The Importance of Easy Runs for a Running Training Plan

At Integra Dietetics, we focus on the physiological "why" behind every mile. While it is tempting to believe that running must be hard efforts to yield results, the biological reality of "easy jogging" tells a different story. To build a faster engine, you must first build a bigger one, and that process happens primarily at a low intensity.

The Physiology

Why dedicate so many miles to easy running? It isn't merely about recovery, it is about fundamental biological adaptations that turn an athlete into a more efficient machine. Primary benefits of low-intensity training include:

• Mitochondrial Biogenesis: The creation of more "powerhouses" within muscle cells.

• Capillary Growth: Increasing the network of small blood vessels to improve oxygen delivery to working muscles.

• Structural Resilience: Strengthening muscles, bones, tendons, and ligaments to better handle the impact of high-volume training.

• Metabolic Efficiency: Enhancing the body’s ability to utilize fat as a fuel source during exertion.

  
  

What the Research Says

Mitochondria are often called the "powerhouses of the cell." In a running context, having a higher density of mitochondria in the muscles means an athlete can produce significantly more energy via aerobic pathways, leading to better performance at any given pace.

To understand how different intensities affect our biology, researchers conducted a massive systematic review of 353 studies, analyzing changes in mitochondrial content across diverse populations: from untrained individuals to elite athletes (Mølmen, Almquist & Skattebo, 2025).

The findings showed that all types of training increased mitochondrial content, with similar results across different modalities:

• Easy Training (ET): +23%

• High-Intensity Interval Training (HIIT): +27%

• Sprint Interval Training (SIT): +27%

  
  

The Efficiency Paradox

This leads to the "Efficiency Paradox." If we look strictly at training efficiency per hour, Sprint Interval Training (SIT) is the clear winner. SIT was found to be 3.9 times more efficient than easy training and 2.3 times more efficient than HIIT for mitochondrial benefits.

In theory, this suggests that if an athlete only has limited hours a week to train, they should spend them all sprinting. However, the human body cannot handle the physical and neurological stress of daily high-intensity sessions without risking injury or overtraining. While easy training is less efficient per minute, its value lies in its sustainability. An athlete can perform easy training much more frequently and for much longer durations. From a physiological standpoint, five hours of easy running over a week provides a far greater total aerobic stimulus than just one hour of high-intensity work.

Olympics distance athletes rely on easy jogging to build their aerobic engine Copyright 2024 The Associated Press.

The Power of Volume: The 3x Rule

The ultimate predictor of success in endurance events is training volume. A study by Tanda and Knechtle (2013) analyzed recreational marathoners to determine which training variables most accurately predicted race times. They found that mean weekly training distance and mean training pace were the most significant predictors of marathon performance.

When researchers categorized marathoners by finishing times, a clear "3x Rule" emerged:

• The 3x Rule: The fastest runners (those finishing under 2 hours and 30 minutes) logged three times the weekly mileage of the slower groups finishing in 4 hours and 30 minutes or more (Tanda & Knechtle, 2013).

  
  

Crucially, the elite group did not achieve this volume by doing three times as many "hard" sessions. Instead, they accumulated the vast majority of that extra volume through easy, aerobic runs. Elite distance runners spend most of their training at a jogging pace, and so should everyone for their marathon running training plan.

My own training zones across 2020-2022, where I set PB's from 5km to the marathon

Summary

The marathon is fundamentally an aerobic event. Because the body cannot safely handle weekly mileage at a high intensity, the only way to reach the volume necessary to "level up" is through the easy run. By slowing down, you are providing your body with the hours of stimulus it needs to multiply those cellular powerhouses and build a more robust aerobic foundation.

References

Mølmen, K. S., Almquist, N. W., & Skattebo, Ø. (2025). Effects of Exercise Training on Mitochondrial and Capillary Growth in Human Skeletal Muscle: A Systematic Review and Meta-Regression. Sports medicine, 55(1), 115–144.

Tanda, G., & Knechtle, B. (2013). Effects of training and body fat on marathon performance in marathon runners. Journal of Strength and Conditioning Research, 27(5), 1361–1367.