Alzheimer's disease begins 20 years before symptoms appear, but resistance training can prevent cognitive decline by building leg strength and triggering myokines that protect the brain. Neurophysiologist Louisa Nicola reveals how heavy weightlifting, high-intensity interval training, and managing blood pressure offer actionable defense against dementia and heart disease during the critical midlife window. Resistance training at 80% of your one-rep max produces neural benefits superior to light weight training, preserving hippocampus function and enhancing processing speed in people with mild cognitive impairment.