Fitness is achieved through proper nutrition, exercise, hygiene and rest. It relates to the ability to perform physical activity and maintain overall health and well-being. The document discusses key principles for improving fitness, including exercising regularly and gradually increasing intensity/duration over time. It also emphasizes training programs should address all fitness components, provide variety to reduce boredom, and be tailored to specific goals for best results. Recovery is important, with easier training days between hard sessions to allow muscles to recover.