VO2 Max Explained: The Marathon Runner's Guide to Lactate Threshold and Endurance Speed
In the age of smartwatches, every runner is obsessed with metrics. The number that often dominates the conversation is VO2 Max—the supposed ultimate indicator of aerobic potential. While a high VO2 Max is vital, relying solely on this number can be misleading for the dedicated marathoner.
To cut through the confusion and deliver actionable, science-backed advice, MarathonJournal.com consulted with Dr. Gregory Grosicki, Assistant Professor and Director of the Exercise Physiology Laboratory at Georgia Southern University. Dr. Grosicki, a seasoned endurance athlete and researcher, provides the definitive guide to understanding, testing, and training the three physiological pillars that truly determine marathon performance.
What is VO2 Max and Why Does it Matter to Runners?
VO2 Max, or the maximal volume of oxygen consumption, is the gold standard for measuring cardiorespiratory fitness. It quantifies the maximum rate at which your body can take in, transport, and utilize oxygen to produce energy (ATP) during intense exercise.
The metric is most commonly presented as a value relative to body weight, expressed in milliliters of oxygen per kilogram of body mass per minute. Dr. Grosicki describes VO2 Max as the size of your engine. A higher number means a bigger engine and greater overall capacity for aerobic work.
"VO2 max simply describes the maximal amount of oxygen that an individual can take up and consume... We're consuming this oxygen to produce energy during exercise." – Dr. Gregory Grosicki
Accuracy Alert: Your Running Watch is Only Estimating
The VO2 Max displayed on your GPS device is a predictive estimate, not a direct measurement. It relies on an algorithm that compares your heart rate and running speed against vast reference datasets.
The truth is, these watch estimates can be 5 to 10% off a true lab-measured value. Dr. Grosicki points out a common confusion: running in high heat or humidity will elevate your heart rate. Your watch, relying on that heart rate data, may incorrectly report a decline in your VO2 Max, even if your fitness has actually improved.
For serious data integrity, obtaining a lab test at a university is the only way to get a definitive measurement. However, for daily tracking, the watch's primary value is simply showing the trend of your fitness over time.
📈 The 3 Pillars of Marathon Speed: The Trainable Edge
The critical lesson for endurance athletes is that while a high VO2 Max is a necessity, it is insufficient on its own. Dr. Grosicki confirms that VO2 Max is largely genetic and tends to plateau after just a few months of intense training.
Marathon race time is determined by the intersection of three factors:
1. The Ceiling: VO2 Max (Engine Capacity)
The Problem: You can only sustain your maximum effort for about 4 to 6 minutes.
The Solution: Shorter, high-intensity efforts are still necessary to lift the maximum potential. Training at this level ensures your ceiling is as high as it can be.
2. The Cruising Speed: Lactate Threshold (LT)
This is the most critical and performance-defining metric. It is the percentage of your total VO2 Max that you can sustain before fatigue-inducing metabolites (like lactate) accumulate faster than your body can clear them.
Why LT is Key: A marathon runner must sustain a high percentage of their capacity typically 85% for elites for the duration of the race. Training the LT directly improves your sustainable marathon pace.
Trainability: Unlike VO2 Max, the Lactate Threshold is highly plastic and responds to targeted training over long periods, making it the primary focus for endurance gains.
3. The Efficiency: Running Economy (RE)
Running Economy is the oxygen cost of maintaining a submaximal speed. It is the measure of your biomechanical efficiency—how smoothly and economically you move.
Why RE is Key: Two runners with the same VO2 Max and LT can run vastly different race times if one is a more efficient mover, using less oxygen to cover the same distance.
Trainability: RE improves through years of consistent running, specific form drills, and targeted strength work that optimizes movement patterns.
Training for Speed: How to Elevate Your Threshold
To truly improve your marathon performance, your training emphasis should shift from merely achieving a high VO2 Max score to maximizing your Lactate Threshold. Dr. Grosicki emphasizes the principle of specificity in training:
Increasing VO2 Max (Lifting the Ceiling): This requires High-Intensity Intervals of shorter duration. Think 3-5 min efforts at a near-maximal pace with ample recovery. This directly stresses the cardiorespiratory system.
Elevating Lactate Threshold (Raising the Floor): This requires Longer Threshold Training at a sustained, challenging intensity. This involves Tempo Runs or 20-30 minute efforts held at a pace you could maintain for about an hour (e.g., strong 10-mile or half-marathon effort). This trains the body to clear lactate more efficiently.
"That submaximal percentage [LT], we're probably going to want to do some longer duration threshold training."
The Strategic Takeaway: The successful marathon runner focuses their quality training on sustained tempo runs to push their threshold higher. While VO2 Max intervals are useful for peaking, consistent threshold work is the most direct path to faster, more sustainable race paces. The true measure of an athlete lies not in the size of their engine, but in their ability to run efficiently at a high gear for the duration.
— Connect with Dr. Grosicki for More Science-Backed Tips
Follow Dr. Grosicki on social media at @Dr.GregGrosicki or reach him via email at ggrosicki@georgiasouthern.edu.