People who devote time to improving their bodies through exercise need to know how to make the most of their workouts, and therefore, the most out of their bodies. To this end, it’s important to understand how your muscles operate in order to make them perform at their best. The ATP molecule is the molecule that muscle cells use for energy transport and is made in two significant ways, aerobically and anaerobically. Understanding both of these methods will help you to target your workouts to match your fitness goals.
What is ATP?
ATP stands for Adenosine Triphosphate. It is a molecule created by combining adenine and ribose and attaching three phosphate groups. Its main role is the conveyance of energy from one spot to another within a muscle cell. The availability of ATP within a cell determines the lengths to which that cell can be pushed.
Muscle cells produce ATP on a constant basis. A muscle cell begins the process of producing ATP in the watery environment between the cell structures. In this process, called glycolysis, the breakdown of one molecule of glucose produces two molecules of pyruvic acid and two molecules of ATP. This process is anaerobic, which means that it takes place in the absence of oxygen. Remember this, as it will be important later.
The next step in this process takes place within the mitochondria of the cell. The mitochondria take the pyruvic acid molecules and input them into the next part of the process. This next part requires oxygen, therefore making it an aerobic process. It is called the Oxidative Phosphorylation process and produces 95% of the ATP used within the cells. The foundation for this process is the creation of water by combining the molecules of hydrogen and oxygen. This chemical reaction releases large amounts of energy which is then used to make ATP.
Begin at the beginning
When at rest, a skeletal muscle cell creates more energy than it uses. This energy is created efficiently in the aerobic, or oxidative system. This excess energy is transferred to creatine to create a phosphagen molecule called creatine phosphate. This is important because, after a muscle contraction, a phosphate group is knocked off of the ATP molecule. The cell then uses the energy stored in the creatine phosphate molecule to reattach the phosphate and restore the ATP molecule. This is the reason for creatine supplements. The hope is that by providing extra creatine, the cell will be able to reassemble more ATP molecules after muscle contractions, thus providing the cell with more energy.
When the cell begins to contract, the mitochondria continue to produce ATP using the oxidative cycle. This is the most efficient way to produce ATP, but the drawback here is that this process requires the constant influx of oxygen. If the supply of oxygen is sufficient, mitochondria will continue to produce ATP using this oxidative process. If the cell becomes stressed beyond its oxygen reserves, the cell is then forced to abandon the oxidative process and produce all of its energy using the aforementioned glycolytic system. Remember, the glycolytic cycle produces ATP using a purely anaerobic process. Since this system is anaerobic, the cell can continue to produce ATP even when the blood supply cannot keep up with the demand for oxygen. The unfortunate consequence of glycolysis is that besides producing ATP, it also produces pyruvic acid. This is fine when the mitochondria are able to make use of the pyruvic acid to make more ATP, but in the absence of oxygen, the mitochondria cannot make use of the pyruvic acid. The excess pyruvic acid is therefore converted into lactic acid. Large amounts of lactic acid change the pH of the muscle cell, which eventually causes the cell itself to temporarily lose its ability to contract. This is called muscle fatigue. Another side effect of lactic acid buildup is muscle soreness. Anyone who has ever experienced soreness and stiffness after a hard workout has felt the effects of lactic acid buildup.
What’s the point?
You might be wondering at this point, “How does this affect me and my workouts?” The truth is, that depends greatly upon the type of workout you’re doing and the goal you have for your exercise routines. Some athletes are primarily concerned with anaerobic endurance. This is the amount of time that a muscle can continue to contract without the presence of oxygen. Brief bursts of strenuous activity force muscle cells to resort to glycolysis for a significant portion of their ATP needs. Continuing to work out in this manner also causes muscles to grow (referred to as muscle hypertrophy), as the muscle cells create more mitochondria in an effort to meet the ATP demand. Bodybuilders use this to their benefit. They are not concerned much about the aerobic benefits of cardio workouts. They want large muscles, so they engage primarily in workouts that promote anaerobic endurance.
Aerobic endurance, on the other hand, concerns stretching the amount of time the muscle cell can continue to work while still using the oxidative process to produce ATP. Increasing this endurance level involves moderate and sustained levels of activity. Exercises like jogging or swimming fit the bill. Remember, aerobic means that the process is supported by the inclusion of oxygen. This is what cardio workouts are all about: increasing the strength of your heart enough to enable it to pump sufficient oxygen to the muscle cells to allow for this oxidative process. Aerobic endurance exercises will not cause muscle hypertrophy. This is fine for some athletes because they don’t want muscle hypertrophy. For example, distance runners don’t need large muscles. They need the endurance to run for miles, so they train with aerobic endurance in mind.
Many athletes, however, utilize a training schedule that incorporates both aerobic and anaerobic exercises. By doing this, athletes can increase the size and strength of their muscles, while also improving their cardiovascular endurance. This is called cross-training. Cross training involves alternating aerobic exercises, like swimming or jogging, with anaerobic exercises like weight lifting.
Knowing your body, and how it works, will give you the ability to target your workouts to maximum effectiveness. It’s also important to know what you want from your workout, which depends on your needs. The more you know, the easier it will be to shape your body into the machine you want it to be.
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This is one of the easiest-understood articles I’ve read describing the ATP process. Understanding is key to future improvement.
I have been an avid Cathlete for 4 years now and look forward to reading the weekly newsletters, but I have to disagree with this one. I have just graduated from the University of Colorado with my master’s degree in sports nutrition and have taken many intense exercise physiology classes. The newest research indicated that it’s the accumulation of hydrogen ions that produce the acidic environment and the drop in PH, not lactic acid.
It should now be common knowledge that lactic acid is NOT responsible for muscle soreness (DOMS).