Mitochondria are affectionately referred to in almost every academic physiology textbook as the powerhouses of the cell. For our purposes we are going to focus on the muscle cells of the skeletal and cardiac (heart) systems but mitochondria populate many other cells of the human body. A mitochondrion is 0.5 to 1.0 microns in size; that represents 0.0000195 to 0.000039 of an inch. To put this in perspective, the head of pin is 2 millimeters in diameter. A mitochondria is merely a 4,000th to 2,000th the size of the head of a pin. Up to one-third of the volume of your skeletal or cardiac muscle cell is taken up by mitochondria. Incredulous that something so miniscule can put you on the podium? Here is a distilled version of the cellular physiology behind the magic and how to manage it to your advantage.
As athletes we all know about oxygen and carbohydrates (sugar). The mitochondria take both of these ingredients (substrates) and use them to produce the energy (product) that makes your heart beat and your muscles perform. Glucose (the form of sugar found in our blood stream) is repackaged inside the complex internal structure of the mitochondria into two key components: pyruvate and NADH (nicotinic adenine dinucleotide). Hey there, stop that yawning, this is where things get exciting! These two chemicals are now transported into the central part of the organelle where, in the presence of oxygen (this is of primary importance), they are used to produce ATP (adenosine triphosphate). ATP is a nifty little chemical that is essentially the energy currency (think money, not electricity) of the cell. This all happens via the Krebs Cycle. Bicycle, Krebs Cycle – starting to sound connected here? Khan Academy has a fabulous video explanation of cellular respiration if you’re a visual person and would like to know more about the process: https://www.khanacademy.org/science/biology/cellular-molecular-biology/cellular-respiration/v/introduction-to-cellular-respiration
Now that I have piqued your interest and you are starting to wonder exactly how that ATP helps you turn the pedals and stride the miles, let’s talk about what ATP actually does. Inside your muscle cell there are tiny little fibrils (essentially filaments of protein) named actin and myosin. The complex physical interaction of these fibrils will be the topic of another article, but in the meantime it’s just important to understand that ATP binds to the myosin fibril and causes the muscle to contract (be it skeletal or cardiac). Rigor mortis ensues when your body is no longer able to supply ATP to your working muscle cells. Hopefully that gives you some perspective on how important ATP is! Ever completely bonked in a race? Your muscle cells were depleted of glucose, oxygen, and ATP.
Production of energy for your working muscles is an extremely complex biochemical recipe, but it can all be boiled down to the simple ingredients of sugar, oxygen, and calcium. Sugar supplies the basic building blocks (remember our friends pyruvate and NADH) that the mitochondria use to produce ATP in the presence of oxygen (the whole process being called oxidative phosphorylation if you must know). Calcium is essential to transformation of glucose into the pyruvate and NADH as well as the interaction of the myofibrils myosin and actin mentioned above.
This process is completely dependent on the presence of oxygen as it represents aerobic respiration inside your working muscle cells. Have a little light bulb over your head blinking “heart rate monitor”? What a good student of exercise physiology you’ve become in just a few short paragraphs. Your working muscles use glucose to produce ATP at a rate 13 times higher in the presence of oxygen than when oxygen is not readily available. Heart rate monitor alarm screaming because you’re exceeding your lactate threshold (going anaerobic)? Guess what, it won’t be long before you bonk. Bonk is a synonym for Not Enough ATP (see above)!
Now here is the best part – exercise actually results in mitochondrial proliferation within muscle cells. What this means is that by exercising you are essentially asking your body to provide you with more energy and it responds by revving up it’s own cellular machinery. The Australian Society for Biochemistry and Molecular Biology published a fascinating article that explains this in more detail if you’re looking for a little light reading before bedtime: https://www.asbmb.org.au/magazine/2013-April_Issue44-1/Showcase%203%20-%20Wadley.pdf
All sounds great, right? Your cellular biochemistry cannot do all the work on it’s own however; it needs you to be it’s teammate in the process. How can you help your physiology to perform at it’s best? Here of some simple things you can do to optimize this process and make the best of your training and have a great race performance:
~Train smart: Overtraining and training without appropriate recovery damages muscles cells and the intracellular machinery. Develop training programs and hire a coach if you are able.
~Stay hydrated: Optimal cellular function is dependent on the right balance of water so that transport of substances occurs readily. Dehydration leads to “gunking” up of the system. Think car engine here!
~Fuel: Feed your mitochondria a steady diet of available sugar. This means consuming carbohydrates in a manner that gives your cells readily available fuel (glucose) for training and racing and well as eating a well-balanced diet and choosing high-quality recovery snacks to boost your glycogen reserves.
~Protein: Muscles and mitochondria need protein to proliferate. Make sure your protein intake is adequate and high quality.
~Constant oxygen supply: Mitochondria cannot function in an anaerobic environment. Know your maximum heart rate and lactate threshold and use your heart monitor to keep that oxygen flowing freely to your cells.
~Electrolytes: As we discussed, calcium is integral to the biochemical process, but calcium does not exist and function in isolation. Calcium’s availability and function is inextricably tied to the levels of other electrolytes like potassium and magnesium as well as the pH of the blood (another article, another time). Make sure you are ingesting a balanced mix of electrolytes when training and racing.