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A long-term Swedish study tracking the same people for nearly five decades shows that measurable declines in aerobic capacity and muscle strength begin much earlier than many expect — around age 35. Yet the research also confirms a hopeful message: becoming active at any adult age yields clear improvements in physical performance.
How the 47-year SPAF study tracked fitness over time
Researchers at Karolinska Institutet followed several hundred randomly selected men and women, originally aged 16 to 63, as part of the Swedish Physical Activity and Fitness study (SPAF). Unlike cross-sectional studies that compare different age groups at one point in time, SPAF repeatedly tested the same participants for 47 years, giving a rare longitudinal view of how aerobic fitness, muscular strength, and endurance evolve across adult life.
Published in the Journal of Cachexia, Sarcopenia and Muscle, the findings reveal a clear pattern: many measures of physical capacity peak by about age 35 and then begin a gradual decline. That decline accelerates later in life, but the early start — mid-30s — was a consistent signal regardless of participants' training level.
Key discoveries and practical implications
The study delivers two main takeaways. First, physiological aging of aerobic and muscular systems can show up decades earlier than commonly assumed, which has implications for preventive health measures and public messaging about lifelong fitness. Second, the benefits of exercise are not limited to youth. Adults who increased their physical activity during the study improved performance by about 5–10 percent — a meaningful gain that can improve daily function and reduce disease risk.
"It is never too late to start moving," says Maria Westerståhl, lecturer at the Department of Laboratory Medicine and lead author of the study. "Our study shows that physical activity can slow the decline in performance, even if it cannot completely stop it. 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."
The researchers plan another follow-up when participants are about 68 years old, aiming to connect changes in fitness with lifestyle, health outcomes, and underlying biological mechanisms such as muscle metabolism and cardiovascular function.
What this means for individuals and policy
- Start earlier but don't give up: Building exercise habits before your mid-30s can maximize peak fitness, yet starting later still produces measurable improvements.
- Focus on both aerobic and strength training: The SPAF data highlight declines in cardio capacity and muscle strength, so balanced programs matter.
- Public health planning: Recognizing that decline can begin in the 30s may encourage earlier preventive strategies and workplace wellness initiatives.
In short, the SPAF study reframes our understanding of when physical aging begins and reinforces a practical, evidence-based message: consistent physical activity across the adult years preserves capacity and quality of life, even if biological decline is inevitable.
Source: scitechdaily
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