We all remember the term "mitochondria" from high school biology class. I remember distinctly hearing my high school science teacher proclaim, "the mitochondria is the powerhouse of the cell" and thinking, "so what?"  My, oh, my, how times have changed. And so, I say to you, "the mitochondrion is the powerhouse of the cell and we can use some more!" 

When we train we are converting chemical energy through several possible pathways to generate Adenosine Triphosphate (ATP).  ATP is our body's energy transfer source.  In this role, ATP transports chemical energy within cells for metabolism. Meaning, from the foods we eat, their nutrients broken down to substrates that absorbed and converted into energy.  This energy is produced in the mitochondria of the cell.  

Studies have shown that inactive sedentary subjects have far fewer mitochondria than those who are considered active.  This is consistent with the idea that our bodies are efficient machines that will not waste any extra energy having an excess of mitochondria around. Our bodies will adapt to conserve energy, always.  You starve it; its metabolism will slow down.  You over feed it; it will store fat (not very metabolically active) for those future epic famines.

There has been growing research in the area of "Mitochodrial Biogenesis" or simply the increase in mitochondrial content within a muscle cell.  Dating back to 1967, Dr. John O. Holloszy study titled, "Effect of Exercise on Mitochondrial Oxygen Uptake and Respiratory Enzyme Activity in Skeletal Muscle" was the first published paper on mitochondria biogenesis.  In this study, Dr. Holloszy treadmill tested rats two hours a day over a twelve week period with increasing intensity.  When he biopsied their gastronemius (calf muscle), he was able to observe a two fold increase in both mitochondrial enzyme activity and max rate oxygen consumption.  What this meant was that there is a pretty good chance that we, as humans, will also have the capability to increase our mitochondria through training.

By increasing the density of the mitochondria could we see a performance benefit?  What type of training could cause increase in mitochondria? 

While you may not be able to see your mitochondria replicating like a mogwai with water splashed on it, mitochondria biogenesis does in fact occur.  For seasoned endurance junkies lactate threshold intensities for short duration is the needed stimulus to facilitate mitochondrial proliferation.  For the beginner in their base phase, just doing the volume will start you on process. 

For the endurance athlete increasing mitochondrial density means you will have:
1.       Greater O2 utilization.
2.       Increase whole body VO2 Max.
3.       Increase utilization of lipid (fat) metabolism.
4.       Decreased reliance on blood glucose and stored glycogen.
5.       Increase in endurance or resistance to fatigue.

So while we build speed, power, endurance with each specific workout that we do, know that there is another level at work and that we are remodeling ourselves at the cellular level.  There is a lot to be learned and is currently being researched on the role of the mitochondria in skeletal muscle disease, aging, and performance.