When does the body start losing muscle strength?

Nour Nour El-Din Many people may assume that the loss of muscle strength and physical fitness begins in one’s fifties or sixties. However, a long-term Swedish study has revealed that certain physical capacities start to decline earlier than expected, specifically around age 35. Notably, this decline was observed even among individuals who maintained physical activity, indicating that aging affects the body’s capabilities gradually, regardless of activity levels. Nevertheless, the study carried an encouraging message: engaging in sports can slow this decline and improve physical performance, even when a person begins exercising in adulthood.

◄ 47 Years of Follow-up Researchers from Sweden’s Karolinska Institute conducted an exceptional study spanning 47 years, with its results published in the journal *Journal of Cachexia, Sarcopenia and Muscle* in 2025. The study included 427 men and women born in 1958, who underwent repeated physical assessments from age 16 up to age 63. The researchers measured three key aspects: aerobic fitness, muscular endurance, and the ability of muscles to generate force rapidly. The study was distinguished by its longitudinal design, tracking the same individuals over decades rather than comparing different age groups, thereby providing a more precise understanding of how physical capacities change over time.

◄ Peak Performance Between Ages 26 and 36 The results showed that aerobic fitness and muscular endurance generally peaked between ages 26 and 36, before gradually declining. Some capacities, such as explosive muscle strength required for jumping and rapid movements, peaked at an earlier age. The decline was initially slow but accelerated with advancing age. By age 63, average performance across various measures had dropped by approximately 30% to 48% compared to peak levels.

◄ Exercise Makes a Difference Among the study’s most notable findings was that regular physical activity did not completely prevent age-related decline, but it helped maintain higher levels of performance. Individuals who became more active during adulthood achieved improvements in their physical capacities ranging from 5% to 10%. Moreover, participants who had been active since adolescence generally maintained better levels of fitness, endurance, and muscle strength throughout their later years. This indicates that reaching age 35 does not mark a point where everyone suddenly begins losing strength; individuals can continue to enhance their performance through training, even after the age at which population averages start to decline.

◄ Why Do Physical Capacities Decline? Scientists believe that age-related changes involve the muscles, the nervous system, and cellular energy production mechanisms. Over the years, muscles may become less responsive to signals that stimulate their growth and repair, and the efficiency of mitochondria—the cellular components responsible for energy production—may also change. However, researchers have not yet identified the precise mechanisms that explain why this decline begins in the mid-thirties.