By Carol Godwin, Cyclemania

Bio 101: The “powerhouse of the cell” and how we depend on it to stay healthy and strong.

Round and round we go; back once again to spring and wondering where winter went and if it came at all. I’ve been out in shorts all December and January, and now in February, it’s in the 60s in the afternoons and almost no trace of the white stuff left in sight. Not great news for our thirsty trees and wildlife, but on the bright side, there’s hardly been a break in the hiking/riding season around here. Trails are mostly dry, and when I go out to ride lately, I come back confused, thinking it’s still fall, with golden leaves strewn across the ground, light cool breezes on my face, and day lengths getting longer each day. 

Trail surfaces are perfect for maintenance right now, but honestly, with zero runoff, there’s not much to do but smooth out a few ruts made by over-eager riders. Weird and disconcerting times, but here’s hoping there’s a late wet snowy winter storm track or an early spring gentle rain to rehydrate our forest floor. Hoping…waiting…thinking.

Besides a couple of fat bike rides on limited snow, I’ve been spending most of the winter riding the bright sunny trails of Watopia in spring. I’ve been enjoying the blooming flowers and green grass of this virtual world as I wait for the real one to spring back to life; sweating inside instead of freezing outside. Why take the time to keep riding, virtually or in real life, all winter? Why not take a break and hibernate with a sleeve of Thin Mints and endless episodes of Judge Judy while I wait for the calendar to tell me to get back outdoors? Here’s why. It’s science. It’s heart health. It’s aging. Its mental stability, and it’s preventing vital cellular mitochondria from trying to leave on vacation from disuse.

Let’s take a virtual field trip back to high school biology class to brush up on why you need to keep on moving, want to or not. Primarily, they’re the mitochondria. We all learned that the mitochondrion is the “powerhouse of the cell” in our biology classes, but there is so much more to learn and understand. 

The mitochondria began as primitive prokaryotic (bacterial) cells billions of years ago before any of our eukaryotic cells even existed and before oxygen was readily present on our planet. These primitive cells could take stored chemical energy from the environment and release that energy to give them the power to move, grow, and reproduce. Mitochondria have their own unique bacteria-style DNA, can reproduce on their own (mitochondrial bio-genesis) and can produce their own proteins. 

Mitochondria also play an important function in keeping calcium balanced in the blood, which is essential for muscle contraction and bone health. Mitochondrial dysfunction is a key factor in the development of osteoporosis and the ability of bones to repair themselves after injury. They are responsible for our body’s energy, muscle contraction, stamina, bone strength, heart and brain health, and our ability to recover from illness and injury. Mitochondria are the reason your first fertilized cell could divide and differentiate, making you a human being. 

Mitochondria are the basis of our entire existence and greatly influence the probable length of our time as living multicellular beings…who knew? Note: It has been a little terrifying and eye-opening to research this article. The number of rabbit holes that information about mitochondria has led me down is mind-boggling…  

About 2 billion years ago, a primitive mitochondrion was absorbed into another primitive cell in a process called endosymbiosis, and thus began one of the two most important biological interactions of all time; the other being photosynthesis, but that’s a story for another time. 

Mitochondria within an eukaryotic (modern) cell allowed that cell to have almost unlimited energy pumped out by their tiny internal invader, and these cells could use that unlimited energy to grow, specialize, and eventually become part of a human bike rider. The tiny mitochondria benefited from having a safe, cozy, larger cell to live in and also from that larger cell providing them with the raw ingredients needed to create this unlimited energy for the bigger cell. 

An interesting point is that the inner working membranes of mitochondria were themselves once independent proteobacterial cells, which now work in a crazy nesting doll scenario over billions of years of endosymbiosis; each less primitive cell benefiting from its internal predecessor. Increased energy for cells and coordination between cells eventually resulted in the complex multicellular organisms we know today. 

Modern eukaryotic cells that used significant energy demanded a lot from each mitochondrion, and those mitochondria, being able to reproduce by themselves (bio-genesis), reproduced and filled these cells with multiple copies of themselves, often connected in complex energy-producing networks. Human egg cells have up to 600,000 mitochondria to power embryo formation; nerve cells have about two million mitochondria apiece to send and receive messages, and brain cells have 1,000-2,500 mitochondria depending on demand. Muscle cells have thousands of mitochondria, many more mitochondria than skin cells have, and exercised muscle cells have more than twice as many mitochondria than sedentary ones…you see where this is leading, I’m sure.  

Cycling is a great way to keep your muscles, both heart and skeletal, demanding increased mitochondrial density and survival. Because of mitochondrial bio-genesis, mitochondrial density is not dependent on the host cell’s reproduction, meaning that you do not need bigger muscles to build mitochondrial density in each individual cell. Your heart replaces cells continually, but it does not add to the total number of cells present in the heart. 

As you exercise, the heart cells gain more mitochondria per cell, each containing 5,000-8,000 per cell, and become more efficient at their job of circulating your blood and using inhaled oxygen to do so. Mitochondria use oxygen to produce the ATP energy they create, so aerobic efficiency is directly related to the density of mitochondria in the muscle and heart tissue, and increased oxygen intake has no effect unless there are sufficient mitochondria to use that increased oxygen. 

