At What Age Does Your Body Start Losing Strength? A 47-Year Study Reveals - Video

Does physical fitness really start declining at just 35 years of age? A long-term Swedish study suggests that aerobic fitness, muscle endurance and physical performance begin declining around the mid-30s, although regular exercise can help slow these changes and improve strength even when started later in adulthood.

Published in the Journal of Cachexia, Sarcopenia and Muscle in 2025, the study conducted by researchers at Karolinska Institutet in Sweden tracked physical fitness changes over 47 years.

The research was part of the Swedish Physical Activity and Fitness (SPAF) study, involving 427 men and women born in 1958. Participants underwent repeated physical assessments from age 16 through 63, allowing researchers to examine changes in fitness, muscular endurance and muscle power throughout adulthood.

The findings revealed that aerobic fitness and muscular endurance generally peaked between ages 26 and 36, with physical performance beginning to decline around age 35.

The decline was initially gradual but accelerated with advancing age. By age 63, average physical performance had decreased by approximately 30% to 48% compared with peak levels.

Importantly, similar patterns were observed among men and women, including participants who remained physically active throughout adulthood.

However, exercise appeared to help preserve physical abilities. Individuals who became physically active during adulthood experienced improvements of approximately 5% to 10% in physical capacity, demonstrating that starting exercise later in life can still provide meaningful benefits.

Researchers also observed that individuals who were physically active during adolescence generally maintained better fitness, endurance and muscle power during adulthood.

A subsequent 2026 analysis of the same cohort, published in Scientific Reports, found that better aerobic fitness at ages 34 and 52 was associated with lower arterial stiffness at age 63, suggesting potential long-term cardiovascular benefits.

However, the observational findings do not establish causation, and further research is needed to understand the biological mechanisms responsible for age-related physical decline.

REFERENCE: Maria Westerståhl, Gustav Jörnåker, Eva Jansson, Ulrika Aasa, Michael Ingre, Kaveh Pourhamidi, Brun Ulfhake, Thomas Gustafsson. Rise and Fall of Physical Capacity in a General Population: A 47‐Year Longitudinal Study. Journal of Cachexia, Sarcopenia and Muscle, 2025; 16 (6) DOI: 10.1002/jcsm.70134