According to research reviewed by Gram, a computer model of muscle energy suggests that a drop in the muscle’s energy-making capacity, a change linked to aging, can sharply shorten how long people can keep exercising. When this capacity fell to 70 percent at the same power output, exercise time dropped dramatically in the simulation.
Getting tired during exercise is a normal part of life, but why older adults may run out of steam sooner is not fully clear. A team of researchers built a computer model of the energy system inside human muscle to find out. According to research reviewed by Gram, the model suggests that a drop in how fast muscle cells make energy, a change linked to aging, can greatly shorten how long a person can keep exercising at the same power output. In contrast, when power output and energy production both fell by the same amount, exercise time barely changed. The model also suggests that regular physical activity, avoiding high-phosphate diets, and being cautious with creatine supplements may help protect muscle endurance. Because this work relies on a simulation rather than human volunteers, it offers clues for future studies rather than firm answers for individuals.
Key Statistics
A 2026 computer modeling study published in Respiratory Physiology & Neurobiology found that cutting muscle energy-making capacity to 70 percent at the same power output sharply shortened how long a simulated person could keep exercising.
The same 2026 model found that reducing both power output and energy-making capacity by the same 70 percent had essentially no effect on exercise time, suggesting that proportional adjustments matter less than the energy system itself.
The 2026 simulation also indicated that a higher peak phosphate tolerance in muscle could partly offset the loss of energy-making capacity seen with aging.
The Quick Take
- What they studied: The researchers asked what makes muscles run out of energy during steady exercise, and how aging might change that. They used a computer model to test which parts of muscle energy production matter most.
- Who participated: No human volunteers took part. The study used a computer simulation of the energy system in human muscle, so no sample size was reported.
- Key finding: When the muscle’s ability to make energy (called OXPHOS activity) dropped to 70 percent at the same power output, exercise time shortened sharply. When power output and energy production both dropped by the same 70 percent, exercise time barely changed.
- What it means for you: Keeping your muscles’ energy-making ability strong may matter more for endurance than simply lowering how hard you work. Regular activity may help protect that ability as you age, though this model has not been tested in people directly.
The Research Details
This study used a computer model, which is a mathematical version of how the body’s energy system works inside muscle cells. The model includes many connected parts, such as phosphate (a chemical that signals low energy), creatine (a compound that helps store and reuse energy), and the cell structures that produce fuel. Researchers adjusted these parts to see how each one affected how long a simulated person could keep exercising before fatiguing.
To study aging, the team lowered specific parts of the model, such as the muscle’s energy-making capacity, to levels that reflect changes often seen in older adults. They then compared how exercise time changed under each adjustment. This approach allows scientists to test many possibilities quickly and safely, without asking people to exercise to exhaustion again and again.
Because the model is built on known biology and was tuned to reflect muscle physiology, it can show cause and effect in ways that are hard to measure in real bodies. However, the results are only as accurate as the assumptions built into the model.
Testing these ideas on a computer lets researchers isolate single factors, such as creatine levels or energy-making capacity, while holding everything else constant. This is difficult to do in living people, whose bodies change many things at once. The method helps identify which factors deserve the most attention in future human studies.
The study is a modeling paper rather than a trial with people, so it cannot prove what happens in real bodies. Its strength is that it tests many factors in a controlled way and uses a detailed model of muscle energy. Readers should treat its conclusions as well-reasoned predictions that still need confirmation in human research. The sample size is not applicable because no participants were studied.
What the Results Show
The model found that exercise time was most strongly affected by a few key factors. Longer exercise times were linked to higher peak levels of phosphate that a muscle could tolerate before fatigue set in, stronger energy-making capacity (OXPHOS activity), and better activation of the muscle’s energy-producing steps. Exercise time was shortened most by higher total creatine and phosphate stores being used up, and by working at a harder power output.
An important pattern emerged at lower effort levels just above what is called critical power, the highest effort a person can sustain for a long time. At these gentler levels, small changes in muscle factors made a much bigger difference to how long someone could keep going. At harder efforts, exercise times were already short, so changes had less room to matter.
The most striking result involved aging. When the model cut both power output and energy production by the same 70 percent, exercise time barely changed, which suggests that simply working at a lighter, proportionally adjusted level does not hurt endurance much. However, when only the energy-making capacity dropped to 70 percent at the same power output, exercise time fell dramatically. This matches the idea that the muscle’s ability to produce energy, rather than raw strength alone, may be a central reason older adults tire sooner.