Studies have shown that understanding and focusing on mitochondrial health can reduce chronic heart issues, increase metabolic efficiency, increase muscle stamina and strength, decrease the need for anaerobic lactic acid formation and the resulting muscle soreness. Mitochondrial health has been shown to lower hypertension and slow atherosclerosis. Increased metabolic efficiency has been shown to help prevent type 2 diabetes and cardiovascular disease. Mitochondrial health, density, and efficiency naturally decrease with age, so focusing on building and maintaining a strong mitochondrial base is essential to slow the rapid muscle fatigue which becomes more prevalent as a body ages, and delay the eventual and inevitable end of our lives. How do we encourage and improve mitochondrial health?  

• Regular physical activity is the primary factor in boosting mitochondrial health: cycling, hiking, brisk walking, and swimming. When we take an extended break in the winter, we lose most of the gains we had during summer, and this is readily apparent when we do the first rides of the season with riders tiring easily and complaining of being “out of shape”. Not only are they “out of shape”, they have decreased their skeletal and cardiac muscle mitochondrial density to the point where an increased breathing rate has no effect on muscle function. If the mitochondria aren’t there to use that inhaled oxygen to provide energy to the muscle cells, no amount of increased oxygen flow will help. 

Mitochondria have a roughly two-and- a -half-week life, which means without stimulation, half of the mitochondria in a cell will age out, dissolve, and be removed from the cell as waste. Another two weeks and you end up having approximately 25% of the original mitochondrial density. Therefore, continuous exercise is vital to “staying in shape” (this includes your brain!). Use it or lose it…unfortunately. On the flip side, mitochondrial density responds fairly quickly to increased exercise demands and shows significant increases over two to six weeks of consistent training, with maximum density being achieved at around eight to twelve weeks. Not good news for weekend warriors, but great news for those who keep on keeping on all winter.

• High Intensity Interval Training (HIIT) is great for improving mitochondrial density and function. Sprint/recovery and climbs/downhills are easy to accomplish on a bike. Varied single track trails with strenuous climbs are totally worth doing-no pain, 

no gain! 

• Heart rate monitoring is an efficient way to vary exercise intensity and increase cardiac muscle mitochondrial density, allowing your heart to more efficiently use oxygen and reduce strain on these muscles. Learn what your heart is telling you and focus on maintaining and understanding your most efficient rates to maximize endurance.  

-Resistance/load-bearing activities like weight lifting or carrying/pushing heavy loads are great ways to push your muscles to the max and have them demand mitochondrial bio-genesis.

• A diet consisting of antioxidant and magnesium-rich foods like leafy greens, foods rich in omega-3 fatty acids like salmon or other fatty fish help support mitochondrial membrane integrity, foods rich in coenzyme Q10 like nuts and seeds support enzyme activity and reduce cellular aging and electrolyte drinks can provide the sodium, magnesium and potassium essential to building the potential energy gradients across both the mitochondrial and muscle cell membranes needed to both produce ATP energy and initiate muscle contraction.

• Avoid unnecessary antibiotics. Why? Remember back to the introduction where I reminded you that mitochondria started out as independent prokaryotic cells (bacteria)? Antibiotics target bacteria. Studies have shown that extended antibiotic use can actually damage our mitochondria to the point where they are less efficient in providing the vital energy our bodies need to fight infection. Disruption of mitochondrial ATP synthesis can lead to elevated oxidizing compound levels, which have been shown to cause genetic cellular mutations (cancer). Follow doctor’s orders: don’t take antibiotics for viruses, don’t take antibiotics not prescribed for you (duh…), and follow up antibiotic regimes with a strongly mitochondrial-healthy diet of antioxidants. Monitor the use of antibacterial creams on injuries because not only do they kill possible invading bacteria initially (a good thing), they can damage the cell’s ability to heal the injury if they are used long term because of compromised mitochondrial function. Soap and water are usually the best bet for minor cuts and scrapes and will let your cells get on with the process of healing more quickly.

Ding! Science class is over. In summary, in order to maintain your physical health, you need to consider your mitochondrial health. Regular exercise increases mitochondrial density and muscle efficiency. Your heart is a muscle; treat it as such and get it out exercising too. Vary the intensity of your exercise and keep it regular. Your brain isn’t a muscle, but it uses 20% of the energy demanded by your body, thus is mitochondria-rich, needing stimulation to maintain mitochondrial health. Diseases like Alzheimer’s, Parkinson’s, and Huntington’s are related to mitochondrial defects, so keeping your mitochondria healthy is a win/win situation for the entire body. 

Beyond mitochondrial health, exercise, especially the outdoor kind, keeps you mentally engaged, levels mood swings, and has shown to provide physiological benefits long past the duration of the exercise. Get out there, or stay inside and exercise, but just do it! Your body will thank you in immeasurable ways…your mighty mitochondria will thank you too.

Extra credit: Overall aging and the resultant eventual death of multicellular organisms are thought to originate in the mitochondria. Over time, the mitochondrial DNA is susceptible to damage from various sources, and inevitably, it eventually becomes less efficient at energy production. Without energy, body cells slow their functions, lose their ability to replace themselves, and will eventually cease their essential functions…resulting in the death of the multicellular organism they are a part of. If that isn’t motivation to keep the mitochondria healthy and avoid potentially damaging oxidative agents, I don’t know what is! 

One more cool fact…Every mitochondrion in your body comes from your mother (Why? Because the male DNA is the only contribution to a fertilized egg, not his mitochondria or other cell parts) and her mother before her and her mother before that, going back 150,000 years ago to the “Mitochondrial Eve” whose mitochondrial DNA footprint is seen in every modern living human being! 

Enjoy this amazing life we have and think about the tiny billions-year-old machines providing our cells with energy since before the dawn of man. Awesome, right?