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Metabolic Pathways: An Overview

Published October 12, 2019
Ben Kissam

Written By: Ben Kissam, BS

Ben has a B.S. in Movement and Sports Science and over 7 years Certified Personal Training Experience.

metabolic-pathways
<script type="application/ld+json"> { "@type":"BlogPosting", "headline":"Metabolic Pathways: An Overview", "datePublished":"October 12, 2019", "description":"Why shouldn’t we do the same workout over and over? Because different workouts train the three metabolic pathways. Here’s an explanation of each.", "image": "https://d1ghrtdbdq2gkr.cloudfront.net/media/public/2019/09/man-jogging-running-bridge-city-early-morning-sunny-thumbnail-0258.jpg" }, } ] } </script> <article> <div> <ul> <li><a href="#section1">What is a Metabolic Pathway?</a></li> <li><a href="#section2">What are the Three Metabolic Pathways?</a></li> <li><a href="#section3">Ever Felt “Weird” at the Beginning of a Workout?</a></li> <li><a href="#section4">How are Metabolic Pathways Regulated?</a></li> <li><a href="#section5">What are the Major Pathways of Carbohydrate Metabolism?</a></li> <li><a href="#section6">Metabolic Pathways—Wrap-Up</a></li> </ul> </div> <section> <p>There are many kinds of workouts—short, all-out sprints, high-intensity interval sessions, and longer endurance workouts just to name a few. And all of these require energy. </p> <p>But did you know these three types of workouts are fueled in different ways? </p> <p>It’s true! Our bodies use different metabolic pathways to fuel different types of movement. Depending on how long and how intense your exercise is, your body will fuel itself accordingly in unique ways.</p> <p>Knowing these pathways is useful for a few reasons. They may help you see which types of exercise you need to do more of, and better understand the types of workouts you should search out to <a target="_blank" href="https://www.warriormade.com/content/exercise/how-to-set-realistic-fitness-goals-you-can-achieve" rel="noreferrer">achieve your specific goals</a>.</p> <p>Let’s look at the three pathways, break each one down, and show you how they self-regulate and work with each other.</p> </section> <hr class="divider-50 divider-medium mx-auto"> <section id="section1"> <script type="application/ld+json">{"@context":"https://schema.org","@type":"FAQPage","mainEntity":[{"@type":"Question","name":"What is a metabolic pathway?","acceptedAnswer":{"@type":"Answer","text":"According to the American Council on Exercise, metabolic pathways are how we get energy from food. The food we eat must be broken down (known as ‘catabolism’) so we can use it to fuel our brains, workouts, and everyday lives.\n\nBut our bodies can’t directly use food as energy—it must be broken down and converted into chemical energy.\n\nPerhaps you remember the term ‘ATP’, or adenosine triphosphate, from high school biology. Food is converted into ATP, which our cells can then use for fuel. Muscles can’t get the needed energy from blood or other body tissues, so they must manufacture it on their own.\n\nHowever, our muscles can only store so much ATP as energy. So depending on the type of exercise we’re doing, our body uses different pathways to supply muscles with the energy needed to keep going."}}]}</script> <h2>What is a metabolic pathway?</h2> <p>According to the <i>American Council on Exercise</i>, metabolic pathways are how we get energy from food <sup>1</sup>. The food we eat must be broken down (known as ‘<i>catabolism</i>’) so we can use it to fuel our brains, workouts, and everyday lives.</p> <p>But our bodies can’t <i>directly</i> use food as energy—it must be broken down and converted into chemical energy.</p> <p>Perhaps you remember the term ‘ATP’, or <i>adenosine triphosphate</i>, from high school biology. Food is converted into ATP, which our cells can then use for fuel. Muscles can’t get the needed energy from blood or other body tissues, so they must manufacture it on their own <sup>2</sup>.