Marathon Training: What Is Zone 5 / VO2 Max?

MarathonZone 5 / VO2
Written By FLJUGA

Summary:
Zone 5 sits around 93–100% of max heart rate with an RPE of 9–10. It represents VO2 max training. It feels intense, sharp and maximal. In marathon training, short sessions in this zone increase oxygen efficiency and develop the speed reserve that makes race pace feel more manageable. In this guide, we’ll explain what Zone 5 running is, how it boosts marathon performance and how to use it without risking burnout.

Black and white photo of elite marathon runners mid-stride during a race surrounded by cheering crowds.

Unlocking your speed ceiling

Zone 5 is not where marathoners live but it is where speed gets built. This is the intensity where your cardiovascular system works close to full aerobic capacity. You cannot sustain it for long but training here lifts every other zone beneath it. When you increase your VO2 max you improve how easily you can run at lower intensities and how long you can hold steady effort without strain. For marathoners that means cruising more efficiently, feeling smoother at pace and finishing with strength when the race begins to bite.

What is Zone 5 running?

Zone 5 is your VO2 max zone. It is the hardest sustained intensity used in structured aerobic training and it is designed to challenge the upper limits of your cardiovascular system. This is fast, demanding work where your breathing becomes heavy, your stride turns powerful and every rep requires full concentration. At this point lactate accumulates faster than it can be cleared and represents the high end of one’s aerobic capacity. Training here raises your ceiling, improves how your body handles extreme effort and unlocks gains that flow down into every other zone.

Zone 5 Defined:

  • Heart Rate: 93 to 100% of max HR

  • Effort Level: 9 to 10 out of 10

  • Breathing: Heavy and unbroken

  • Pace: Faster than threshold pace and close to all out

You will not hold this effort for long but the gains can be lasting. This zone builds power, sharpens form at speed and strengthens the engine that supports your entire marathon build.

Why Zone 5 matters in marathon training

Marathon training is built on endurance but speed matters too. The ability to stay strong in the final miles or respond when the race demands it depends on the capacity you build at the top end. Zone 5 develops that upper range. It challenges your aerobic system close to its full capability, strengthens the muscles that drive faster turnover and improves how efficiently you can run at every lower intensity. Training here is short, sharp and uncomfortable but it creates meaningful adaptations that support your entire marathon performance.

Top Benefits of Zone 5 Running:

  • Increases VO2 Max: Improves the maximum volume of oxygen your body can process

  • Improves Aerobic Power: Strengthens your ability to hold faster speeds without strain

  • Develops Neuromuscular Speed: Trains fast twitch fibres and running economy at high speeds

  • Sharpens Form Under Stress: Improves running mechanics during high intensity fatigue

  • Builds Mental Toughness: Pushes you to stay focused under serious discomfort

Even though you will never race a marathon in Zone 5, the benefits filter down through every pace zone and make marathon pace feel smoother, lighter and more sustainable.

How to use Zone 5 in a marathon plan

You only need small amounts of Zone 5 to see big returns. These sessions deliver major benefits when your aerobic base is already solid and your body is ready for short, intense work. Zone 5 should be used with intention because the effort is demanding and the recovery cost is high. When applied correctly it sharpens your top end, improves efficiency at all lower paces and adds the finishing edge to your marathon build.

When to Use It:

  • During sharpening phases in the final 6 to 8 weeks: Add VO2 work once your fitness and structure are well established

  • After building base in Zones 2 and 3: Ensure aerobic durability is in place before introducing high intensity

  • In short intervals with full recovery: Use controlled reps to keep quality high and form consistent

When to Avoid It:

  • Early in a base building cycle: Avoid high intensity before aerobic foundations are set

  • When fatigued or injured: Zone 5 demands full freshness and stability

  • Without accurate pacing and control: Guessing the effort leads to strain rather than progress

Zone 5 works best when it is strategic, purposeful and supported by the rest of your training. When used wisely it gives you the lift that carries through every other part of your marathon plan.

Sample Zone 5 Workouts for Marathon Runners

Option 1: Short VO2 Max Repeats

  • 6 x 1 minute fast

  • 2 minutes Zone 1 between

  • Focus on form and controlled turnover

Option 2: Long Hill Repeats

  • 6 x 90 seconds uphill

  • Walk or slow jog back down

  • Power based session to develop strength and speed

Option 3: VO2 Max Fartlek

  • 4 sets of 2 minutes fast and 2 minutes easy

  • Zone 5 during the effort, Zone 1 or 2 during recovery

  • Controlled pacing with sharp effort and full recovery

Use no more than one Zone 5 workout per week. More does not lead to better results. The best progress comes from strategic timing, full recovery and high quality intensity that supports your overall marathon training plan.

How do you know you are in Zone 5?

