A comprehensive long-term study has revealed that measurable declines in physical fitness and strength commence as early as age 35. Conducted by researchers from the Karolinska Institutet, the research tracked individuals for nearly five decades, focusing on various aspects of physical health, including aerobic fitness, muscle strength, and physical activity habits.
The study is part of the Swedish Physical Activity and Fitness cohort, which began in 1971 with participants born in 1958. A total of 427 individuals, comprising both men and women, were enrolled and tested repeatedly over the course of 47 years. These repeated examinations allowed researchers to observe long-term trends in individual physical performance.
Findings on Physical Decline
The study utilized models to estimate age- and sex-specific changes within the cohort. Follow-up examinations were conducted at several points throughout adulthood, allowing researchers to track changes in the same individuals rather than relying on comparisons between different age groups. Participants underwent standardized physical testing, which included assessments of aerobic fitness through peak oxygen uptake tests, a standard measure of cardiovascular capacity. Muscle strength and endurance were evaluated using controlled performance tests, such as grip strength and repetitive movement tasks. Basic physical measures, including height and weight, were also recorded, alongside self-reported physical activity habits.
The results indicated that physical performance peaks in early adulthood, typically before age 35, and tends to decline steadily thereafter. This decline was evident across multiple measures, including aerobic fitness and muscle strength. While individuals who maintained physical activity levels generally exhibited better overall fitness, the study found that activity alone could not fully prevent age-related decline. Nevertheless, participants who increased their activity levels later in life experienced an improvement in physical capacity of approximately 5% to 10%, suggesting that the body remains responsive to exercise even beyond its peak years.
Study Limitations and Future Plans
The findings, published in the Journal of Cachexia, Sarcopenia and Muscle, come with certain limitations. The study comprised individuals born in the same year and living within Sweden, which may affect the applicability of the results to other populations with differing social, environmental, or genetic backgrounds. Additionally, the observational nature of the study means that factors such as diet, occupation, and underlying health conditions may have influenced the outcomes.
As is common in long-term studies, some participants dropped out over time, potentially impacting the sample’s representativeness of the original population. Physical performance was measured at specific intervals, meaning that short-term fluctuations between testing periods were not captured.
The research team plans to continue monitoring the cohort as participants age, with the intention of linking changes in physical capacity to health outcomes later in life. This ongoing study aims to provide further insights into how physical fitness impacts overall health as individuals progress into older age.
