By Cyrus Khambatta — FitStar Contributor

Over the past few decades there has been considerable focus on the effect of exercise, diet, aging and disease on mitochondrial health.  Understanding the basic physiology of mitochondria and how they replicate in response to your lifestyle can have profound impacts on your overall health.

In this article I’ll share with you some insights gained from extensive research on the process of exercise-induced mitochondrial biogenesis – a term that refers to the synthesis of new mitochondria in muscle tissue.  Muscle physiology, here we come.

What are Mitochondria?

Mitochondria are cellular organelles that function as power plants within a cell.  In the same way that a local power plant produces electricity for an entire city, mitochondria are responsible for the production of energy derived from the breakdown of carbohydrates and fatty acids.  Mitochondria oxidize or “burn” carbohydrates, amino acids and fatty acids for energy, yielding ATP.  ATP (Adenosine Triphosphate) is the cellular form of energy utilized by cellular processes all throughout the body, providing the energy to pump your heart, power neurons in your brain, contract muscles in your limbs, exchange gases in your lungs, extract nutrients from food and regulate body temperature, just to name a few.

Simply stated, mitochondria produce ATP, and ATP is absolutely essential for survival.  Without a sufficient generation of ATP, life would cease to exist.

Where are Mitochondria Found?

Mitochondria are located in every cell type and tissue in the human body, from your brain to your thyroid gland to your Achilles tendon.  In short – trillions of mitochondria are distributed all throughout your body with the sole purpose of generating ATP.  Red blood cells are the only cell type that do not contain mitochondria.

Scientists believe that mitochondria were once free living organisms that developed a symbiotic relationship with mammalian cells over millions of years of evolution.  The reason for this is simple – mitochondria contain their own DNA.  Mitochondria are the only subcellular organelle that contain DNA outside of the nucleus.  They contain a simpler, circular copy of DNA that is transcribed with nuclear DNA in a coordinated symphony when it comes time to synthesize more mitochondria.

Muscles contain the highest mitochondrial content of any tissue in your body, in order to provide massive amounts of ATP for movement and exercise.  Muscle is generally divided into three types – white muscle, red muscle and mixed muscle.  The terms “red” and “white” are derived from the way these muscles appear during surgery or autopsies, but largely refer to the mitochondrial content of the muscle itself.


Red muscles contain a large quantity of mitochondria, white muscles contain fewer mitochondria and mixed muscles contain both red and white muscle fiber types.  Whereas a single cell contains one nucleus, muscle cells often contain hundreds or even thousands of mitochondria in order to support the generation of large quantities of ATP during exercise.

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In this electron micrograph, many adjacent mitochondria are visible within the muscle cell.  It’s no coincidence that they are located close to one another – they do that in order to share glucose, amino acids and fatty acids in order to distribute the production of ATP across a coordinately linked network.

What is Mitochondrial Biogenesis?

Mitochondrial biogenesis is a process that was first described over 40 years ago by a pioneer in the field of exercise physiology named John Holloszy, a professor at Washington University in St. Louis, MO.  Think of him as the godfather of exercise physiology.  In his seminal paper on the effects of exercise on mitochondrial structure and function, he found that endurance training induced large increases in muscle mitochondrial content and increased the ability of muscle to uptake glucose during and after exercise.

For more information on why glucose is your best friend during and after exercise, read What Happens to Muscles During Exercise and Eating for Optimal Muscle Recovery: Carbohydrates are Not the Enemy.

The term “mitochondrial biogenesis” simply refers to the process of replicating mitochondria within a cell, in order to increase ATP production in response to an increased demand for energy. 

The result of mitochondrial biogenesis is an expansion of the network of mitochondria within a cell, and an increase in the maximal amount of ATP that can be generated during intense exercise.  In short – more mitochondria means more ATP production at peak exercise conditions.

Muscle Mitochondria: Use Them or Lose Them!

