Starting Strength, 3rd Edition - Mark Rippetoe [115]
These examples illustrate a way to consider the relationship of absolute strength to power: you can think of the power clean as being done with a percentage of the deadlift. In other words, explosive strength is displayed as a percentage of absolute strength. The ratio between the two depends on training and genetics, and the vertical jump might be the indicator of the ratio. Training can improve the ratio to a certain extent, but genetics will limit this extent. What is certain is that as the ability to produce force increases, the potential to display that force as power goes up with it. The extent to which this is true at the extreme limits of performance is unclear, but for novice lifters, there is no question that the best way to make the clean stronger is to make the deadlift stronger.
If this is true, why train the power clean at all? For some people, this is a legitimate question. Older people with old-people’s elbows, shoulders, and wrists may elect not to perform the exercise at all, as may very young trainees, people with poor athletic ability, older women, or people with osteoporosis, chronic knee tendinitis, or other problems that make the power clean more trouble than it is productive. But for most other people and all athletes, the power clean is the best way to increase the ability to explode – to display power – where this ability needs to be developed.
The Neuromuscular System
To understand the nature of power production by the human body, you need to understand the way the nervous system controls the muscles. A detailed discussion of the physiology of muscle contraction is outside the scope of this discussion, and can be found in Practical Programming for Strength Training, Second Edition (Aasgaard, 2009) and in many other sources. Very short version: The muscles are composed of muscle fibers; these are controlled by the motor neurons; and the whole system of muscles plus the controlling nervous system is collectively referred to as the neuromuscular system. Each motor neuron controls many muscle fibers, and the term motor unit refers to one motor neuron and all the muscle fibers it innervates (supplies with nerve fibers). The contraction, or firing, of motor units by the neuromuscular system is called recruitment. It is considered to be an all-or-none phenomenon: the muscle fibers of the motor unit, when fired by a nervous impulse, come into contraction at 100% of their capacity to do so. This means that a submaximal muscle contraction is the result of a submaximal percentage of motor units being recruited. The greater the force production requirements of the task, the more motor units are recruited into contraction.
Figure 6-4. Motor unit recruitment is the total activity of varying numbers of motor units, all of which operate to the limits of their capacity when individually called into contraction. The recruited motor units are in full contraction, while the unrecruited motor units are not.
The ability to recruit motor units with great efficiency – i.e., recruit high numbers of them quickly when a task demands instantaneous high levels of force production – is largely controlled by the genetic endowment of the individual. This ability depends on the density of motor neuron populations within the muscles, the quality of the nerve tissue, the quality of the nervous system interface with the muscle fibers, the type of muscle fibers and their ratio within the muscles, and other factors. Some of these factors can adapt to the stress imposed by training, and some cannot. The vertical-jump test is a naked look at the quality of the neuromuscular system and is an indicator of the ultimate ability of an athlete to be explosive.
Exercises that require the body to explode into a high level of motor unit recruitment with heavy loads can develop the aspects of the neuromuscular system that are capable of adapting to the stress of the exercise. Athletes with a high vertical jump have the potential to be more explosive than athletes with a