</p> <p>However, our muscles can only store so much ATP as energy. So depending on the type of exercise we’re doing, our body uses different pathways to supply muscles with the energy needed to keep going.</p> </section> <hr class="divider-50 divider-medium mx-auto"> <section id="section2"> <script type="application/ld+json">{"@context":"https://schema.org","@type":"FAQPage","mainEntity":[{"@type":"Question","name":"What are the three metabolic pathways?","acceptedAnswer":{"@type":"Answer","text":"Below is a review of the three pathways. The “Exercise example” at the top of each section is a type of workout that primarily uses that energy system. Phosphagen, Glycolytic, Oxidative"}}]}</script> <h2>What are the three metabolic pathways?</h2> <p>Below is a review of the three pathways. The “Exercise example” at the top of each section is a type of workout that primarily uses that energy system.</p> <picture class="lazy-load"> <source data-srcset="https://d1ghrtdbdq2gkr.cloudfront.net/blog-content/bar-weights-one-end-lifting-0258.webp" type="image/webp"> <source data-srcset="https://d1ghrtdbdq2gkr.cloudfront.net/blog-content/bar-weights-one-end-lifting-0258.jp2" type="image/jpf"> <source data-srcset="https://d1ghrtdbdq2gkr.cloudfront.net/blog-content/bar-weights-one-end-lifting-0258.jpg"> <img src="https://d1ghrtdbdq2gkr.cloudfront.net/blog-content/bar-weights-one-end-lifting-LR-0258.jpg" class="img-fluid" alt="bar-weights-one-end-lifting"> </picture> <h3>Phosphagen</h3> <p><b>Exercise example</b>: Usain Bolt running the 100m sprint at the Olympics.</p> <p>The phosphagen system is more easily understood if you can remember it’s the “immediate” system. A quick sprint, a heavy lift, or anything involving <i>maximum power</i> uses this pathway.</p> <p>Two types of energy power you here: stored ATP and <i>creatine phosphate</i>. The phosphagen (ATP) system doesn’t last long, though; stored ATP can only sustain 1 or 2 seconds of maximum effort exercise <sup>2</sup>. At this point, your stores of creatine phosphate take over.</p> <p>The whole idea is kind of amazing to think about, actually. Your body can access stored energy through catabolic processes (remember, catabolism means “break down”) without you having to do anything.</p> <p>Understanding this system may help you see why some weightlifters take creatine supplements. If your muscles are full of creatine, you’d—in theory—be able to lift heavier weights. Or at least, perform at your best during short and intense bouts of exercise.</p> <p>(We don’t really suggest taking creatine, though. It’s been known to lead to weight gain, bloating, and digestive issues <sup>3</sup>.</p> <p>If you exercise, you know short breaks during workouts are important to regain stamina. During these breaks the phosphagen system replenishes itself. It takes about 30 seconds to restore 70 percent of phosphagen and up to 5 minutes to get back to 100 percent <sup>4</sup>.</p> <p>This gap of time explains why you need a break after giving all-out effort on something if you’re going to be able to repeat the performance.</p> <picture class="lazy-load"> <source data-srcset="https://d1ghrtdbdq2gkr.cloudfront.net/blog-content/man-push-up-plank-track-field-0258.webp" type="image/webp"> <source data-srcset="https://d1ghrtdbdq2gkr.cloudfront.net/blog-content/man-push-up-plank-track-field-0258.jp2" type="image/jpf"> <source data-srcset="https://d1ghrtdbdq2gkr.cloudfront.net/blog-content/man-push-up-plank-track-field-0258.jpg"> <img src="https://d1ghrtdbdq2gkr.cloudfront.net/blog-content/man-push-up-plank-track-field-LR-0258.jpg" class="img-fluid" alt="man-push-up-plank-track-field"> </picture> <h3>Glycolytic</h3> <p><b>Exercise example</b>: A 4-minute tabata high-intensity interval (HIIT) workout where you do 8 cycles of 20 seconds of work followed by 10 seconds of rest. </p> <p>Have you ever done <i>anaerobic exercise</i> before? </p> <p>(Anaerobic exercise is high-intensity exercise, usually with built in breaks to recover. HIIT and circuit workouts are both examples.) </p> <p>If you have, then you’ve used your glycolytic energy system. This energy system uses a process called ‘glycolysis’ to break glucose, or sugar into ATP for your muscles. It can sustain anywhere from 30 seconds to 4 minutes <sup>2</sup>.