What is Intensity?

Updated: Jan 11, 2019

What is Intensity?


"Intensity is the independent variable most commonly associated with maximising favourable adaptation to exercise.”

  • Greg Glassman

In short and simple terms - intensity can can be seen as how fast or how much work you can get done.

In physiology this translates to:

Intensity is the amount of physical power that the body uses when performing an activity

So intensity is defined as power.

Power is equal to force x distance divided by time.

This means that intensity can have a tangible, undebatable number put to it....

Or can it?

In reality intensity is being comfortable with being uncomfortable, and this makes intensity relative to each individual.

One persons 100% effort on any given workout might equal to a greater power output than someone with a lower overall fitness level. The difference between them can be made up of one or several different aspects.

A more experienced athletes body has been conditioned over numerous years of high intensity exercise to adapt and get stronger, faster and more efficient. Their capacity has grown as has their resolve to be uncomfortable for longer and longer durations at higher levels.

Someone who is has less experience with high intensity workouts may not have the cardio respiratory endurance, the strength, or the mental resolve to grit though those few extra reps. They likely also won’t have the efficiency of mechanics that have to be learned and continue to refined as we strive for virtuosity.

All of the above will factor into the total workout output - the power generated. However the perceived exertion when working at 100% is the same for both of us.


So intensity can be seen as a measurable, un-debatable number - power output.

It can also be a perceived level of exertion that is nearly impossible to measure with numbers.


We need and want both to be high in order to elicit the fastest and greatest changes to our fitness.

Anyone who has ever done the workout Fran (21-15-9 thrusters & Pull ups) can understand both the forms of intensity described above.

Finish that workout as fast as possible and you’ll be left in a puddle of your own sweat pondering your life choices. Both mentally and physically you will have given 100%, your power output can be measured simply by the time it took you to complete the work.

Your perceived level of exertion can be seen by the puddle, the gasping for air, and how long it takes for you get up off the floor!

If you’ve given 100% intensity and got a sub 3 minute Fran, or 100% and got a 6 minute Fran, the aftermath is the same the perceived exertion is the same, only the power output differs.

Think of Ferrari at max speed - 100% of it’s power output, it’s faster than a Fiesta going thats also going flat out. Both are going at their full effort, however the Ferrari has a bigger engine and thus greater power output. That’s what we’re doing by training - building a bigger engine!

If you did Fran with a 95lb thruster and full pull ups rather than a 40lb thruster and ring rows the only difference is the size of your engine, the intensity and perceived exertion of the workout remains the same.

That is how scaling works. It is adapting the workout for an individuals level of fitness and experience so that they can maintain 100% intensity and receive the intended stimulus of the workout.

The beauty of CrossFit is that it can be scaled to fit anyone from an experienced athlete, to someone doing their first workout, to your grandmother.

There is no shame in scaling a workout in order that you can give 100% and not miss out on the intended stimulus and benefit to your fitness.

So intensity is two fold.

It’s the total work output generated through a workout and measured by time, reps or load.

it is also the level of exertion given during a workout that is measured by your level of effort.

Do you workout with enough intensity? Do you scale your workouts appropriately?


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