| Course | EF205 Principles of Exercise Science |
|---|---|
| Unit | Unit 7 |
| Paper type | Energy systems paper |
| Length | About 1,090 words, 6 pages double-spaced |
| Format | APA 7 student paper |
| School | Purdue University Global |
| Program | BS in Health Science |
| Updated | October 2026 |
Free sample paper for EF205 Unit 7
Ten Seconds of Sprint, Ninety Seconds of Burn, Thirty Minutes of Steady: A Unit 7 Paper on the Energy Systems Behind Soccer and a 5K
[Student Name]
Purdue University Global
EF205: Principles of Exercise Science
Unit 7 Energy Systems Paper
[Instructor Name]
[Date]
The student and examples are composite; the physiology and studies cited are real.
ATP: The Energy Muscles Actually Use
Muscle contraction is powered by adenosine triphosphate, or ATP. Muscles store only enough ATP for a few seconds of hard work, so they must constantly rebuild it. The body has three main pathways for doing so, which differ in how fast they work and how long they can keep going.
The Phosphagen System
The fastest pathway uses creatine phosphate stored in muscle to regenerate ATP almost instantly, without oxygen. It powers the first seconds of maximal effort, such as a sprint to a loose ball or a jump for a header. Its stores are small and largely used up within about ten seconds of all-out work, then take a few minutes of rest to replenish.
Glycolysis
The second pathway breaks down glucose, from blood sugar or stored glycogen, to make ATP quickly without needing oxygen at first. It supplies a large share of energy in hard efforts lasting from several seconds to a couple of minutes, such as a long run up the field with a defender in pursuit. It produces ATP fast but not for long at high rates, and the conditions it creates in hard-working muscle contribute to the burning sensation and fatigue of intense efforts.
The Oxidative System
The third pathway uses oxygen in the mitochondria to break down carbohydrates and fats completely, producing far more ATP per molecule but more slowly. It dominates in efforts lasting more than a couple of minutes and supplies almost all the energy at rest and during steady exercise such as jogging.
The Systems Overlap
A common simplification describes the systems as switching on one after another. Gastin (2001), reviewing studies of maximal exercise, showed instead that all three contribute from the start of an all-out effort, with their relative share shifting as the effort continues, and that the aerobic system contributes more, and earlier, than older textbooks suggested; by roughly the first minute and a half of maximal exercise, aerobic and anaerobic contributions are about equal. Baker et al. (2010) similarly describe the systems as interacting continuously, regulated by the muscle's energy needs, rather than operating in sequence.
My body never chose between sprinting energy and jogging energy; it always used both, in proportions set by how hard and how long I was working.
What Soccer Demanded
Soccer is intermittent: short sprints, changes of direction and jumps, separated by jogging and walking, over a long match. The sprints draw heavily on the phosphagen system and glycolysis, and the recovery between them depends on the oxidative system, which also replenishes creatine phosphate. A midfielder needs all three systems, and in particular a strong aerobic base to recover between sprints.
What a Beginner's 5K Will Demand
At my current fitness, a 5K will take around 35 to 40 minutes of jogging. Almost all the energy for an effort that long comes from the oxidative system, with glycolysis contributing more during hills or a final push to the finish. The phosphagen system matters only for a sprint at the end, if I have one left. The race is therefore mostly a test of my aerobic system, which my walk test showed is my weakest area.
Implications for Training
Build the oxidative system first. Most of my training should be steady, moderate-intensity walking and jogging, which improves the heart's stroke volume, increases the density of mitochondria and capillaries in muscle and improves the use of fat for fuel. These adaptations are what allow a given pace to feel easier, and they are the reason the exercise position stand puts regular moderate aerobic work at the center of training for adults (Garber et al., 2011).
Use intervals as a bridge. Walk-jog intervals let me spend more total time jogging than continuous jogging would, while the walking breaks allow recovery. Later in the plan, short faster intervals can add a glycolytic stimulus, but they are not the priority for a beginner.
Include strength work. Stronger leg and hip muscles help maintain running form as I tire.
How I Will Notice Each System in Training
Even without laboratory equipment, each system shows up in how training feels. In the first ten seconds of a short sprint at the end of a session, my legs feel powerful and then suddenly heavy, as the phosphagen stores run low. During a hard two-minute segment, the familiar burning builds in my thighs and my breathing becomes ragged, signs that glycolysis is contributing heavily. During a steady 30-minute jog, I should be able to talk in short sentences and keep going, because the oxidative system is supplying nearly all the energy at a rate I can sustain. Learning to recognize these sensations will help me pace the race: starting too fast would draw on glycolysis early and leave me exhausted halfway.
What My Soccer Background Gives Me
My years of soccer did not leave me fit, but they left habits that help. I know how to pace a long effort in bursts, how to recover between them and what the burning of a hard effort feels like and how long it lasts. Those experiences make walk-jog intervals feel familiar rather than strange. They also warn me against my instinct to sprint at the start, which served me in soccer but would undermine a steady 5K.
