【Deep Dive】How Gravel Cyclists Break Through Plateaus with Zone 2 Running? Exploring the Science of LT1 and Capillary Angiogenesis: 2026 Latest Sports Medicine Perspectives

Chapter 1: Introduction: The Physiological Background of Endurance Demands in Gravel Biking

Gravel biking is one of the fastest-growing disciplines in the global endurance sports world in recent years. Unlike smooth paved roads, gravel sections (including crushed stone, dirt roads, forest trails, and unpaved paths) feature extremely high rolling resistance and highly irregular vibration. Riding on such surfaces, cyclists not only need to overcome aerodynamic drag but also expend enormous energy coping with the micro-muscle damage and kinetic energy loss caused by surface vibration.

Physiologically, gravel events (such as the famous Unbound Gravel 200-mile race, which often takes 10 to 15 hours) are an ultimate test of aerobic endurance. In such prolonged events, the key determinant of a rider’s performance is not short-duration maximal anaerobic power, but rather the rider’s Aerobic Base—the ability to utilize fat as the primary energy source during extended riding while efficiently sparing muscle glycogen stores.

However, many gravel cyclists hit a “performance ceiling” after accumulating years of aerobic training. No matter how much they increase their weekly riding mileage, their aerobic capacity (primarily maximal fat oxidation rate and aerobic threshold power) becomes increasingly difficult to improve. At this point, simply adding more riding time often leads to excessive localized muscle fatigue and joint overuse. Research from 2026 in sports medicine and cross-training indicates that incorporating “Zone 2 Running” into a cycling training schedule can activate capillary angiogenesis and mitochondrial metabolic pathways through novel physiological stimuli, helping gravel cyclists break through their aerobic endurance plateau.

Chapter 2: Exercise Physiology: Definitions and Interactions of the First Lactate Threshold (LT1) and Second Lactate Threshold (LT2)

In exercise physiology, accurately defining two key lactate threshold points is essential for evaluating a cyclist’s aerobic capacity: the first lactate threshold (LT1) and the second lactate threshold (LT2).

• First Lactate Threshold (LT1): This represents the critical point where the body transitions from “pure aerobic metabolism” to “mixed metabolism.” Below LT1, blood lactate concentration remains at resting baseline levels (typically below 2.0 mmol/L), fat oxidation reaches its maximum rate (FATmax), and slow-twitch muscle fibers can easily clear all produced lactate.
• Second Lactate Threshold (LT2 / Lactate Turnpoint): This represents the maximum limit where lactate production and clearance rates reach dynamic equilibrium (blood lactate concentration typically between 3.0 – 4.5 mmol/L). Once power output exceeds LT2, lactate accumulates exponentially, and the body rapidly shifts to reliance on the glycolytic system, leading to fatigue onset within a short period.

Many cyclists have a serious training misconception: they overemphasize improving LT2 (i.e., FTP) while neglecting the development of LT1 (aerobic threshold). In fact, LT1 is the true foundation that determines endurance limits.

$$V_{\text{aerobic capacity}} \propto LT1_{\text{power}}$$

When a cyclist has a higher LT1 power, it means that during high-speed cruising, the body remains in the fat oxidation zone, sparing glycogen. If LT1 is too low, even with a high LT2, the rider will face “bonking” in a long gravel race due to premature glycogen depletion.

The core physiological purpose of Zone 2 running is to force the body to undergo prolonged low-intensity stimulation in the zone below LT1, thereby shifting the LT1 curve to the right (i.e., lactate begins to accumulate only at higher power/heart rate). Once LT1 is elevated, the rider’s aerobic base expands, and LT2 naturally gains greater upward headroom.

Chapter 3: Why Can “Running” Help Cyclists? Exploring the Cross-training Effects of Aerobic Adaptations Between Running and Cycling

For a long time, the cycling world has held a belief: “To ride fast, you can only ride; running will ruin pedaling muscle memory.” However, research in molecular biology and cardiopulmonary physiology shows that aerobic system adaptations possess a high degree of Cardiovascular Cross-transfer Effects.