</p> <p>Anyone that’s done an anaerobic workout before knows that exercising at this intensity can be quite challenging. High-intensity exercise is, by definition, anaerobic exercise <sup>4</sup>.</p> <p>It’s challenging because you’re moving at a relatively high percentage of your max effort (roughly 70 to 90 percent), but not high enough that it’s a true “sprint”, which would use the phosphagen system.</p> <p>Perhaps you know or have felt lactic acid build up in your muscles. That “burning” sensation is a byproduct of anaerobic exercise. The body uses all of the glycogen in your muscles and liver, which results in a buildup of lactic acids and other byproducts <sup>4</sup>.</p> <p>That’s why muscles start to fatigue quickly when lactic acid builds up. Like the phosphagen system, your muscles need a break to replenish glucose so it can be converted into ATP.</p> <picture class="lazy-load"> <source data-srcset="https://d1ghrtdbdq2gkr.cloudfront.net/blog-content/woman-outdoor-jogging-sunny-early-morning-0258.webp" type="image/webp"> <source data-srcset="https://d1ghrtdbdq2gkr.cloudfront.net/blog-content/woman-outdoor-jogging-sunny-early-morning-0258.jp2" type="image/jpf"> <source data-srcset="https://d1ghrtdbdq2gkr.cloudfront.net/blog-content/woman-outdoor-jogging-sunny-early-morning-0258.jpg"> <img src="https://d1ghrtdbdq2gkr.cloudfront.net/blog-content/woman-outdoor-jogging-sunny-early-morning-LR-0258.jpg" class="img-fluid" alt="woman-outdoor-jogging-sunny-early-morning"> </picture> <h3>Oxidative</h3> <p><b>Exercise example</b>: Running a 5k race.</p> <p>Think of the oxidative system as “steady-state” exercise. This metabolic pathway is active during longer-duration, lower-intensity activities like walking, running, cycling and swimming. You’re doing <i>aerobic exercise</i> when the oxidative system is fueling your muscles.</p> <p>The oxidative pathway is unique because it requires oxygen to produce ATP. Carbs and fatty acids can only be burned when oxygen is present <sup>4</sup>. </p> <p>It’s the most efficient system of the three pathways, but it does require a lot of energy to maintain. Your circulatory system and mitochondria must be strong and a constant supply of oxygen is required. </p> <p><i>(This is why a long run is so unpleasant if you’re out of shape. The systems you need to run on oxygen aren’t fit enough to sustain exercise.)</i></p> <p>Amazingly, it takes up to 2 minutes of consistent movement for your body to start running off oxygen <sup>1</sup>. Prior to that, your phosphagen and glycolytic systems dominate. </p> <p>After a few minutes, though, the oxidative system is primarily responsible for converting ATP into chemical energy for your muscles.</p> </section> <hr class="divider-50 divider-medium mx-auto"> <section id="section3"> <script type="application/ld+json">{"@context":"https://schema.org","@type":"FAQPage","mainEntity":[{"@type":"Question","name":"Ever felt “weird” at the beginning of a workout?","acceptedAnswer":{"@type":"Answer","text":"Have you ever noticed how your body feels “weird” during a warm up or at the beginning of a run? That uncomfortable feeling has to do with the metabolic pathways. It takes about two minutes for everything you need to sustain exercise to activate or get online."}}]}</script> <h2>Ever felt “weird” at the beginning of a workout?