Which type of fitness involves understanding one’s principles and the values worth defending?

The correct choice is spiritual fitness, as it encompasses the understanding of personal principles and the values that one holds dear. Spiritual fitness is about the inner strength, purpose, and meaning in life, which helps individuals navigate challenges and maintain resilience. In the context of military training and personal development, it reflects the importance of knowing what you stand for and being able to align your actions with your core values. This aspect of fitness contributes to overall well-being and is crucial for sustaining motivation and commitment, especially in high-pressure environments like military service.

Physical fitness focuses primarily on the body's ability to perform tasks, mental fitness relates to cognitive capabilities and emotional well-being, and combat fitness emphasizes physical readiness for combat situations. These areas do not directly address the notion of principles and values in the same depth as spiritual fitness.