Power: Work done or energy transferred per unit of time; The time rate of doing work.
Power = Force x distance
Intensity: Magnitude, as of energy or a force per unit of area, volume, time, etc.
Power = Intensity
Why is power so important? Because power = intensity, and intensity = results. Intensity pushes you past what you think you can do, thus extending your limits. If you can run an 8 minute mile, then running an 8 minute mile isn't going to increase your threshold. Running a 7:30 mile will. Why? Because power is force x distance / time. If the force and the distance (numerator) stay the same, then decreasing time (denominator), will increase power. And power = intensity = results.
Power gives us something to measure. If we can't measure our output, how will we know when we improve? It's simple if we run the same distance on the same course and measure our time. It gets more complicated when we do Fran or Diane. In these workouts, time, weight, and distance are all variables. A 5'9" athlete will have a different power output than a 6'6" athlete, if the other variables are the same. A 95 lb Fran will have a different power output than a 65 lb Fran. And, obviously, a 3 minute Fran has a drastically different power output than a 10 minute Fran. But, how do we relate and measure all this? Certainly it would be confusing, and hard to compare, if we tracked all three variables for all of our workouts. And how would we compare Fran to Diane? By combining these variables - force (weight), distance, and time - we have one observable, measurable, and repeatable data point for each of our workouts. And that's power.
Let's take a look at how to calculate power. Force is simply mass x acceleration. Acceleration is gravity and on Earth that is equal to 9.81 m/s^2. Mass is your body weight and the weight of whatever implement you are lifting. Distance can be measured as the displacement of the lifter's and the weight's center of mass. And time is quite obviously the length it takes to complete a task.
In CrossFit, the goal is to move large loads, long distance, quickly. But, which of those variable is most important - the load, the distance or the time? Is it better to be faster with a lighter load? Or move a heavier load more slowly? It all depends on your goals, but if you really want to push your limits, keep an eye on your power output.
Let's do some theoretical calculations. See all calculations in this document. [Download Power.xls]
Running the numbers, you will see that a 3 minute Fran does not necessarily generate more power than a 4 minute Fran, even with two athletes doing 95 lb Thrusters.
First, we'll consider a 6' 6", 200 lb athlete. Let's say he does Fran in 4:00 with 95 lbs. He produced .438 horsepower for 4 minutes.
Now, let's compare an impressive 3 minute Fran done by a 5'9", 135 lb athlete. He produced .403 horsepower for 3 minutes.
As you can see in the above calculations, the 4-minute Fran time generated more power. But, the 3-minute Fran time was 25% faster! What gives? As CrossFitters, we want to move large loads, long distances, quickly. Although the larger athlete was slower, he had to move more weight (in the form of his own bodyweight), further (as demanded by his anthropometrics). The larger athlete also sustained his power output for a longer period of time. So, now what is more impressive?
The ability to move our bodies and other objects quickly and safely is really what we are after. We measure it in one metric or another just about every workout. That metric is power. It is observable, measurable and repeatable. While we place an emphasis on completing workouts lightening fast, if you look a little further into athletic ability, you will find that the elite are both strong AND fast. They are powerful.
Unfortunately, producing massive power-output can be quite uncomfortable (which explains the hoards of lost souls reading magazines on the elliptical machine). If you've never done Fran, you may not realize this fully yet. But, when people look at you like you've lost your mind when you tell them your workout lasted less than 5 minutes and it took you half the day to recover, you know what I'm talking about.