Metabolic Pathways During Exercise
Everyone knows we get our energy from the food we eat. But how is that food processed in our bodies during exercise to sustain movement? This blog will explore a quick overview of the metabolic pathways used by our bodies to most efficiently utilize stored energy during different types of exercise.
You may have heard of aerobic vs. anaerobic exercise. What do those mean to you? Do you know the difference? Many people think of cardio work-outs or long distance running when they hear the word aerobic. While this is true, we can dive a little deeper and see that aerobic exercise is defined as any sustained activity that stimulates the heart and lungs, thereby improving the body’s utilization of oxygen. Other forms of aerobic exercise include but are not limited to walking, rowing, swimming, cycling, hiking, spinning, dancing, cross-country skiing, and kickboxing. Conversely, anaerobic exercise can be defined as any activity requiring and using energy without the utilization of oxygen. Anaerobic exercise is usually high-intensity and short duration, and can include activities such as heavy weight lifting, sprinting, and box jumping, and other plyometric activities. Now, you may be thinking how am I performing exercises without the use of oxygen? Surely I am breathing while I’m doing box jumps! The answer is the different metabolic pathways that the body uses.
The common denominator for both aerobic and anaerobic exercise, and in fact for all types of movement within the body, is adenosine triphosphate (ATP). Because the body cannot easily store ATP, it must be formed during exercise. The forming and then breaking down of ATP at the cellular level is how muscles contract, but how that ATP is utilized determines aerobic vs. anaerobic. Aerobic exercise utilizes oxygen to break down carbohydrates, fats, and proteins in order to form ATP. This system is a bit slower than the anaerobic pathways because it relies on the circulatory system to transport oxygen to working muscles, but it can produce greater amounts of ATP. Therefore, the metabolic pathways for aerobic exercise are better suited to sustain lower-intensity, long-duration types of movements seen mostly in endurance athletes.
Regular aerobic exercise (3-5 times a week for 30 minutes) has many benefits such as improved stamina and endurance, lowered resting heart rate, and better sleeping cycles. Aerobic exercise also reduces the risk of developing some cancers, diabetes, depression, cardiovascular disease, and osteoporosis.
For anaerobic exercise, ATP is produced in three different ways depending on the intensity and duration of the movements. Earlier we said that anaerobic exercise does not require oxygen and does not have to rely on the circulatory system, therefore ATP is generated (but also used) more quickly. The creatine-phosphate (CP) system is the first metabolic pathway utilized anaerobically. The CP system supplies the body with ATP for about 10 seconds and is used for short bursts of high-intensity movements such as the 100-meter sprint. After the ATP from the CP system is all used up, and the muscles are still requiring energy, the body moves on to the Glycolysis system.
The glycolysis system creates ATP exclusively from carbohydrates. In this system the body breaks down glycogen, the stored form of glucose from carbs, and forms ATP along with the by-product lactic acid. The glycolysis system can only sustain high-intensity movements for around 1-2 minutes before enough lactic acid builds up that the muscles reach a lactate threshold and can no longer function properly. This is why and how we experience muscle pain, burning, and fatigue during exercise.
Regular anaerobic exercise also has many benefits such as increasing strength and muscle mass, increasing bone density, raising the lactate threshold, boosting metabolism, and burning fat.
When the body can no longer produce enough ATP through anaerobic pathways to meet the energy demands of the muscles, the body switches to an aerobic pathway. Many types of exercises utilize a mix of aerobic and anaerobic pathways such as jumping rope, circuit training, and CrossFit.
So the next time you are at the gym, at a class, or even out on a trail, take some time to think about the different metabolic pathways that you may or may not be using, and have a greater appreciation for the complexities and wonders that our bodies go through to help keep us moving!
Kevin Hatley, SPTA