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All about Vo2 max and Zone 5



VO2 max, or maximal oxygen uptake, is a measure of your body's ability to consume oxygen during intense exercise, and it's particularly important in endurance sports like cycling. It essentially indicates the maximum amount of oxygen your body can use in one minute per kilogram of body weight. The concept originated from the work of Scandinavian scientists in the 1920s, who were looking to understand how the body uses oxygen during physical activity. They developed the term to describe the point at which oxygen consumption plateaus, no matter how much the exercise intensity increases. This measure has since become a fundamental indicator of aerobic endurance and cardiovascular fitness

Understanding VO2 max, Zone 5, and sprinting involves delving into the intricate relationship between aerobic capacity, energy systems, and athletic performance. Let's break down these concepts further to appreciate how they influence an athlete's cycling capabilities, particularly during high-intensity efforts.

VO2 Max: The Aerobic Ceiling

VO2 max represents the maximum volume of oxygen that the body can utilize in a minute per kilogram of body weight. It is a crucial determinant of an athlete’s endurance capacity, especially in sports like cycling where sustained aerobic effort is required. During exercise, oxygen is used to break down substrates (like fats and carbohydrates) to produce ATP, the energy currency of the cells. The higher the VO2 max, the more ATP can be produced aerobically, enabling longer and more intense exercise.

Zone 5: High-Intensity Effort

In cycling, training zones are used to specify intensity levels. Zone 5, often referred to as the "VO2 max" zone, typically encompasses efforts at 106-120% of an athlete’s FTP (Functional Threshold Power), which is the highest power an athlete can sustain for an hour. Training in this zone pushes an athlete to operate at or near their VO2 max, improving their ability to sustain high-intensity efforts.

Exercises in Zone 5 are intense and cannot be sustained for long periods. They are typically done in intervals, such as 3-8 minutes of hard effort followed by equal or slightly longer recovery periods. This type of training is anaerobic and highly glycolytic, meaning it relies heavily on the metabolism of glucose without oxygen to produce energy quickly.

Sprinting: Beyond the Aerobic Scope

Sprinting in cycling often exceeds even the intensity of Zone 5, pushing into what might be considered an anaerobic burst. This requires quick energy that cannot be supplied fast enough by aerobic metabolism. Instead, the body relies on the anaerobic glycolysis system and the phosphocreatine (PCr) system. These systems provide rapid ATP but are only sustainable for short durations, usually less than 30 seconds.

Metabolic Responses in High-Intensity Zones

During high-intensity efforts, such as those in Zone 5 and during sprinting:

  • Anaerobic Glycolysis: The body rapidly converts glucose into lactate, producing ATP quickly but also accumulating lactate and hydrogen ions, leading to muscular fatigue and the eventual need to decrease intensity.

  • Phosphocreatine Breakdown: For the very highest efforts, like sprints, the body taps into its phosphocreatine stores. PCr can quickly regenerate ATP but depletes rapidly, usually within seconds, necessitating a shift back to glycolysis or a reduction in effort as PCr stores are replenished.

  • Oxygen Utilization: At VO2 max and during sustained high-intensity efforts, the body is using oxygen at its maximal rate, but the demand for ATP outstrips the supply that can be provided aerobically. Thus, while aerobic metabolism is maximized, anaerobic pathways play crucial roles.

Physiological Adaptations

Training in Zone 5 and performing sprints induce specific physiological adaptations:

  • Increased Cardiac Output: The heart's capacity to pump blood improves, increasing both stroke volume (the amount of blood ejected per beat) and heart rate at maximal efforts.

  • Muscle Fiber Efficiency: There is an increase in the efficiency of Type II muscle fibers, which are more powerful and quicker to fatigue but essential for high-intensity efforts.

  • Capillary Density: Regular high-intensity training increases the number of capillaries around muscle fibers, enhancing the delivery of oxygen and nutrients and the removal of waste products.

  • Mitochondrial Efficiency: Although these efforts are anaerobic, improvements in the number and efficiency of mitochondria (the cell's powerhouses) help quickly transition from anaerobic to aerobic metabolism, improving recovery between high-intensity efforts.


