Having reviewed 400m runner Roger Black’s autobiography on Monday and talked about training for the 400m yesterday, I found this great research article to talk about today. It’s a brilliant way to discuss the energy systems and the development of sports science thought when it comes to aerobic and anaerobic respiration.
400m runners – photo courtesy of the talented William Warby
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What’s the study again?
It’s called Energy system contribution during 200- to 1500-m running in highly trained athletes, by Spencer and Gastin, Medicine and Science in Sport in Sports & Exercise, 2000.
The purpose of the study was to estimate the aerobic and anaerobic energy system contribution during simulated 200m, 400m, 800m, and 1500m running events.
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Why is it interesting?
The study caused some waves when it was released (it was even discussed on the Charlie Francis forum) because the estimates of aerobic involvement by this study for the shorter distances was much higher than the studies that were done in the 1970′s.
Why was this?
The study authors explain that the 1970′s studies were using a flawed methodology, in that they worked with oxygen debt. This study used a different approach that I’ll describe below.
The authors of this study argue that the 1970′s studies, as a result of their flawed methodology, estimated that the anaerobic systems had a much bigger role to play than is actually the case.
Of course, this caused many people who favour short distance sprint work, heavy weight lifting and other anaerobic methods to get hot under the collar. After all, we ditched long, slow distance running for sprint events ages ago, right? Have we messed up?
Let’s find out.
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The anaerobic system: a recap
Before we get stuck into methods of measuring the anerobic component of different distance races, let’s just go over some basic exercise physiology (care of Exercise physiology, McArdle, Katch and Katch, 1991). If you are an exericise physiology genius then skip this section or you’ll get bored…
ATP – the basic energy “currency” of the body is ATP. If you study the three main energy system pathways (creatine-phosphate, lactate and aerobic), you’ll see that the purpose of each pathway is to produce ATP. The body does store some ATP in the muscles but the amounts are very small. They are usually considered together with the creatine-phosphate system.
Energy systems working together – there is a tendency for many people to think of the three main energy systems as consecutive (and in a sprint event, there is some justification for this). However, that line of thought will get you into all sorts of trouble, as a number of studies using radioactive tracers on glucose molecules have demonstrated that lactic acid is formed continuously, even at rest.
Creatine-phosphate system - for immediate, short-term energy, the body stores some ATP and high-energy phosphates in the muscles. Have you ever noticed that when you do a very low-rep set, a quick movement, or a very short sprint, you are often not winded? That’s because you stopped before you came out of the creatine-phosphate system. Depending on who you read (and what activity you are doing), it’s good for between five and twelve seconds of high effort.
Lactate system – after the creatine-phosphate system runs out, at continually high levels of effort, the body needs another anaerobic system to create ATP. Aerobic respiration won’t do the job because the body can’t get enough oxygen to the muscles fast enough. Enter the lactate system, which is another term for anaerobic glycolysis. Glycolysis is just the splitting of glucose (which happens in aerobic respiration also). Anaerobic means “without oxygen” so anerobic glycolysis is just the splitting of glucose without oxygen.
Blood lactate accumulation – while lactate is produced continually, blood lactate does not accumulate at all levels of exercise. At low intensities, the lactate produced by anaerobic glycolysis is oxidised in the muscles and used for energy. So why does it accumulate? There are several theories:
Muscle tissue hypoxia – all glycolysis in the body produces pyruvate, which is then oxidised to produce CO2 and water. The traditional explanation for blood lactate accumulation is therefore that the cell capacity for dealing with hydrogen ions produced in glycolysis hits a maximum capacity and excess hydrogen ions combine with the end product of glycolysis (pyruvate) to form lactate, which accumulates. However, this theory is seemingly contradicated by the fact that lactate is produced at all exercise intensities, even at rest. Nevertheless, it continues to pop up everywhere you look.
Lactate removal – another theory states that while lactate is produced constantly, the lactic acid is oxidised by other tissues. Since removal matches production at lower intensities, it is only accumulated at higher intensities.
Fast-twitch fibres – another theory suggests that conditions in fast-twitch muscle fibres favour the production of pyruvic acid to lactic acid. As fast-twitch fibres are recruited (remember that slow-twitch fibres are always recruited first in any movement), the amount of lactate generated increases.
OK, I think that’s quite enough of that. I’ve got a specific review article that I’ll look at in a couple of weeks purely about the concept of the anaerobic threshold so I’ll save any comments I’ve got until then.
Let’s now have a look at how the contribution of the anaerobic and aerobic systems to various different exercises have been measured.
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The concept of oxygen debt
The concept of an oxygen debt is relatively simple. Everyone knows that when you exercise at higher intensities, your breathing takes a while to come back to normal resting levels.
A simple way of measuring this oxygen debt was to measure the actual oxygen consumed by someone after exercise and compare it to the volume of oxygen they normally use at rest. The difference is your oxygen debt.
Based on this observation and studies in the area, some of the first sports scientists first coined the term “oxygen debt” and suggested that most of the excess oxygen consumed post-exercise was used to convert the lactic acid back into glycogen in the liver by the Cori cycle.
