What is Fitness?

The Kinematic Theory of Health states that anything you do that advances your work capacity in any activity, will make you healthier.

It’s an interesting (and a little bit confusing) assertion, but a fascinating one nonetheless. It stands in stark contrast against the medical world’s use of blood pressure, weight, resting heart rate, a1C, triglyceride count, among many others. These predictive indicators are great correlates to chronic illness, but they shed little light on the health of non “sick” people.

Health is so much more than not having a sickness. At RxFIT, we define health as being able to do anything, at anytime, with anyone. In other words, can you hike Timpanogos at age 25 and age 55? When you fall at age 75, can you catch yourself in a burpee without breaking a hip? Do you have the strength to help your kids move into their new house all day Saturday, and then still have the energy to play with their kids (your grandkids) at the end of the day?

Health, therefore, has little to do with sickness and everything to do with capacity. If I’m no longer an asset to my family and friends, I am no longer healthy.

Instead of using these biological indicators, the Kinematic Theory of Health uses your ability to produce work across broad time and modal domains. Let’s break this apart:

Work Capacity

Work capacity, as defined by the physicists of the world, is also the equation for power ((force x distance) / time). If you tell me how heavy something is, how far you moved it, and how long it took you, I can plot your work capacity in that time duration (“time domain”). I can also plot your work capacity in that activity (“modal domain”).

This applies to everything inside the gym (i.e. weight on the bar) as well as everything outside the gym (i.e. shoveling the snow).

Broad Time

“Fringe” athletes are those individuals that train at the edges; they either only do short (and heavy) weightlifting sets or only do long-cardio bouts of running and cycling. There are benefits to both of these types of training, but you leave so much on the table when you do this. In general, I usually see men do the former while women only do the latter.

For example, exercising men lack developing cardiorespiratory endurance when they train only weightlifting at the fringes of short-time domains. Exercising women lack developing strength and power when they train only cardio at the fringes of long-time domains.

In order to develop work capacity across broad time domains, we need to train both short- and long-time durations… along with everything in between.

We ensure this at RxFIT by writing up on a whiteboard five time variables every week when we review the workouts. We want to make sure that we have at least one workout that falls under each of these variables: Heavy, <5-minutes, 5-10 minutes, 10-20 minutes, 20+ minutes.

Modal Domains

If I can deadlift a barbell that weighs 500-lbs, but I can’t pick up a 200-lb bale of hay, how fit am I actually? This is one of the reasons why I love sports so much. Sports bring your training to life, ensuring that those things you do in the gym are transferring to other things in life.

Mixed-modal training ensures exactly this. At RxFIT, we ensure that workouts contain bodyweight, kettlebell, dumbbell, medicine-ball, barbell, rowing, biking, and running movements every week. Similar to the time domains, we make tally marks in these “modal”-domains, attempting to have an equal balance across all of them.

In addition to mixing up the equipment, we also strive to program “skill days” where our neurological capabilities (“body-awareness”) are being developed. Things like jumping rope, walking on your hands, or alternating, consecutive split jerks are movements that develop an individual’s athleticism. These, among others, are commonplace in our workout programs.

Fitness needs to be transferable to other things in life, so your training needs to mimic this in a mixed-modality fashion. Adopt the philosophy that routine is the enemy.


In summary, you and I are only as fit as we are capable or accomplish work within broad time and modal domains. I want to increasingly develop my ability to do anything. This is fitness.

But health adds two additional components: anytime with anyone. Your age and relationships with family and friends matter.

The only way we begin that conversation, however, is to get fit. Ensure that your workouts constantly vary across broad time and modal domains.


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