[Professional Guide] Analyzing Ultra-Slow Running (Zone 2 Training) for Gravel Bikes: The Perfect Balance of First Lactate Threshold (LT1), Capillary Angiogenesis, and Fatigue Control (Part 2) Practical Guide

Gravel bike Zone 2 training is often reduced to an oversimplified slogan: Ride slow, build a thick aerobic base. That statement isn’t wrong, but almost all the engineering details are missing. For gravel riders, the real challenge has never been whether they’re willing to ride slow, but rather how to keep most of your time at or below the first lactate threshold (LT1) amidst terrain, vibration, rolling resistance, fueling, heart rate drift, and fatigue accumulation.

Although the topic says “ultra-slow running,” in the gravel bike context, it’s not actually running, but rather long-duration, low-to-moderate intensity steady-state endurance riding with LT1 as the upper boundary. The value of this type of training isn’t just about “logging more miles,” but because it simultaneously addresses three things gravel riders care deeply about:

1. Improving the stability of long-duration power output
2. Promoting capillary and peripheral metabolic adaptations
3. Building better durability at a lower fatigue cost—that is, the ability to maintain performance over extended periods

This is a practical guide. The focus isn’t on rehashing theory, but on directly translating LT1, capillary growth, and fatigue management into how you ride each week, how you control each session, and how you judge whether you’re still in the right zone during the latter half of a ride.

1. First, Let’s Define Terms: For Gravel, Zone 2 is Best Operationalized as “At or Below LT1”

The biggest source of confusion with Zone 2 is that different systems use different numbering. Five-zone, seven-zone, and three-zone systems all refer to different ranges for Zone 2. If you directly apply someone else’s workout numbers, you often end up with the same name referring to a different thing.

For gravel practice, the safest approach is to think in a three-zone model first:

• Zone 1: Below LT1 / VT1
• Zone 2: Between LT1 and LT2
• Zone 3: Above LT2

However, in common training parlance, what people usually mean by Zone 2 Training is: long-duration, low-intensity endurance riding with LT1 as the upper limit. This article will use this operational definition from here on to avoid naming errors.

Why is this definition more reasonable? Because Sanders et al., tracking well-trained road cyclists over ten weeks of training, found that when using power or heart rate zones, approximately 79.5-86.8% of training time fell into the first zone, demarcated by the first and second lactate thresholds—that is, a large volume of low-intensity work below LT1. This shows that mature endurance training doesn’t pile most of the time into the moderately hard middle zone, but rather keeps the vast majority of training volume below LT1.

Therefore, for gravel riders, the first principle is simple:

If your Zone 2 ride consistently feels like tempo by the end, you're probably not doing LT1 training—you're accidentally doing gray-zone training.

2. How to Find Your Practical LT1 Range: Look at Power, Heart Rate, and RPE Together, Not Just One Number

If you have lab testing, the best approach is to use:

• Power at LT1 or VT1
• Heart rate at LT1 or VT1
• Cadence, breathing pattern, and perceived effort at that intensity

If you don’t have lab testing, you can use field-based approximations to create a very practical setup. The goal isn’t perfection, but avoiding obvious errors.

1. Power Ceiling

For most endurance riders, gravel LT1 training can initially target:

Approximately 65-78% of FTP

But this is just a starting point, not an absolute. Because FTP, LT1, and MLSS are not the same thing, and terrain and fatigue will shift your actual metabolic boundaries.

2. Heart Rate Ceiling

If you know your LT1 / VT1 heart rate, the most practical approach isn’t to “ride right at it the whole time,” but to treat it as a ceiling:

• Early on, aim to stay 5-10 bpm below your LT1 heart rate
• In the middle and later stages, if heart rate drifts upward due to heat, dehydration, or terrain, prioritize not exceeding LT1 heart rate for extended periods

3. Perceived Effort and Breathing

This intensity should have the following characteristics:

• You can speak in full short sentences
• Breathing is deeper but not rapid
• Legs feel like they’re working, but not continuously building up acid
• After 2 hours, you feel like you “could keep riding,” not just “gritting your teeth to finish”

Here’s a practical reference table:

3. Why Gravel Zone 2 is Harder to Control Than Road: Metabolic Cost is Usually Higher at the Same Speed

If you ride gravel with road bike instincts, the most common mistake is pushing too hard based on speed. Because the metabolic cost of off-road or gravel terrain is often higher than what the speed suggests.

Macdermid et al., comparing road and off-road climbing, found that at the same terrain profile and prescribed speed, off-road conditions required higher power (312 vs 280 W), higher VO2, and higher heart rate (170 vs 161 bpm). The researchers attributed the difference to higher vibration, rolling resistance, and additional damping demands. Mastroianni et al.'s gravel course study also showed that off-road cycling energy demand can reach approximately 68.5% VO2peak, similar to trail running.

