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Exercise Makes Muscle Mitochondria Happy!!

Over the past several decades there has been an increased focus on the effect of exercise, diet, aging and disease on mitochondrial health.  Why? Your mitochondria are the POWER HOUSES within your cells. Therefore, understanding the basic physiology of mitochondria and how they replicate in response to your lifestyle can have profound impacts on your overall health.

Today we’re going to discuss exercise-induced mitochondrial biogenesis – a term that refers to the synthesis of new mitochondria in muscle tissues.

What is Mitochondrial Biogenesis?

The term “mitochondrial biogenesis” refers to the act 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.

Muscle Mitochondria: Use Them or Lose Them!

Mitochondria are small structures inside human cells that produce energy. They continuously work to change the energy gained from food into cellular energy that powers the muscles and tissue of the body. These essential structures are not constant though. They may increase or decrease, depending on your age and physical activity. Increasing the amount of mitochondria in your body results in more energy and a longer duration. How do we measure this?

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 poor 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.

Reversing the effects of diabetes, aging and cardiovascular disease through mitochondrial biogenesis is as simple as getting off your butt and exercising more!

Various studies 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, 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.