutes use of a cardio machine (e.g. rower, bike, treadmill etc.) Forty minutes are then devoted to resistance and weights, and it ends with another 10 minutes of cardio. The day after my first session, I couldn’t lift my arms above my head. For all intents and purposes, I may as well have been a tyrannosaurus rex, minus the other awesome bits.



Slowly, the weights I was using were getting heavier and it was getting easier. The cardio side of it, however, seemed to improve more slowly. This perplexed me – my heart is a muscle, so logically shouldn’t it be strengthening at the same rate? After all, my heart rate is raised for the entire time, thus disputing any argument to do with time spent on cardio vs weights. So, I Googled.

This is how I discovered that there exists a significant difference between the two forms of exercise. So, now armed with a reputable source (my beloved Guyton), I’ll outline the difference so you too can stop living in ignorance (unless of course you already knew this).

It is generally well known that men and women differ physically (men have broad shoulders and small hips (inverted triangle); women tend to have narrower shoulders and much broader hips). In mammals, it is usually males that are larger. Much research that has been undertaken into exercise physiology has been done on males.

The body uses three different pathways (basically ways) of generating energy in the context of exercise. The phosphagen (or phosphocreatine-creatine system) system involves the breakdown of phosphocreatine to creatine and phosphate. It can provide maximal energy for a very brief period – in fact, only 8 to 10 seconds – and it utilised in the body in events requiring only short bursts of muscle power. This pathway is anaerobic.

The second pathway is the glycogen-lactic acid system involves the splitting of glycogen in the muscles (the stored form of glucose). This occurs in the absence of oxygen yet again and is therefore anaerobic. This system is well known – the by-product of it is lactic acid, which is responsible for ‘stitches’ and pain. It is less rapid than the phosphagen system, but lasts longer – this time, 1.3 to 1.6 minutes.

The final pathway is the aerobic pathway. This is whereby mitochondria (cool green organelles that ‘manufacture’ energy in the cell) use oxygen to generate ATP. This system continues for an unlimited time and is restricted only by the availability of nutrients.

So, in a 100-metre sprint, the first two systems (perhaps only the first in some) is activated and no aerobic elements are involved. In opposition, a marathon runner would make little use of the first two systems, given that the event is for a much longer duration.

Thus, the difference between the pathways comes down to what exercise is undertaken and, to a further extent, what muscles are engaged (e.g. your neck doesn't do a whole lot when you're running other than holding your head up). It is therefore important to undertake exercise that conditions both your muscles and your cardiovascular endurance. This of course is less relevant to elite athletes who train to enhance their performance in a given area.