Ventilatory thresholds (so called because respiration begins to increase or the oxygen I breathe is already insufficient) are key concepts in understanding exercise physiology and athletic performance. They tell us how the organism behaves under different intensities of effort and which energy systems it uses to produce the necessary energy. In addition, they help us to design customized training according to the objectives and capabilities of each person.
To better understand ventilatory thresholds, let us first explain the three-phase model, which was proposed by Skiner and McLellan in 1980. This model is based on the observation of the physiological responses that occur during an incremental exercise test, i.e., a test in which the intensity is progressively increased until exhaustion is reached.
According to this model, there are three phases or exercise zones, which correspond to two points of metabolic change: the first ventilatory threshold (VT1) and the second ventilatory threshold (VT2). Let’s see what each of them means:
- VT1: the first point of metabolic change, also called aerobic threshold. It occurs when the body begins to use more intensively the aerobic system for energy, i.e. the system that uses oxygen to metabolize nutrients. At this point, there is an increase in the production of lactate and hydrogenions in the muscles, but they can still be eliminated by respiration and other buffer mechanisms. Heart rate, respiratory rate and oxygen consumption increase linearly with exercise intensity. VT1 is usually between 50% and 60% of maximal oxygen consumption (VO2max) and can be identified by a change in the slope of the ventilatory curve.
- VT2: is the second metabolic change point, also known as the anaerobic threshold (although this is an inaccurate definition). It occurs when the production of lactate and hydrogenions exceeds the body’s ability to maintain acid-base balance, resulting in metabolic acidosis. At this point, the aerobic system is no longer sufficient to cover the energy demand and the anaerobic system, which uses glycolysis to obtain energy without oxygen, becomes more active. Heart rate, respiratory rate and oxygen consumption skyrocket and VO2max is reached. VT2 is usually between 80% and 90% of VO2max and can be identified by an exponential increase in the ventilatory curve.
We must take into consideration that the energy systems used by the human body to produce energy are complex and overlap with each other. Depending on the intensity of the exercise we perform, the body will use more or less one or the other system. For example, if we make a very intense effort, the body will mainly resort to glycolysis, which is the degradation of glucose in the cytoplasm of the cells. This process generates lactic acid, which can alter the internal balance of the organism. This point is known as the anaerobic threshold or VT2, and corresponds to the maximum intensity we can maintain for an hour or an hour and a half without ingesting carbohydrates. However, this term can be confusing, because if we keep increasing the intensity we will reach the point of maximum oxygen consumption, which is the limit of aerobic capacity.
Ventilatory thresholds are very useful indicators for measuring and improving sports performance. They allow us to establish specific training zones to improve endurance and optimize the use of energy systems. In addition, ventilatory thresholds also have health implications. They are related to lung capacity, cardiovascular efficiency and exercise tolerance. Assessment of ventilatory thresholds can help us to detect possible respiratory problems or diseases, as well as to monitor the body’s response during rehabilitation or physical training programs.
How do we calculate ventilatory thresholds?
These are some of the most commonly used methods:
- Respiratory gas analysis: This is the most accurate method for determining ventilatory thresholds. It consists of performing an incremental exercise test in which the body’s oxygen consumption and carbon dioxide production are measured. This requires a gas analyzer that is connected to a mask worn by the athlete. The ratio of oxygen to carbon dioxide varies according to the level of exercise intensity, and allows identification of the points at which ventilatory thresholds occur.
- Blood lactate analysis: This method is based on measuring the concentration of lactate in the blood at different phases of exercise. Lactate is a product of anaerobic metabolism, i.e. when the body uses glucose without oxygen. Lactate accumulates in the blood when oxygen demand exceeds supply, which occurs around ventilatory thresholds. To measure lactate, a blood sample is needed, which is obtained by pricking the finger or earlobe. The analysis can be done with a portable device or in a laboratory.
- Subjective evaluation: This method is based on the athlete’s perception of effort during exercise. Numerical or verbal scales are used for this purpose, such as the Borg or RPE scale, in which the athlete indicates how hard it is to breathe or keep pace. Subjective evaluation is a simple and practical method, but it also has limitations, since it depends on psychological, environmental and personal factors that can alter the sensation of effort.
- Indirect tests: These methods consist of estimating ventilatory thresholds from other variables related to sports performance, such as speed or power. Some examples are:
- MAS (Maximum Aerobic Speed): MAS is the maximum speed that an athlete can maintain using primarily aerobic metabolism. A field or laboratory test, such as Léger’s test or Balke’s test, can be used to calculate VAM. From the VAM, ventilatory thresholds can be estimated by applying approximate percentages. For example, VT1 is usually around 70-75% of MAP, while VT2 is between 85-90% of MAP. These percentages may vary according to the level and sport modality.
- FTP (Functional Power Threshold): FTP represents the maximum power a cyclist can sustain for one hour. To calculate FTP, a specific test can be performed or data obtained during training or competitions can be used. As with VAM, ventilatory thresholds can be estimated from FTP by applying similar percentages. VT1 is usually around 70-75% of FTP, while VT2 is between 85-90% of FTP. These percentages may also vary according to individual characteristics and environmental conditions.
As you can see, there are several methods for calculating ventilatory thresholds, each with its advantages and disadvantages. The important thing is to choose the most appropriate method for each case and use it consistently to evaluate progress and plan training.