Why Does VO2 Training Matter for Marathon Runners?

Summary:
VO2 training allows marathon runners to challenge the upper end of their aerobic fitness through short periods of very hard running. Although this intensity is far greater than you would sustain across a marathon, developing your ability to deliver and use oxygen can support your aerobic performance at the lower intensities used throughout training.

Why Does VO2 Training Matter for Marathon Runners?

Marathon running is built around sustaining an effort for a long time, so training at the very high intensity of Zone 5 can seem quite removed from what you actually need for the distance. You are not trying to make Zone 5 sustainable for 26.2 miles. Instead, this type of training challenges the upper end of your aerobic fitness, placing a high demand on your ability to deliver oxygen to the working muscles and use it to produce energy.

Developing this upper end can give you a higher aerobic capacity to work with across the rest of your training. That does not mean improving your VO2 max will automatically make you a faster marathon runner, as the amount of this capacity you can sustain across 26.2 miles is influenced by several other aspects of your fitness. VO2 training simply develops a different part of your aerobic performance, giving it a useful role alongside the more marathon-specific work that prepares you for the demands of the distance.

What Happens as You Move Into Zone 5?

As you move into Zone 5, the energy required to keep your muscles contracting rises rapidly. This energy comes from ATP, the molecule your muscles use to power each contraction. Because only a small amount of ATP is stored within the muscles, it must continually be regenerated as you run. At Zone 5 intensity, this needs to happen at a very high rate, increasing the contribution from both aerobic and anaerobic energy production. Your oxygen consumption, known as VO2, also rises as more oxygen is delivered to and used by your muscles to support aerobic ATP production. As the effort continues, VO2 can move towards VO2 max, the highest rate at which your body can transport and use oxygen during exercise.

VO2 does not reach this level as soon as you start running hard. It rises progressively as your aerobic energy production responds to the increased demand, a process known as VO2 kinetics. While this response develops, other energy-producing processes contribute alongside aerobic metabolism to meet the immediate need for ATP. This is important for VO2 training because the length of each interval and the recovery between repetitions influence how high your VO2 rises and how much time you can accumulate at a very high rate of oxygen consumption.

How Does Zone 5 Training Challenge Oxygen Delivery?

As your VO2 rises during Zone 5 running, your heart needs to pump more blood to support the increasing demand for oxygen. This is reflected in cardiac output, which describes the amount of blood your heart pumps each minute and is determined by heart rate and stroke volume. Stroke volume is simply the amount of blood pumped with each heartbeat. During very hard running, cardiac output can reach very high levels as your cardiovascular system works to supply the oxygen needed for aerobic energy production.

Repeated Zone 5 training places a strong demand on this process and can contribute to an increase in maximal stroke volume, allowing the heart to pump more blood during demanding exercise. This can support a higher maximal cardiac output and contribute to improvements in VO2 max. For marathon runners, the benefit is not about reaching this maximum during the race. Developing the upper limit of oxygen delivery can provide greater scope for aerobic energy production at the intensities below it. Zone 5 therefore develops your aerobic capacity at the top end, which can support the lower intensities that may be more specific to marathon training and performance. Explore our Marathon Running Zones Guide to understand the role of each zone and how they can work together across your training.

What Happens When Oxygen Reaches Your Muscles?

Getting more oxygen to your muscles is only part of the process. Once it arrives, your muscle fibres need to extract that oxygen from the blood and use it to help produce energy. Much of this aerobic energy production takes place within the mitochondria, structures inside your muscle cells that use oxygen to help regenerate ATP. During Zone 5 running, aerobic energy production reaches a very high rate, placing a substantial demand on the mitochondria as your muscles work to meet the energy requirements of the effort.

Repeated Zone 5 training can provide a strong stimulus for mitochondrial biogenesis, the process through which your muscles increase their mitochondrial content and develop their ability to produce energy aerobically. It can also contribute to increases in capillary density, creating a greater network of tiny blood vessels around the muscle fibres and supporting the exchange of oxygen between the blood and muscles. These adaptations are not exclusive to Zone 5, but they form part of the muscular response to VO2 training and can improve how effectively your muscles use the oxygen available to them.

What Happens to Lactate During Zone 5 Running?

