Performance diagnostics and threshold models
Cycling is an endurance individual sport where the personal performance level is crucial. Since training control and design in cycling depends on individual performance, sports science has attempted to describe and explain the performance of cyclists over the past 40 years. In the course of this, many different models were developed. The most widely used are the so-called “threshold models”, which describe a “maximal work output at which a parameter (e.g. heart rate, oxygen uptake or lactate formation) is in a stable range and an increase in work output would lead to a continuous increase in the threshold parameter” (Heck, 1990).
The parameters most commonly used to determine a “performance threshold” in cycling are respiratory gas analysis to determine oxygen uptake and lactate formation, which is determined by drawing capillary blood. Since the early 1970s, it has been possible to measure lactate concentrations quickly and reliably using very small capillary blood samples. Due to this technical development, the lactate concentration became more and more important in the determination and prediction of performance-determining parameters.
Since respiratory gas analysis for the determination of training ranges for cycling has an enormous potential for error and it has not yet been possible to develop conclusive and practical analysis systems for this purpose, we concentrate on the analysis of lactate samples.
The lactate level test
Due to its key role in the transition between glycolytic and oxidative metabolism, lactate measurement plays a central role in modern performance diagnostic investigations (Dickhuth, 2000). Lactate formation at rest is around 0.5 to 1.5 mmol/litre of blood and can rise to up to 20 mmol/litre during peak athletic performance (Neumann et al 1999). Various factors can strongly influence lactate formation and thus affect the predictive accuracy of a performance diagnostic. These parameters must therefore be monitored and controlled to avoid falsification of the test results. One factor that plays a big role in this is the testing protocol. It describes entry power, step duration and step height in the lactate step test. It is crucial for the comparability of performance tests to always use the same protocol. However, there is no single correct model; there are various ways to arrive at a conclusive result.
For all testing protocols, it is critical that the athlete begins the test as recovered as possible and with replenished glycogen stores to allow for accurate test evaluation. Furthermore, the room temperature should not be very high during performance diagnostics and the room should have good ventilation.
The procedure of a lactate level test is always quite similar. Start with a low power of 50 to 100 watts, as no increased lactate formation is to be expected here. Then the power is increased stepwise, whereby the step length and step height have an effect on the measurement accuracy of the diagnostics and determine the underlying evaluation protocol. It is very important that the test protocol and the evaluation protocol match, because only then can reasonable measurement results for performance diagnostics be expected.
Time trial and field tests
In addition to the lactate tests carried out in the laboratory, the training ranges can also be determined very precisely on the basis of field tests. These are time-trial tests that, depending on the discipline, are carried out either by mountain bike off-road or by road bike on the road. They allow approximate determination of the anaerobic threshold and are the simplest form of performance diagnostics. The time trials should be completed on an “even” course that has as constant a gradient as possible over the entire length. This allows the rider to maintain a consistent continuous power output. During the time trial, the heart rate is recorded, the average of which, divided by an appropriate percentage, gives an approximation of the anaerobic threshold. This method can be performed both in training and as a competition.
Such a test is much more accurate if the power is recorded with a power meter. This is ideal for all athletes who train with a power meter.
Here, time trials on the flat or uphill lasting about 20 minutes have proven to be a very accurate measure of endurance performance. This is based on the rule of thumb that the maximum average power or continuous power capacity over 20 minutes (DLF-20) is approximately 110 percent of the maximum continuous power capacity over 60 minutes (DLF-60). We have been able to observe this correlation for years in the comparison of lactate level tests and time trial performance or field tests. In 2009, this correlation was scientifically investigated and could be proven by statistical analyses of field performance data and laboratory diagnostic values in more than 30 highly trained cyclists (cf. Bontenackels, 2009).
This gives you the opportunity to check your own endurance performance yourself. From my own experience, a combination of laboratory and field testing during the season is most effective, depending on training planning and periodization, because in winter the field test is often much more difficult than the laboratory test. In summer, the opposite is usually the case.
Threshold concepts – an overview
The practical relevance of the performance diagnostics is enormously important for the athlete, because he wants to know according to which training ranges (watts or heart rate) he has to control his training. The values determined in the laboratory must therefore reflect the conditions existing in practice, so that realistically realisable training ranges can be obtained. In order to clarify the practical relevance of different evaluation models and load protocols (step height and step duration) in lactate performance diagnostics, comparisons were made with the so-called maximum lactate steady state (maxLass). At maxLass, “a continuous performance of up to one hour duration is just possible without the lactate value rising further” (Schmidt, 2007). These comparative studies showed that different threshold concepts, depending on training level and test protocol (initial load, step height, step duration), sometimes overestimate or underestimate maxLass (GREEN et al., 1983; HECK, 1990b; STOCKHAUSEN et al., 1997).
The threshold concept according to Lörcks
In daily practice we use a modified model of the individual anaerobic threshold according to Dickhuth. This modification has resulted from observations and comparisons of laboratory and competition performance data from many of our athletes.
According to the method of Dickhuht (1991), the individual anaerobic threshold (IAS) is determined by adding a value of 1.5 millimoles per litre to the lowest lactate equivalent as the wattage increases. The lowest lactate equivalent is also called the “lactate threshold” (LT). The LT describes the onset of lactate increase with gradually increasing load. The point on the lactate power curve added with 1.5 millimoles per litre indicates the load corresponding to IAS. The IAS describes the maximum intensity of a continuous effort – not the lactate value that can be measured after a continuous effort.
Through our observations, we have found that this method underestimates the practical value of continuous power over 60 minutes (DLF-60). However, this is decisive for the determination of the training areas and must therefore be determined as precisely as possible. Therefore, we adjusted the model by statistical analysis of our data and increased the value from 1.5 to 1.8 mmol/l. Thus, we were able to achieve a very high agreement of 98.8 percent between the individual anaerobic threshold determined in the laboratory and the performance determined in the field test.
The “threshold” is a much-discussed topic in cycling. In most cases, the decisive factor is not whether one model is better than the other, but whether it is used correctly. Often, different definitions and approaches are thrown together here and then not applied correctly.
If you look at older studies in particular and re-analyze the results, you won’t find any gross errors even today. The results reflect the measured values of partly quite large groups of test persons, and correct calculations were also made. On closer inspection, however, it is noticeable that the subject groups often consisted of untrained or very weakly trained participants. The fact that these results can then be transferred poorly to competitive athletes seems then again obvious.
Over time, therefore, new models were developed that dealt more and more specifically with the performance of the individual athlete and were also able to represent this more and more accurately.
This is also how our threshold model has been developed over the years to improve training in cycling. We have intensively studied the existing methods and their results, checked them in practice and adapted them. With the model of equating the anaerobic threshold to a maximum continuous performance over 60 minutes (DLF-60), the definition of the training areas, the structure of our training plans, in short, the entire methodology was modified to offer the athlete a practical overall concept for optimal performance improvement.
At the end of the day, “the threshold” is like a tool. It depends on whether it is used correctly and sensibly, i.e. the results of our analyses only help the athlete if they are interpreted and used correctly.