An unexpected way to protect against depression has been revealed

Scientists from University College London have made an unexpected discovery: it is muscular strength, rather than endurance, that may prove to be the main shield against depression. The results of this large-scale study have been published in the Journal of Affective Disorders (JAD).

It has long been known that physical activity reduces the risk of depression, yet the specific mechanisms behind this effect have remained a mystery. For the first time, researchers separated the two key components of physical fitness — cardiorespiratory endurance and muscular strength — and tested which one truly affects mental health.

The analysis drew on data from more than 340,000 people from the UK Biobank, one of the largest biomedical databases. To identify causal relationships rather than mere correlations, the scientists employed the method of Mendelian randomization — which allows the influence of factors to be assessed through genetic characteristics, minimizing distortions related to lifestyle.

Grip strength served as the measure of strength — a widely recognized and reliable marker of overall muscular strength. Participants' mental health was assessed using clinical diagnoses and questionnaires covering key symptoms of depression: low mood, loss of interest in life, difficulty concentrating, and changes in appetite.

The findings surprised even the authors themselves. No link between endurance and depression could be detected. Muscular strength, however, demonstrated a consistent protective effect.

The figures are impressive: an increase in grip strength of just 0.1 kg per kilogram of body weight reduced the risk of depression by approximately 14%. Among stronger participants, individual symptoms were also notably less common: the likelihood of anhedonia — the loss of the ability to experience pleasure — dropped by 21%, while appetite disturbances fell by as much as 44%.

Interestingly, the effect turned out to be significantly more pronounced in women. Muscular strength in women was associated with a reduction in manifestations such as depressed mood, loss of interest, and difficulty concentrating. In men, this pattern was considerably weaker.

Why muscles affect the psyche has not yet been fully determined. One hypothesis is of a practical nature: a decline in strength impairs the ability to cope with everyday tasks, which may intensify feelings of helplessness and push a person toward depression. Another is biological: when muscles contract, they release special proteins — myokines — that potentially have a protective effect on the brain.