Anaerobic Threshold: Definition, Importance, Measurement, and Training Strategies

What is the anaerobic threshold set?

The anaerobic threshold (AT), often used interchangeably with lactate threshold, represents a critical exercise intensity at which the body's rate of lactate production begins to exceed its rate of lactate clearance, leading to a rapid accumulation of lactate and associated metabolic byproducts in the blood. Understanding and training at or around this "set" point is fundamental for enhancing endurance performance and efficiently managing fatigue during sustained high-intensity exercise.

Understanding the Anaerobic Threshold

The human body possesses a remarkable ability to produce energy through various metabolic pathways, primarily categorized as aerobic (with oxygen) and anaerobic (without oxygen). During low to moderate intensity exercise, the aerobic system efficiently provides most of the energy, utilizing fats and carbohydrates. As exercise intensity increases, the demand for energy outstrips the aerobic system's immediate capacity, prompting a greater reliance on the anaerobic system.

The Energy Continuum: Exercise intensity exists on a continuum, with both aerobic and anaerobic systems contributing. The anaerobic threshold signifies a physiological tipping point where the anaerobic contribution becomes substantial and unsustainable for prolonged periods.

Lactate: Friend, Not Foe: A common misconception is that lactate (or lactic acid) is a waste product solely responsible for muscle fatigue and soreness. In reality, lactate is a valuable fuel source that can be utilized by various tissues, including the heart, brain, and even other muscle fibers. It's continually produced, even at rest. The issue arises when its production rate significantly surpasses its clearance rate, leading to an accumulation of hydrogen ions, which increase muscle acidity and interfere with muscle contraction, ultimately causing fatigue. The anaerobic threshold is precisely the point where this imbalance occurs.

The "Threshold" Defined: At the anaerobic threshold, the body struggles to clear lactate and hydrogen ions as quickly as they are produced. This metabolic shift marks the highest intensity that can be sustained for an extended period (typically 20-60 minutes for well-trained individuals) before rapid fatigue sets in.

Key Terminology and Nuances

While "anaerobic threshold" is a widely used and understood term, exercise science often employs more precise terminology to describe similar physiological markers.

Lactate Threshold (LT): This is typically defined as the first significant increase in blood lactate concentration above resting levels during incremental exercise. It represents the highest exercise intensity that can be maintained primarily by aerobic metabolism.

Onset of Blood Lactate Accumulation (OBLA): OBLA refers to the point where blood lactate reaches a specific, elevated concentration, commonly set at 4.0 mmol/L. This is a more arbitrary marker but signifies a clear shift towards higher anaerobic contribution.

Maximal Lactate Steady State (MLSS): Considered the gold standard for defining sustainable high-intensity endurance exercise, MLSS is the highest exercise intensity at which blood lactate concentration remains relatively stable over time (i.e., production equals clearance). Exercising above MLSS leads to continuous lactate accumulation and eventual fatigue. MLSS often aligns closely with what most athletes refer to as their "anaerobic threshold."

Why "Anaerobic Threshold" is Common: Despite the more precise terms, "anaerobic threshold" remains popular due to its intuitive nature, conveying the idea of a limit to sustainable aerobic performance and a reliance on anaerobic pathways. It serves as a practical marker for coaches and athletes.

Why is the Anaerobic Threshold Important for Performance?

The anaerobic threshold is a cornerstone concept in endurance training due to its profound implications for performance.

Predictor of Endurance Success: A higher anaerobic threshold indicates that an athlete can sustain a faster pace or higher power output for a longer duration before succumbing to fatigue. It is often a better predictor of endurance race performance than VO2 max (maximal oxygen uptake), especially in events lasting longer than a few minutes.

Defining Training Zones: The AT serves as a critical physiological marker for establishing personalized training intensity zones. Training at, below, or above this threshold elicits different physiological adaptations, allowing athletes to target specific energy systems and improve various aspects of their fitness.

Fatigue Onset: Understanding your AT helps predict when fatigue will likely set in during sustained hard efforts. Pushing beyond your AT for too long leads to a rapid accumulation of hydrogen ions, metabolic acidosis, and ultimately, the inability to maintain intensity.

How is the Anaerobic Threshold Measured?

While precise measurement typically requires laboratory conditions, several methods can estimate or directly determine an individual's anaerobic threshold.