When you're training in Zone 5 and focusing on VO2 max efforts, there are a few common misconceptions that can affect how you approach these high-intensity workouts:

  • More Is Better: You might think that since Zone 5 training can rapidly boost fitness, doing more of it is better. However, because these efforts are so demanding, overdoing them can lead to overtraining, burnout, and increased risk of injury. It's crucial to balance high-intensity training with adequate recovery and lower intensity workouts.

  • Immediate Results: Another misconception is expecting immediate improvements in performance. While VO2 max and Zone 5 training can lead to significant fitness gains, these adaptations take time and consistent effort. Patience and persistence are key, as physiological adaptations, such as increases in mitochondrial density and improvements in lactate threshold, develop over weeks and months.

  • VO2 Max Is the Sole Indicator of Performance: It’s easy to focus too much on VO2 max as the ultimate measure of your cycling prowess. While it's a significant indicator of cardiovascular fitness, other factors like efficiency, technique, and tactics also play vital roles in your overall performance. Moreover, psychological resilience and tactical intelligence can sometimes overshadow raw physiological power.

  • High Intensity Replaces Endurance Work: There's a tendency to think that once you start doing high-intensity training, you don't need to invest as much in longer, slower distance rides. In reality, endurance rides are critical because they help develop a strong aerobic base which supports recovery and overall cardiovascular health, enhancing your ability to perform repeated high-intensity efforts.

  • Specificity Isn't Important: When targeting improvements in VO2 max, you might undervalue the role of specificity in your training. It's important to simulate the specific demands of your cycling events in training sessions. For instance, if you compete in road races with lots of hills, your high-intensity efforts should include hill climbs to condition your body and mind for what you'll face in competition.

By understanding these misconceptions, you can more effectively integrate Zone 5 and VO2 max training into your overall cycling regimen, balancing intensity with recovery, endurance, and race-specific preparations to optimize your performance and enjoyment in the sport.


Testing your VO2 max and enhancing it effectively involves a balance of accurate assessment and targeted training. As a coach, it’s crucial to guide this process carefully, ensuring that you not only measure and improve VO2 max but also maintain proper form and technique to prevent injuries and optimize performance.

Cost-Effective Testing of VO2 Max

To test your VO2 max without breaking the bank:

  • Field Tests: There are several field tests that you can conduct which provide a good estimate of your VO2 max. For cyclists, a popular choice is the 20-minute time trial. Here, you would warm up and then cycle at the highest intensity you can sustain for 20 minutes. The average power output for this period is often used to estimate your FTP (Functional Threshold Power), which correlates with VO2 max.

  • Online Calculators and Mobile Apps: Some tools and apps use data like your heart rate at certain intensities, along with your age, weight, and sex, to estimate your VO2 max. These are less accurate than lab tests but can be a good starting point for planning training.

  • Step Tests with a Heart Rate Monitor: Using a basic step test protocol where you incrementally increase your effort while monitoring your heart rate can also provide estimations of your VO2 max based on how quickly your heart rate increases in response to the stepped increase in activity.

Increasing VO2 Max Through Training

Improving your VO2 max involves structured and progressive training. Emphasizing good form and technique is essential, as these not only enhance performance but also reduce the risk of injury. Here’s how you can build VO2 max effectively:

  • High-Intensity Interval Training (HIIT): Integrate intervals where you push to near-maximal efforts (close to or at Zone 5) for short durations (3-5 minutes), followed by equal or slightly longer recovery periods. These intervals elevate your heart rate close to its max, forcing your cardiovascular system to become more efficient.

  • Tempo Rides: Include tempo rides at a sustained moderate intensity (Zone 3 or 4), which improve your muscular endurance and cardiovascular capacity, helping to enhance your VO2 max over time.

  • Long Slow Distance (LSD) Rides: These rides are crucial for building an aerobic base. They should be long (lasting several hours) and conducted at a lower intensity (Zone 2). LSD rides enhance mitochondrial density and capillary networks in muscle tissues, supporting oxygen delivery and utilization.

  • Strength and Plyometric Training: Incorporating strength training, especially plyometric exercises, can improve your power and efficiency, which indirectly affects your VO2 max by enabling you to exert more force during each pedal stroke, thus using oxygen more effectively.

  • Consistency and Progression in Training: Gradually increasing the volume and intensity of training while ensuring enough recovery and rest days helps prevent plateauing and promotes continuous improvement.


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