There’s a scientific explanation as to why the vast improvement in your workout times don’t always show on race day.

Have you ever had a perfect training cycle and made breakthroughs in all your most important workouts, only to find that your workout times don’t seem to translate to similar performances on race day?

Don’t worry, you’re not alone and there is an answer — even if you don’t want to hear it.

In one of my previous articles, I explained how long it will take you to reap the benefits of a given workout in the short term. However, by understanding how the long-term process of training works, we can shed a little light on why runners can sometimes work out faster than they can race, especially in the marathon.

In non-scientific terms, I call this phenomenon the “backlog” of fitness. Think of it like investing — you’re banking fitness and miles, but you can’t withdraw them yet because the investment hasn’t matured.

Physiologically, this all relates to the development and lifecycle of mitochondria (the aerobic powerhouse that supplies our muscles with energy). By examining how mitochondria contribute to your racing performance, and analyzing how they are developed, you’ll get a clear understanding of how this “backlog” of fitness works and why it pays to keep training year after year. For our purposes here, we’ll keep the explanations simple and easy to understand.

First, we’ll take a look at the role of mitochondria and how they are developed. Second, we’ll examine how the density and volume of mitochondria play a role in both your short- and long-term development. Finally, we’ll put it all together for you so you can appreciate how your body adapts to a workload and performance improves after a training segment. By the end of this article, you’ll have a very clear understanding how micro and macro cycles work in regards to your aerobic progression.

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The Importance Of Mitochondria

Mitochondria are microscopic organelle found in your muscles cells that contribute to the production of ATP (energy). In the presence of oxygen, mitochondria breakdown carbohydrate, fat, and protein into usable energy. Therefore, the more mitochondria you have, and the greater their density, the more energy you can generate during exercise, which will enable you to run faster and longer.

Contrary to popular belief, you can increase the volume and density of your mitochondria with both long, slow runs (research study) and more intense training sessions (research study). This is one reason it’s critical to have a mix of training stimuli in your training plan, which includes long runs at both easy and faster paces as well as tempo runs and more intense VO2 max sessions. Neglecting one of these energy systems for a long period of time limits your long-term mitochondrial development.

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Mitochondria Volume

Now that we can appreciate the value of mitochondria to your performance on race day, let’s examine how mitochondria contribute to your long-term development.

Most importantly, the volume (total number) of mitochondria contained in each muscle cell takes years to fully develop. In fact, most coaches believe that you can infinitely increase mitochondria volume; however, there is a point after a few years where increases are minuscule. The main thing to keep in mind here is that after years of running you’ll develop a mitochondria powerhouse that will enable you to realize continual gains in your fitness.

Mitochondria volume represents the macro cycle of training. In each training cycle, you’ll develop more mitochondria and carry over those positive gains to your next training cycle. It’s a slow process, but it’s why Olympic caliber athletes train for many years to get to the top of their sport. For reference, in The Anatomy of a Medal, Dr. Joe Vigil outlined the training of Deena Kastor during her transition from a good college runner to bronze medalist at the 2004 Athens Olympics. Dr. Vigil attributes the majority of Deena’s success to the slow and gradual progression from 40 miles per week to 110+ miles per week.

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Mitochondria Density

On the other side of the spectrum regarding mitochondria development is their density (the size of each mitochondrial). Like volume, mitochondria density can be developed with both slower and faster training sessions. However, mitochondria density is more effected by training volume — the more you run, the faster you will increase the density.

Unlike mitochondria volume, which can be developed infinitely, there is an absolute mitochondrial density that each individual can attain, usually reached after 8-12 weeks of training. Not surprisingly, this time frame usually correlates with when you start “feeling fit” during your training segment.

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Mitochondria Development

The final aspect to consider when looking at the short- and long-term effect of training is at what rate you realize the benefits of mitochondria development.

Mitochondria have a half-life of one week. Simply speaking, you’re able to gain half of the potential benefits to your mitochondria each week that you train. For example, if you went from no training to running 25 miles over a 7-day stretch, you’ll realize 50 percent of the benefits of that 25-mile week. Run 25 miles the next week at the same intensity and you’ll realize 25 percent of the benefits from week 1. This continues until you reach 100 percent.

This is a simplistic progression, since it assumes you do not increase your mileage or workout intensity over this six-week period. However, it does demonstrate how you benefit from mitochondria development and how it is critical to slowly increase training stimulus and training volume with time.

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Putting It All Together

Now that you’ve learned how mitochondria work and how they can benefit you as a runner, how does this relate to the “backlog of fitness” theory mentioned earlier?

The backlog of fitness concept is a result of the micro and macro development of mitochondria. As we’ve seen, on the micro level, mitochondria density peaks at 8-12 weeks of training. Likewise, the positive adaptations to mitochondria you realize from training get smaller and smaller each week. Therefore, at some point within the micro cycle of training, you’re going to stagnate mitochondria development, which is the most crucial component of training. However, you can still improve your running economy, VO2 max and lactate threshold, which enables you to run workouts that exceed your marathon ability or readiness.

Luckily, mitochondria development from the macro level never ceases. Each training cycle you complete enables you to develop a greater volume of mitochondria. So, during the next marathon training cycle you tackle, you’ll still be limited to the same relative gains in regards to mitochondria development, but this time you’ll have a greater total number of mitochondria, which means you’ll be better able to capitalize on your fitness on race day.

Your Takeaway
Don’t get frustrated when you have a difficult time translating the vast improvement in your workout times to your upcoming race. Sometimes, a race that is good but still a little under your expectations is just a sign that you reached a peak at the micro level. However, you’ll be able to carry those benefits over to your next training cycle and realize effects of all the hard work you put in further down the road.

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