Running and cycling differ in their physiological adaptation emphases:

1. Overall Stimulation of the Cardiopulmonary System: Running is a full-body anti-gravity exercise that recruits more skeletal muscle groups (including the core, upper body arm swing, glutes, and lower limbs). This means that at the same perceived exertion (RPE), stroke volume and oxygen uptake during running are typically higher than during cycling. This provides more significant stimulation for left ventricular hypertrophy and myocardial contractility.
2. Diversity of Muscle Group Recruitment: Cycling primarily engages the quadriceps and gluteus maximus in concentric contraction, lacking impact forces. Running, however, involves substantial eccentric contraction, effectively activating the gluteus medius, deep calf muscles, and plantar fascia. These muscle groups primarily serve as auxiliary stabilizers during cycling; running enhances the endurance of these stabilizers, thereby improving pelvic stability when riding and reducing the likelihood of lower back pain.
3. Systemic Stimulation of Capillaries and Mitochondria: Running induces more dramatic redistribution of systemic blood circulation, promoting capillary network development in non-cycling primary muscle groups.

The table below compares the aerobic training characteristics between running and cycling:

For gravel cyclists, incorporating 1-2 Zone 2 running sessions per week can maintain and enhance systemic cardiopulmonary aerobic adaptations without adding localized cycling muscle fatigue (avoiding chronic inflammation of the quadriceps from excessive pedaling), achieving a “relieving the siege by attacking the source” cross-training effect.

Chapter 4: The Scientific Mechanisms of Zone 2 Running on Capillary Angiogenesis and Mitochondrial Density

From a cellular and molecular biology perspective, the reason Zone 2 running can break through endurance plateaus lies at its core in activating the PGC-1α (mitochondrial biogenesis master gene) metabolic pathway, thereby driving dramatic improvements in capillary angiogenesis and mitochondrial density.

1. The Scientific Mechanism of Capillary Angiogenesis

Capillaries are microscopic channels that deliver oxygen and nutrients to skeletal muscle fibers and carry away carbon dioxide and lactate. The capillary density surrounding slow-twitch (Type I) fibers directly determines the aerobic ceiling of the muscle.

• Stimulus: During Zone 2 super-slow running training, the shear stress of blood flowing through the muscles stimulates the release of Vascular Endothelial Growth Factor (VEGF).
• Outcome: VEGF initiates signal transduction, prompting existing capillaries to branch out and form new vascular networks. The increased capillary density shortens the distance oxygen must diffuse from the blood to the interior of the muscle fibers and greatly enhances the transmembrane transport and clearance efficiency of lactate.

2. Mitochondrial Density and the PGC-1α Pathway

Mitochondria are the cell’s “power plants,” where fats and glucose undergo aerobic oxidation to generate ATP.

• Molecular Mechanism: Zone 2 training causes a sustained, slight rise in calcium ion concentration within muscle cells and a mild hydrolysis of ATP, which activates the AMP-activated protein kinase (AMPK) and p38 MAPK pathways. Together, these activate the transcriptional coactivator PGC-1α.
• Outcome: PGC-1α enters the nucleus, promoting the replication and transcription of mitochondrial DNA, leading to a significant increase in mitochondrial density and volume.

Super-slow running Zone 2 training (sustained isotonic contraction)
      │
      ├───► Sustained slight rise in calcium ions & increased AMP/ATP ratio
      │
      ▼ Activation
 AMPK & p38 MAPK signaling pathways
      │
      ▼ Activation
   PGC-1α (transcriptional coactivator)
      │
      ├───► Promotes VEGF release ───► Capillary angiogenesis (denser vascular network)
      │
      └───► Promotes mtDNA replication ───► Increased mitochondrial density (enhanced fat metabolism)

When a gravel rider enhances their capillary network and mitochondrial reserve through super-slow running, their quadriceps and glutes gain a qualitative improvement in their ability to uptake and utilize oxygen upon returning to the bike. This manifests as a lower heart rate and sustained power output on the same climbs.

Chapter 5: Super-Slow Running Schedule for Gravel Riders: Balancing Cycling and Running Volume to Prevent Injury

Despite the immense physiological benefits of super-slow running, the greatest risk for cyclists transitioning to running is injury. Cycling is a non-impact sport; a rider’s joints and bones have long adapted to a non-impact environment. When running, however, each foot strike subjects the body to impact forces of 2 to 3 times body weight. Jumping into high-intensity or long-distance running without preparation can easily lead to shin splints (medial tibial stress syndrome), patellofemoral pain syndrome (runner’s knee), or Achilles tendinitis.

