Introduction
Aging is an inexorable biological process, but its visible consequences — loss of strength, stamina and mobility — need not be accepted as inevitable and untreatable. A new, unusually long-term study from researchers at the Karolinska Institutet adds important detail about exactly when—and how quickly—physical capacity declines in the general population. The key message is both worrying and encouraging: measurable decline begins decades earlier than many assume, yet regular physical activity can substantially blunt that decline, even when begun later in life.
Why this matters
Loss of muscle mass and function (sarcopenia) is a major contributor to disability, falls, frailty and loss of independence in older adults. Traditionally, sarcopenia has been framed as a disorder of the elderly — a clinical problem of people in their 70s and beyond. That perspective risks under-emphasizing a long preclinical phase during which physiological reserve falls away silently. Early decline in aerobic fitness, strength endurance and explosive power reduces the margin of safety around daily tasks and raises vulnerability to acute stressors (illness, injury, surgery).
For clinicians, public health professionals and the public, understanding when decline begins and how modifiable it is matters for prevention strategies: if decline begins in mid‑life, interventions need to start earlier than previously thought.
What the data tell us: The 47-year Karolinska longitudinal study
In a paper published in Journal of Cachexia, Sarcopenia and Muscle, Westerståhl and colleagues report results from a 47‑year longitudinal follow-up of 427 participants (48% women) who underwent serial objective tests of physical capacity from ages 16 to 63. Tests included measures of aerobic capacity, muscle endurance and muscle explosive power. The dataset is rare: long follow‑up with repeated, objective performance testing in the same individuals across decades.
Key findings
– Peak physical capacity occurred broadly between ages 26 and 36 across the different domains measured.
– From around age 40 the decline accelerated — described in the paper as a “cliff‑like” or steep phase of decline compared with earlier adult life.
– By age 63, cumulative declines from peak were substantial: aerobic capacity fell by approximately 37–40% (women and men, respectively), muscle endurance by about 32–35%, and explosive power by 41–48% depending on sex and test.
– Men started from higher absolute levels than women across most measures, but the pattern of decline with age was similar between sexes; there were no significant sex differences in the shape of decline trajectories.
Exercise effects
The study also examined associations between habitual physical activity and the trajectories of decline. Individuals who were physically active at age 16 had higher adult physical capacity across domains — on average 4–11% higher than less active peers. Importantly, the benefits of starting exercise later in life were evident too: people who adopted or increased activity in mid‑life showed improved capacity that persisted into older age. Athletes followed the same pattern of age‑related decline as nonathletes, but the magnitude of decline in the general population was larger — suggesting fitness provides a buffer but is not immune to aging.
Other associations
Higher education level correlated with better aerobic capacity and muscle endurance, though not with explosive power — a finding that raises interesting questions about socioeconomic determinants of activity patterns and occupational differences in physical demands.
How to interpret the magnitude and timing of decline
The study paints a more nuanced picture than the simplistic idea that “everything is fine until 70.” Peak physical capacity in the late 20s–30s followed by an accelerating decline around age 40 means that the process of losing physiological reserve is a decades‑long continuum. The clinical implication: by the time people reach their 60s, many have already lost a large chunk of the capacity they once had — and that loss limits functional options and recovery from stressors.
That said, the absolute rates of decline found in this cohort represent averages in a general population. Individual trajectories vary widely: genetics, baseline fitness, occupational activity, chronic disease, nutrition and life events all influence the slope.
Misconceptions and common pitfalls
– Misconception: “Sarcopenia is a problem only for the very old.” Reality: Biological processes that produce muscle loss and reduced aerobic fitness begin decades earlier. Waiting until symptoms or disability appear misses an opportunity for prevention.
– Misconception: “If I didn’t exercise when I was young, it’s too late.” Reality: The new study and other evidence show that initiating or increasing activity in mid‑life still yields measurable gains and delays decline into older age.
– Pitfall: Focusing only on resistance training or only on aerobic exercise. Both are important. Aerobic capacity, muscle endurance and explosive strength decline at different rates and serve different functional purposes; an effective program addresses multiple domains.
What works: Practical, evidence-based advice
The primary, evidence‑backed intervention to slow muscle and fitness decline is regular physical activity combining aerobic and resistance elements. Major guidance sources such as the World Health Organization and professional societies recommend a mix of aerobic, strengthening and balance training across the lifespan. Practical recommendations:
– Aim for at least 150–300 minutes per week of moderate‑intensity aerobic activity (or 75–150 minutes of vigorous activity), as per WHO guidance, spread across most days.
– Do muscle‑strengthening activities involving major muscle groups on two or more days per week. Include both multi‑joint exercises (e.g., squats, lunges, push‑ups or machine/free‑weight alternatives) and single‑joint work when needed.
