A 40-year longitudinal study of Swedish women found a powerful correlation between mid-life fitness and late-life cognitive function. Women who were categorized as "high fit" in their 40s experienced, on average, nine more years of good cognitive health in their 80s compared to their low-fit counterparts.

Physical activity stimulates the release of Brain-Derived Neurotrophic Factor (BDNF), crucial for neuron growth, via two mechanisms. Muscles release a protein (a myokine) and the liver, in response to exercise stress, releases a ketone (beta-hydroxybutyrate). Both cross the blood-brain barrier to stimulate BDNF production.

Focusing on building muscle is crucial for long-term health, particularly for women entering perimenopause. Muscle helps regulate blood sugar, reduces inflammation, and protects against osteoporosis, dementia, and heart disease, making it a vital health indicator.

While BDNF is associated with exercise's brain benefits, the BDNF produced in muscles doesn't readily cross into the brain. Instead, lactate produced during intense exercise enters the brain and acts as a signaling molecule, stimulating local BDNF production and improving hippocampal function.

While light weightlifting builds muscle, lifting heavy (around 80% of one-rep max) is required to produce specific neural effects. This intensity releases myokines—chemicals that cross the blood-brain barrier, reduce inflammation, and stimulate the growth of new neurons in the hippocampus.

A study on "low-fit" adults (exercising <30 mins/week) showed that starting a modest cardio regimen of two to three 45-minute sessions weekly for three months yielded significant cognitive benefits. This included improved performance on memory tasks classically dependent on the hippocampus, demonstrating a low barrier to entry for brain health.

It's possible to have a brain full of amyloid plaques (a hallmark of Alzheimer's) yet show no cognitive decline. This is due to 'cognitive reserve,' the brain's ability to withstand damage. Building this reserve through activities like reading, writing, and exercise is a key defense.

Despite common belief, only about 3-5% of Alzheimer's cases are driven by inherited genetic mutations. The vast majority are linked to lifestyle factors like diet, exercise, and sleep, making it a largely preventable disease if proactive measures are taken early in life.

Each workout releases a cocktail of neurochemicals, including dopamine, serotonin, and the growth factor BDNF. This "bubble bath" for the brain directly stimulates the growth of new cells in the hippocampus, making it larger and more resilient, which improves long-term memory and can delay dementia.