The fitness component most effectively improved by resistance training is muscular strength. Resistance training involves exercises that enhance the ability of muscles to exert force against resistance, thus resulting in increased muscle mass and strength. Regularly incorporating resistance exercises can lead to significant improvements in muscular endurance, hypertrophy, and overall physical performance. Additionally, resistance training contributes to increased bone density, improved metabolism, and better functional fitness, making it a core component of a comprehensive fitness program for overall health and well-being.