By Jonathan Edwards, MTI Athlete Team
Lactate threshold (commonly referred to as LT, LT2, or anaerobic threshold) is a key metric in predicting performance in endurance events. It is the intensity at which your body starts accumulating lactate faster than it can clear it, and it’s directly linked to performance over long distances. Athletes commonly rely on lab-based lactate testing to find this threshold. However, not everyone has access to expensive lab equipment. That’s why I decided to compare my home lab lactate test (using a well regarded lactate meter) with a 30-minute field test—a low-cost (free), accessible method—to see how the results compare.
The Simple Science Behind Lactate Threshold
In simple terms, LT is the exercise intensity at which lactate begins to accumulate rapidly in your bloodstream. You can only continue at this intensity for a limited time, around 30-60 minutes depending on your fitness level and sport. Training just below or at this threshold can improve your endurance and delay fatigue. In the lab, this is measured during an incremental exercise test where blood samples are taken at regular intervals as intensity increases. The point where lactate levels start to rise steeply (non-linear) marks your LT. It is commonly stated that LT is exactly at a concentration of 4.0 mmol, which is a good starting point, but is certainly not definitive. It is also useful to set your other training zones based on a percentage of your threshold, making it more effective than a generic formula based on your age or max heart rate.
Given the importance, I was curious if I would get similar results from a practical test that is much more accessible. That’s where the 30-minute field test comes in—a protocol popularized by Joel Friel, and designed to mimic the conditions of a lab test in your regular training environment.
Methodology
Lab Lactate Test
For the lab test, I followed a standard incremental protocol:
- Sport: I am primarily a runner, so I ran on a treadmill at a constant 10% grade to mimic the mountain trail races I am training for
- Procedure: I began with a 15 minute warm-up at 3.0mph and then gradually increased the speed by 0.4 mph each step, with blood samples taken at 5 minute intervals.
- Data Collection: My heart rate and lactate concentration were recorded at each stage. The LT was identified as the point where there was a distinct inflection in the lactate curve. I continued for 2 more stages to show the full curve and continued increase.
- Graph: The graph below plots lactate concentration versus heart rate. You can see the characteristic upward inflection that signifies my LT (labeled LT2), which was pinpointed at a heart rate of 164bpm. The lactate reading was 3.0 mmol (lower than the often stated 4.0) and rose sharply after that point.
30-Minute Field Test
The field test, on the other hand, was much simpler:
- Procedure: The process is simple, but not easy, You go as hard as you can for 30 minutes, and your average heart rate over the last 20 minutes should be your estimated lactate threshold. I also ran this on the treadmill at 10% to eliminate other variables as much as possible.
- Measurements: I recorded my heart rate continuously with a reliable monitor (Garmin HRM Pro Plus), and steadily increased my speed throughout the 30 minutes to an effort that was hard but doable.
Results: A Promising Correlation
After conducting both tests, I was pleased to see that the LT heart rate identified in the lab matched the average heart rate during the field test exactly.
This means that my body responded similarly in both controlled and real-world settings. For athletes looking for a simpler way to test, this is great news—your 30-minute field test can serve as a practical substitute for expensive lactate measurements.
This seems to be even more precise than the estimate from Garmin, which has my lactate heart rate at 168bpm. Referring back to my home lab test, my blood lactate concentration was 4.7 mmol at 168bpm, definitely over threshold.
Discussion: Implications for Training
Practicality Over Precision
While lab tests offer precise measurements under controlled conditions, the field test’s comparable results suggest that it’s a valid method for determining lactate threshold. The field test is not only simple, but also convenient. It allows you to test yourself in the conditions you train in, something that can be more reflective of your day-to-day performance.
How to Implement the Field Test
If you’re considering the 30-minute field test, here are a few tips based on my experience:
- Pacing is Key: If you’re not used to pacing a 30 minute effort, it can be easy to go out too hard (or easy). This is the hardest part. It should start as moderately difficult, and if it’s getting increasingly harder as you maintain the same speed, you’re probably right where you need to be.
- Use Reliable Gear: A dependable heart rate monitor is essential. Accuracy in your heart rate readings is what makes the comparison valid.
- Controlled Conditions: Try to perform the test under similar conditions that you train or race in
Training Adjustments
Knowing your LT heart rate is important for structuring your workouts. You can use this data to set your training zones, ensuring that you’re working at the optimal intensity to boost your aerobic capacity without overreaching. There are multiple views on zones and training, but to stick with Joel Friel, he recommends the following for running:
Run Zones
Zone 1 Less than 85% of LTHR
Zone 2 85% to 89% of LTHR
Zone 3 90% to 94% of LTHR
Zone 4 95% to 99% of LTHR
Zone 5a 100% to 102% of LTHR
Zone 5b 103% to 106% of LTHR
Zone 5c More than 106% of LTHR
Conclusion: A Viable Alternative
My findings support the use of the 30-minute field test as an effective, accessible substitute for lab-based lactate testing. The similar heart rate readings from both methods confirm that athletes can use the field test to monitor and adjust their training intensity. This is was an n=1 experiment, but is still encouraging to see.
Incorporating regular field tests into your training regimen can help track progress and fine-tune your workouts.