The practical implications of these findings are straightforward:

1. The same 25 km/h is not necessarily low intensity on gravel
2. When the surface is loose, tire pressure is low, or vibration is significant, your Zone 2 power might not change, but your heart rate and perceived fatigue will be higher
3. If you only use speed as a metric, you’ll often turn what should be LT1 into tempo or higher

So for gravel Zone 2, use this priority order:

Power / Heart Rate > Breathing and RPE > Speed

Speed should be treated as an outcome, not a control variable.

4. The Relationship Between LT1 and Capillary Growth: Why Long, Low-Intensity Riding Isn’t “No Stimulus”

Many people mistakenly believe that only high intensity counts as a training stimulus. This doesn’t hold true for capillary and peripheral metabolic adaptations.

Shono et al. had 11 young men perform 6 weeks of training at 60 minutes per session, 5 times per week, at the lactate threshold (LT) and found:

• capillary-to-fiber ratio increased from 1.97 to 2.49
• VO2max improved by approximately 5%
• LT-VO2 improved by approximately 27%

In other words, sustained endurance training at low to moderate-low intensity can, by itself, increase skeletal muscle capillary supply.

Even more interesting is the work of Hoier et al. They compared the stimulation of angiogenic signals between moderate-intensity and intense intermittent exercise and found that the increase in VEGF from high-intensity intervals was significantly lower—about 60% lower than from moderate-intensity work. Furthermore, 4 weeks of high-intensity training in individuals who had already completed moderate-intensity endurance training did not further increase capillarization.

This doesn’t mean high intensity isn’t important; it means:

If your goal is to steadily build a peripheral oxygen-delivery and metabolic foundation, moderate-to-low intensity, long-duration, repeatable work is often more suitable than constantly going hard.

For gravel, this is especially important because the limits of gravel riding come not only from the cardiorespiratory system, but also from:

• The local muscular load of constantly correcting bike stability
• Postural tolerance under prolonged low-to-moderate torque
• The additional cost of high-frequency, low-amplitude vibration

If your capillary supply and peripheral metabolic foundation are better, the same long gravel cruise will be less prone to accumulating “invisible but ever-building” local fatigue.

5. The Key to Fatigue Control: Ride in Zone 2 Long Enough, and LT1 Itself Will Drift Down

This is what most people overlook. LT1 isn’t fixed for the whole day after a morning test; it can drift downward after prolonged riding.

Research by Stevenson et al. showed that after subjects completed a 2-hour ride at 90% VT1, when the moderate-to-heavy transition was re-measured, they found:

• Power at VT1 dropped from 217 W to 196 W
• The lactate-derived transition estimate also decreased
• But the corresponding heart rate actually increased

Another study from the same team showed that after prolonged exercise, power at VT1 dropped by approximately 10%, with increased breathing frequency and decreased tidal volume. Research by Hamilton et al. further indicated that individuals with better VT1 durability showed smaller declines in 5-minute TT performance after prior prolonged moderate-intensity riding.

These results have very strong practical implications for gravel:

1. Your Zone 2 in the first half may not still be Zone 2 by hour three
2. In long gravel rides, if you only hold a fixed power and ignore later-stage heart rate and breathing, you’ll often slowly ride into the gray zone
3. Durability isn’t an abstract term—it’s your ability to hold your metabolic boundary after hours of riding

Therefore, LT1 training for gravel cannot just set a fixed wattage; it needs a late-ride correction mechanism.

6. Practical Guide: How to Structure, Ride, and Adjust Gravel Zone 2 Workouts

Below are three of the most practical templates. They aren’t the only answers, but they cover the needs of most gravel riders.

Template A: Basic Steady-State Ride

Suitable for those just building LT1 capacity.

• Duration: 90-150 minutes
• Intensity: Below LT1, recommended starting at 65-75% FTP
• Terrain: Rolling is fine, but avoid sustained steep climbs
• Goal: Steady breathing, steady fueling, steady pedaling

The focus isn’t average speed; it’s maintaining the following in the second half:

• RPE 3-4/10
• Not exceeding LT1 heart rate for extended periods
• No frequent high-torque surges due to terrain

Template B: Segmented LT1 Accumulation Workout

Suitable for busy people with limited total hours who want to accumulate time more precisely.

• 20-30 minutes warm-up
• 2-3 × 25-40 minutes of steady LT1 segments
• 5-8 minutes very easy between segments

The benefit of this workout is higher focus and easier intensity control on complex gravel routes.

