Swedish study reveals when fitness and strength begin to fade

January 21, 2026

A 47-year Swedish study (SPAF-1958) from Karolinska Institutet tracked over 400 individuals born in 1958, revealing physical fitness and strength peak around age 35 before gradually declining, with aerobic capacity dropping notably after 45. Participants who increased activity later in life improved capacity by 5-10%, slowing but not halting the decline, as noted by lead author Maria Westerståhl in the Journal of Cachexia, Sarcopenia and Muscle. The longitudinal design outperforms prior cross-sectional studies, with ongoing exams planned at age 68 to explore links to lifestyle and biology. Health Economic Ties