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Short answer: In a 47-year Swedish study, several measures of physical capacity reached their highest average levels between the late 20s and mid-30s. Aerobic capacity and muscular endurance peaked between ages 26 and 36, while explosive muscle power peaked earlier—at 27 for men and 19 for women. Performance then declined gradually before losses accelerated at older ages.
What the 47-year study measured
The findings come from Rise and Fall of Physical Capacity in a General Population: A 47-Year Longitudinal Study, published in the Journal of Cachexia, Sarcopenia and Muscle in 2025. Researchers followed 427 people in Sweden, 48% of them women, who were all born in 1958. The Swedish Physical Activity and Fitness study (SPAF) tested participants repeatedly from age 16 in 1974 through age 63 in 2021.
Because the same birth cohort was measured over decades, the researchers could estimate how several kinds of capacity changed within people rather than comparing unrelated age groups at one point in time. The tests covered aerobic capacity, muscular endurance and muscle power. They do not represent every aspect of health or strength, and they do not provide a personal timetable for any one reader.
When each type of physical capacity peaked
| Measure | Average peak | How it was assessed |
|---|---|---|
| Aerobic capacity | Between ages 26 and 36, in both sexes | Estimated aerobic-capacity testing |
| Muscular endurance | Between ages 26 and 36, in both sexes | Bench-press repetitions |
| Muscle power | Age 27 in men; age 19 in women | Sargent jump test |
These results explain why “around age 35” is a useful headline but an imprecise rule. It describes the transition from peak performance to decline for several measures, not a single biological switch. Explosive power reached its average high earlier than aerobic capacity and bench-press endurance, and people’s trajectories became more different from one another as they aged.
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How quickly performance declined
The early part of the decline was modest on average. Estimated aerobic capacity and muscular endurance fell by roughly 0.3% to 0.6% per year at first. At older ages, the estimated annual loss accelerated to about 2.0% to 2.5%.
Power showed a similar pattern, beginning with an estimated decline of about 0.2% to 0.5% per year and reaching approximately 2.2% per year at older ages. Looking from each measure’s peak to age 63, the average total reduction ranged from 30% to 48%.
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| Outcome | Earlier estimated annual decline | Older-age estimated annual decline | Average loss from peak to age 63 |
|---|---|---|---|
| Aerobic capacity and muscular endurance | 0.3%–0.6% | 2.0%–2.5% | Within the study’s overall range of 30%–48% |
| Muscle power | 0.2%–0.5% | About 2.2% | Within the study’s overall range of 30%–48% |
The percentages are averages estimated from this cohort’s repeated measurements. They are not a prediction that every individual loses the same amount each year, nor proof that aging alone causes a fixed percentage loss.
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Participants who reported more leisure-time physical activity at age 16 generally performed better on aerobic-capacity, muscular-endurance and power tests. People who became active during adulthood also had better measured capacity than less-active peers. The association supports staying active and shows that starting later can still matter.
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Activity did not erase the age-related pattern. The study did not test a particular workout plan, supplement, device or brand, so it cannot establish that one exercise method prevents decline better than another. Lead author Maria Westerståhl, a lecturer at Karolinska Institutet, summarized the next research question this way: “Now we will look for the mechanisms behind why everyone reaches their peak performance at age 35 and why physical activity can slow performance loss but not completely halt it.”
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How to use the finding in real life
The study is most useful as a reason to preserve capacity early and to avoid assuming that a later start is pointless. A practical approach is to build activity that you can repeat and progress safely:
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- Train strength progressively. Use resistance that allows controlled movement and increase the challenge gradually as your ability improves. Bands, body-weight exercises and free weights can all provide resistance; SPAF did not compare them.
- Keep an aerobic component. Walking, cycling, swimming or another sustained activity can address cardiovascular fitness, while resistance work targets force and endurance.
- Include power only when appropriate. Fast, explosive movements place different demands on the body than slow strength work. Beginners, older adults and anyone with pain or a medical condition should obtain qualified guidance before adding jumps or other high-impact drills.
- Measure trends, not a single score. Repeating the same safe test under similar conditions can show whether capacity is changing, but home results are not directly interchangeable with the study’s laboratory and field measurements.
- Prioritize consistency. The activity association covered both teenage activity and becoming active in adulthood, making regular participation more relevant than a short-lived burst of training.
Why the results do not give everyone the same “strength-loss age”
SPAF is an observational study of one Swedish birth cohort. Its participants were all born in 1958 and grew up within a particular physical-activity, education and health-care context. Differences in later birth cohorts, countries, disease rates and access to exercise could change the pattern.
The study also measured selected capacities rather than every definition of strength. A lower bench-press repetition count, for example, is not identical to a decline in maximum lifting strength, grip strength, balance or the ability to perform daily tasks. The reported percentages describe group averages, while individual variation widened substantially with age.
For that reason, a 35-year-old who notices a change should not assume it is inevitable, and a 63-year-old should not assume the study’s average loss is their personal result. Health conditions, injuries, training history, sleep, nutrition and medication can all affect performance and deserve individual assessment.
The practical bottom line from the evidence
Many forms of physical capacity reach their average peak before 40, with explosive power often peaking first. Decline usually starts gradually and becomes steeper later. Remaining active—or beginning regular activity in adulthood—is associated with better performance, even though it cannot completely stop the underlying age trend observed in this cohort. Treat the study as a population-level timetable, not a deadline for your own body.
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