Determining Your Aerobic Threshold (AeT) in Cycling: Finding Your Optimal Base Training Intensity

Introduction

The aerobic threshold (AeT), also known as the first lactate turnpoint (LT1), is the most overlooked yet most important intensity marker in cycling training. It represents the critical point where the body shifts from “pure aerobic metabolism” to “slight engagement of the anaerobic system.” Correctly mastering AeT is the prerequisite for effective Zone 2 training and the foundation for building long-term training capacity.

The Physiological Significance of AeT

When riding below AeT:

• Energy comes primarily from fat oxidation (60–80%)
• Blood lactate concentration remains stable at 1.5–2.0 mmol/L
• Can be sustained for long periods with almost no fatigue accumulation
• The mitochondrial system operates at full capacity, making this the optimal intensity for training mitochondrial biogenesis

Above AeT (but below FTP):

• The glycolytic system gradually kicks in, and lactate begins to rise slightly
• Although still sustainable, prolonged accumulation creates excessive training stress
• Many cyclists’ “easy rides” actually fall in this range, creating the predicament of “always tired, never improving”

Main Testing Methods

Method 1: Blood Lactate Testing (Gold Standard)

In an exercise physiology laboratory or with a portable lactate analyzer (such as Lactate Scout):

• Ride at incremental power, taking a drop of earlobe or fingertip blood every 4 minutes
• Find the power point where blood lactate just begins to rise consistently—that is AeT
• Cost: approximately NT$3,000–8,000 in Taiwan
• Accuracy: highest, but requires professional equipment

Method 2: Cardiac Drift Test

This method, popularized by triathlon coach Phil Maffetone, is suitable for cyclists without lactate testing equipment:

Test procedure:

1. Ride steadily at a fixed heart rate (e.g., 130 bpm) for 60 minutes
2. Record power every 10 minutes
3. If power continuously declines more than 5% while maintaining the same heart rate, the intensity exceeds AeT
4. Lower the heart rate by 5–10 bpm and retest until you find the intensity where power remains stable

Method 3: Talk Test

The simplest on-the-bike assessment method:

• Below AeT: can speak in full sentences with steady breathing
• Near AeT: can still speak in full sentences, but requires slight effort
• Above AeT: speaking becomes difficult, needing to catch breath every few words

Limitations: Lower accuracy and high individual variability, but very practical as a quick daily riding check.

Method 4: Maffetone Heart Rate Formula Estimation

Phil Maffetone’s MAF (Maximum Aerobic Function) formula:

• Base: 180 minus your age
• Adjustment: Add 5 if you have trained for more than 2 years without injury; subtract 5–10 if you have injuries or irregular training
• Example: A healthy 40-year-old rider, MAF heart rate = 180 - 40 + 5 = 145 bpm
• Accuracy: Moderate, and serves as a very practical starting point

The Gap Between AeT and FTP: An Indicator of Aerobic Base

For well-trained endurance athletes, the power at AeT is typically 70–80% of FTP. If AeT power is only 55–60% of FTP, it indicates a weak aerobic base that requires substantial Zone 2 training to fill.

• AeT/FTP ratio < 65%: Insufficient aerobic base; prioritize extensive Zone 2 training
• AeT/FTP ratio 65–75%: Typical level for recreational training cyclists
• AeT/FTP ratio > 75%: Excellent aerobic efficiency; suitable for introducing more high-intensity training

Practical Recommendations

• At least 3 Zone 2 rides per week, each no shorter than 60 minutes, to effectively stimulate mitochondrial adaptation
• AeT is not fixed: As training improves, the power at AeT gradually rises, requiring retesting every 8–12 weeks
• Avoid the “Zone 3 trap”: Easy rides must be easy enough—do not hover near AeT. This is the most common training mistake among amateur riders
• Taiwan’s terrain challenge: Maintaining intensity below AeT is difficult on climbs; consider flat roads (such as along Provincial Highway 1) or a stationary trainer for Zone 2 training

Conclusion

AeT is the “red line” for low-intensity training—once you cross it, you are no longer doing pure aerobic training. Find and respect this line so that Zone 2 training truly delivers results, and you will see significant aerobic capacity gains after every training cycle. The essence of scientific training is not pushing yourself to the limit every time, but doing the right thing at the right intensity in every session.

Related Reading

• Lactate Threshold Training: How to Find Your Critical Cycling Pace
• Cycling Lactate Testing: Applications of Blood Lactate Concentration in Training Zone Setting
• Lactate Threshold Testing Methods: Accuracy Comparison Between Laboratory and Field Tests
• Cycling Lactate Threshold Training: Sweet Spot 88–93% FTP Interval Design