We have shared in our earlier blogs about Mitochondria. Mitochondria are also called powerhouse of cells & play an important role in our exercise performance specifically endurance/aerobic exercise.
Mitochondria are specific structures or organelles in our cells that are responsible for producing energy. Briefly, Mitochondria carry out cell respiration- a process by which we convert chemical energy from food into a common energy source that can be used to fuel various cellular functions. Such functions include transport of molecules, contraction of muscle fibres & growth of new cells, all of which require energy currency molecules called adenosine-triphosphate or ATP.
Inside our Mitochondria are various enzymes that can generate energy from various fuel sources including glucose ( breakdown of carbs), amino acids(breakdown of protein) & fatty acids(breakdown of fats). This process of generating energy requires oxygen & is therefore called aerobic respiration.
Mitochondria plays a vital role in two stages of Aerobic respiration- Krebs cycle & electron transport. Both of these produce ATP which is then used to fuel various cells.
In Skeletal muscles cells, aerobic respiration is our main means of providing energy for repeated muscle contraction that is sustainable over a period of time. Therefore Mitochondria is very important to fueling long & intense workout such as long distance running, jogging & swimming( endurance exercises)
Increase in mitochondrial content of cells is referred to as Mitochondria biogenesis. This may include:
- Growth & enlargement of new Mitochondria components
- Dividing existing mitochondria to generate more Mitochondria.
Since Mitochondria produces ATP, Mitochondria biogenesis helps in providing great energy supply for our cells. When Mitochondria biogenesis occurs in our skeletal cells, it enables both growth of new Mitochondria components & generating more Mitochondria as discussed above, thereby allowing us to sustain repeated muscle contraction over a long period of time. This is beneficial for endurance workout. When our muscles are frequently used, its mitochondrial content increases.
This made us realise why endurance athletes continue going on & one. Over months of training, their muscles have developed a better ability to extract oxygen from the bloodstream. Growth in capillaries that increases blood supply to muscle fibre is an important reason for increase in oxygen extraction. Besides, due to Mitochondrial biogenesis response to training, athlete’s muscle fibers have higher mitochondrial content. This higher mitochondrial content enables muscle cells to use more oxygen for the process of aerobic respiration. This improves muscle’s ability to produce ATP which helps in sustaining workout for a longer period of time. This is the reason Mitochondria Biogenesis is also referred to as Training Adaptation- a beneficial response by our body to our repeated stress of exercise.
MItochondria Biogenesis plays a role in the cell’s sensitivity to insulin & improve our blood sugar levels. It is an interesting fact to learn that muscle cells of people with Type-2 diabetes have fewer & smaller mitochondria. This finally results in less efficient use of fatty acids for respiration. This build of fatty acids blocks blood insulin signalling pathways & makes cells less sensitive to Insulin.
As a part of Aerobic respiration, Mitochondria produces substances known as Reactive Oxygen Species which are a form of free radicals.
Free radicals are atoms or molecules with unpaired electrons which make them highly reactive & ability to cause damage to our cells & DNA. This damage is called oxidative damage & is associated with inflammation, damage of blood vessels & poor insulin sensitivity. Our Mitochondria has a mechanism that prevents accumulation of such free radicals. However when Mitochondria functions less efficiently, such defence mechanisms take a back seat resulting in production of such free radicals.
Mitochondria biogenesis can protect our body against these free radicals by growth of new mitochondrial components, increase in number of mitochondria & improving the efficiency of existing mitochondria thereby resulting in less production of such free radicals during aerobic respiration process.
How can we stimulate & improve efficiency of Mitochondria? The answer is exercise. As shared above Mitochondrial biogenesis is nothing but training adaptation which occurs when we stress our muscle cells through frequent workout. Let us discuss this in detail
- Strength training or endurance? It is generally said that endurance training stimulates Mitochondrial biogenesis which strength training causes changes to our parts of muscle fibres that contract, also referred to as myofibrils. Although strength training can also stimulate Mitochondrial genesis, effect is generally weaker as compared to that created by endurance training. In this sense our Mitochondria responds more to slow twitch & fast twitch ( type IIa) muscle fibre rather than fast twitch type IIb.
- High volume or intensity? This has been a debatable question whether Mitochondrial biogenesis is stimulated by training volume or intensity. Often it is thought that high intense workout such as Metabolic Resistance Training or HIIT is said to stimulate Mitochondria Biogenesis more & are more efficient in producing energy without increasing size or number of mitochondria much. However, it is good to consider that both HIIT & steady state are equally effective in improving efficiency of mitochondrial biogenesis.
- Calorie restriction: This refers to restricting the amount of calories we consume while ensuring you are getting the essential nutrients. Intermittent fasting is one example of calorie restriction. It is a known fact that calorie restriction is said to improve efficiency of Mitochondria.
- Temperature extreme: Both extreme hot & cold temperature is said to improve efficiency of mitochondria. During endurance workout, chemical energy gets converted into heat energy & this build up temperature within muscles. This mild heat stress stimulates mitochondrial biogenesis. Besides, as Mitochondria generates heat energy as a part of respiration, exposure to cold may trigger development of more mitochondria to negate the impact of drop in temperature.
PGC-1α is a key protein that stimulates mitochondrial biogenesis. As response to our training, we produce more PGC-1α which stimulates growth, enlargement & division of Mitochondria in skeleton muscle cells
This protein is encoded by PPARGC1A gene . Variant of this gene impact how well your product PGC-1α which impact how effectively your body triggers mitochondrial genesis & hence this gene can impact your endurance training performance
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