</h2> <p>Have you ever noticed how your body feels “weird” during a warm up or at the beginning of a run? That uncomfortable feeling has to do with the metabolic pathways. It takes about two minutes for everything you need to sustain exercise to activate or “get online”.</p> <p>In that first 120 seconds, your body must:</p> <ol> <li>Burn through it’s stored ATP and creatine phosphate,</li> <li>Switch to stored glycogen, and burn through that,</li> <li>Activate your cardiovascular system (blood vessels dilate, heart rate elevates, pH levels change) <sup>5 6</sup>,</li> <li>Circulate oxygen through the blood to muscles so carbs and fat can be burned.</li> </ol> <p>That’s a lot of work! But even if you’re out of shape, your body accomplishes all of this in roughly the same amount of time as a fit person (even if it’s a little more uncomfortable when you first start working out again).</p> </section> <hr class="divider-50 divider-medium mx-auto"> <section id="section4"> <script type="application/ld+json">{"@context":"https://schema.org","@type":"FAQPage","mainEntity":[{"@type":"Question","name":"How are metabolic pathways regulated?","acceptedAnswer":{"@type":"Answer","text":"By this point you might be wondering how the three pathways interact with each other. They are interdependent, meaning all three systems depend on each other to deliver energy."}}]}</script> <h2>How are metabolic pathways regulated?</h2> <p>By this point you might be wondering how the three pathways interact with each other. They are interdependent, meaning all three systems depend on each other to deliver energy<sup>7</sup>.</p> <p>There are two types of metabolic pathways: <i>anabolic</i> and <i>catabolic</i><sup>8</sup>:</p> <ul> <li><i>Anabolism</i> refers to the building up or ‘<i>biosynthesis</i>’ of molecules (example: replenishing stored ATP)</li> <li>Catabolism refers to the breaking down of molecules (example: breaking down glucose)</li> </ul> <p>But the main objective in regulating any pathway is to <a target="_blank" href="https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Book%3A_General_Biology_(Boundless)/6%3A_Metabolism/6.1%3A_Energy_and_Metabolism/6.1C%3A_Metabolic_Pathways" rel="nofollow noreferrer">return your body to homeostasis</a> <sup>9</sup>. Cells must remain in a certain condition (pH, temperature, etc.) to stay healthy and functioning, so the body constantly reacts to the type and intensity of exercise you’re doing <sup>9</sup>.</p> <p>Things like <i>enzymes</i>, which are substances in the body that cause a specific chemical reaction, work to regulate the body and three pathways. </p> <p>As fitness improves, returning to homeostasis becomes much more efficient. That’s why a fit person’s heart rate returns to normal quicker after an intense workout <sup>8</sup>.</p> <picture class="lazy-load"> <source data-srcset="https://d1ghrtdbdq2gkr.cloudfront.net/blog-content/bowl-full-blueberries-0258.webp" type="image/webp"> <source data-srcset="https://d1ghrtdbdq2gkr.cloudfront.net/blog-content/bowl-full-blueberries-0258.jp2" type="image/jpf"> <source data-srcset="https://d1ghrtdbdq2gkr.cloudfront.net/blog-content/bowl-full-blueberries-0258.jpg"> <img src="https://d1ghrtdbdq2gkr.cloudfront.net/blog-content/bowl-full-blueberries-LR-0258.jpg" class="img-fluid" alt="bowl-full-blueberries"> </picture> </section> <hr class="divider-50 divider-medium mx-auto"> <section id="section5"> <script type="application/ld+json">{"@context":"https://schema.org","@type":"FAQPage","mainEntity":[{"@type":"Question","name":"What are the major pathways of carbohydrate metabolism?","acceptedAnswer":{"@type":"Answer","text":"Some pathways use carbohydrates for fuel, while others use a combination of carbs and fats. So if you’re following a low carb diet, you may wonder which uses carbs.\n\nThe glycolytic and oxidative pathways break down and metabolize carbohydrates for energy.