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Strength & Conditioning

The Power Principle

Understanding the physics behind training to improve power can make a CrossFitter stronger.


CrossFit boxes are filled with physically transformed people who once felt stale doing the same old strength-training routines on the same old equipment in their gyms. Those routines typically involved a prescribed speed of movement that was “slow and controlled.” So, right off the bat, a newcomer to CrossFit has to adjust to the often all-out, high-speed pace of many CrossFit movements. Part of what that new CrossFitter is experiencing is, quite simply, the application of power. Because the term “power” is commonly misused, what follows is an explanation from the point of view of human performance.

During an exercise movement, muscles create force, which causes joints and bones to move some specific distance. The muscles’ ability to produce force through that distance is called “work,” which is written in an equation as “force x distance.” As an example, let’s assume an athlete is deadlifting 200 pounds. He may move the bar 20 inches in the lift. That amount of work would calculate, for the sake of this example, as 4,000 joules (the unit for work). Easy enough.

Now, consider this question: Is there a difference if he performs that lift in one second or five seconds? From a work standpoint, there is no difference; the same amount of work was done — 4,000 joules. Intuitively, however, we all recognize that those two lifts are not quite the same. What’s different about them is their power output. Power is defined as “work per unit time.”

Let’s delve further into the physics. Look closely at these two formulas:

Work = Force x Distance

Power = Work / Time

Because work is “force x distance,” power can be rewritten as:

Power = Force x Distance / Time

And because distance per unit time is “velocity,” power can be further summarized to:

Power = Force x Velocity

In other words, power contains the element of speed. Power is, simply put, the ability to produce muscular force with speed. Strength, on the other hand, is related to maximal force production without the influence of speed. Therefore, it is possible for person A to be “stronger” than person B but person B to be more “powerful” than person A.

Now, what does all this have to do with CrossFit? Well, CrossFit — perhaps more than any other style of training — uses many movements that must be performed with high speed (high power output) in order to be successful. For instance, because of the very nature of the snatch, it is a power movement; a person must produce a great deal of speed during the second pull in order for the necessary acceleration to be achieved so that the lifter can pull himself or herself under it. The same is true for the clean, thruster, box jump, muscle-up, kettlebell swing and many other common CrossFit movements.

It would be a mistake to assume that gaining strength in low-speed movements like a heavy back squat will naturally result in more power (i.e., a better clean, etc.). Not true. One’s training predicts one’s adaptation. In fact, research has found that explosive ballistic training enables an athlete to produce more muscular force in a shorter amount of time (called “rate of force development”) than low-speed training. That is, athletes who regularly train explosively achieve higher levels of muscular force early in the movement compared to those training with heavy loads (i.e., low speed).

So while low-speed lifts such as heavy back squats, deadlifts and presses can help an athlete increase maximal muscle force (and that is good), it is high-speed work that will make the best use of the strength gained by training muscles to apply that force rapidly. The bottom line is that you must train for power — explosively and with a focus on high speed — to be more powerful. If you can do that, your CrossFit performance will improve measurably.