Zone 5 does not feel moderate. It is a full commitment effort where your breathing, pace and focus all rise sharply. You are working near your maximum capacity and every rep requires intent. There is no settling in and no relaxing into rhythm. This is the intensity where your form must stay controlled even while your body is demanding more oxygen than it can comfortably deliver.

Key Indicators:

  • Heart Rate: 93 to 100% of max

  • Breathing: Hard with no conversation possible

  • Effort: RPE 9 to 10

  • Pace: Faster than 5K pace

You should feel spent at the end of each rep with a clear sense that you reached a high level of effort. Zone 5 is designed to push your upper limit so the intensity should feel sharp, demanding and unmistakably challenging.

Common Mistakes with Zone 5 Training

Zone 5 training delivers huge benefits when used properly but it can derail your progress if misused. This is the most intense zone in structured marathon prep and it demands precision, patience and respect. Many runners make the mistake of treating Zone 5 like another hard workout rather than a targeted tool. Zone 5 only works when the effort is sharp, controlled and supported with full recovery. If the sessions feel chaotic or rushed you are no longer training the right system and the gains begin to disappear. The goal is quality, not exhaustion. Use this zone with intent and it will elevate your entire aerobic engine.

Common Errors to Avoid:

  • Doing Too Much: Zone 5 training is intense and small doses are enough. Adding extra sessions or pushing volume only increases fatigue and heightens burnout risk.

  • Poor Recovery Between Intervals: Zone 5 requires full rest to repeat high quality efforts. Shortening the recovery turns the session into survival work which removes the intended benefit and increases injury risk.

  • Incorrect Pacing: Running too slow will not reach VO2 max and running too fast sacrifices form and wastes energy. Zone 5 is controlled intensity not an all out sprint.

  • Adding Without Purpose: Zone 5 should only be added when a specific performance goal requires top end development. Using it randomly or too early in your build disrupts your plan and drains your freshness.

Zone 5 is a powerful tool when applied with strategy. Treat it carefully, keep the work sharp and protect your recovery so the top end gains can filter down into every part of your marathon performance.

Zone 5 vs Other Training Zones

Each zone serves a purpose in marathon training. Zone 5 is the highest gear. Use it to sharpen all other zones.

Use our free FLJUGA calculator to find your exact heart rate zones before you begin.

Why Elites Train in Zone 5

Elite marathoners do not build their fitness only in Zone 2. They rely on every training zone for a specific purpose and Zone 5 plays a crucial role in raising their overall performance ceiling. While most of their weekly mileage sits in easier aerobic work they still need high intensity running to sharpen speed, improve oxygen uptake and strengthen the ability to surge late in races. Zone 5 teaches them how to run fast with control and it lifts the quality of every pace beneath it. When elites increase their VO2 max marathon pace becomes easier, steadier and far more sustainable which is why this zone remains a key part of their training toolkit.

Elite Advantages of Zone 5:

  • Raises the Performance Ceiling: Higher VO2 max improves the ease of all sub-maximal running

  • Improves Finishing Speed: Allows elites to change gears and surge in the final miles

  • Enhances Running Economy at Speed: Refines mechanics during fast turnover

  • Strengthens Mental Resilience: Builds confidence when intensity climbs

  • Completes the Training Spectrum: Ensures no physiological system is neglected

Zone 5 is not where elites spend most of their time but it is essential to why they run so fast. When used sparingly and with precision it sharpens the edge of their fitness, elevates their speed and makes marathon pace feel smoother, lighter and far more controlled on race day.

FAQs: Zone 5 and Marathon Training

Can beginners use Zone 5?
Not at first. Focus on Zones 1 and 2. Add Zone 5 only after a strong aerobic base is built.

How often should I train in Zone 5?
Once per week at most. Quality matters more than quantity.

Do elites use Zone 5 for marathons?
Yes, especially in sharpening phases. Even though they race slower than VO2 max pace, they train to raise their aerobic ceiling.

Is it better than threshold training?
No. It is complementary. Use Zone 4 for sustainable intensity and Zone 5 for short, sharp stimulus.

FURTHER READING: EXPLORE THE FULL MARATHON ZONE SERIES

Training Sessions:

Final Thoughts: Lift Everything Else

Zone 5 is not where your marathon is raced but it is the zone that helps you finish fast, push through tough moments and lift your entire training ceiling. It sharpens the qualities that make marathon pace feel smoother and more controlled. When layered on top of a strong aerobic base it gives you the confidence to handle harder efforts and the strength to keep form when fatigue rises.

These sessions are not about volume. They are about precision. Just a few minutes at this intensity can drive meaningful gains in speed, oxygen uptake and mental sharpness. When used in the right phase of your plan, Zone 5 gives you the ability to surge, to respond and to stay composed when the race begins to bite. It is not about going hard all the time. It is about choosing the right moments to go hard and allowing those moments to count.

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.

FLJUGA
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