– Add high‑velocity or power work and balance exercises, especially for people at risk of falls; explosive power declines steeply and is important for quickly correcting balance losses.
– Start where you are: even modest increases in activity yield benefits. Progress intensity and volume gradually.
– For people with chronic conditions, tailor exercise with clinical input. Structured programs such as supervised resistance training yield strong results for sarcopenia.
Simple weekly sample plan for a generally healthy adult (adapt to fitness level):
– 3 sessions of 30–40 minutes moderate aerobic activity (brisk walking, cycling) +
– 2 sessions of 30–45 minutes resistance training (full‑body, 6–10 exercises, 2–3 sets, 8–12 reps) +
– Twice weekly balance/functional power drills (e.g., sit‑to‑stand with speed, step‑ups)
Expert recommendations and clinical implications
For clinicians: view mid‑life as an opportunity window for primary prevention of sarcopenia and functional decline. Screening for activity levels and offering brief counseling or referral to exercise programs should be part of routine care for adults from their 40s onward. Consider objective or simple performance tests (gait speed, chair‑stand times, grip strength) in middle‑aged and older patients with risk factors.
For public health practitioners: framing physical activity as a life‑course intervention against future frailty strengthens the case for policies that encourage active transport, workplace wellness, community exercise programs and accessible recreation spaces.
For researchers: more work is needed to clarify critical windows, dose–response relationships for different exercise modalities, and how social determinants interact with activity to shape long‑term trajectories.
Patient scenario: Michael, 48
Michael is a 48‑year‑old accountant who has been largely sedentary since his 30s. He has noticed his energy and ability to climb stairs have worsened over several years. After reading about age‑related muscle loss, he asks his primary care physician whether it’s too late to improve. Using insights from the Karolinska cohort, his physician explains that meaningful decline often accelerates around age 40 but that starting a combined aerobic and resistance program now can boost his physical capacity and delay further decline. Michael begins a supervised program of twice‑weekly resistance training plus brisk walking. Over 6–12 months he gains measurable strength, reports improved stamina and reduces his fatigue — illustrating how mid‑life exercise changes trajectory.
Limitations and unanswered questions
The Karolinska study offers long follow‑up but like any cohort study has limitations. Participants were measured up to age 63 — trajectories beyond that age require other cohorts. The sample size, while robust for a long-term study, is modest relative to large population surveys and may not capture certain subgroups. Causal inference about exercise is constrained by observational design; randomized trials remain the gold standard for quantifying the effect of specific training programs on long‑term trajectories. Nonetheless, the consistency of associations across measures and alignment with experimental data on the benefits of exercise lend weight to the conclusions.
Conclusion
The striking message from this long‑term study is twofold: first, that many elements of physical capacity peak in the late 20s–30s and begin an accelerated decline from roughly age 40; second, that habitual physical activity — even when started later in life — can materially delay that decline. Rather than waiting for disability to appear, clinicians, public health systems and individuals should treat mid‑life as a strategic window to build reserve. Exercise is the most potent, accessible, and cost‑effective intervention we have to maintain function with age.
Funding and clinicaltrials.gov
Refer to the original article for detailed funding disclosures and trial registration. Westerståhl M, Jörnåker G, Jansson E, Aasa U, Ingre M, Pourhamidi K, Ulfhake B, Gustafsson T. Rise and Fall of Physical Capacity in a General Population: A 47-Year Longitudinal Study. J Cachexia Sarcopenia Muscle. 2025 Dec;16(6):e70134. doi: 10.1002/jcsm.70134. PMID: 41243424; PMCID: PMC12620399.
References
Westerståhl M, Jörnåker G, Jansson E, Aasa U, Ingre M, Pourhamidi K, Ulfhake B, Gustafsson T. Rise and Fall of Physical Capacity in a General Population: A 47-Year Longitudinal Study. J Cachexia Sarcopenia Muscle. 2025 Dec;16(6):e70134. doi: 10.1002/jcsm.70134. PMID: 41243424; PMCID: PMC12620399.
Cruz‑Jentoft AJ, Bahat G, Bauer J, Boirie Y, Bruyère O, Cederholm T, et al. Sarcopenia: revised European consensus on definition and diagnosis. Age Ageing. 2019;48(1):16–31.
World Health Organization. WHO Guidelines on physical activity and sedentary behaviour. 2020. https://www.who.int/publications/i/item/9789240015128
Additional reading:
– Peterson MD, Rhea MR, Sen A, Gordon PM. Resistance exercise for muscular strength in older adults: A meta‑analysis. Ageing Res Rev. 2010;9(3):226–237.
– DeFronzo RA, Tripathy D. Skeletal muscle insulin resistance is the primary defect in type 2 diabetes. Diabetes Care. 2009;32 Suppl 2(Suppl 2):S157–63.
