In endurance sport, data is a powerful tool — but only when it’s accurate. Thresholds like FTP (Functional Threshold Power) on the bike or threshold pace on the run form the backbone of nearly every structured training plan. They guide intensity, inform fueling strategies, and define the limits we build toward in races.

But what happens when those numbers are wrong?

Whether inflated by wishful thinking, outdated testing, or a desire to train “harder,” inaccurate thresholds are more common than most athletes realize. And while they might offer a short-term ego boost in your training logs, the physiological cost can be significant — especially on race day.

This article isn’t about calling anyone out. It’s about protecting your potential. Because when your numbers are off, your zones are wrong, your training stimulus is misaligned, and your race pacing becomes a gamble. The goal is to help you understand why accurate thresholds matter, how to test them properly, and why a slight underestimation might actually be your secret weapon for a breakthrough race.

Thresholds aren’t arbitrary targets or nice round numbers — they’re physiological markers. Your Functional Threshold Power (FTP) on the bike, or your threshold pace on the run, represents the maximum effort you can sustain without accumulating fatigue-causing byproducts like lactate at a faster rate than your body can clear them.

Each training zone — from aerobic endurance to VO2 max — is defined as a percentage of these thresholds. And each zone drives a specific adaptation:

• Zone 2 (roughly 60–70% FTP or threshold pace) builds mitochondrial density and fat-burning capacity.
• Sweet spot (88–94%) develops muscular endurance without overstressing recovery.
• Threshold training (95–105%) enhances lactate clearance and increases sustainable power.

These zones are only valid if your thresholds are accurate (Allen & Coggan, Training and Racing with a Power Meter, 3rd Ed.). Misjudge your threshold, and every training zone shifts — which means you’re now chasing the wrong adaptation entirely.

Let’s say your true FTP is 300W, but your coach or platform has you training at 330W. On paper, it looks like you’re crushing workouts. In reality, you’re no longer training at threshold — you’re training in the VO2 max or anaerobic zone.

The consequences?

• You build fatigue, not fitness.
• You accumulate lactate too quickly, leading to premature muscular failure.
• Your intended aerobic adaptations don’t happen, because you’ve skipped the zone entirely.

This isn’t theory — it’s physiology. Research by Coyle et al. (1988) showed that increasing workload by just 4–5% above threshold intensity drastically reduced time to exhaustion and caused exponential lactate accumulation. A similar study by Heck et al. (1985) confirmed that blood lactate concentration spikes once work exceeds the maximal lactate steady state.

On the run, the issue compounds. Running is weight-bearing, so overestimating your threshold pace results in biomechanical strain on top of metabolic overload. Studies like Paavolainen et al. (1999) have shown that lactate accumulation combined with neuromuscular fatigue significantly limits endurance running performance.

In short: if you think you’re training like a beast because you’re hurting more than others, you might actually just be training wrong.

For Cyclists: Finding FTP

• The 20-Minute Test: Ride as hard as possible for 20 minutes and take 95% of the average power. It’s effective if you pace it well — but many athletes start too hard.
• The Ramp Test: Power increases each minute until failure. It’s convenient and fast, but can overestimate FTP for those with strong anaerobic systems.
• The 60-Minute Test: The gold standard. Ride at the highest power you can sustain for a full hour. Your average power = FTP. Brutal, but accurate.

Tip: Always do these tests when fresh, indoors if possible, and under consistent conditions for reliable comparisons.

For Runners: Setting Threshold Pace

• 30-Minute Time Trial (Daniels’ Method): Run 30 minutes at a best sustainable effort and use the average pace from the final 20 minutes as your threshold pace.
• Critical Speed Testing: Perform all-out efforts across a few distances (e.g. 400m, 1500m, 3K). Use a regression line to calculate critical speed — a close cousin to threshold pace.
• Heart Rate Drift Test: On a long steady run, track your heart rate. If it rises more than 5% in the second half without a pace change, you’re likely above aerobic threshold.

If you’re not sure where your true threshold lies, it’s often safer to slightly underestimate than overreach. Why?

• It keeps your race pacing within a sustainable physiological zone.
• It ensures your training hits the right adaptation, not just a harder effort.
• You stay consistent, recover better, and arrive at races fresh — not fried.

And if you’re truly chasing marginal gains or elite performance, VO2 max and lactate testing can provide the clarity and confidence to dial in your training precisely. Tools like INSCYD or lab-grade lactate tests can give you:

• Real lactate thresholds (LT1 and LT2)
• Fat vs carbohydrate usage
• VLamax (lactate production rate)
• Accurate zone targets

The 20-minute test is ideal for endurance athletes with a strong aerobic base, while ramp tests can flatter athletes with high anaerobic power (i.e., sprinters or athletes with high VLamax).

Why Physiology Matters

Your metabolic profile influences how valid each test is:

• High VLamax (high anaerobic power) = more contribution from anaerobic stores in short efforts → ramp test will likely overestimate your true FTP.
• High VO2 max with low VLamax (well-developed aerobic engine) = better suited to longer, steady efforts → 20-minute test or even a full 60-minute effort gives a more accurate FTP.

Coggan’s Original Protocol: The “5-Minute Blowout”

Dr. Andy Coggan’s original FTP test includes:

1. 5-minute all-out effort (to drain anaerobic reserves)
2. 10-minute easy spin
3. 20-minute time trial (FTP = 95% of avg power)

The 5-minute effort reduces anaerobic contribution to the 20-minute TT, making the result more reflective of true aerobic threshold. It’s particularly useful for athletes with high anaerobic capacity who may otherwise over-inflate their FTP.

How a Small FTP Error Can Wreck Your Race

Below is a real graph from Endure IQ based on lactate testing. It shows how lactate rises exponentially once you exceed your lactate threshold — even slightly:

*Source: *Endure IQ

Riding just above threshold = rapid lactate accumulation = early fatigue.

Even a 10% FTP overestimate (e.g., training at 330W instead of 300W) puts you well past your lactate turn point. That’s not “getting fitter.” That’s preparing to fail.

Glycogen Depletion: The Hidden Risk of Over-Estimating

Source: Winkert et al., 2022 (Frontiers in Physiology********)

This visual illustrates how higher exercise intensity leads to significantly faster glycogen depletion. When athletes train at intensities above their actual threshold — often unknowingly due to inflated zones — glycogen is burned at a rate that’s difficult to sustain or refuel in real time. This accelerates fatigue, impairs recovery, and increases the risk of hitting the wall mid-race.

Thresholds are the foundation of endurance training — but they only work if they’re real. Inflating your zones doesn’t make you fitter. It just makes you tired.

Train smart. Test honestly. Slight underestimation might cost you a few watts in training, but it could save your entire race.

Train to what your body can truly handle — not what your ego wants to believe. The race will reveal the truth either way.