However, this theory was knocked by the discovery that it was possible to incur an oxygen debt without incurring any lactic accumulation! The sports scientists therefore proposed a modified theory, that there were two phases of oxygen debt:
- Alactic oxygen debt – oxygen debt that occurs without lactic build up, which is used to restore the reserves of ATP/CP depleted during exercise.
- Lactic oxygen debt – oxygen debt with lactic build up, which is used to reconvert lactic acid to glycogen in the liver.
Using this modified theory, which stood for a very long time, well into the 1970′s, it was assumed that the excess oxygen used after exercise could be taken as an indication of the anaerobic contribution to exercise.
A simple experiment might be that a runner used 10L of oxygen during an event. After the event, he used an additional 10L of oxygen over and above his resting levels before it returned to normal. The obvious conclusion is that the anaerobic and aerobic contributions to the event were 50/50.
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It’s not oxygen debt, it’s recovery oxygen uptake
Much later, however, it was found that there was no such replenishment of glycogen in the liver in tandem with blood lactate reductions. It appeared that the blood lactate was in fact oxidised for energy.
It was then discovered that a significant proportion of the so-called “oxygen debt” uptake was actually caused by physiological processes that took place during recovery. For example:
- body temperature rises by 3 degrees and stimulates metabolism;
- blood is reoxygenated;
- oxygen dissolved in bodily fluids is replenished;
- tissues are repaired; and
- ions are redistributed.
Hence, the idea of oxygen debt has been replaced by recovery oxygen uptake.
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Excess post-exercise oxygen consumption
Since it was realised that the idea of oxygen debt is flawed, many studies have been done looking at excess post-exercise oxygen consumption (EPOC), which you will probably have heard discussed before.
EPOC is the idea that the energy you burn as a result of exercise is not just the calories you burn doing work. EPOC varies depending on intensity and tends to be greater at higher intensities.
EPOC had lead some coaches and personal trainers to advise very high intensity workouts during dieting periods to increase calorie burn. Whether this is a good idea is another question entirely but you can see the logic.
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OK, let’s look at the study!
Now we’ve sorted out that issue, let’s look at the study. The researchers took 20 national level competitors at various distances and subjected them to two categories of test, as follows:
- A series of submaximal discontinuous treadmill runs at varying speeds of 6-min duration. Steady state VO2 was determined by averaging the VO2 during the last 2mins of each submaximal run. The linear relationship between steady state VO2 and treadmill velocity was extrapolated and used to estimate energy demand, or O2 cost, during supramaximal treadmill exercise.
- A supramaximal, specific event simulation on the treadmill (either 200m, 400m, 800m, or 1500m). Athletes stepped on to a moving treadmill, with the required velocity being achieved within a few seconds of the commencement of the trial.
During the tests, the researchers measured expired gases of the subjects. The researchers then measured what they called the Accumulated Oxygen Deficit (AOD) as the difference between the estimated O2 cost of the supramaximal treadmill run and the actual VO2 used and measured.
The estimated O2 cost of the supramaximal treadmill runs were calculated using the mean running velocity for each subject and the data collected during the submaximal runs.
The researchers then used this data to calculate the relative aerobic and anaerobic energy system contribution.
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What did they find?
The researchers found that the contribution of aerobic metabolism increased with event duration (as you might expect). The total relative contribution of the aerobic energy system for the events was as follows:
- 200m – 29%
- 400m – 43%
- 800m – 66%
- 1,500m – 84%
Surprising, yes? If you look back at William Black’s article about training for the 400m, you will see he quotes an aerobic component of just 15 – 20% for the 400m, which is less than half of what this study indicates.
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So what?
Well, as the researchers themselves are quick to point out, “the principal finding of this research was that the aerobic energy system contributes significantly to the energy supply during long sprint and middle distance running.”
In fact, they later go on to say that “the relative contribution of the aerobic energy system is considerable and greater than has been traditionally accepted during 200m, 400m, 800m and 1500m running. The results demonstrate that the aerobic energy system is the predominant energy system by the 30s time period during the 400m, 800m, and 1500mm running events.”
The researchers also note that “the data would suggest that the 800m and 1500m athletes have similar anaerobic capacities.” This ties perfectly in to the analysis I performed yesterday where the 100m and 200m are very close together and the 800m and 1,500m are also quite close but the 400m is out on its own.
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Slow down, you’re going too fast
Now before you go off with the idea that it’s necessary to start training long, slow distance for sprinting, let’s take a moment.
I believe that long, slow distance training is done primarily for the muscular adaptations, not the cardiovascular adaptations.
As I noted in talking about intervals for rowers, you can increase your VO2-max more effectively using intervals than by steady-state work. You’ll get into trouble if you equate aerobic fitness with the ability to go long distance, though, as the CrossFit guys have discovered. People quickly find out that just because you are cardiovascularly fit and have a high VO2-max doesn’t mean you can run a marathon. So what is the missing link? The muscles, of course.
After all, if the cardiovascular system were the key factor, switching between endurance sports would be a lot easier and Lance Armstrong would be a lot better at marathons than he actually is. The ability to go long distance is about muscular adaptations, not cardiovascular adaptations.
So while the aerobic system may be important for the sprint distances, it doesn’t imply long, slow distance training. It may, however, have implications for how much interval work is required, compared with how much strength training or speed work.
Let’s leave it there for today.