Therefore, gravel riders must strictly adhere to the principles of “progressive overload” and “low intensity” when scheduling their super-slow running.

1. Gravel Rider Super-Slow Running Transition Schedule (6-Week Plan)

• Weeks 1-2: Adaptation Phase
  • Super-slow running schedule: 1 session per week, 20 minutes each.
  • Execution method: Use the Run-Walk Method, running for 3 minutes and walking for 1 minute, strictly keeping heart rate in the aerobic zone (Zone 2, approximately 60-70% of max heart rate).
  • Cycling schedule: Maintain normal riding.
• Weeks 3-4: Foundation Phase
  • Super-slow running schedule: 2 sessions per week, 30-40 minutes each.
  • Execution method: Continuous super-slow running, maintaining a cadence of 170-180 SPM (a high cadence shortens airtime, reducing the impact force of each landing).
• Weeks 5-6: Consolidation Phase
  • Super-slow running schedule: 2 sessions per week. One 45-minute base super-slow run; one 60-minute long slow distance (LSD) run, keeping heart rate at the lower end of Zone 2.

2. Determining Training Zones and Heart Rate Control

When performing super-slow running, you must ensure the intensity is in Zone 2 (below the first lactate threshold, LT1).

• Subjective Feel Test: The Talk Test. You should be able to hold a full conversation with someone else comfortably without needing to stop and gasp for air. If you can only utter single words, the intensity has crossed into Zone 3 (threshold zone), and you must slow down immediately.
• Heart Rate Calculation: The Karvonen Formula can be used to precisely calculate the Zone 2 heart rate range:
  $$HR_{\text{target}} = (HR_{\text{max}} - HR_{\text{rest}}) \times (0.60 \sim 0.70) + HR_{\text{rest}}$$

Chapter 6: Latest 2026 Sports Medicine Perspective: The Strengthening Effects of Running Impact Loading on Bone Density and Joint Connective Tissue

A 2026 clinical study published in the Journal of Bone and Mineral Research focusing on long-term cyclists indicated that pure cyclists, due to their long-term exposure to a non-weight-bearing and non-impact exercise environment, have significantly lower bone mineral density (BMD) in the lumbar spine and femoral neck compared to runners of the same age. Some veteran riders even showed early signs of osteopenia.

In mountain and gravel bike off-road events, riders frequently face impacts and vibrations from rough terrain. If a rider’s skeletal system and joint connective tissues are not strong enough, these high-frequency vibrations are transmitted directly to the spine and joints, causing lower back pain and chronic knee inflammation.

The “Ground Reaction Force” (GRF) of running becomes an invaluable bone-strengthening agent:

1. Bone Remodeling: The vertical impact of running foot strikes causes microscopic deformations in the bone, activating osteocytes to release chemical signals. This promotes osteoblast activity, accelerating calcium deposition, thereby significantly increasing bone density in the spine and pelvis and enhancing shock resistance.
2. Tendon Stiffness: The eccentric contractions of running stimulate collagen synthesis in the Achilles tendon, patellar ligament, and plantar fascia, increasing the tendons’ elastic energy storage and stiffness. Stronger tendons transmit the force generated by the quadriceps more efficiently during the pedal stroke, reducing energy loss during transmission.

In summary, super-slow running (Zone 2 training) for gravel cyclists is not only a tool for aerobic breakthroughs at the cardiorespiratory and metabolic levels, but also a sports medicine prescription for strengthening bones and preventing joint overuse injuries. By scientifically balancing running and cycling, riders can build a more powerful aerobic engine and a sturdier skeletal frame without increasing muscular oxidative fatigue, allowing them to confidently tackle the harsh challenges of any rugged wilderness.

Related Reading

• 【Professional Guide】Analyzing Gravel Bike Super Slow Jogging (Zone 2 Training): The Perfect Balance of First Lactate Threshold (LT1), Capillary Angiogenesis, and Fatigue Control: A Systematic Data-Driven Approach
• 【Professional Guide】Analyzing Gravel Bike Super Slow Jogging (Zone 2 Training): The Perfect Balance of First Lactate Threshold (LT1), Capillary Angiogenesis, and Fatigue Control (Part 2) Practical Guide
• 【Sports Science】Application of Super Slow Jogging (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
• 【In-Depth Analysis】How Can Road Cyclists Use Super Slow Jogging (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 Pushing Limits