If you've spent any time in the endurance training world, you've probably heard coaches and athletes throw around terms like "lactate threshold," "ventilatory threshold," "FTP," and "critical power." It can feel overwhelming – like there's a secret language you need to learn just to understand your training zones.
The truth is, there are many different thresholds used in endurance sports, and they're all trying to answer the same basic question: At what intensity does your body shift substrate use (from fat to carbohydrate), and when does exercise go from sustainable to unsustainable?
What Are Thresholds, Really?
Think of thresholds as physiological landmarks. Just like highway mile markers help you understand where you are on a journey, exercise thresholds help you understand where you are on the spectrum from easy aerobic exercise to all-out effort.
These thresholds represent points where your body changes how it responds to exercise stress. Generally, they mark shifts in what energy source the body is relying on and how your body produces that energy – moving from primarily fat-burning (sustainable) to increasingly carbohydrate-dependent (less sustainable) exercise.
The Two Physiological Transition Points (Thresholds)
Here's where it gets interesting: there are actually two thresholds that most of these terms are trying to identify, but there are many different ways to measure them.
First threshold (lower intensities) marks the first major shift away from primarily fat burning toward increased carbohydrate use. Exercise near or below this point can generally be sustained for hours.
Common names and measurements:
- LT1 (Lactate Threshold 1) - First rise in blood lactate above baseline
- VT1 (Ventilatory Threshold 1) - First increase in breathing relative to oxygen uptake
- BP1 (NIRS Breakpoint 1) - First change in muscle oxygen saturation slope
- DFA-alpha 1 = 0.75 - Heart rate variability marker for first threshold
Second threshold (her intensities) represents the highest sustainable intensity – the upper limit of what you can maintain in steady state. Exercise above this point leads to progressive fatigue.
Common names and measurements:
- LT2 (Lactate Threshold 2) - Second more abrupt increase in blood lactate concentrations
- VT2 (Ventilatory Threshold 2) - Sharp increase in breathing and CO2 output
- BP2 (NIRS Breakpoint 2) - Point where muscle oxygen continuously decreases
- MLSS (Maximal Lactate Steady State) - Highest sustainable lactate level
- CP (Critical Power) - Theoretical maximum sustainable power output (in practice, sustainable power for 20-40 minutes)
- FTP (Functional Threshold Power) - Field-based estimate of sustainable power (usually ~95% of CP)
- CS (Critical Speed) - Running equivalent of critical power
- DFA-alpha 1 = 0.5 - Heart rate variability marker for higher threshold
Taken together, measuring first and second threshold can help determine your training zones, whether you are using a 3-, 5- or 7-zone model!
How Are Threshold Measurements Similar?
All these thresholds are trying to identify the same two fundamental physiological transition points. Whether you're measuring lactate in blood, gases in breath, oxygen in muscle, or heart rate patterns, you're looking for those same inflection points where your body's response to exercise changes.
Research shows that these different measurement methods often identify thresholds at very similar exercise intensities. For example, studies have found that NIRS breakpoints (BP1 and BP2) occur at nearly identical intensities to lactate thresholds (LT1 and LT2).
How Are Threshold Measurements Different?
While they're measuring the same underlying physiology, each method has unique characteristics:
Lactate Testing:
- Requires blood samples and lab analysis
- Requires pauses in testing to collect samples
- Invasive but highly accurate IF proper measurement technique is used
- Can't be monitored continuously during training
Ventilatory Testing:
- Measures breathing patterns and gas exchange
- Requires wearing a mask connected to metabolic equipment
- Accurate but largely impractical for field use
- Limited to laboratory settings
NIRS (like Moxy Monitor):
- Measures muscle oxygen saturation in real-time
- Non-invasive and can be used during any workout
- Provides continuous feedback during training
- Allows for real-time training adjustments
Heart Rate Variability (DFA-alpha 1):
- Uses heart rate pattern analysis
- Non-invasive and can be monitored continuously
- Requires specialized analysis software
- May be affected by factors beyond exercise intensity (like controlled breathing)
- Has not been validated against other thresholds
Power/Pace-Based (FTP, CP, CS):
- Uses performance output as a proxy
- Practical for everyday training
- Easy to implement and understand
- May not account for daily physiological variations
Which One Is "Best"?
Here's the key insight: There is no single "best" threshold method. Each has strengths and limitations, and the "best" choice depends on your specific needs, available equipment, and training goals.
More importantly, research suggests that consistency matters more than accuracy. Using the same threshold measurement method over time allows you to track meaningful changes in your fitness, even if the absolute values aren't perfectly "accurate."
Why Consistency Trumps Accuracy
Think of it this way: if you're using a scale that consistently reads 2 pounds heavy, you can still track weight loss progress accurately – you just need to use the same scale each time. Similarly, if your chosen threshold method consistently identifies your transition points, you can effectively guide your training and track improvements over time.
The key is to:
- Pick one method that fits your available tools and training situation
- Use it consistently for assessments and training guidance
- Track changes over time to monitor fitness improvements
- Adjust training intensities based on daily variations when possible
The Practical Takeaway
Rather than getting caught up in which threshold is most "accurate," focus on finding a method that:
- Fits your budget and available equipment
- Can be used consistently over time
- Provides actionable information for your training
- Allows for real-time adjustments when needed
Whether you choose lactate testing, NIRS monitoring, heart rate variability analysis, or simple power/pace-based estimates, the most important thing is using your chosen method consistently to guide your training and track your progress.
Remember: thresholds are tools, not destinations. They're meant to help you train more effectively, not to create perfect precision. Choose the tool that works best for your situation, use it consistently, and focus on the bigger picture – becoming a stronger, more efficient endurance athlete.
The Bottom Line
There are many thresholds because there are many ways to measure the same underlying physiology. They're all trying to identify those crucial transition points that separate sustainable from unsustainable exercise intensity.
The "best" threshold isn't about finding the most accurate measurement – it's about finding the method you can use consistently to guide your training and track your improvements over time. Whether that's a $20,000 metabolic cart or a simple field test, what matters most is that it helps you train smarter and perform better.
If you are interested in learning how you can determine your thresholds using the Moxy Monitor NIRS technology check out download the training and racing with Moxy ebook!
