Threshold test: why measure the anaerobic threshold?

Running, cycling, triathlon, trail running: what do endurance sports have in common? Performance and fatigue. The Training methodology  in all of these sports are very similar and improvisation should be avoided. We need to evaluate the athlete’s capacities through specific tests in order to adjust training goals according to subjective characteristics.

What is anaerobic threshold?

The term "threshold" suggests a watershed, something that delimits two distinct conditions, one before and one after, characterised, in this case, by distinct chemical and physiological processes.

In sports medicine, the anaerobic threshold, or lactate threshold, is an index that determines the maximum level of physical effort that the body can support without accumulating lactic acid and hydrogen ions (H+) in the blood and muscles. In other words, it indicates the moment beyond which the energy mechanism is transformed from aerobic to anaerobic (lactacid).

Let's now take a step back to understand the differences between the two energy systems and their role in cycling.

Our body uses chemical energy which is stored by a molecule called ATP (Adenosine Triphosphate). Energy is produced by the splitting of this molecule following precise mechanisms that can be of two types: aerobic or anaerobic. In the first case the energy process is made possible by the presence of oxygen, while in the second case the mechanism can be triggered even in its absence.
The energy reserves are not infinite, however, and when the ATP contained within the cells is about to end, it must be "created from scratch", through its synthesis. To do this, the body uses first of all carbohydrates (especially glycogen stored in the muscles and liver), fatty acids in the adipose tissue and then, when the effort is prolonged excessively, proteins. The latter case is very dangerous, since it is a catabolic process in which the muscle, in order to work, "consumes" itself.
The glycogen is broken down within the cell into simpler molecules of glucose. The latter, with a process called glycolysis, is further split, turning into pyruvate. Specific organizations, the mitochondria, then transform the latter into ATP with the use of hydrogen. This complex process allows to synthesize from scratch the precious energizing molecule. Glycogen is the most efficient "fuel", since with 1gr of glycogen 967gr of ATP is obtained, while using 1gr of fatty acids 831 is produced, 13% less.

And what does oxygen do in all this? The presence of oxygen is fundamental to determine an efficient synthesis of ATP. In fact, it is thanks to the reaction with oxygen (called oxidation), that pyruvate is converted into ATP. The amount of oxygen that an athlete can use, the VO2max, is closely linked to the level of production of ATP: each liter of oxygen used by our body allows the synthesis of 161.61gr of precious ATP.
Therefore, work in aerobic, anaerobic threshold and lactate accumulation all depend on the volume of oxygen that our body is able to introduce and use under stress.

When oxygen is scarce, cells must find an alternative route to ATP synthesis. Pyruvate "stagnates" in the cell instead of being synthesized in the mitochondria. Here it binds to hydrogen forming lactate. The latter accumulates in the cell, suffocating it and slowing down vital processes. In conclusion, we could say that an anaerobic effort is much less efficient than an aerobic one, since in the presence of oxygen glycolysis produces 39 molecules of ATP with 1 glucose, while in the absence of oxygen it produces only 3.

From everything we have written so far, one can easily see the importance of measuring anaerobic threshold in endurance sports such as cycling. These sports are purely aerobic but, at times, the cyclist switches to a type of aerobic work: knowing how far you can push certainly helps to better manage your oxygen and, consequently, athletic preparation and performance.

How to measure the anaerobic threshold

It can be detected by various methods based on different parameters:

• on the concentration of blood lactate;
• on the measurement of fan parameters;
• on the deflection of the heart rate curve/operating intensity ( Conconi test).

The first method is invasive and does not guarantee optimal precision. The measurement of fan parameters, on the other hand, gives extremely accurate results. Unfortunately, this method requires the use of very expensive equipment (respiratory gas analyser). The third method, the Conconi test, is the simplest and most used way to determine an athlete's anaerobic threshold. We would like to point out that being a maximum test is not suitable to evaluate subjects who are not trained or have physical problems.

During physical exertion, heartbeats increase to ensure a greater blood supply to the muscles. The more intense the effort, the more the pulsations rise. However, as one might think, there is a limit beyond which heart rate cannot be increased further. With the Conconi test, you can study the subtle relationship between heart rate and intensity of effort. During his studies Professor Conconi noted that this relationship was linear to a certain extent, beyond which the increase in intensity of effort exceeded the increase in heart rate. In this area Conconi identified the anaerobic threshold that corresponds to the point where the lactacid anaerobic mechanism is activated in an important way.

