Starting Strength, 3rd Edition - Mark Rippetoe [113]
The term power has a very specific meaning in the study of mechanics. Work is the amount of force applied to an object that makes it move a resulting distance, and this quantity expended per unit of time is power. Written as an equation, it is (FD)/T = P, where P is power, F is the force, D is the distance over which the force acts, and T is the time it takes to perform this work. When we’re referring to the total amount of work done over a longer period of time – the duration of a set of five reps, for example – the proper term is average power. When the timeframe in question becomes very short, like the duration of a clean or snatch, the term used is instantaneous power. Physicists measure it in joules per second, or watts. In our discussion of the power clean and its application to explosive training and athletics, instantaneous power is what we are concerned with. It can be best understood as the ability to exert force rapidly – to display strength quickly.
More terms now: Speed is the rate of change in the position of an object. If the direction of the speed is specified, we refer to the velocity of the object – the bar moving up at 2 meters per second. Acceleration is the rate of change of velocity over time – the increase in velocity (or decrease, known as deceleration), or how fast the velocity is changing. Force is the influence that causes acceleration; for an object to accelerate, force must be applied to it. Strength is the physical ability to generate force against an external resistance. (It is difficult to define strength when it is applied isometrically, i.e., when the application of force causes no movement of an object outside the body, but rather stays within the physical system of the muscles and skeleton. Isometric force production is an important part of barbell training, but for purposes of defining strength, movement of the bar is our primary quantifying measurement.)
Power in the weight room is therefore the ability to generate force rapidly. A more familiar term for this might be “quickness,” especially when applied to the movement of the body itself. For many sports, just being strong is not enough; you must also possess the ability to rapidly employ your strength so that you can accelerate better – both your own bodyweight and that of a physical opponent or a thrown implement. A strong man might very well be able to apply enough force to a very heavy weight to get it moving, but a powerful man can get it moving more quickly.
The vertical jump is a valuable diagnostic test for power. It directly measures an athlete’s ability to generate force rapidly enough to accelerate his bodyweight off the ground, and it is a valuable assessment of genetic capacity. It is used by the NFL as part of their Combine test to predict this aspect of performance. Studies have shown that vertical jump performance is predictive of sports proficiency, that power clean performance is predictive of vertical jump performance, and that power clean performance is predictive of squat strength. Squat performance is predictive of squat jump performance, and squat jump performance is predictive of power clean performance. The power clean, by training the athlete’s ability to move a heavy weight quickly, is the glue that cements the strength training program to sports performance.
One way to understand the concept of power in this specific situation is to compare performances in the power clean and the deadlift. As we have already seen, the deadlift is a straight pull off the floor, with the lifter standing up with the bar and the bar stopping at arms’ length, whereas the power clean continues the pull on up through an explosive phase to a catch on the shoulders. A power clean has a bar path that is twice as long as the deadlift’s, and it uses 50–75% of the load of a heavy deadlift. Since work is calculated by multiplying the amount of force used to