Fitness

Marathon Training: The Optimal Number of 20-Mile Runs and Key Principles

By Jordan 7 min read

Most well-structured marathon training plans recommend completing one to three long runs of 20 miles or slightly more during the peak 8-12 weeks before the race for optimal preparation.

How many times should you run 20 miles before a marathon?

Generally, most well-structured marathon training plans recommend completing one to three long runs of 20 miles (or slightly more, up to 22-23 miles) during the peak training phase, typically within the 8-12 weeks leading up to the race.

The Purpose of the Long Run

The long run is the cornerstone of marathon training, serving multiple critical purposes that prepare your body and mind for the demands of 26.2 miles. It's not just about covering distance; it's about eliciting specific physiological and psychological adaptations:

  • Physiological Adaptations:
    • Mitochondrial Biogenesis: Increases the number and efficiency of mitochondria, the "powerhouses" of your cells, improving aerobic capacity.
    • Capillary Density: Enhances the network of tiny blood vessels, improving oxygen and nutrient delivery to working muscles and waste removal.
    • Glycogen Storage: Trains your body to store more glycogen (carbohydrate fuel) in muscles and liver.
    • Fat Utilization: Improves your body's ability to burn fat more efficiently at a given pace, sparing precious glycogen stores.
    • Musculoskeletal Resilience: Strengthens muscles, tendons, ligaments, and bones to withstand prolonged impact.
  • Psychological Benefits: Builds mental toughness, confidence in your ability to cover the distance, and teaches you to manage discomfort over extended periods.
  • Practical Application: Provides opportunities to practice race-day pacing, refine your nutrition and hydration strategy, and test out gear.

The "Magic Number" for Peak Long Runs

While individual training philosophies and runner experience levels vary, the consensus among exercise scientists and experienced coaches points to one to three runs of 20 miles or more as optimal during a marathon training cycle.

  • One 20-mile run: Often sufficient for first-time marathoners or those with a history of injuries, focusing on completing the distance once to build confidence and trigger adaptations without excessive stress.
  • Two 20-mile runs: A common recommendation for many intermediate runners, offering a good balance between physiological benefit and recovery demands. These are typically spaced 2-3 weeks apart.
  • Three 20-mile runs: Sometimes incorporated by more experienced runners or those aiming for specific performance goals, allowing for greater adaptation and confidence in handling sustained effort. These are carefully spaced to allow for adequate recovery.

The 20-mile mark is often chosen as the peak long run because it provides most of the physiological benefits of running the full marathon distance in training, without incurring the excessive fatigue, recovery time, and injury risk associated with regularly running 26.2 miles in training. The remaining distance on race day is covered by the cumulative training effect, the taper, and race-day adrenaline.

Why Not More (or Less)?

Understanding the rationale behind this recommendation is crucial for effective training.

  • Why Not More?
    • Overtraining Risk: Repeatedly pushing beyond 20 miles can lead to chronic fatigue, hormonal imbalances, compromised immune function, and a higher risk of overtraining syndrome.
    • Increased Injury Susceptibility: The cumulative stress on the musculoskeletal system from multiple very long runs significantly elevates the risk of overuse injuries (e.g., stress fractures, tendinitis).
    • Diminishing Returns: The physiological benefits gained from exceeding 20-22 miles in training tend to diminish, while the recovery cost and injury risk escalate disproportionately.
    • Recovery Demands: Each very long run requires significant recovery time, which can interfere with other important training elements like speed work, tempo runs, and strength training.
  • Why Not Less?
    • Insufficient Adaptation: Not completing long runs of sufficient duration (at least 18-20 miles) may mean your body hasn't fully adapted to the prolonged demands of a marathon, potentially leading to "hitting the wall" due to inadequate fuel utilization or muscular fatigue.
    • Lack of Confidence: The psychological boost from knowing you've successfully covered a significant portion of the marathon distance in training is invaluable on race day.

Key Principles for Long Run Success

Beyond the number of peak long runs, how you execute them is paramount.

