Resistance training, also called strength or weight training, involves working muscles against an external force (like weights, bands, or body weight) to build strength, endurance, and muscle mass. It's an effective way to improve bone density, metabolism, joint health, and reduce injury risk, making daily tasks easier and improving overall physical and mental well-being. Key methods include free weights, machines, bands, and bodyweight exercises, requiring consistent, progressive effort for muscle fibers to adapt and grow stronger.