Threshold Power: Understanding, Testing, and Improving Your Athletic Performance

What is my threshold power?

Your threshold power, commonly referred to as Functional Threshold Power (FTP) in cycling, represents the highest average power output you can sustain for approximately 60 minutes. It's a critical metric for athletes, indicating the upper limit of your sustainable aerobic effort before significant fatigue sets in.

Understanding Threshold Power

Threshold power is a cornerstone metric in endurance sports, particularly cycling, but its principles apply broadly to any activity where power output can be measured (e.g., rowing, running with power meters). Scientifically, it's closely related to your lactate threshold – the exercise intensity at which lactate production in your muscles begins to exceed its clearance, leading to a rapid accumulation in the blood. This accumulation is associated with increased acidity (hydrogen ions), which impairs muscle contraction and leads to fatigue.

While the lactate threshold is a physiological concept typically measured in a laboratory, Functional Threshold Power (FTP) is a practical, field-testable proxy. It defines the maximum power output you can maintain in a quasi-steady state without fatiguing rapidly. Above this threshold, your body relies more heavily on anaerobic metabolism, leading to a faster depletion of glycogen stores and a build-up of metabolic byproducts, forcing a reduction in intensity.

Why is Threshold Power Important?

Knowing your threshold power is invaluable for several reasons:

• Personalized Training Zones: Your threshold power serves as the anchor point for establishing personalized power training zones. These zones dictate the intensity of your workouts, ensuring you train effectively for specific physiological adaptations (e.g., endurance, tempo, threshold, VO2 max).
• Performance Pacing: In events like time trials, long climbs, or sustained efforts, your threshold power provides a crucial benchmark for pacing. Riding at or just below your threshold allows you to maximize performance without "blowing up" too early.
• Tracking Progress: Regular re-testing of your threshold power allows you to objectively track improvements in your fitness over time. An increase in threshold power for the same perceived effort indicates enhanced endurance capacity.
• Workout Prescription: Coaches and athletes use threshold power to prescribe specific interval durations and intensities, ensuring that training stimulus is appropriate and progressive.

How to Determine Your Threshold Power

While laboratory testing provides the most precise measure of lactate threshold, several accessible field tests can accurately estimate your threshold power.

• 20-Minute Functional Threshold Power (FTP) Test:

  • Procedure: After a thorough warm-up, perform a maximal, sustained effort for 20 minutes. This is a time trial where you aim to maintain the highest possible average power for the duration.
  • Calculation: Multiply your average power from the 20-minute effort by 95%. This 95% adjustment accounts for the fact that a 20-minute maximal effort is typically slightly higher than what you could sustain for a full 60 minutes.
  • Pros: Widely accepted, practical, can be done outdoors or indoors on a smart trainer.
  • Cons: Requires significant mental fortitude and accurate pacing; not a true 60-minute effort.

• Ramp Test:

  • Procedure: Start at a low power output and increase the power by a set increment (e.g., 20-25 watts) every minute until exhaustion.
  • Calculation: Typically, software (e.g., Zwift, TrainerRoad) calculates an estimated FTP based on your highest sustained power and the duration you were able to hold it. Some methods use 75% of your peak 1-minute power.
  • Pros: Shorter, less psychologically demanding than the 20-minute test, no pacing required.
  • Cons: May not be as accurate for all athletes, as it tests peak power rather than sustained threshold.

• Critical Power Test:

  • Procedure: Involves performing several maximal efforts of different durations (e.g., 3 minutes, 7 minutes, 12 minutes) on separate days or with ample recovery.
  • Calculation: Plotting power vs. inverse time for these efforts allows for the calculation of "critical power," which theoretically represents the highest power that can be maintained for a very long time without fatigue.
  • Pros: More theoretically robust as it's based on a physiological model of fatigue.
  • Cons: More complex, requires multiple maximal efforts, less commonly used by general fitness enthusiasts.

