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Force, Distance and Time by Greg Glassman - CrossFit Journal

Force, Distance and Time

By Greg Glassman

Video Article

Fitness programs should be based on a proper understanding of force, distance and time, Coach Greg Glassman told participants at a CrossFit Level 1 Certification Seminar at CrossFit Brisbane in Brisbane, Australia on May 16, 2009.

Coach Glassman said that as a college student he had been interested in both math and physical education. He looked unsuccessfully for a department that studied human performance in the fundamental physical units physicists use to estimate and analyze all performance: force, distance and time.

Velocity, acceleration, kinetic energy and momentum all derive from force, distance and time. From a rock, to a rocket ship, to a galaxy, everything that moves is discussed in terms of force, distance and time. But when it comes to the human body, most scientists stop talking about force, distance and time and start talking about other things that do nothing to improve performance.

“What we want to do is develop not an exercise science per se, but a technology of advancing human performance,” Glassman said. Today, the study of human performance is splintered across 1,000 different sports. Good coaches have figured out what works. “What I’d like to do is look at the union and intersection of all these different adaptations.”

5min 47sec

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9 Comments on “Force, Distance and Time”


wrote …

this is driving me nuts, i cant find the other two


wrote …

electricity and magnetism bro :)


wrote …

When can we see the rest?


wrote …

One of the other two fundamental units of measure is temperature. Racking my brain to come up with the last one...


wrote …

Mass? But he may have meant it as a part of force (after all, Force=Mass*Acceleration).


wrote …


How could it be electricity and magnetism? There aren't even units for those two things.

Temperature may be one, but then, we usually get it by measuring the distance mercury moves, or the difference in current in a thermocouple, or something like that... I'm not sure. Mass is a derivative of measuring force though.


wrote …

The fundamental units that are of concern to us are time, distance and mass. (Sorry to disagree with you on this Coach.) Force is equal to mass times acceleration, and since acceleration is a function of distance divided by time squared, force is directly proportional to mass and distance, and inversely proportional to time squared. The extension of this (in case anyone is interested) is that power (read “intensity”) is directly proportional to Mass and Distance squared, and inversely proportional to the cube of Time. This assumes uniform motion, which is an over simplification of most functional movements, but is a good model to work with.


wrote …

He said "measurable" entities. You can't directly measure mass, it's a measurement of force that we can extrapolate mass from.


wrote …

Mass can be measured using a balance; since it involves a standardized counterweight, gravity plays no role in it. That's why a balance is just as effective on Earth as it is on the moon. This is also one of the fundamental differences in the Gravitational, Engineering, and Absolute systems of units.

I'm still a little shaky when it comes to "proving functionality" of biomechanical systems using Newtonian Mechanics. Concepts of work and energy for instance, are really skewed when they're applied to the body.

If you don't believe me, try and derive an expression for the calories burned in running a mile. Assume whatever pace and mass you want. It cannot be done. The factors in play are countless, and it's a coupled Mechanics, Thermodynamics, Fluids, Heat Transfer, and Chemistry problem.

Experimental rigor (and probably quite a few peoples' theses) has given us some kind of correlation between heart rate, CO2 output, and caloric burn. But elementary particle physics just doesn't hold up, and I'm unsure why there's so much handwaving science. I mean, scientists are still bickering as to why a muscle that's held taut fatigues over time.

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