The anaerobic threshold (AT) represents a critical turning point in exercise intensity, separating sustainable endurance efforts from those that lead rapidly to fatigue. Understanding this metric is extremely beneficial for anyone participating in endurance sports or seeking to optimize their fitness program. Knowing your AT allows for precise pacing and focused training, ensuring that the time spent exercising is directly contributing to specific fitness goals.
Defining the Anaerobic Threshold
The anaerobic threshold is the highest intensity level at which the body’s production of lactate is matched by its ability to clear or buffer that lactate. Below this point, the primary energy production is aerobic, relying on oxygen to fuel the muscles. As exercise intensity increases, the demand for energy outstrips the immediate oxygen supply, causing the body to increasingly rely on anaerobic metabolism. This shift generates lactate and hydrogen ions (H+) within the muscle cells and bloodstream.
The AT is often closely associated with the Maximum Lactate Steady State (MLSS), which represents the greatest workload that can be maintained without a continuous rise in blood lactate concentration. Once the AT is surpassed, the rate of lactate production exponentially exceeds the rate of clearance. The accumulation of hydrogen ions, which are co-produced with lactate, lowers the pH balance in the muscles and blood, leading to metabolic acidosis. This drop in pH is the primary physiological mechanism that causes the characteristic “burning” sensation and forces a reduction in exercise intensity.
Methods for Determining Your Threshold
The most accurate measurement of the anaerobic threshold is obtained through clinical testing in a laboratory setting. This involves an incremental exercise test, typically on a treadmill or stationary bike, where blood samples are taken at regular intervals to measure blood lactate concentration. Specialized equipment can also non-invasively measure gas exchange to find the ventilatory threshold, which closely correlates with the AT, by tracking changes in oxygen consumption and carbon dioxide production.
For most individuals, a practical field test offers a highly effective method for estimating the anaerobic threshold. A common and reliable protocol is the 30-minute time trial, where you perform a maximal, steady effort for the entire duration. The estimated anaerobic threshold heart rate (AT-HR) is calculated as the average heart rate recorded during the last 20 minutes of this 30-minute effort.
It is important to use a heart rate monitor for this test, as heart rate lags behind effort in the initial minutes of intense exercise. While general guidelines suggest the AT-HR falls between 85-92% of maximum heart rate, this is a broad and highly individual estimate. The field test provides a personalized number that accounts for your current fitness level, yielding your threshold pace or power (the average speed or wattage maintained during the time trial).
Applying the Threshold to Training
Once the anaerobic threshold heart rate or pace is established, it becomes the foundation for structuring endurance training zones. The AT serves as the dividing line between high-intensity endurance work (Zone 3/Tempo) and very high-intensity work (Zone 4/VO2 Max). Training just below, at, or slightly above this threshold is what drives the most significant endurance adaptations.
For long-distance events like a half-marathon or triathlon, the AT pace directly informs your sustainable race-day pacing strategy. You can aim to maintain a pace or heart rate just at or below your threshold to maximize speed without crossing into the unsustainable zone of rapid fatigue. Knowing your threshold pace allows you to set structured intensity intervals, ensuring you stress the system appropriately without cutting the workout short by fatigue.
Strategies for Raising Your Anaerobic Threshold
To improve endurance performance, the goal is to shift the anaerobic threshold higher, meaning you can sustain a faster pace before lactate accumulation becomes unmanageable. This requires specific training protocols that challenge the body’s ability to clear and buffer lactate. Tempo workouts are a highly effective strategy, involving a sustained effort just below the AT heart rate or pace.
A typical tempo session might involve a continuous run or ride lasting 20 to 40 minutes at this comfortably hard intensity. Another method is threshold intervals, where you perform repeated, shorter efforts exactly at or slightly above your AT. Examples include three to eight-minute repeats at your threshold pace, separated by short recovery periods. The goal of both training types is to force the body to become more efficient at utilizing lactate as a fuel and increasing its capacity to buffer hydrogen ions.