Laboratory Testing:

• Lactate Testing: Involves incremental exercise (e.g., treadmill, cycle ergometer) where exercise intensity is gradually increased while blood samples are taken at regular intervals to measure lactate concentration. The AT is identified by plotting lactate levels against intensity.
• Gas Exchange Analysis (Ventilatory Thresholds): During incremental exercise, a mask is worn to analyze inhaled and exhaled gases (oxygen and carbon dioxide). Ventilatory Threshold 1 (VT1) and Ventilatory Threshold 2 (VT2) are identified by changes in breathing patterns. VT1 often correlates with the lactate threshold, while VT2 (also known as the Respiratory Compensation Point or RCP) is closely aligned with the anaerobic threshold/MLSS.

Field Tests:

• Critical Power/Velocity Test: This involves performing maximal efforts over two or three different durations (e.g., 3 minutes and 12 minutes). By plotting power output (or velocity) against the inverse of time, a linear relationship can be established, with the asymptote representing the critical power/velocity, which closely approximates MLSS.
• 30-Minute Time Trial (Cycling/Running): A practical field test where an athlete performs a maximal sustained effort for 30 minutes. The average power output (for cycling) or pace (for running) during the final 20 minutes of the test is often used as an estimate of the anaerobic threshold.
• Conconi Test: An incremental speed test where heart rate is plotted against running speed. The point where the heart rate curve deviates from linearity is considered an estimate of the anaerobic threshold.

Training to Improve Your Anaerobic Threshold

Elevating your anaerobic threshold is a primary goal for endurance athletes, as it allows for faster sustained speeds or higher power outputs. Training strategies focus on improving the body's ability to produce energy aerobically, clear lactate more efficiently, and buffer hydrogen ions.

Threshold Training/Tempo Work: This involves sustained efforts at or just below your estimated anaerobic threshold. Examples include 20-60 minute runs or rides at a challenging but sustainable pace, where you can speak in short sentences but not comfortably hold a conversation. This type of training directly stimulates adaptations that improve lactate clearance and buffering capacity.

High-Intensity Interval Training (HIIT): Short bursts of intense exercise performed above your anaerobic threshold, followed by periods of recovery. While challenging, HIIT can significantly improve VO2 max and enhance the body's ability to tolerate and clear lactate, pushing the AT higher. Examples include 3-5 minute intervals at near-maximal effort with equal or slightly longer recovery periods.

Long-Duration, Moderate-Intensity Training: While not directly targeting the AT, building a strong aerobic base through longer, easier efforts (below LT) is crucial. This improves mitochondrial density, capillary density, and fat utilization, all of which contribute to a more robust aerobic system and thus support a higher AT.

Benefits of an Elevated Anaerobic Threshold

Improving your anaerobic threshold yields significant performance advantages for endurance athletes and fitness enthusiasts alike.

Sustained Higher Intensity: You'll be able to maintain faster paces or higher power outputs for longer durations without experiencing overwhelming fatigue. This is crucial for competitive events and personal bests.

Improved Endurance Performance: A higher AT directly translates to better race times in events ranging from 5Ks to marathons, and in cycling or triathlon races.

Reduced Fatigue: By improving your body's ability to clear lactate and buffer hydrogen ions, you delay the onset of metabolic acidosis, allowing you to feel stronger and more comfortable at higher intensities.

Practical Application for Athletes and Trainers

For athletes and personal trainers, understanding the anaerobic threshold is not just academic; it's a powerful tool for optimizing training.

Personalized Training Programs: Using AT as a benchmark allows for highly individualized training plans, ensuring that intensity is appropriate for specific adaptations.

Performance Benchmarking: Regular AT testing (lab or field) provides objective data to track progress and adjust training phases.

Injury Prevention: Training consistently within appropriate zones, respecting your AT, helps prevent overtraining and reduces the risk of injury.

Conclusion

The anaerobic threshold, or lactate threshold, represents a pivotal physiological marker in endurance sports. It defines the highest intensity at which an individual can sustain effort primarily through aerobic means before a rapid accumulation of metabolic byproducts leads to fatigue. By understanding its physiological basis, methods of measurement, and targeted training strategies, athletes and coaches can effectively elevate this critical threshold, unlocking new levels of endurance performance and pushing their physical limits with greater efficiency and less fatigue.