Sitting all day? Weak legs could be hurting your brain, experts warn

Long hours spent sitting at work or in classrooms may be doing more harm than expected, with experts warning that weak leg muscles can accelerate cognitive decline, leading to conditions like dementia and Alzheimer’s disease. 

The leg muscles are the body’s largest muscle group, and exercising them regularly improves overall health and energy levels. Missing your leg day at the gym might literally be costing you more than weak lower body muscles.

What is the link between leg muscles and the brain?

A landmark study from King’s College London published in the Journal of Gerontology in November 2015, which followed more than 300 female twins over a decade, attests to the connection between leg muscles and long-term brain health.

Researchers tracked the health of over 150 pairs of sisters aged between 43 and 73 at the start of the study. They found that the twin with greater leg power at the outset showed better cognitive preservation and fewer age-related brain changes 10 years later. Crucially, these results held true even after factoring in lifestyle and other health risks for dementia.

Why exercise the leg muscles?

After the age of 40, adults typically lose 1–2% of muscle mass each year, a decline that is accelerated by sedentary lifestyles. This loss affects metabolism, circulation and, increasingly, brain volume. Research also shows that both the prefrontal cortex, which governs decision-making, and the hippocampus naturally shrink with age; the decline is far more severe in people with Alzheimer’s.

Scientists say inactivity weakens leg muscles, leading to sarcopenia — the age-related loss of muscle mass — which is strongly associated with cognitive decline. Exercise stimulates the release of brain-derived neurotrophic factor (BDNF), a protein essential for the growth and survival of neurons, particularly in the hippocampus, the brain’s memory centre.

Inflammation is another major contributor to cognitive decline. As people age, the immune system becomes more inflammatory, releasing cytokines that damage neurons and blood vessels. 

Activating the leg muscles enhances blood circulation, increases insulin sensitivity and supports healthier mitochondrial function. Consistent lower-body training also improves balance and mobility, helping older adults remain active and socially engaged.

Healthy blood flow is equally crucial. Conditions such as hypertension, diabetes and high cholesterol reduce circulation to the brain, raising the risk of dementia. Exercise improves production of nitric oxide, which helps keep blood vessels flexible and enhances cerebral blood flow.

Regular physical activity also regulates the body’s stress system, the HPA axis. Chronic stress elevates cortisol, a hormone known to damage the hippocampus. Mind–body practices, including yoga and tai chi, lower cortisol levels and promote relaxation, providing what researchers describe as a reset for the brain.

Evidence published in the Journal of Aging Research further shows that even modest increases in activity — about 52 hours over several months — can deliver noticeable cognitive benefits in previously inactive adults.

The message from experts is clear: it is never too late to move more. Whether by taking the stairs more, enrolling for gym ot dance classes or just taking daily walks, strengthening the legs can help keep both body and mind resilient with age.