How Aging Affects Fitness for Men and Women Over 40 Around age 40, the body undergoes several physiological changes that influence fitness: Metabolism slows down by about 1-2% per decade, making weight management harder. Muscle mass declines roughly 3-8% per decade without resistance training. Bone density decreases, increasing fracture risk. Hormonal shifts affect energy, muscle growth, fat distribution, and recovery. Recovery time lengthens, requiring smarter training and r
