Swedish Cohort Shows How Aerobic Fitness, Power and Endurance Shift From Age 16 to 63

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Strength & Muscle

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In 2025, the Journal of Cachexia, Sarcopenia and Muscle published a 47-year analysis of physical capacity from adolescence to later adulthood. The research examined the Swedish Physical Activity and Fitness Study (SPAF), according to ScienceDaily’s account.

Researchers followed the same cohort from age 16 to 63

The study began with 427 people born in Sweden in 1958. The starting group included 222 men and 205 women, selected as Swedish adolescents. Researchers followed them from age 16 to 63.

This was a longitudinal cohort study, not an exercise trial. Researchers repeatedly assessed the same people over 47 years rather than comparing separate age groups at a single point in time.

Assessments took place at ages 16, 27, 34, 52 and 63. The tests covered aerobic capacity plus bench-press muscular endurance and vertical-jump power. These were separate measures of performance, not different names for the same ability.

That distinction matters for men reading the findings through the lens of muscle loss. The bench-press result concerned muscular endurance. The jump test concerned power. Readers focused on muscle and physical function should keep those outcomes separate.

The long follow-up also changes how the results should be read. This was a record of performance across much of adult life, not a short program in which volunteers followed the same training routine.

Physical capacities peaked at different ages and later declined

The researchers’ models placed peak ages across the measured capacities between 19 and 36. The timing varied by sex and by test. The main findings were:

Aerobic capacity reached an estimated peak in adulthood.
Bench-press muscular endurance also reached an estimated adult peak.
Vertical-jump power peaked earlier than aerobic capacity and muscular endurance.
Decline was gradual at first and became faster with age.
Losses from peak capacity to age 63 ranged from 30% to 48% across the measures studied.

The shape of the decline matters as much as the peak ages. The study described gradual change that accelerated over time, rather than an abrupt loss at a particular birthday. It is a picture of changing capacity across adulthood, not a sudden break between being capable and being incapable.

Activity was associated with higher performance across the tests

The authors also estimated what happened when participants moved from an inactive to an active leisure-time activity category. The associated differences were:

About 6% to 7% higher aerobic capacity.
11% higher bench-press performance.
4% higher vertical-jump performance.

These estimates describe different outcomes, which is why the separate figures are more useful than a single overall improvement number. The largest estimated difference was in bench-press endurance. The smaller estimated difference for jump performance still pointed in the same direction.

The authors interpreted physical activity as a modifiable factor associated with better capacity across the observed period. They suggested that activity may affect performance levels and the later rate of decline without substantially shifting the age of peak performance.

The peak-age results and the activity results answer different questions. One concerns when average performance reached its highest point. The other concerns whether an activity-category change was linked with a higher performance level. A past peak and a useful improvement later in life are not competing ideas.

The study’s design limits claims about training

A headline about strength loss and continued exercise captures the tension in the findings. The methods call for a more precise reading before turning that tension into advice.

The study was observational. It found associations between activity and capacity, not proof that activity alone caused the differences. That is the main boundary around the performance estimates.

Activity was recorded through a simple yes/no self-report. In adolescence, this concerned leisure-time sports participation. Later questions covered free-time activity that could include walking or gardening. The measure did not record detailed frequency or duration, or how hard people exercised.

That prevents the study from identifying an optimal exercise dose or showing which specific program produced the associations. An active classification should not be read as a record of consistent resistance training across the full follow-up.

The cohort also represents one Swedish generation born in 1958. Its results may not transfer exactly to other countries or generations. Not every test was performed at every assessment, and aerobic testing at age 16 differed from the later methods.

Finally, these tests cover selected dimensions of physical capacity. They do not represent every aspect of health or everyday function. Individual paths also varied, so the average curve is not a fixed forecast for any one man.

The practical lesson is to follow present capacity

For a man returning to exercise after 45, the useful question is what he hopes to regain or maintain now. The study supports attention to attainable activity and personally relevant outcomes. Earlier inactivity is not a reason to treat later progress as impossible.

A practical reading keeps three ideas in view:

Choose the outcome before judging the claim. If the concern is endurance, an endurance result is relevant. If the concern is power, the jump result answers a different question.
Follow personal change rather than an age label. Repeated observations offer a useful way to frame the discussion without assuming a birthday tells the whole story.
Keep activity attainable and sustained. The paper’s activity findings support continued engagement rather than treating a younger peak as a reason to stop.

The aim is to connect the research with a useful personal goal. A goal centered on strength for everyday movement keeps attention on capability rather than a younger person’s test score. Where health concerns affect exercise choices, individual decisions belong with qualified care.

The most useful comparison is not necessarily with a modelled peak decades earlier. For someone returning to activity, it may be with his own recent starting point. That keeps the discussion grounded in what he is trying to maintain or improve, rather than in a contest with the cohort average.

What this changes: The findings reinforce the case for sustained activity rather than changing current best practices or establishing a new training prescription.

How Everfitguys helps

Once the cohort averages are understood, attention can turn to maintaining useful strength, a subject Everfitguys covers through research-led reporting. Its articles address muscle loss and reduced physical capability after 45, helping regular trainers and returning exercisers understand healthy-aging evidence in plain English while keeping independence in view.

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