  • Progressive Overload: Build your long run distance gradually, increasing by no more than 10-15% week-over-week. This allows your body to adapt safely.
  • Pacing: Long runs should be performed at an easy, conversational pace – significantly slower than your goal marathon pace. This trains your aerobic system without causing undue stress and promotes fat burning.
  • Nutrition and Hydration: Use your long runs to practice your race-day fueling strategy. Experiment with different gels, chews, drinks, and hydration practices to find what works best for your body.
  • Recovery: Prioritize recovery after long runs. This includes adequate sleep, proper post-run nutrition (carbohydrates and protein), hydration, and potentially active recovery like light walking or stretching.
  • Listen to Your Body: Pay attention to signs of fatigue, pain, or unusual soreness. It's always better to cut a run short or take an extra rest day than to push through and risk injury.

Tapering: The Crucial Final Phase

The timing of your last peak long run is critical due to the tapering phase. Most training plans recommend that your final 20-mile run occur 3 to 4 weeks before race day.

This allows sufficient time for your body to fully recover, repair, and supercompensate (store extra glycogen) before the race. During the taper, training volume is significantly reduced, allowing you to arrive at the starting line feeling fresh, strong, and fully energized, rather than fatigued from overtraining.

Listen to Your Body and Adapt

While general guidelines are helpful, every runner is unique. Factors such as your running history, current fitness level, injury susceptibility, age, and lifestyle all influence how your body responds to training stress.

  • Flexibility is Key: Be prepared to adjust your training plan based on how you feel. If you're consistently tired or experiencing persistent aches, it might be a sign to reduce volume or intensity, even if it means skipping a planned 20-miler.
  • Professional Guidance: If you're unsure about your training plan or are experiencing recurring issues, consider consulting with a certified running coach or sports medicine professional.

Conclusion and Final Recommendations

In summary, for most marathoners, aiming for one to three long runs of 20 miles or slightly more during the peak training phase (typically 8-12 weeks out from race day, with the last one 3-4 weeks before the race) strikes the optimal balance between physiological adaptation, psychological readiness, and injury prevention.

Focus on the quality of these runs, ensuring they are executed at an appropriate pace, with diligent attention to nutrition, hydration, and recovery. Remember, the marathon is not won in training, but it can certainly be lost there through overtraining or under-preparation. Train smart, listen to your body, and arrive at the starting line confident and ready.

Key Takeaways

  • Most marathon training plans suggest completing one to three 20-mile long runs during the 8-12 weeks leading up to the race.
  • Long runs are crucial for physiological adaptations like increased mitochondrial efficiency and glycogen storage, as well as building mental toughness.
  • Exceeding three 20-mile runs increases overtraining and injury risk, while fewer may lead to insufficient adaptation.
  • Successful long runs require progressive overload, easy pacing, diligent nutrition, hydration, and prioritizing recovery.
  • The final 20-mile run should be completed 3 to 4 weeks before race day to allow for proper tapering and recovery.

Frequently Asked Questions

What is the main purpose of the long run in marathon training?

The long run serves to build physiological adaptations like improved aerobic capacity and fat utilization, enhance musculoskeletal resilience, and provide psychological benefits for race day.

How many 20-mile runs are generally recommended before a marathon?

Most training plans recommend completing one to three long runs of 20 miles or slightly more during the peak training phase, typically 8-12 weeks before the race.

Why is it not recommended to do more than three 20-mile runs?

Running more than three 20-mile runs increases the risk of overtraining, chronic fatigue, overuse injuries, and provides diminishing returns while demanding excessive recovery time.

When should the last 20-mile long run be completed before race day?

Your final 20-mile run should typically occur 3 to 4 weeks before the marathon to allow sufficient time for your body to recover fully and taper effectively.

What are key principles for effective long runs?

Key principles include progressive overload, maintaining an easy conversational pace, practicing race-day nutrition and hydration, prioritizing recovery, and listening to your body's signals.