What Makes Up Health-Related Fitness?

Being “fit” can mean very different things depending on what aspect of the body is being considered. Someone may be able to run for a long time, lift a heavy load, repeat a movement many times, or move comfortably through a large range of motion. These abilities are related, but they are not the same. A traditional health-related fitness model separates them into several components so that each can be considered more clearly.

In this five-part model, health-related fitness includes cardiorespiratory endurance, muscular strength, muscular endurance, flexibility, and body composition. Newer classifications may organize these qualities differently, but the traditional model remains useful for distinguishing their basic characteristics. Cardiorespiratory endurance describes the ability to perform large-muscle, whole-body exercise at moderate-to-high intensity for extended periods .¹

Muscular strength and muscular endurance sound similar, but they describe different capacities. Muscular strength is the ability of a muscle or muscle group to exert force. Muscular endurance concerns what happens over time: it is the ability of a muscle or muscle group to sustain force or repeatedly produce force .¹

Flexibility describes the range of motion available at a joint. That definition does not imply that greater range is always better or that everyone should reach the same maximum. Appropriate range of motion can differ between joints and among individuals .¹

Body composition differs from the other components because it describes relative amounts of body tissues rather than a capacity for performing a task. It refers to the relative amounts of fat mass, fat-free mass, and other body components .¹

Looking at fitness in separate components helps explain why being strong in one area does not automatically mean being equally capable in another. A person’s fitness profile can include a different combination of strengths and limitations, and those qualities may also change independently with training. The value of this traditional model is therefore not in reducing fitness to a single score, but in showing that physical fitness has several distinct dimensions that can be considered and developed in different ways.