Lactate is continually produced and used by your body while you run, even at easier intensities. As running intensity increases, the rate of lactate production also increases. Eventually you reach the second lactate threshold, referred to as LT2, where lactate begins to accumulate more rapidly because its production increasingly exceeds the rate at which it can be removed and utilised. Zone 5 generally sits above LT2, so lactate levels can rise considerably as a hard interval continues.

This rising lactate is a sign of the high metabolic demand of Zone 5, but lactate itself is not simply a waste product. Repeated training at these intensities can contribute to adaptations that improve how lactate is transported and utilised. For marathon runners, these adaptations can help manage lactate more effectively at the lower intensities used during training and racing, where its production and utilisation are more closely balanced. The purpose of Zone 5 is therefore not to become better at tolerating high lactate levels, but to develop metabolic processes that can also support more sustainable running below LT2.

How Does Zone 5 Change Muscle Fibre Recruitment?

Your muscles do not recruit every available muscle fibre from the moment you start running. During easier running, much of the work is handled by Type I or slow-twitch muscle fibres, which are well suited to producing energy aerobically and sustaining repeated contractions. As you move into Zone 5 and the demand for force increases, your body recruits more Type II or fast-twitch muscle fibres to help maintain the effort. Type IIa fibres become particularly important because they can produce greater force while still having a good ability to use oxygen for aerobic energy production.

For marathon runners, this provides a way to place a strong aerobic demand on fast-twitch fibres that may be recruited less during easier running. Repeated Zone 5 training can improve the oxidative capabilities of Type IIa fibres, helping them use oxygen and produce energy aerobically. This can become particularly useful during a marathon because of how long the muscles are required to keep working. As fatigue develops within the muscle fibres already contributing to your running, additional fibres can be recruited to help maintain your pace. Developing the aerobic capabilities of Type IIa fibres through Zone 5 training can therefore give these recruited fibres a greater ability to contribute aerobically when they are called upon later in prolonged running.

How Can Zone 5 Improve Neuromuscular Coordination?

Running at Zone 5 speeds requires your brain and muscles to communicate quickly to produce and coordinate each stride. Movement begins with signals from the brain travelling through motor nerves to the muscles, where motor units are recruited to produce force. As running speed increases, more motor units are recruited and the timing of their activation becomes increasingly important. Repeated exposure to very hard running can improve this communication, helping you recruit the required muscle fibres more effectively and coordinate force production at faster speeds.

For marathon runners, this can have value even though marathon pace is considerably slower than Zone 5 running. Improving the recruitment and coordination of your muscles at faster speeds may make lower running speeds feel more mechanically manageable and could contribute to improvements in running economy. It can also give you experience producing efficient movement at speeds above those required for the marathon. These benefits should not be treated as automatic, however, as running economy is influenced by many factors and VO2 training is only one possible stimulus for developing it.

Why Does Interval Structure Matter for VO2 Training?

VO2 takes time to rise when you begin a very hard interval, which means you do not immediately reach a very high level of oxygen consumption simply because you are running at a Zone 5 pace. VO2 intervals typically last anywhere from around 30 seconds to 5 minutes, depending on how the session is structured. Longer repetitions give VO2 more time to rise during each effort, while shorter repetitions can achieve a similar aim when repeated with brief recoveries. If the recovery is short enough, VO2 can remain elevated before the next repetition begins, allowing it to rise again more quickly. The aim is not necessarily to reach VO2 max during every interval, but to accumulate useful time with oxygen consumption close to the upper end of what you can achieve.

This allows VO2 training to take many different forms. Common formats include Tabata-style intervals (20/10), Rønnestad-style intervals (30/15) or longer repetitions such as the Norwegian 4 x 4-minute format. Although these sessions are structured differently, each can be used to accumulate time at a high aerobic demand. For marathon runners, intervals provide a practical way to create this stimulus without attempting to sustain Zone 5 continuously, with the work and recovery periods adjusted to manage intensity and duration across the session. A VO2 session may typically accumulate around 15–30 minutes of work at Zone 5 intensity, depending on the athlete and the purpose of the session. Explore our 10 Example Marathon VO2 Sessions for different ways to structure Zone 5 intervals within your marathon training.

What Should Zone 5 Feel Like During Marathon Training?

Zone 5 should feel very hard from early in the effort, with breathing becoming deep and rapid as the interval progresses. On an RPE scale of 1–10, Zone 5 sits around 9–10, where maintaining a conversation is no longer realistic and your attention is largely focused on sustaining the effort. The aim is not necessarily to run as fast as possible. You still want enough control to complete the planned intervals without your pace falling significantly as the session progresses.

