Physically fit and healthy Fitness is the condition of being physically fit and healthy and involves attributes that include, but are not limited to mental acuity, cardiorespiratory endurance, muscular strength, muscular endurance, body composition, and flexibility. Research has shown that it's important to get all four types of exercise: endurance, strength, balance, and flexibility. Each one has different benefits. Doing one kind also can improve your ability to do the others, and variety helps reduce boredom and risk of injury.