Your muscles start ageing at 35

We notice that older people find it hard to climb stairs or carry heavy shopping, and we may assume that muscle weakness is only a problem of old age. But what we blame on daily stress and family life may be a silent ageing inside our cells. So when does muscle weakness really begin?

An exceptional new study that lasted almost half a century has settled when muscle decline starts and how much exercise helps.

The study was led by Maria Westerståhl of the Department of Laboratory Medicine at Karolinska Institutet in Sweden and published in 2025 in the Journal of Cachexia, Sarcopenia and Muscle. It followed 427 men and women born in 1958 as part of the Swedish Physical Activity and Fitness study (SPAF). Participants had repeated physical tests over 47 years, from the age of 16 to 63. The tests measured how efficiently the body uses oxygen during exercise, how well muscles cope with sustained work, and muscle power in quick movements such as jumping and climbing stairs.

Oxygen use and muscle endurance both peaked between the ages of 26 and 36, and physical performance generally started to decline at around 35 in both men and women. Muscle power peaked even earlier. The decline is slow at first but gradually speeds up, so that by 63 average physical capacity is 30 to 48 percent below its youthful peak. Regular exercise did not fully prevent this age-related decline, but people who took up exercise as adults were about 5 to 10 percent fitter than inactive people. The decline comes from natural biological changes, such as falling efficiency of the mitochondria (the energy plants inside cells) and a weaker response of muscle cells to signals to build, which gradually lead to loss of muscle mass with age.

The study confirms that losing some strength is a natural part of ageing and not just the result of moving too little. The team is continuing its research to find out exactly why the peak comes at 35, and plans another round of tests at 68. Another study from the same group, published in 2026 in Scientific Reports, found that being fit at 34 and 52 is linked to less stiffening of the arteries at 63, which supports heart health and lowers the risk of clots.

Although some physical decline seems inevitable, it is never too late to start managing it and softening its effects. Anyone can protect their muscles and heart with simple steps at home, starting today: brisk walking regularly, taking the stairs instead of the lift, and using light weights or doing squats during daily chores to stay strong and independent for many years.