Metabolic Systems: Understanding the Essentials

Metabolic Systems: Understanding the Essentials

Metabolic systems are necessary for the supply of energy to all organs. In sport and exercise, we are mainly interested in the metabolic systems of the skeletal muscle.

There are two important systems: aerobic and anaerobic. If there is a continuous and sufficient supply of oxygen, the aerobic is our main energy provider. This is the system giving you energy right now—or, as a matter of fact, almost 24 hours a day, 365 days a year. The moment you start running up the stairs, lifting weights, sprinting or cycling uphill, the oxygen supply becomes insufficient and you start using the anaerobic system as a back-up.

This results in the production of lactic acid, which is the signal that this intensity cannot be maintained for an extended period of time.

Although there is still an ongoing scientific discussion, we assume this happens at a specific intensity or level of exertion, and that it can be measured. The heart rate at which we start to produce lactic acid may not be the only cause of fatigue, but it is at least a good biomarker for anaerobic fatigue.

Keep in mind, however, that we always produce lactic acid, even in complete rest. But, in rest, the lactate clearance capacity is in balance with the continuous production of lactate, so the resting level of lactate is more or less constant at around 1 mmol/L.

It is called the aerobic-anaerobic threshold or lactate threshold. So if your endurance is insufficient, your threshold might be 140 BPM or lower. When you have better endurance, your threshold can be at 170 BPM or higher. Basically, the higher your threshold, the later you start producing lactic acid and the longer you can maintain an exercise at a higher level of intensity. It’s not easy to shift this threshold upward by training—it might go up a few points, but never 20 points. The lactate threshold reflects your aerobic fitness.

It should also be mentioned that working under the threshold does not mean that the work is 100% aerobic, nor does working above the threshold mean that the work is 100% anaerobic—it’s always a mixture of aerobic and anaerobic processes supplying energy. It is an indicator that the production of lactate starts to surpass the lactate clearance rate.

This threshold is the foundation of the heart rate zones as shown by the Omegawave system. It indicates with which heart rate you have to train in order to train the right metabolic system.

The threshold is interesting in the longer term development of aerobic fitness. It is not very useful to measure on a daily basis, which is why the measure itself is not displayed by the Omegawave system. Compare it to the gas tank of your car: the size of your tank will not change, no matter how frequently you drive. What does change, however, is your fuel level—which is always displayed on your dashboard.

Our body has the advantage of having two fuel systems (aerobic and anaerobic). They complement each other, but are relatively independent.

aerobic anaerobic
 fuel fats and carbohydrates only carbohydrates
 dependent on oxygen supply yes no
 capacity (total amount of energy) very high low
 power (energy per time unit) low high
 breakdown products carbon dioxide and water lactate
 aerobic-anaerobic threshold under over

For daily training, the status of the aerobic and the anaerobic systems are much more important than the lactate threshold. These systems will change on a daily basis, depending on the kind of workout you do: the exercises, the intensity, the volume and the rest periods. With some exercises, only one system is tapped into—if you jog slowly for an hour with a heart rate of 130 BPM (while your threshold is 160 BPM), you will only use your aerobic system. If you run 400 meters at full speed with a maximum heart rate of 190-200 BPM (and your threshold is 160 BPM), you will mainly use your anaerobic energy supply system. During most workouts, however, both systems are used simultaneously.

If you want to train again the next day, you can use the Omegawave system to check which energy system has recovered from the previous training and which system you should avoid using, since it did not recover from the previous training. You can do this by checking the aerobic readiness and anaerobic readiness, which reflect the actual status of each system.

Keep in mind that both systems do not recover at the same pace! The aerobic system recovers faster than the anaerobic system. For example: on the day of the finals of a World Championship or Olympic competition, one can see the elite long distance runners running fast and long in the morning, or at their warm-up before their finals. Their aerobic system, which is a recovery system in itself, recovers very quickly—especially in highly-trained, elite athletes. Running a hard anaerobic run (e.g. 400 or 800 meters) right before the finals, however, will result in an unrecovered anaerobic system.

If you test yourself with the Omegawave system before a workout, then again immediately after, and also every 2, 3 or 4 hours after the workout, you will see the “famous” recovery curve or supercompensation curve. And this for each separate system! It might not always look like the smooth line you see in the books, but if you continue testing you will find it.

This supercompensation curve is very important, as you are now able to adjust your daily workload or training to the actual status of your body—and this is what counts. In other words: it will show you your Windows of Trainability (more about this in my next article). Are the different physiological systems (in this case metabolic system) ready to be tapped into again, or not yet?

From time to time, you will find you have to adjust the workout because the Omegawave system suggests doing a different kind of training, different exercises, or a change in intensity and/or volume from what you had in mind. Why is this?

1. If both systems are recovered, both can be trained again today.

2. If one or both systems have not completely recovered, the Window of Trainability will not be fully opened. This does not mean you cannot train at all—you can choose to do some light technical work, work on drills and skills, and not tap into your energy sources too deeply. In this case, a light workout with a very low heart rate.

3. If the aerobic system is not recovered, you could still work anaerobically (e.g. lift weights).

4. If the anaerobic system is not recovered, you can work aerobically with a heart rate below or just above the threshold (which you can find in the table with the heart rate zones).

5. Even if a system is not recovered, you can still train that system. However, keep in mind not to do this too often, as it might lead to overreaching. This doesn’t have to cause a problem, as long as you monitor the results and you realize what you are doing. If not, you will probably experience a loss of sharpness (feeling flat on a competition day), with the potential to reach an over-trained state or experience injuries

6. For some people, it is disappointing to see the numbers of the aerobic and anaerobic system not increasing in the long term. Keep in mind that even after driving your car for 10 years, the size of the petrol tank will still be the same. The body has a limited capacity for energy storage.

Never forget that the level of the metabolic system or the levels of aerobic and anaerobic readiness depend not only on the intensity of the training, but also on the speed of your recovery. This explains why—even after performing the same workout—the next day one athlete will be completely recovered, while the other (of the same level) is not. If you are always in the green, your metabolic recovery is fast… great!

Remember that each individual measurement is only a snapshot: the long term overview of the measurements will give you a clearer picture of the dynamic quality of adaptations to training. Always keep an eye on your own baseline values—that is, the results of the past measurements—to interpret your current result.

Here’s an example of the development of aerobic readiness:

All measurements were made before the workout. If you look at the latest test on the right, you see the aerobic readiness is low (107). This is really low: the earlier 7 tests gave an aerobic readiness between 120 and 130. This significantly lower level of aerobic readiness in comparison with the earlier measurement serves as a warning that the aerobic system is insufficiently recovered. In other words: today, be very cautious when doing an aerobic workout. There might be a price to pay.

Have fun, be smart and do well!

Henk Kraaijenhof
February 2015