The relationship between fitness levels and immune function is significant; higher fitness levels often enhance the body's immune response. Regular physical activity can lead to improved circulation, better inflammatory responses, and reduced risk of chronic illnesses, which in turn can boost immune health. Conversely, excessive or intense exercise without adequate rest can impair immune function. Research shows that moderate exercise is beneficial for overall immune resilience, while sedentary lifestyles can lead to increased susceptibility to infections. Therefore, maintaining a balanced exercise routine is crucial for optimal immune performance.