Physical fitness is defined as:

The definition of physical fitness as the ability of body systems to perform daily tasks easily with enough reserve energy encompasses a comprehensive view of what it means to be physically fit. This definition highlights not only the capacity for physical exertion but also the importance of efficiency in daily activities. It indicates that a physically fit individual can carry out regular tasks—such as walking, climbing stairs, or engaging in recreational activities—without excessive fatigue, and has enough energy to handle unexpected physical challenges.

This understanding of physical fitness incorporates various components, including cardiovascular endurance, muscular strength, flexibility, and body composition, all of which work together to enable overall functionality in daily life. The focus on "reserve energy" underlines the idea that physical fitness isn't just about performing during a workout or an athletic event but maintaining an active lifestyle with a buffer of energy for additional demands.

In contrast, definitions that focus strictly on running long distances, performing strength exercises, or high-intensity performance do not encompass the broader concept of physical fitness. These narrower definitions neglect the everyday applications of fitness in various lifestyles and might not reflect an individual's overall health and efficiency in daily life.