Understanding the Three Energy Systems Used During Exercise

PYEONGTAEK, 41, SOUTH KOREA

03.23.2022

Story by Inkyeong Yun 

549th Hospital Center/Brian D. Allgood Army Community Hospital

In celebration of National Nutrition Month, Jessica Pastino, a registered dietitian at Brian D. Allgood Army Community Hospital, takes the opportunity to share the knowledge of performance nutrition to help you bring maximum results in your fitness goals.

Understanding the Three Energy Systems Used During Exercise

Jessica Pastino, RDN


Have you ever experienced tiredness in your muscles while working out and you couldn’t continue exercising after a certain point? Or have you wondered what can make you lift heavier weights or run longer than you can today? If you have, understanding the mechanism of the energy system can help you find answers to these questions.

Three metabolic pathways generate the energy required to perform an exercise: the phosphagen pathway, the glycolytic pathway, and the oxidative pathway, altogether known as the energy systems. Although your body is always using all three simultaneously, depending on the intensity and duration of the exercise, your body will choose which pathway it will use the largest percentage of its energy from.

As you are generally aware, all energy our bodies use is generated from the breakdown of food and drink. The three macronutrients are protein, carbohydrate, and fat. Those are metabolized to create adenosine triphosphate (ATP) which is the source of fuel for all body processes including muscle contraction. Unfortunately, the supply of readily available ATP is very limited. It means our bodies constantly have to make it otherwise muscle contraction would stop. This re-synthesis of ATP is done by the three energy systems.

The first 10-20 seconds of high-intensity physical activity is fueled by the “ATP-CP” also known as the “phosphagen” energy system. Once the available ATP is used up, which occurs in a few seconds, a molecule called phosphocreatine is used to reform ATP in the muscle. This energy system operates very quickly and can bring the highest output of the three systems. However, it is limited by the availability of creatine phosphate, which is usually consumed within 15 seconds.

Your body can eventually refill these stores when you rest. This is why this system is most active for athletes who engage in short bouts of very intense, explosive movement; like the 50-meter dash or powerlifting. This is also the reason we can sprint full speed for only a few seconds or lift maximum loads only 1-2 times before requiring to rest or a decrease in exercise intensity using another metabolic pathway.

The second pathway, the glycolytic pathway, is the primary energy system used for exercise lasting from 15 seconds to three minutes. 800-meter runners, for example, use this pathway the most. This energy system uses the glucose stored in the muscle, broken down primarily from carbohydrates, to form ATP. The benefit of this pathway is that it can quickly kick in but it doesn’t make very much, hence it can only supply a maximum of about three minutes of energy. This pathway is responsible for the buildup of lactic acid in our muscles, which contributes to fatigue.

For exercise lasting longer than three minutes, the oxidative pathway is used. Unlike the others, this energy system requires oxygen. The increase in respiratory rate meets the oxygen demand during physical activity. The oxidative system is slow but it is the most efficient. Using fat as its primary energy substrate, it produces enough ATP to sustain longer duration activities but only at submaximal exercise output. It means fat is the predominant fuel source used during low to moderate-intensity activity, like biking or jogging long distances.

Now you are more knowledgeable on how your body relies on each of these systems working together to meet the energy demands needed for activities of daily living and exercise. The system your body will primarily use depends on the type of activities you mostly engage in. The more you train in that particular type of exercise, the better your body adapts to being able to efficiently use that energy system. For example, individuals who have trained in powerlifting can store more phosphocreatine and ATP than a marathon runner or sedentary individual. On the other hand, endurance-trained individuals have better ventilation ability, maximizing oxygen availability for the oxidative pathway. At the end of the day, consistency is key. If you want to excel at a particular type of exercise, just keep doing it and in time, your body will adapt.

If you are interested in learning more about how you can adjust your diet to best fuel your exercise? Book an appointment with your on-post dietitian and unlock the power of nutrition to achieve your performance goals. Brian D. Allgood Army Community Hospital Nutrition Clinic offers both face-to-face and virtual appointments with a dietitian covering a variety of range of nutrition goals and needs. Make an appointment today by calling DSN: 315-737-1570.

Reference: Wells GD, Selvadurai H, Tein I. Bioenergetic provision of energy for muscular activity. Pediatric Respiratory Reviews. 2009;10(3):83-90. doi:10.1016/j.prrv.2009.04.005 Bioenergetic provision of energy for muscular activity - ClinicalKey

• Date Taken: 03.23.2022
• Date Posted: 03.23.2022 00:24
• Story ID: 416974
• Location: PYEONGTAEK, 41, KR