\n\nThe former converts stored glucose in muscles to ATP. The latter takes place during “steady-state” exercise, when oxygen is present and your cardiovascular system is activated."}}]}</script> <h2>What are the major pathways of carbohydrate metabolism?</h2> <p>Some pathways use carbohydrates for fuel, while others use a combination of carbs and fats. So if you’re following a low carb diet, you may wonder which uses carbs.</p> <p>The <i>glycolytic</i> and <i>oxidative</i> pathways break down and metabolize carbohydrates for energy <sup>10</sup>. </p> <p>The former converts stored glucose in muscles to ATP. The latter takes place during “steady-state” exercise, when oxygen is present and your cardiovascular system is activated.</p> </section> <hr class="divider-50 divider-medium mx-auto"> <section id="section6"> <h2>Metabolic pathways—wrap-up</h2> <p>Varying your workouts trains the three pathways, helping them become more efficient, which makes you more fit. A sprinter like Usain bolt has a highly-developed phosphagen system. But that’s entirely different than marathon runner, who’s oxidative system gets trained the most.</p> <p>Perhaps you won’t remember every bit of biology regarding the three pathways. But you can use the information to make more informed decisions regarding your workouts. </p> <p>A balanced workout program trains <i>all three</i> pathways. Doing so will round out your fitness, crafting a strength ability that easily transfers your hard work to the rest of your life!</p> <h3>Resources:</h3> <ol> <li><a target="_blank" href="https://www.acefitness.org/fitness-certifications/ace-answers/exam-preparation-blog/3256/the-three-primary-energy-pathways-explained" rel="nofollow noreferrer">The Three Primary Energy Pathways Explained</a></li> <li><a target="_blank" href="https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/phosphagen" rel="nofollow noreferrer">Learn more about Phosphagen</a></li> <li><a target="_blank" href="https://www.healthline.com/nutrition/creatine-safety-and-side-effects" rel="nofollow noreferrer">Is Creatine Safe, and Does It Have Side Effects?</a></li> <li><a target="_blank" href="http://umich.edu/~medfit/resistancetraining/timingiseverything101705.html" rel="nofollow noreferrer">Timing is Everything: Why the Duration and Order of Your Exercise Matters</a></li> <li><a target="_blank" href="https://med.libretexts.org/Bookshelves/Allied_Health/Book%3A_Concepts_of_Fitness_and_Wellness_(Flynn_et_al.)/3%3A_Cardiorespiratory_Fitness/3.05%3A_Oxidative_Energy_System_(Aerobic)" rel="nofollow noreferrer">Oxidative Energy System (Aerobic)</a></li> <li><a target="_blank" href="https://source.colostate.edu/study-causes-blood-vessels-expand-exercise/" rel="nofollow noreferrer">What causes blood vessels to expand during exercise?</a></li> <li><a target="_blank" href="http://www.chemistry.wustl.edu/~edudev/LabTutorials/CourseTutorials/bb/Buffer/Buffers.pdf" rel="nofollow noreferrer">Blood, Sweat, and Buffers: pH Regulation During Exercise</a></li> <li><a target="_blank" href="https://www.news-medical.net/life-sciences/Metabolism-Control.aspx" rel="nofollow noreferrer">Metabolism Control</a></li> <li><a target="_blank" href="https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Book%3A_General_Biology_(Boundless)/6%3A_Metabolism/6.1%3A_Energy_and_Metabolism/6.1C%3A_Metabolic_Pathways" rel="nofollow noreferrer">Metabolic Pathways</a></li> <li><a target="_blank" href="https://www.livestrong.com/article/346711-why-would-a-physically-fit-persons-heart-rate-return-to-normal-faster-than-an-unfit-persons/" rel="nofollow noreferrer">Why Would a Physically Fit Person's Heart Rate Return to Normal Faster</a></li> <li><a target="_blank" href="https://www.tocris.com/cell-biology/carbohydrate-metabolism" rel="nofollow noreferrer">Carbohydrate Metabolism</a></li> </ol> </section> </article>

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