We are convinced, after decades of training and coaching, that the best way to measure and regulate intensity is through a combination of noticing both breathing and heart rate. Why does this work? Because ventilation is directly related to the rate of ATP production as well as the metabolic processes that dominate that production. Since the rate of ATP synthesis determines the intensity of exercise ventilation can give a very accurate picture of intensity.
Aerobic Threshold (AeT) aka Ventillatory Threshold (VT1)
When ventilation is slow and controlled to the point where the athlete can carry on a conversation without needing to catch his or her breath or can maintain breathing through the nose then aerobic fat metabolism is providing half or more of ATP for locomotion. This ventilation threshold is often referred to as the Aerobic Threshold (AeT) or the First Ventillatory Threshold (VT1). Its upper limit corresponds to the point where the blood lactate levels have risen by 1mMol/L above their base line reading or have hit the 2mMol/L level of blood lactate. Up to that point exercise can be carried out essentially indefinitely and will ultimately be limited in duration by fuel stores.
Once this threshold has been passed then glycolytic metabolism begins to dominate and makes a steadily increasing contribution to ATP production. At moderate intensities, lactate, which is a by-product of glycolysis, is easily re-metabolized in the working muscles. This rate of lactate uptake plays an important role in determining endurance capacity. The faster this by-product lactate can be utilized by the working muscles as a fuel source and not accumulated as a waste product the higher the endurance capacity of those muscles.
As the power output (speed) increases so does the percent of glycolytic metabolism’s contribution to the overall energy demands. With this higher intensity comes a higher lactate production rate. At some point the lactate removal rate is surpassed by the lactate production rate. At that point the Second Ventillatory Threshold (VT2) or anaerobic threshold is reached. Beyond this point the athlete is operating on borrowed time and will, within no more than minutes and perhaps as short as seconds, be forced to slow the pace.
VT2: Maximum Lactate Steady State (MLSS) aka Anaerobic Threshold (AnT)
CO2 is one of the products of the metabolic processes at the cellular level. As the ATP production rate increases so does the production of CO2. This triggers the ventilation center of the brain to breath deeper and faster in an effort to blow off the excess CO2 through exhalations.
When the MLSS/VT2/AnT point is reached another ventilation marker becomes obvious. This intensity corresponds very closely to the point where breathing becomes noticeably deeper and more rapid. It has been referred to as the “Breakaway Breathing Point”. Above this, conversation becomes difficult and only a couple of words can be spoken before one needs another breath. Above this intensity, exercise will not be sustainable for more than a few minutes. One common definition of VT2 is the intensity of exercise that can be maintained for 1 hour or about the length of a world class men’s half marathon time or a 40 km cycling time trial.
The duration that the exercise can be sustained is inversely proportional to the intensity above VT2.
How AeT Affects an athlete’s best performance
The main determinant of the VT2 or MLSS pace is the lowly AeT pace. That is because: The faster the slow twitch muscle fibers can remove the lactate being produced by the faster twitch, high power fibers the greater the intensity that can be sustained for longer. Therefore having a high AeT pace will mean that you will have a higher MLSS/VT2 pace. This very important point is often misunderstood by coaches and athletes alike.
Many studies have shown that VT2 or MLSS or AnT is the best predictor of endurance performance in events lasting from around 2 minutes to about 2 hours. Increasing the MLSS is clearly one of the best ways known to improve endurance performance. However, increasing the pace at AeT is the first and most important step in increasing the pace at MLSS.
- Ventilation is a direct measure of the intensity of exercise.
- Ventilation offers a personalized, instantaneous metric for each athlete to control training intensity.
- Ideally you are using a sports watch that is recording heart rate and other relevant data such as pace, distance, and duration. At a minimum you want to record intensity (either actual heart rate data or a note about perceived intensity) and duration. More on that in another post.
- Gaging where your VT1 heart rate is plus breathing-rate in real-time during training allows the athlete and coach to gage recovery and readiness for the next high intensity session (or climb) as it will vary based on fitness and recovery state.
This is a series of three articles: