Mileage Matters: How Appropriate Increases in Training Volume Help Young Runners Improve

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Adequate mileage isn’t the only component needed to perform your best in distance running, but it just might matter the most.

The Little Engine That Couldn’t

When I left for college the summer of my freshman year, I loaded all of my belongings into a tiny 1991 Geo Metro. It wasn't the prettiest piece of machinery, and beyond basic "A to B" commutes, the car had some serious limitations. With only a 3-cylinder engine to generate power, it was apparent from the start that me and my Metro would be living life in the slow lane. It didn't matter how hard I pressed the pedal to the metal, the tiny engine just couldn’t keep pace with all of the other cars gifted in horsepower.

Early on, most of us can relate to the Metro. Equipped with limited aerobic power, it seems as though no matter how hard we try, more seasoned runners pass us by, oftentimes at speeds hard to fathom. Frankly put, these more mature runners are hitting on all cylinders: they have a bigger engine.

The good news is, we don't have to settle for our pre-installed engine: we can upgrade. This is where mileage comes into play.

In his popular presentation, “Seiler’s Hierarchy of Training Needs”, exercise scientist, Dr. Stephen Seiler touts training volume and frequency of work as the most important aspects of endurance performance. In fact, Seiler’s research found that elite endurance athletes put such a premium on mileage, that they perform roughly eight out of ten sessions with the primary goal of accumulating training volume.

Magic Microscopic Adaptations

From the outside looking in, it might seem like success in distance running would be a case of simple mathematics: train at the speed you want to race, rest, rinse and repeat. And if you come from a speed and power background, running lots of easy miles might seem ludicrous- or at best, counterproductive.

However, there’s some real magic in the miles.

When a runner increases mileage on a consistent basis, the brain takes that as a cue to begin making a series of adaptations intended to make running easier. Although invisible to the naked eye, these microscopic changes can help you erase big chunks of time from your race performances. The adaptations from endurance training are complex and not entirely understood, but there are a couple of key changes that occur inside the body that help give purpose to the miles.

To begin with, increased mileage influences the heart to become stronger and more efficient at pumping blood. Blood contains all sorts of important ingredients, most notably a vital element for distance runners called oxygen.

From the heart, blood is pushed through a network of arteries and arterioles as it makes its way towards the working muscles. It’s helpful to think of arteries as an expansive interstate system and the arterioles as off-ramps that lead to different muscle groups. At the end of the arterioles are fingerlike outlets called capillaries that route blood directly to the muscle fibers.

Through endurance training, capillaries grow and expand up to 15%, allowing for more blood to make its way to working muscles. From the capillaries, oxygen is picked up by myoglobin, the Uber of the cardiovascular system, which delivers the oxygen to the powerhouse of the cell: the mitochondria.

The Cylinders of the Muscle Fiber: Mitochondria

Of the interconnected changes that occur due to increased training volume, growth of the mitochondria is the most exciting for runners. Mitochondria are tiny organelles found in muscle fibers that- like the cylinder of a car engine- serve as the epicenter for energy production.

The size and number of mitochondria determine the horsepower of our aerobic engine. And unlike static physical traits such as height or wingspan, mitochondria can be drastically changed as a response to endurance training.

In the book Science of Winning, Dr. Jan Olbrecht explained that an increase in the size and density of mitochondria in muscle fibers is a major determinant of endurance performance.

For high school runners in particular, the means to increase mitochondria is fairly simple: run more.

Progression of Mileage over a Season

If you’re tired of being a weak Metro and would like to be a powerful Mustang, then you’re a good candidate for increasing mileage.

To boost mileage safely, you need an intelligent plan not only to take you through a season, but an entire high school career.

Initially, it’s sensible to start at a mileage level that’s easy to manage, and within your current state of fitness, before moving onto a higher level. In the popular training manual, Daniels’ Running Formula, Dr. Jack Daniels recommends staying at same mileage for at least three weeks before increasing to a new level. Daniels then suggests increasing mileage by no more than one mile for each day of the week you run. For example, if you knocked out three weeks of 30 miles on six days of running, Daniels would advise a maximum of 36 miles per week during your next block of training.