Limits
Energy system contributions vary with fitness, diet, muscle fiber type and environment. The percentages in studies come mostly from laboratory tests of maximal effort, not from recreational races, so the estimates for my 5K are approximate.
Fueling for the Race
Because the oxidative system will supply almost all my energy, and it uses both carbohydrate and fat, a beginner's 5K does not require special fueling. A normal meal two to three hours before and water afterward should be enough. Fueling matters more for longer races, where glycogen stores can run low.
Conclusion
The phosphagen system, glycolysis and the oxidative system all rebuild ATP, at different speeds and capacities, and they work together rather than in turn. Soccer drew on all three; a beginner's 5K depends mostly on the oxidative system. That makes steady aerobic training, supported by walk-jog intervals and strength work, the right foundation for my plan.
References
Baker, J. S., McCormick, M. C., & Robergs, R. A. (2010). Interaction among skeletal muscle metabolic energy systems during intense exercise. Journal of Nutrition and Metabolism, 2010, 905612. https://doi.org/10.1155/2010/905612
Garber, C. E., Blissmer, B., Deschenes, M. R., Franklin, B. A., Lamonte, M. J., Lee, I.-M., Nieman, D. C., & Swain, D. P. (2011). Quantity and quality of exercise for developing and maintaining cardiorespiratory, musculoskeletal, and neuromotor fitness in apparently healthy adults: Guidance for prescribing exercise. Medicine & Science in Sports & Exercise, 43(7), 1334-1359. https://doi.org/10.1249/MSS.0b013e318213fefb
Gastin, P. B. (2001). Energy system interaction and relative contribution during maximal exercise. Sports Medicine, 31(10), 725-741. https://doi.org/10.2165/00007256-200131100-00003
What the EF205 Unit 7 assignment asks for
Unit 7 often asks students to explain the body's energy systems and how each contributes during different activities. Describe how ATP is regenerated by the phosphagen system, glycolysis and oxidative metabolism, with the speed and capacity of each. Instructors want the overlap between systems explained with research, since a simple handoff from one to the next is outdated. Applying the systems to two contrasting activities, such as a team sport and an endurance event, shows understanding. Many prompts ask what the analysis means for training and for pacing. Linking each training choice to the system it targets makes the application clear. Describing what each system feels like during training helps connect the physiology to experience the student can recognize.
Inside the EF205 Unit 7 example
The paper opens with ATP as the energy muscles use and why it must be rebuilt constantly. Sections describe the phosphagen system, glycolysis and oxidative metabolism with examples from soccer. A section on overlap cites Gastin's finding that aerobic and anaerobic contributions are roughly equal by about a minute and a half of all-out effort, and Baker and colleagues' account of continuous interaction, under a highlighted line that the body never chose between sprint and jog energy. Soccer's intermittent demands are contrasted with a beginner's 5K. Training implications follow: aerobic base first, walk-jog intervals as a bridge and strength work. Sections on recognizing each system, what soccer left behind and fueling precede limits and a conclusion.
Reading the EF205 Unit 7 grading rubric
Energy systems papers are graded on scientific accuracy, use of research and application. Each system's mechanism, speed and capacity should be described correctly. Graders reward correcting the sequential switch-on simplification with evidence. Comparing two activities with different demands shows understanding. Each training recommendation should name the energy system it targets. Practical signs of each system in training add depth. Statements about energy contributions should note their laboratory origin and variability. Clear headings for each system help readers. Gastin's review, Baker and colleagues and Garber and colleagues each need an APA 7 entry. Noting how each system feels in training helps a grader see that the physiology was connected to experience.
EF205 Unit 7 help from the desk
Energy systems papers often present the three systems as a timeline, each taking over when the last runs out, which current research does not support. Another frequent weakness is describing the systems with no link to a real activity or training plan. Some writers attribute fatigue solely to lactic acid, an oversimplification. Percentages from studies are sometimes presented as exact for any activity. Papers that skip pacing miss a practical lesson. Before writing, pick two activities you know, one with bursts and one steady, and estimate how long each effort lasts. Tell us those two activities, and we can work through the energy demands of each with you.
Get an EF205 Unit 7 example written to your instructions
Send the activities and the instructions with the rubric. A custom paper explains the energy systems with examples. Delivery is within 24-48h, and a first paper is free. The paper above is an original model document written by our desk, not a submitted student paper and not an official Purdue University Global document.
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EF205 Unit 7 questions, answered
What are the main energy systems?
The phosphagen system, glycolysis and the oxidative system.
Do the systems work separately?
No. They work together, with the balance shifting by intensity and duration.
Why does this matter for training?
It helps match training to the demands of a sport or goal.
Where can I find a free EF205 Unit 7 sample paper?
The complete EF205 Unit 7 energy systems paper is available here, comparing the energy demands of soccer with those of a beginner's 5K.
Do the energy systems switch on one after another in the EF205 Unit 7 sample?
No. Research shows all three contribute from the start of an effort, with their shares shifting by intensity and duration; aerobic supply rises earlier than older textbooks suggested.