It is wrong to say that at this threshold the aerobic mechanism is exhausted or terminated, just as it is wrong to say that it reaches its maximum level of activation. It should be borne in mind that the anaerobic system is not activated suddenly but gradually. This energy metabolism is already activated at operating intensities well below the anaerobic threshold. In this case, the quantities of lactic acid produced are small and the body can metabolize them with tranquility. Once the Anaerobic Threshold is exceeded, carbon dioxide (CO2) production, ventilation (respiratory acts per minute), and the level of lactic acid produced rapidly increase. If the intensity of the exercise does not decrease, the lactate produced accumulates more and more until it forces the athlete to slow down. For this reason, the threshold intensity can be maintained for a maximum of 20-60 minutes depending on the training level.

The test involves performing an incremental stress test of a maximum type. First of all the athlete must wear the heart rate monitor and perform an adequate warm-up (depending on the characteristics of the subject a more or less intense protocol will be proposed). Monitoring your heart rate during this first step can provide important data that will help you choose the most suitable protocol. Once the warm-up is over, the subject performs a test on a measured track, on a cycle ergometer such as MYCYCLING or on a treadmill according to the discipline and the sporting needs. If you are performing the Conconi test outdoors, you should perform it on a windy day to avoid weather conditions interfering with the test performance.  The increase can be expressed in WATT in case of a cycle ergometer, or as a decrease in the travel time of a fixed stretch of track (increase in speed) in case the subject to be tested prefers the race.

When the athlete is no longer able to withstand a further speed increase, he is asked to make a final sprint. This sprint, which will last until it is completely exhausted, will allow you to calculate your maximum heart rate. At the end of each step, the watts (or partial times of individual fractions) and heart rate are measured. These data pairs together with the max HR are reported on a graph that represents the speed or watts in the abscissa and the heart rate in the ordinate. Observing the results of a Conconi test, one notices that at low speeds there is linearity, then at a certain point a deflection appears with a sudden change of slope. The speed at which linearity ceases corresponds to the anaerobic threshold. Reading the chart of a Conconi test is sometimes not so easy and its correct interpretation depends on the skill and experience of the doctor or coach.

In addition to providing an estimate of athletic performance, the Conconi test allows you to obtain useful information for scheduling workouts. Simple mathematical steps that take into account the threshold heart rate make it possible to determine the various training rhythms. In particular with heart rate at the threshold of 180 bpm:

• Slow: 144- 153 bpm
• Medium: 153 - 169 bpm
• Fast: 175-185 bpm

Let us point out at once that there are no "absolute" interpretations of the values obtained, as they must be analysed in relation to sport or the competition in which one has to compete. The reference value of the anaerobic threshold, which for many coincides with the 4 moles, cannot therefore be considered valid in absolute terms and the test must be interpreted on an individual basis. However, in simplifying it can be said that in athletes who perform for a long time and at a constant pace the threshold is usually below 4 mmoles, while in athletes who compete in tests of 60-90 min or with frequent variations in rhythm and intensity, the value can also be higher than the standard reference data.

For example, our body must be trained differently if the goal is a marathon or a 10 km race, or a cycling granfondo. In addition, the data obtained will have to be "read" according to the athlete's level: a good runner will run the half marathon at speeds similar to or slightly above the anaerobic threshold, while a low level amateur will have to choose a rhythm between the middle and the threshold. If the race pace is generally constant during the race, the situation in cycling is very different, where the altitude characteristics of the course will dictate the intensity of effort. In a race with short climbs it will be possible to exceed the intensity of the threshold for a few minutes while on tracks with long climbs it will be essential not to exceed these rhythms to avoid being in crisis: if you overestimate your skills you run the risk of being in reserve of energy with a dramatic decline in performance (in cycling the infamous hunger crisis).
So to avoid these risks, knowing your characteristics is valuable for training and racing.

When should I perform the threshold test? Considering that the performance level indications provided by the test should guide the training schedule, it is advisable to perform the test approximately 2-3 months after the race for which you are preparing. This time frame will allow for the correction of any deficiencies in the preparation and in any case for the best possible finalisation of the pre-competition period. A good athlete who has to face several races throughout the year will have to repeat the evaluation every 3-4 months to check the fitness and adjust the workload. It is important that each test is carried out in constant situations, that is following the same protocol and without having done intense training or races in the two previous days.

One final consideration: during the test, the FC and lactate are measured with reference to the power delivered. The final data are therefore indicative of the powers (in watts) to be developed at various training rates while the heart rate can vary significantly from one day to another. It is therefore important to have a power meter on the bike that accurately detects the watts delivered during the pedalling. Only in this way will it be possible to make the best use of the indications from the threshold test.