The lactate threshold (LT) is a key physiological marker for endurance athletes seeking to maximize performance and refine pacing strategies. It represents the highest exercise intensity an individual can maintain without a rapid, unsustainable accumulation of metabolites in the blood. Understanding this metric allows athletes to train with precision and race effectively.
Lactate is a byproduct of carbohydrate metabolism and a valuable energy source, not a harmful waste product. Lactate is constantly being produced and cleared, even at rest. The threshold marks the point where the rate of its production significantly overtakes the body’s ability to remove it from the bloodstream.
The Physiology of Lactate Threshold
Lactate is produced in muscle cells through glycolysis. When energy demand is high and the aerobic system cannot meet it alone, lactate is formed. Even during low-intensity exercise, lactate is continually produced and simultaneously cleared by various tissues, such as the heart and liver, which use it as fuel.
The lactate threshold is the point where this balance shifts, and the lactate concentration in the blood begins to rise exponentially. Below this point, the body is in a metabolic steady state where the aerobic system manages the lactate produced. When intensity increases beyond the threshold, anaerobic energy production accelerates, overwhelming the clearance mechanisms. This rapid increase in circulating lactate is associated with the onset of fatigue and the inability to sustain the effort.
Methods for Determining Your Threshold
Determining your lactate threshold is a prerequisite for effective endurance training. The most accurate method involves laboratory testing. This process typically uses a graded exercise test on a treadmill or cycle ergometer, where intensity is progressively increased every few minutes. At the end of each stage, a technician takes a small blood sample to measure the blood lactate concentration.
The data is plotted to pinpoint the exact exercise intensity, heart rate, and power output where the lactate level spikes. This method provides the most precise measure of the pace and corresponding heart rate at your threshold. However, due to the cost and accessibility constraints of laboratory testing, athletes often rely on field testing protocols.
A common field test is the 30-minute time trial, performed on a track or flat road while wearing a heart rate monitor. The athlete performs a warm-up, then runs or rides for 30 minutes at the maximum effort they can sustain for the entire duration. The goal is to determine the highest steady-state effort.
To calculate the Lactate Threshold Heart Rate (LTHR), the average heart rate recorded during the final 20 minutes of the effort is used. The average pace maintained over the 30 minutes is the estimated Lactate Threshold Pace (LTP). This metric closely correlates with laboratory LTHR, allowing for immediate application to training.
Applying the Threshold to Endurance Training
Once the LTHR or LTP is established, it defines training zones. The intensity level right at the threshold is often called Zone 4, or the Threshold Zone. This represents a sustained effort that is challenging but manageable for up to an hour, forcing the body to improve its ability to clear lactate.
For race strategy, the lactate threshold pace is valuable for preventing premature exhaustion. Athletes in events lasting longer than an hour, such as half-marathons, aim to maintain a pace just below their established LT pace. This strategy ensures the body remains in a steady state, allowing them to sustain the effort without crossing the threshold into rapid fatigue. Monitoring heart rate or pace relative to the LT provides real-time feedback for precise pacing.
Specific Training to Raise Your Threshold
The goal of targeted threshold training is to shift the lactate curve to the right, allowing the athlete to sustain a faster pace or higher power output before lactate accumulation begins. This adaptation is achieved through workouts that stress the body’s lactate clearance mechanisms. The two most effective types of workouts are continuous tempo runs and threshold intervals.
Continuous tempo runs involve sustained efforts performed at the established lactate threshold pace. This workload is long enough to elevate the blood lactate concentration, forcing the body to improve its ability to shuttle and utilize lactate. Consistent tempo work promotes improved oxidative capacity in muscle fibers.
Threshold intervals, sometimes called cruise intervals, break the threshold intensity into manageable segments with short recovery periods. For example, running four repetitions of one mile each at LT pace, separated by two to three minutes of light jogging. The short rest prevents full recovery, keeping the lactate concentration elevated and providing a stimulus for the body to become more efficient at clearing the lactate produced.