• Lactate Threshold Test (Laboratory-Based):

  • Procedure: Performed in a lab, you exercise at incrementally increasing intensities while blood samples are taken at each stage to measure lactate levels. The lactate threshold is identified as the point where lactate begins to accumulate rapidly.
  • Pros: Gold standard for physiological accuracy.
  • Cons: Expensive, requires specialized equipment and personnel, less accessible.

Interpreting Your Threshold Power

Once you have determined your threshold power, you can use it to establish your power training zones. While specific zone percentages can vary slightly by coaching philosophy, a common framework is Dr. Andrew Coggan's power zones:

• Zone 1: Active Recovery (<55% FTP): Very light, for recovery rides.
• Zone 2: Endurance (56-75% FTP): Steady, comfortable pace for long rides, building aerobic base.
• Zone 3: Tempo (76-90% FTP): Moderately hard, "sweet spot" for building aerobic fitness efficiently.
• Zone 4: Threshold (91-105% FTP): Hard, sustainable efforts, directly targeting threshold improvement.
• Zone 5: VO2 Max (106-120% FTP): Very hard, short efforts to improve maximal oxygen uptake.
• Zone 6: Anaerobic Capacity (>120% FTP): Maximal, very short efforts for anaerobic power.
• Zone 7: Neuromuscular Power (Maximal): Sprint efforts, targeting peak power.

Improving Your Threshold Power

Improving your threshold power involves a combination of consistent training at various intensities, with a particular focus on workouts that stress your aerobic system and lactate clearance mechanisms.

• Threshold Intervals: These are the most direct way to improve FTP. Examples include:
  • Sweet Spot Training (88-94% FTP): Longer intervals (e.g., 2x20 minutes, 3x15 minutes) at a challenging but sustainable pace. This provides significant aerobic stimulus with less accumulated fatigue than full threshold efforts.
  • FTP Intervals (95-105% FTP): Slightly shorter, harder efforts (e.g., 2x10-15 minutes, 3x8 minutes) directly at or slightly above your current FTP.
  • Over-Unders: Alternating periods slightly above FTP with periods slightly below FTP (e.g., 2 minutes at 105% FTP, 2 minutes at 90% FTP) for a sustained duration. This trains your body to clear lactate while still producing power.
• Longer Endurance Rides: Consistent Zone 2 riding builds your aerobic base, improving your body's efficiency at fat burning and overall endurance capacity, which supports higher threshold power.
• High-Intensity Interval Training (HIIT): While not directly training FTP, short, maximal efforts (Zone 5 and above) can improve your VO2 max, which raises the ceiling for your aerobic potential and can indirectly contribute to a higher threshold power.
• Consistency and Progressive Overload: The key to long-term improvement is consistent training and gradually increasing the duration, intensity, or frequency of your workouts over time.
• Recovery and Nutrition: Adequate rest, sleep, and proper fueling are crucial for adapting to training stress and allowing your body to build fitness.

Considerations and Limitations

While threshold power is a powerful metric, it's important to keep the following in mind:

• Not a Fixed Number: Your threshold power can fluctuate based on fatigue, stress, nutrition, and even time of day. It's a snapshot of your current fitness.
• Test Accuracy: Field tests are estimations. Factors like pacing, warm-up, and environmental conditions can affect the results. Consistency in testing protocol is key for tracking progress.
• Individual Variability: Different athletes respond differently to training stimuli. What works for one person may not be optimal for another.
• Context Matters: A higher threshold power is generally better, but it's only one piece of the performance puzzle. Other factors like sprint power, repeatability, technique, and mental fortitude are also critical.
• Power Meter Calibration: Ensure your power meter is accurately calibrated for reliable readings.

Conclusion

Your threshold power is a fundamental metric that provides deep insight into your aerobic fitness and endurance capabilities. By understanding what it is, how to test it, and how to train to improve it, you gain a powerful tool for optimizing your training, pacing your efforts, and objectively tracking your progress in endurance sports. Regularly assessing and targeting your threshold power through structured training is a highly effective strategy for unlocking your full athletic potential.