Swedish Physical Activity and Fitness Study Tracks Decline
Physical fitness, muscle endurance, and overall physical performance begin to decline around age 35, according to a 47-year Swedish study published in the Journal of Cachexia, Sarcopenia and Muscle. Researchers at Karolinska Institutet tracked 427 randomly selected men and women born in 1958 through the Swedish Physical Activity and Fitness study (SPAF). Participants underwent repeated physical assessments from age 16 through age 63, allowing scientists to observe how physical abilities changed within the same population over nearly five decades rather than comparing different generations at a single point in time.
Aerobic Fitness and Muscle Power Peak in Mid-Thirties
Measurements of aerobic fitness, muscular endurance, and muscle power revealed a consistent downward trajectory beginning in the mid-30s. Aerobic fitness and muscular endurance generally reached peak levels between ages 26 and 36, while explosive muscle power peaked even earlier. The initial decline was modest but accelerated with age. By age 63, average performance across all measurements dropped by roughly 30 to 48 percent from peak levels. Men and women displayed similar overall rates of age-related decline, despite individual differences in baseline fitness.
Adult Exercise Improves Capacity Despite Natural Aging
Regular physical activity did not entirely prevent age-related decline, as even active participants showed diminishing performance over time. However, exercise altered the rate of loss. Participants who became physically active during adulthood achieved capacity improvements of approximately 5 to 10 percent. Maria Westerståhl, lecturer at the Department of Laboratory Medicine and lead author of the study, stated that physical activity slows performance loss even if it cannot halt it entirely.
Follow-Up Research Connects Fitness to Arterial Health
A 2026 follow-up study published in Scientific Reports examined the SPAF cohort to determine how early fitness impacts cardiovascular health at age 63. Researchers found that participants with higher aerobic fitness at ages 34 and 52 exhibited less arterial stiffness later in life. Arterial stiffness reduces blood vessel flexibility, raising cardiovascular risks. This association remained significant even after adjusting for blood pressure, smoking, and obesity. Additional 2026 research published in GeroScience and The American Journal of Medicine demonstrated that older adults participating in cycling or resistance and aerobic training maintained high functional capacities or built new strength.
Frequently Asked Questions About the Swedish Fitness Study
How was the Swedish Physical Activity and Fitness study conducted?
The study followed 427 randomly selected men and women born in 1958 through repeated physical assessments administered from age 16 until age 63.
What specific physical abilities were measured over the 47 years?
Researchers evaluated aerobic fitness, muscular endurance, and muscle power, which measures the ability to produce force quickly for activities like jumping or climbing stairs.
What did researchers discover about heart health in the 2026 follow-up?
A 2026 study in Scientific Reports showed that participants with better aerobic fitness at ages 34 and 52 had less arterial stiffness at age 63.
By age 68, the Karolinska Institutet team plans to conduct the next round of participant assessments to further evaluate how long-term physical performance relates to lifestyle and aging.
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