Starting Strength

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 lower vertical jump. Likewise, athletes with lower verticals who work harder to develop their neuromuscular efficiency, compared to gifted athletes who sit on their asses, have the potential to be better athletes than their gifted counterparts. The power clean and other explosive exercises can develop this ability in an incrementally increasable fashion: more weight can be loaded on the bar each workout, and the increase can be precisely adjusted to match the lifter’s ability to adapt, thus forcing the adaptation to occur. This process allows for the controlled and programmed development of explosive capacity and power.
     
    Power, Force Production, and Velocity
     
    Understanding power and its relationship to force production and velocity is essential to understanding how to effectively train this capacity and why the power clean works so well at doing so. Figure 6-5 shows the velocity-power graph. The dashed line represents bar velocity – very high when the load is light, and slowing down to a stop as the load approaches maximum. The dashed line represents power production – the force displayed quickly.

    Figure 6-5. The velocity-power graph. The dashed line represents velocity, and the solid line represents power output. Peak power occurs at approximately 30% of maximal isometric force and 30% of maximal movement velocity. This would equate to 50–80% of 1RM, depending on the exercise. “Strength” movements are those that are limited by strength, such as the squat, press, deadlift, or similar exercises. “Power” movements are those limited by power output, such as the snatch, jerk, clean, or other similar exercises. From Practical Programming for Strength Training, Second Edition , 2009, The Aasgaard Company.

    Power is low on the left side of the graph, at very light weights, because light weights don’t require much force to make them move fast. They move fast easily because the weight is light. Power is also low on the right side of the graph, where the weights get very heavy, because a very heavy weight is hard to move fast. Remember: power requires velocity. Power peaks in the range of 50–75% of 1RM, where a moderately heavy weight can still be moved relatively fast. The range represents differences in the nature of the various