Template C: Long-Duration Durability Ride

Suitable for preparing for gravel events or races lasting 3+ hours.

• Duration: 180-300 minutes
• First 60-90 minutes: conservative start, below the LT1 ceiling
• Middle: settle into a steady cruise
• Final portion: allow power to drift slightly down, but do not accept RPE running out of control

The core of this session isn’t producing the highest average watts; it’s practicing:

1. How to adjust power based on heart rate and breathing in the later stages
2. Whether fueling is sufficient to prevent excessive drift
3. Whether you can return to a steady state after technical sections, rather than progressively riding harder and harder

7. The Three Most Important Practical Monitoring Metrics

1. Pa:HR decoupling or Heart Rate-Power Decoupling

Can be simplified as:

Decoupling % = (HR/Power ratio in second half - HR/Power ratio in first half) / HR/Power ratio in first half × 100%

This isn’t an official threshold from the studies cited here, but a common practical monitoring method. For most LT1 riding:

• If decoupling is less than approximately 5%, intensity, fueling, and environmental control are usually stable
• If it clearly exceeds 5-6%, it often means you’re riding too hard, too hot, too dehydrated, or your LT1 has already dropped in the later stages

2. Uphill Torque Surge Count

The place where gravel most easily breaks Zone 2 isn’t the flats—it’s loose climbs, gravel ascents, and accelerating out of corners. It’s recommended to simply record:

• How many times in a ride you exceed 120% of target power
• Whether those surges were necessary

If it happens every 10 minutes, you’re mostly not doing LT1 riding—you’re doing variable tempo in disguise.

3. Late-Ride Technical Quality

Observe whether, in the final 1/3 of the ride, you experience:

• Worse line choice
• Braking points becoming more conservative or erratic
• Delayed acceleration out of corners
• Especially stiff upper body

These usually tell you earlier than average power that fatigue cost is already eroding true gravel performance.

8. How to Schedule Your Week: Zone 2 Should Build You Up, Not Steal from High-Quality Sessions

For gravel riders, Zone 2 success isn’t about any single session; it’s about the overall weekly fatigue structure. Here’s a practical weekly template:

A simple criterion for judging whether your scheduling is correct:

The day after a Zone 2 session, you should still be able to complete technical or high-quality training—not just feel exhausted.

If that’s not the case, your so-called Zone 2 is actually too close to the gray zone.

IX. Conclusion: Gravel Zone 2 Is Not Just Riding Slow—It’s Using LT1 to Guard the Metabolic and Fatigue Boundaries

Truly high-quality gravel Zone 2 is not fundamentally about “riding slow,” but rather:

• Keeping most of your time below or near LT1 whenever possible
• Accepting that gravel terrain raises metabolic cost, so don’t chase intensity with speed
• Using long, repeatable low-to-moderate intensity stimuli to build capillary and peripheral endurance adaptations
• Acknowledging that LT1 drifts downward in the latter half of long rides, so heart rate, breathing, and power must be corrected together

If we distill the original research into practical sentences, it roughly comes down to:

1. Endurance riders should naturally spend the bulk of their training time below LT1
2. Low-to-low-moderate intensity training increases capillary supply—this is not “no stimulus”
3. Off-road / gravel often carries higher power and cardiorespiratory cost at the same speed
4. After prolonged riding, VT1/LT1 declines, so Zone 2 must be managed dynamically

Therefore, for gravel riders, the most mature Zone 2 capability is not whether you can endure slowness, but whether you can continuously keep yourself within the correct physiological boundaries throughout the entire ride, and stack up usable training volume at the lowest fatigue cost. That is the true intersection of LT1, capillary angiogenesis, and fatigue control.

Related Reading

• 【Professional Guide】Analyzing Gravel Bike Zone 2 Training: The Perfect Balance of First Lactate Threshold (LT1), Capillary Angiogenesis, and Fatigue Control—A Data-Driven Systematic Approach
• 【In-Depth Analysis】How Gravel Riders Use Zone 2 Training to Break Through Plateaus? Exploring the Scientific Mechanisms of First Lactate Threshold (LT1) and Capillary Angiogenesis: 2026 Latest Sports Medicine Perspectives
• 【In-Depth Analysis】How Road Cyclists Use Zone 2 Training to Break Through Plateaus? Exploring the Scientific Mechanisms of First Lactate Threshold (LT1) and Capillary Angiogenesis: The Key to Sub-3 Marathons and Breaking Limits
• 【Sports Science】The Application of Zone 2 Training in Mountain Biking (MTB): Exploring the Physiological Evidence of First Lactate Threshold (LT1) and Capillary Angiogenesis, and the Golden Rules of Workout Planning