Defining Fitness

A friend and I were discussing our misconstrued notion of fitness from our younger days. Many individuals dedicate countless hours to the gym without a clear direction. I came across a valuable excerpt from FIT’s “Chapter 1 – Fitness: What It Is” that shed light on the importance of defining the parameters of fitness. This excerpt from FIT emphasizes that having clear definitions enables us to quantify, providing a purpose to our training. In essence, training should have a purpose; otherwise, merely “working out” is akin to stumbling through the woods without a map. For more insightful content on fitness and well-being, you might want to explore

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The human body is an integrated living system, one that must follow the laws and theories of biology, chemistry, and physics. These fields are structured upon foundations of definition and measurement. Any definition of fitness must be quantifiable. If we focus our definition of fitness on the many decades old works of Darwin, Nietzche, Bernard, Selye, and many more, we will create a definition rooted in the science of physical abilities, adaptation, and survival (9,10,11,12). But what physical abilities are related to survival? If we consider the physical abilities that help us function and conquer the spectrum of physical stresses and life tasks with which have historically and presently encountered, we can categorize them into three basic physical abilities:


Strength is the ability to move the body under load and is expressed as an ability to generate muscular force across a spectrum of movement speeds. Strength is a physical entity driven by the biological need to overcome the force of gravity acting on the body or on environmental entities with which the body interacts. It is easily measured using apparati commonly found in gyms (barbells) or laboratories (force platforms, dynamometers, and other force measurement devices). Strength can be further subdivided into muscular force generated with no body movement – isometric strength; muscular force generated at slow speeds – low velocity strength; and muscular force generated at high speeds – high velocity strength. One can go on to find health supplements to enhance their fitness and workout routine.

Endurance is the ability to sustain a task over time. Standing and sitting are the two most sustained things humans do in modern life. Neither require any type of physical effort as the body is anatomically structured to minimize exertion and caloric expenditure when seated or standing. Endurance is a characteristic of movement, physical activity, exercise, and sport. Many things we do require a level of endurance – walking across campus, carrying groceries up to a fourth story walk up, jogging a couple miles, and playing a hard half of football for example. Endurance is primarily a bioenergetic entity, related to the ability to deliver oxygen and energetic nutrients to the working muscles at adequate rates and for long enough duration to accomplish the task at hand. As endurance is time dependent, it is easily measured with a watch and measuring tape or any number of other common or laboratory measurement devices. Endurance can be subdivided into continuous endurance, where the activity is sustained, as in jogging – and intermittent endurance, where work-recovery cycles are repeated for long durations, as in digging post holes for a fence row.

Mobility is the ability to move the body and its constituent parts in a variety of directions and carry out both simple and complex motor tasks. Mobility is an important – but under attended – element of fitness. Stable, controlled, and coordinated movement within our occasionally unstable and frequently unpredictable home, work, and play environments facilitates adequate function and survival. Mobility is likely the most complicated element of fitness as it is comprised of range of motion, agility, balance, and coordination. Each of these entities is measurable in the gym or in the laboratory using simple instruments.


Once we know what fitness is comprised of, we can create a functional definition. The definition for physical fitness used in this book is simple, functional, and measurable: Possession of adequate levels of strength, endurance, and mobility to provide for successful participation in occupational effort, recreational pursuits, familial obligation, and that is consistent with a functional phenotypic expression of the human genotype (13).

This definition applies to the general population but it can be extended to occupational and sporting populations. We can also abbreviate it to make it precisely applicable and measurable by the average coach, trainer, or trainee through omission of the clause about genotype – an assessment of ones genetic make-up and function which is measurable only in the laboratory. This will be our approach throughout this text. Various occupations require more (or less) of one of the elements of fitness, and sport has goals and specializations that merely emphasize or de-emphasize pre-determined components of physical fitness to varying degrees – a weightlifter has focused on strength, a marathoner on endurance. Each has accelerated fitness in one area and has an average ability or potential weakness in the others. As we progress though this book you will find out how to develop each component of fitness individually and also how to develop all three elements simultaneously – enabling the tailoring of training to any purpose or goal.

One would hope that it is a logical concept that knowing what fitness is and what it is not is essential knowledge before it can be manipulated and improved. The definition here clearly states that physical fitness is functional and that the elements of fitness are strength, endurance, and mobility. It follows that improvements in physical fitness are dependent on progressive strength, endurance, and mobility training that force our bodies to adapt. It should also be apparent that physical fitness is not a set of variables that cannot be directly measured or do not manifest as outward physical performance. Further, physical fitness should not be considered an abstract concept or set of intangible feelings. These things are by-products of fitness – as a trainee becomes more physically fit, their ability to function within their own circumstances improves, making them feel better about themselves. This change is not “fitness” but rather a change in self-perception driven by their awareness of the tangible increases in performance produced by training and of becoming more fit. The perception of wellbeing is directly attributable to systematic and progressive exercise training delivering something of substance and value to the trainee, fitness.

8 thoughts on “Defining Fitness

  1. Fitness to me: I can go home to my babies after every shift alive. I can kick open a door and save a child. I can perform my job in the way the public hopes I can in their time of need. I can carry my brother or sister to safety if wounded. I can beat the odds upon retirement and enjoy life because I fucking worked for it.

    ….and all the other stuff you said :-)

  2. I thoroughly enjoy this post/book chapter. I particularly like the separation of “feeling” fit and actual tangible performance increases. I also like that this book focuses on all aspects of fitness.

    So many people seem to think a slim figure (male or female) equates to being fit. Similarly jogging is often thought to be exercise for health and lifting weights is for guys monkeying around in the gym hoping to get bigger arms.

    End rant.

  3. By far my largest weakpoint is mobility. I go in spurts where I’m really good and I do it every night then other weeks for some reason (laziness/tiredness mainly) I won’t do it. I need to be more vigilant in this regard. Good post to reinforce the fundamentals.

  4. If anyone’s tossing up whether or not to get this book, the answer is ‘get it’. I own a shitload of S&C books, and this probably stands out as my most used. I’d say it was worth every cent, except Justin was nice enough to give me a free copy.

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