Heart rate can be useful for reviewing a VO2 session, but it is less useful for controlling short intervals because it takes time to respond when your pace suddenly increases. Your heart rate may therefore still be rising even though you are already running at a Zone 5 pace. Using pace and RPE alongside heart rate can give you a better picture of the intensity, particularly when repetitions are short. If you want to identify your individual training zones, you can use the FLJUGA Running Zone Calculators to estimate them from your own running data.

Where Should Zone 5 Fit Into Your Marathon Training?

Zone 5 is one of the most demanding intensities you can include in marathon training, so where you place it should allow enough recovery for the session to produce the adaptation you are looking for. The interval itself provides the stimulus, but many of the adaptations associated with training develop during the recovery that follows. Your muscles need time to repair and adapt, while the cardiovascular changes stimulated by repeated high aerobic demand also depend on adequate recovery. Starting another demanding session before you have recovered can reduce the quality of that training and increase the amount of fatigue carried through the rest of your week.

Very hard running also places a high demand on the processes responsible for recruiting muscle fibres and maintaining force production. The central nervous system or CNS, which includes the brain and spinal cord, plays an important role in controlling this activity. Fatigue after Zone 5 training can therefore involve more than simply having tired muscles, potentially affecting your ability to produce force during subsequent hard running. For marathon runners, this makes recovery particularly important because Zone 5 needs to sit alongside longer and more marathon-specific sessions. Giving demanding sessions enough separation allows you to absorb the VO2 stimulus without unnecessarily compromising the training that has greater specificity to 26.2 miles.

Common Mistakes With Marathon VO2 Training

One of the most common mistakes with Zone 5 training is turning every interval into an all-out effort. VO2 training should be very hard, but running considerably faster than required can increase fatigue without necessarily creating a better aerobic stimulus. Starting too aggressively can also cause your pace to fall across later repetitions, reducing the amount of useful work you can complete. The aim is to manage the intensity so you can accumulate quality time in Zone 5 rather than treating each repetition like a sprint.

Another mistake is allowing Zone 5 training to compete with the sessions that are more specific to marathon preparation. VO2 work can provide a valuable stimulus, but it does not replace the longer and more sustainable running needed for 26.2 miles. Adding too much high-intensity work or placing it too close to other demanding sessions can make recovery harder and affect the quality of the training around it. Zone 5 works best when it has a clear purpose within the wider programme rather than simply being added because harder training feels more productive.

FAQ

Do Marathon Runners Need VO2 Training?

VO2 training is not essential for every marathon runner, but it can provide a useful way to develop the upper end of your aerobic capacity. Marathon performance depends heavily on what you can sustain for a prolonged period, so Zone 5 should complement rather than replace the training that prepares you more specifically for the distance.

How Often Should Marathon Runners Do Zone 5 Training?

There is no fixed frequency that suits every runner. How often you include Zone 5 will depend on your individual training and how much demanding work is already included within your programme. Because VO2 training creates considerable fatigue, enough recovery should be allowed before another demanding session.

Should You Use Heart Rate to Control VO2 Intervals?

Heart rate can help you understand the overall intensity of a session, but it responds slowly. During shorter repetitions, you may already be running at a Zone 5 pace before your heart rate reaches Zone 5. Pace and RPE can therefore be particularly useful alongside heart rate when managing these sessions.

Can Marathon Runners Improve VO2 Max Without Zone 5 Training?

Improvements in VO2 max are not exclusive to Zone 5 training and adaptations that contribute to aerobic capacity can occur across different training intensities. Zone 5 simply provides a particularly strong way of challenging oxygen delivery and utilisation by taking aerobic energy production towards its upper limit.

Final Thoughts

Zone 5 can be a useful addition to marathon training when it is included with a clear purpose. It does not need to closely match the intensity you will sustain during the marathon to have value. Instead, it provides a different training stimulus that can help develop areas of your fitness that may benefit the more sustainable running used throughout marathon preparation.

The important part is finding the right place for it within your training. VO2 sessions create a high level of fatigue, so they need to work alongside your marathon-specific training rather than interfere with it. How much you include will depend on the individual runner, but when used appropriately, Zone 5 can add another useful training stimulus as you prepare for the distance.

Always consult with a medical professional or certified coach before beginning any new training program. The information provided is for educational purposes only and is not a substitute for personalized advice.