Another strategy, as advocated by Scott Simmons and Will Freeman in the book Take the Lead, is to use a gradual, coffee-drip approach to increasing mileage throughout the season. The Simmons/Freeman approach, which they coined the “Diamond Model”, gradually builds mileage (along with all other training qualities) from week one, all the way up to the penultimate week of the season.

Other coaches prefer increasing mileage by 10% per week, which has existed in distance running dogma for decades.

Any of these strategies can be effective to create a logical, progressive method for increasing training mileage.

Sample Mileage Progression for a Cross Country Season


12 week season

40 miles per week max

Combined Daniels, Simmons/Freeman & 10% approach to increasing mileage

Slight taper

Week #1: 30 miles

Week #2: 30 miles

Week #3: 30 miles

Week #4: 33 miles

Week #4: 33 miles

Week #5: 33 miles

Week #6: 36 miles

Week #7: 36 miles

Week #8: 36 miles

Week #9: 40 miles

Week #10: 40 miles

Week #11: 36 miles (Qualifying)

Week #12: 33 miles (State Championships)

Progression of Mileage over a High School Career

One of the best ways to promote long-term performance improvement is to leave some stones unturned each season, and weekly mileage is a good place to start.

It’s useful to think of seasonal mileage jumps like the rungs of a ladder. When you’re climbing a ladder, it’s not smart to skip a step due to the obvious risk of a fall. Some people will get lucky and keep climbing, but most of us are going to slip, fall and get hurt. Young runners who try to skip steps on the mileage ladder often end up injured and end up going back to where they started in the first place.

Patient progression in all aspects of training, especially mileage, is vital.

The following is a model our team uses, which allows for scholastic success along with room for growth in college and beyond. Mileage ranges are provided for each year of participation, but by no means do these mileage suggestions apply to all athletes.

There is an element of art, rather than science, that factors into deciding how each athlete should ascend the mileage ladder.

Oftentimes, taking a step back or simply "staying put" are better choices than continuing the climb.

Sample High School Career Mileage Progression

1st Year

Boys: 35-40 miles Girls: 25-30 miles

2nd Year

Boys: 45-50 miles Girls: 35-40 miles

3rd Year

Boys: 50-55 miles Girls: 40-45 miles

4th Year

Boys 55-60+ miles Girls: 44-50+ miles

How Fast?

The intensity of easy endurance running, which will consist of ~80% of your training sessions, is a topic of contention for many coaches and runners. The truth is, there is a large range of intensities in which you can perform your weekly mileage and still get the same cardiovascular adaptations.

Dr. Daniels recommends endurance runs be completed in the range of 59-74% of VO2 max. The elites that Dr. Seiler has researched typically ran their easy mileage days somewhere in the middle: ~65% of their VO2 max.

I prefer that mileage be conducted somewhere in the 65% VO2 range, which is roughly consistent with endurance runs at about two-three minutes per mile slower than 5k race pace.

As an example, an athlete running 18:40 in the 5k, is racing at about 6:00 per mile. This particular runner would perform their endurance runs around 8:00-9:00 per mile, depending on how they felt on the day. Being able to “feel” what is an honest easy pace comes with experience, but I recommend high school students stay on the slower, more cautious end of intensity for most of their runs. Intensity of daily endurance runs is a nice stone to leave unturned for high school students.

Finalizing the Upgrade

Turning your Metro into a Mustang will take work, but fortunately, it’s work that anyone can do.

Simply set aside an hour or so each day to put in the miles and invest in your engine. This simple habit can change the entire trajectory of your running career.

And the formula for an engine upgrade? It’s almost too simple to be true:

  • Create a sensible plan.

  • Run more.

  • Most of it easy.

  • Have fun and see where running takes you.


Baechle, T & Earle, R, editors. (2008). Essentials of strength and conditioning (3rd ed.): Champaign, IL Human Kinetics.

Daniels, J. (2014). Daniels running formula (3rd ed.). Champaign, IL: Human Kinetics.

Olbrecht, J. (2000). The science of winning: Planning and optimizing swim training: F&G Partners.

Seiler, Stephen, (2016, Nov 23). Seiler’s hierarchy of endurance training needs. Retrieved from

Simmons, S & Freeman, W. (2006). Take the lead. Simmons and Freeman.

Wilmore, J & Costill D. (2004). Physiology of sport and exercise. Champaign, IL: Human Kinetics.

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