Lactate testing and zone 2 training

Introduction 

Earlier this year, I trained extensively in preparation for my first ultra trail marathon (60km) in Southern Spain, which took place on the 5th of April 2025. Along the way, I discovered just how transformative Zone 2 training can be—not only for endurance but also for energy efficiency and lactate utilization. Using my own experience as an example, I hope to share insights on how proper training affects performance and recovery.

Training Overview: Three Phases
Phase 1 – Strength and Power
The first phase focused on building strength and power through resistance training while gradually increasing Zone 2 running volume. The goal was to move weight quickly, improve muscular power, and slowly introduce my body to endurance running.

Phase 2 – Speed and Leg Strength
During the second phase, I concentrated on leg strength and speed. This involved hill repeats, VO2max efforts, and tempo runs, while maintaining long Zone 2 runs on weekends. The combination of strength and endurance work prepared my legs to handle the demands of long off-road runs.

Phase 3 – Peak Volume
The final phase aimed to increase running volume, peaking three weeks before the race. I completed back-to-back 30km off-road runs to simulate race conditions and build resilience. During this period, I had a minor right-side adductor tendon issue. I treated it early with targeted isometric exercises, including the Copenhagen exercise, and was able to continue training without setbacks.

Blood Lactate Testing
A crucial part of understanding my performance was a blood lactate test conducted on a treadmill ramp test by my Physio and Physiology student, Maggie. This test highlighted how Zone 2 training had improved my ability to use lactate as a fuel source, expanded my Zone 2 range, and raised my second lactate threshold (LT2). Lactate is not a waste product; it is a fuel source for muscles and the brain. When we exercise at low intensities like Zone 2, lactate is produced in small amounts and efficiently recirculated. Only a small fraction enters the bloodstream, which is what we measure with a lactate test.

Understanding Lactate and Zone 2
Zone 2 training is low-intensity exercise where you can breathe through your nose and hold a conversation, allowing your body to use both fats and carbohydrates for energy efficiently. Fat stores are vast but slow to access, so at higher intensities, the body relies more on glycogen, producing more lactate and hydrogen ions. These hydrogen ions cause the acidic environment that leads to muscle burn and the need to slow down. Many athletes still believe lactate is “poison” and call it lactic acid, but in reality, lactate is a valuable fuel. Blood lactate thresholds allow us to track training intensity: LT1 (~2 mmol/L) marks leaving Zone 2 to enter Zone 3, and LT2 (~4 mmol/L) indicates the Threshold Zone (Zone 4). During my test, my heart rate of 144 bpm corresponded to a lactate of 1.3 mmol/L, confirming that I could sustain long runs in Zone 2 comfortably. Even at 150–155 bpm, I stayed in Zone 2, which was excellent preparation for a long ultra trail race in hilly terrain.

Comparing Athletes
Sprinters or triathletes focusing on short, intense events produce and tolerate more lactate due to fast-twitch muscle fibers. However, they struggle to sustain long efforts and have a smaller Zone 2 capacity. Endurance athletes, like myself, develop slow-twitch fibers, mitochondria, and capillaries that allow efficient fat and lactate utilization, delaying fatigue. Even elite cyclists like Tadej Pogačar can produce 350W while remaining in Zone 2, under 2 mmol/L of lactate, illustrating the efficiency of trained endurance metabolism.

Physiological Adaptations from Zone 2 Training
Zone 2 training results in several key physiological adaptations: increased mitochondria for energy production, better capillary density, enhanced fat oxidation reducing glycogen reliance, and more slow-twitch fibers for high oxidative capacity and efficient lactate clearance. These adaptations allowed me to recover quickly between consecutive long runs and maintain consistent training leading up to the ultra trail marathon.

Race Reflections
By the time the race occurred in April 2025, I was physically and mentally prepared. My Zone 2 training enabled me to sustain long periods of running, efficiently using fats and carbohydrates, and avoid excess lactate buildup. The structured approach to training, attention to lactate thresholds, and recovery strategies played a pivotal role in my performance.

Conclusión
This journey highlighted the power of understanding and respecting your body’s energy systems. Zone 2 training is not only beneficial for endurance but also promotes recovery, energy efficiency, and optimal lactate utilization. For athletes aiming to improve performance in long-distance events, prioritizing Zone 2 work and monitoring lactate thresholds can make a significant difference.