Cycling Threshold Value: Understanding, Measurement, and Training

What is Threshold Value in Cycling?

Threshold value in cycling refers to the highest intensity a cyclist can sustain for a prolonged period without a rapid accumulation of metabolic byproducts, such as lactate, that would necessitate a significant reduction in effort. It represents a critical physiological tipping point that dictates endurance performance and training intensity.

Understanding Energy Systems and Exercise Intensity

To grasp the concept of threshold, it's essential to understand how your body produces energy during exercise. At lower intensities, the primary energy pathway is aerobic, relying on oxygen to convert fats and carbohydrates into usable energy. As intensity increases, your body begins to rely more heavily on anaerobic pathways, which produce energy more quickly but also generate metabolic byproducts like lactate. While lactate itself isn't the sole cause of fatigue, its rapid accumulation often correlates with other physiological changes that lead to a sensation of "burning" and the inability to sustain effort.

Defining Threshold Value: The Physiological Crossroads

The "threshold" in cycling signifies a specific exercise intensity—measured in power (watts), heart rate (beats per minute), or perceived exertion—at which the rate of lactate production begins to exceed the rate at which the body can clear it. Beyond this point, lactate and other metabolic byproducts accumulate more rapidly, leading to a quick onset of fatigue and a sharp decline in sustainable power output. Below this threshold, you can typically sustain an effort for a much longer duration, as your body is in a more steady-state balance of production and clearance.

Key Threshold Concepts in Cycling

Several terms are used interchangeably or to describe slightly different facets of the threshold concept in cycling:

• Lactate Threshold (LT): This is the foundational physiological concept. It refers to the exercise intensity at which blood lactate concentration begins to rise significantly above resting levels. There are often two key lactate thresholds identified:
  • Aerobic Threshold (AeT or LT1): The point at which lactate just begins to rise above baseline, marking the upper limit of purely aerobic exercise.
  • Anaerobic Threshold (AnT or LT2): Also known as the Maximal Lactate Steady State (MLSS), this is the highest intensity at which lactate production and clearance are balanced, allowing for a sustained effort for a significant duration (e.g., 40-60 minutes for well-trained athletes). Beyond this point, lactate accumulates exponentially.
• Functional Threshold Power (FTP): This is the most widely used practical measure of threshold in cycling. FTP is defined as the maximum power a cyclist can maintain for approximately one hour. While not a direct measure of lactate, it is highly correlated with MLSS and serves as an incredibly useful benchmark for training and pacing. It's often determined via a 20-minute maximal effort field test, with the average power from that test multiplied by 0.95 to estimate a 60-minute power output.
• Ventilatory Thresholds (VT1 and VT2): These thresholds are determined by analyzing respiratory gases during a graded exercise test. They correspond to specific changes in breathing patterns that reflect underlying metabolic shifts. VT1 typically aligns with the aerobic threshold, while VT2 often correlates closely with the anaerobic threshold or MLSS, indicating the point where ventilation increases disproportionately to oxygen consumption.

Why is Threshold Value Crucial for Cyclists?

Understanding and knowing your threshold value is paramount for effective cycling training and performance for several reasons:

• Establishing Training Zones: Threshold value forms the basis for setting personalized training zones (e.g., endurance, tempo, threshold, VO2 max, anaerobic). Training within these zones ensures you are targeting specific physiological adaptations effectively.
• Pacing Strategies: Knowing your threshold power or heart rate allows you to pace effectively during races, time trials, or long rides, preventing you from starting too hard and "blowing up" or not pushing hard enough to maximize performance.
• Performance Prediction: A higher threshold value (e.g., higher FTP) generally indicates better endurance performance potential, as you can sustain a higher power output for longer periods.
• Tracking Progress: Regular threshold testing allows you to track improvements in your fitness over time. An increase in FTP, for example, demonstrates enhanced aerobic capacity and lactate tolerance.

How to Determine Your Threshold Value

Several methods exist to determine your threshold, ranging from highly accurate laboratory assessments to practical field tests:

• Laboratory Testing:
  • Lactate Profile Test: Involves incremental exercise while blood samples are taken periodically to measure lactate concentration. This provides a precise lactate curve and identifies LT1 and LT2.
  • VO2 Max Test with Gas Analysis: Measures oxygen consumption and carbon dioxide production during incremental exercise, allowing for the identification of ventilatory thresholds (VT1 and VT2).
• Field Testing (Functional Threshold Power - FTP Test):
  • The most common method for cyclists. It typically involves a structured warm-up followed by a maximal 20-minute effort. Your average power for this 20-minute segment is then multiplied by 0.95 to estimate your 60-minute FTP.
• Perceived Exertion (RPE): While less precise, experienced cyclists can often identify their threshold effort by how it feels. It's an intensity you can sustain for a long duration (e.g., 40-60 minutes) but where talking becomes difficult, and you feel a significant, sustained effort. On a 1-10 RPE scale, threshold is often around an 8.

Training Around Your Threshold

Training at or around your threshold is highly effective for improving endurance performance. Common threshold-based workouts include:

• Sweet Spot Training: Efforts sustained slightly below FTP (88-94% of FTP) for extended periods (e.g., 2 x 20 minutes). This intensity provides significant physiological benefits with less accumulated fatigue than full threshold efforts.
• Threshold Intervals: Sustained efforts at or just above FTP (e.g., 3 x 10-15 minutes at 100-105% of FTP), designed to improve your ability to tolerate and clear lactate.
• Over-Under Intervals: Alternating efforts slightly above (over) and slightly below (under) your FTP. This type of workout trains your body's ability to clear lactate while still producing power.

The Importance of Regular Reassessment

Your threshold value is not static. As you train, your physiology adapts, and your threshold will likely increase. It is crucial to reassess your threshold periodically (e.g., every 4-8 weeks) to ensure your training zones remain accurate and that you are continuing to challenge your body appropriately for continued progress.

Conclusion

The threshold value is a cornerstone concept in exercise physiology and a vital metric for any serious cyclist. By understanding what it represents, how to measure it, and how to train effectively around it, cyclists can unlock significant improvements in endurance, pacing, and overall performance. It is the physiological line in the sand that separates sustainable, high-intensity aerobic effort from the rapid onset of fatigue, and mastering it is key to maximizing your cycling potential.