The model also suggested that a rise in the peak phosphate level a muscle can tolerate could partly offset the loss of energy-making capacity. It further indicated that lowering total creatine and accessible phosphate stores might lengthen exercise time, which is relevant to how creatine supplements and phosphate intake may influence performance.
The authors connected these model results to practical choices. They suggested that regular physical activity and training may help keep muscle endurance strong, which could support daily life quality in older adults. They also suggested that creatine supplements should be used with caution, and only when advisable for other health reasons, since the model indicated that higher creatine stores can shorten exercise time. Finally, they suggested that avoiding a high-phosphate diet may help improve muscle performance during long, steady exercise. These points are based on the simulation and should be viewed as hypotheses to test rather than settled advice.
Previous research has consistently linked aging with reduced muscle endurance, and many studies have found that older adults have lower energy-making capacity in their muscles. This modeling work adds detail by showing how a single drop in energy production, without a matching drop in effort, can sharply shorten exercise time. It fits with the broader view that muscle energy metabolism is central to fatigue, while also highlighting how the interaction of several factors shapes the outcome.
The biggest limitation is that the findings come from a computer model, not from people. Real bodies vary widely in fitness, diet, genetics, and health conditions, and the model may not capture all of these differences. The model also depends on assumed values for many muscle parameters, so its results are only as good as those assumptions. The paper does not report a human sample, so it cannot tell us how these effects would look in a group of real older adults. Further studies with volunteers are needed to confirm these patterns.
The Bottom Line
Based on this modeling study, staying physically active is a reasonable step to support muscle endurance as people age, and this has strong support from broader research on exercise and aging. Using creatine supplements with caution, and only if a doctor considers them appropriate, is a sensible approach given the model’s findings. Limiting high-phosphate foods may also be worth considering, though confidence in this specific advice is lower because it comes from simulation and needs testing in people. Confidence is highest for activity and lowest for diet-specific suggestions.
Older adults who notice they tire quickly during long walks, gardening, or other steady activities may find these ideas useful. Coaches, physical therapists, and researchers studying aging muscle may also find the model helpful for planning future work. People with kidney disease, heart conditions, or other health issues that affect phosphate or creatine levels should talk with a doctor before changing supplements or diet. Younger, healthy adults may find the general message about energy-making capacity interesting, but the aging focus applies most directly to older people.
Changes in muscle endurance from regular activity typically develop over several weeks to months of consistent training. Any benefit from diet or supplement adjustments would likely take a similar amount of time to show, and results vary from person to person. Because this study is a simulation, there is no set timeline for when its suggestions will be confirmed or changed by human research.
Frequently Asked Questions
Why do muscles get tired faster as we get older?
A 2026 computer model published in Respiratory Physiology & Neurobiology suggests that lower energy-making capacity inside muscle cells is a major factor. When that capacity fell to 70 percent at the same power output, the simulated exercise time dropped sharply, though human studies are still needed to confirm this.
Can creatine supplements help older adults keep exercising longer?
The computer model in this 2026 study suggested that higher creatine and phosphate stores may shorten exercise time rather than lengthen it. Creatine use should be considered cautiously and only when a doctor agrees it is appropriate for a person’s overall health.
Does exercising at a lighter effort protect muscle endurance with age?
The model found that reducing power output and energy production by the same 70 percent had essentially no effect on exercise time. Regular physical activity is still widely supported by research as a way to help maintain muscle health and endurance throughout life.
Does a high-phosphate diet affect how long muscles can work?
This 2026 simulation suggested that avoiding a high-phosphate diet may help improve muscle performance during long, steady exercise. Because the result comes from a computer model rather than human volunteers, it should be viewed as a hypothesis that requires testing in people.
Want to Apply This Research?
- Track how many minutes you can sustain a steady, comfortable effort, such as brisk walking or cycling at the same speed, and log it weekly. Also record your perceived effort on a 1 to 10 scale so you can see whether the same effort lasts longer over time.
- Set a goal to add a few minutes of steady activity, such as a 10-minute walk, on at least 5 days each week, and gradually increase the time. Use the app to remind you to stay consistent, and note any days you feel unusually tired so you can spot patterns.
- Review your steady-effort logs every month to see whether your endurance is improving, holding steady, or declining. Share trends with a doctor during regular checkups, especially if you use creatine supplements or have questions about diet, and update your routine as your health and goals change.
This article summarizes a computer simulation study and does not include results from human volunteers. The findings are not medical advice and should not be used to start, stop, or change any supplement, diet, or exercise program without first talking with a qualified healthcare provider, especially if you have kidney, heart, or muscle conditions.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.