Chronic disuse of muscle, sedentary behavior and aging each independently result in a decline in mitochondrial content and function, leading to the production of free radicals and cell death.  The muscle tissue of people with type 2 diabetes has also been extensively studied, revealing gross defects in mitochondrial number and function.  Although the cause-and-effect still remains unknown, muscle tissue from people with type 2 diabetes often is associated with reduced aerobic capacity, insulin resistance and deficient mitochondrial biogenesis.  In addition, studies have also shown that defective mitochondrial biogenesis in the heart can predispose individuals to cardiovascular complications, heart disease and the metabolic syndrome.

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Luckily, reversing the effects of aging, diabetes and cardiovascular disease via increased mitochondrial biogenesis is as simple as exercising moreStudies have shown that in aged individuals those with existing metabolic disease, the resumption of an active lifestyle can significantly improve preexisting cellular damage and promote gains in muscle mass.  Regular endurance exercise by itself (independent of changes in diet) can normalize age-related mitochondrial dysfunction simply by activating mitochondrial biogenesis. 

Exercise is the Most Effective Way to Make New Mitochondria

Exercise is the most potent signal for the increased production of mitochondria in muscle, by increasing the ability of the muscle to burn carbohydrates and fatty acids for ATP.

When you perform exercise, muscle cells generate a low-energy signal known as AMP, and the accumulation of AMP over time signals for increased ATP production.  An increasing AMP:ATP ratio initiates a cascade of signals within the muscle tissue to produce more ATP to protect against an energy deficit.  At the same time, during periods of sustained muscle contraction, calcium is released from intracellular stores, resulting in a 300% to 10,000% increase in intracellular calcium.  Increased calcium and AMP are powerful signals for the production of more mitochondria, which occurs in the resting state immediately following exercise.

In response to a large demand for ATP production, muscle cells respond by overcompensating in their ability to produce energy for the next round of exercise, by inducing mitochondrial biogenesis in the resting state. 

By doing this, mitochondria are able to consume larger amounts of oxygen, carbohydrates and fatty acids, the fuels needed to power the production of ATP.  The ability of muscles to overcompensate for exercise “stress” is exactly why frequent exercise results in increased strength, endurance, resistance to fatigue and whole body fitness.

Are All Forms of Exercise Created Equal?

It turns out that the amount of mitochondrial biogenesis that occurs in response to aerobic (endurance) exercise, resistance exercise (bodyweight exercise and weight training) or high intensity interval training (HIIT) are similar but not equal.

Aerobic exercise is the most extensively studied type, and has been shown to induce large increases in muscle mitochondria and the ability to oxidize glucose as fuel.  Endurance training such as jogging, running, cycling, swimming and cross country skiing result in profound increases in aerobic capacity, muscular endurance and resistance to fatigue over the long-term, all of which are made possible by mitochondrial biogenesis at the cellular level.

Resistance training such as FitStar, Crossfit, weight lifting and body weight training can amplify the signal for mitochondrial biogenesis beyond that of aerobic exercise by itself, resulting in increased aerobic capacity, strength and resistance to fatigue.  Performing a combination of resistance and aerobic exercise enhances mitochondrial biogenesis beyond that of either form of exercise in isolation.

High intensity interval training (HIIT) is characterized by repeated bursts of brief intense exercise interspersed with periods of brief recovery, and include popular sports such as soccer, lacrosse, wrestling, basketball and Crossfit, to name a few.  HIIT has been shown to increase muscle mitochondrial ATP production and improve muscle endurance despite a significantly reduced total exercise volume than traditional aerobic exercise.

In conclusion, a single bout of low-volume HIIT can activate mitochondrial biogenesis and even double endurance capacity as compared with aerobic exercise of the same energy expenditure. The key is consistency, and finding what works best for your life.

What Does This Mean For You as an Avid FitStar Athlete?

Lucky for you, FitStar workouts are a combination of intense aerobic and resistance exercise, and are therefore classified as HIIT workouts.  What this means is that by performing frequent workouts, you get the most bang-for-your-buck at the cellular level, resulting in potent muscle signals to induce mitochondrial biogenesis.  Think of FitStar’s HIIT approach as a time-efficient form of exercise that allows you to lead a busy lifestyle and kick-start mitochondrial biogenesis into high gear.

So the next time you perform a FitStar workout, imagine the work that your mitochondria are doing to keep up with the “stress” you create.  I assure you, the behind-the-scenes work is nothing short of magical.

FitStar Contributor Profile

Cyrus Khambatta

Cyrus Khambatta

Cyrus in an avid athlete, personal trainer, nutrition coach and mango addict. He holds a PhD in Nutritional Biochemistry from UC Berkeley, and is a nutrition and fitness coach for diabetics and the founder of Mangoman Nutrition and Fitness

  • Smallbzzz

    Great explanation of mitochondria! Thank you so much!

    • FitStar

      Glad you enjoyed it! I’ll be sure to let Cyrus know you appreciated his piece :).

  • BOKinLarksville

    Awesome article!

    • FitStar

      Thanks! Great to hear you enjoyed it :).

  • Yessi Young

    This is exactly what I was looking for. A lot of Lyme Disease patients are in so much pain that it is hard to justify exercising, but the way you lay this out makes it pretty clear to me that whatever exercise chronically ill patients can do, they should do.

    • FitStar

      Hey Yessi!

      Great to hear you enjoyed the article!

  • Graham Answerth

    I re visited old exercise regimes yesterday. I walked a very steep section of a hill three times of 30 second flat out. My heart and my body could not have gone any faster. Last evening, I felt fantastic. The endorphins were surging through my body. I only hope I can continue. I am 73 and pre diabetic. Best thing I have done for about five years.

    • FitStar

      Wow, well done Graham!

  • Dr. Jaime E. Contreras

    I am a firm believer of all of them, normal aerobic training, resistance training and HIIT which I have been practicing for years. And, let me tell you, I feel not only superb but also the fittest and healthiest man in the world!
    I am 57, and after several medical check ups that my physician has carried out on me along the latest years, his diagnostic has been always the same: “you are in excellent shape and your biological age is of a 35 years old man!”.
    This is one of the most powerful reasons to keep going and to think in being a FitStar Athlete!
    Thanks for your educational and interesting article.

    • Sylvain Martel

      Dr Contreras, Cyrus,
      Do you think that we can acheive “almost” the same results via, a combination of yoga stretching and bodyscanning or some kind of autogenic training?
      Thank you!

  • Louis Satterthwaite

    I train all aspects my physiology weights sprinting repetition running hill sprints I am 75 years old and figure in the top ten athletes in my age group in most distances from 100 metres 200 metres 400 metres 5k and 5 miles In the UK I believe I am the only one at this level at such diverse distances

    • FitStar

      Amazing, thanks for sharing Louis.

  • Jacob Henley

    Sweet article. I am a pro cyclist and am on a research kick to learn about mitochondria. You seem to have a vast knowledge on the topic. I’d love to see some links for further reading!
    Question: if time or training volume isn’t limiting factor is hiit best or lots of endurance miles better? Able to train say 20-30 hrs a week. Given that a zone 2 ride is much longer in terms of training stress than a hiit workout. Recovery is also less with the zone two work it seems.

    For the same energy expenditure you say hiit almost doubles the process. Do you happen to have the correlating time values for these two levels of exercise? I find this to be fascinating and thank you for the great post!

    • FitStar

      Hi Jacob! So glad you enjoyed the article! It was written by Cyrus Khambatta, a good friend of FitStar, and he might have the answers you seek. You can learn more about his work by visiting his site Cheers!

  • Kyle McCormack


  • Lisa

    Thank you for an amazing article !!!

  • Marty Kendall

    Good article. Thanks Cyrus.

  • Simon Saunders

    good read thank you

  • elevenvelo

    Actually, it’s SIT, or Sprint Interval Training, (characterized by 20-30 second 100% maximal efforts), rather than HIIT that have been shown to make significant increases to mitochondrial counts.