In this lesson, we continue our examination about adaptations associated with an athlete's strength and power training. In the previous lesson, we discussed adaptations occurring outside the central nervous system, and we called these the peripheral structural adaptations. Our focus in this lesson is on the central nervous system adaptations. Both peripheral structural changes and central nervous system's adaptations explain why athletes who appear to have the same muscular development generate different forces when performing the same sports skills. Central adaptations increase the athlete's force and power through control and synchronization of muscle fibers and muscle groups. The central nervous system controls muscles, and therefore the athlete's strength and power, and can be examined from two perspectives. The first perspective is at the intramuscular level, and the second perspective is at the intermuscular level. Control at the intramuscular level involves how well the individual fibers in the muscle synchronously contract and relax. When more muscle fibers are recruited to contract and relax synchronously, the athlete will have a higher force production. When comparing two athletes of the same body size, the stronger athlete will be the one who can activate a large number of muscle fibers in the appropriate muscles. In addition to this, their muscle fibers are activated in an organized way. In other words, they are synchronized better. In contrast, the activation of an untrained, novice athlete's muscle fibers is more haphazard. Through training, the activation of muscle fibers become much better synchronized. Producing a maximal force also requires activation and coordination of several muscles, and this is referred to as intermuscular coordination. Inexperienced athletes have an inefficient coordination of their muscles, and as a result, when performing a skill, their movements are not smooth. Intramuscular and intermuscular coordination improves with continued practice due to neural adaptation. This is the reason superior athletes look really smooth and effortless when they perform the skills associated with their sport. Now, just to refresh your memory from part one of this training science series, muscle fibers within a single muscle are activated into, or organized into small bundles of motor nerves. The bundle of fibers and the nerves stimulating them is referred to as a motor unit. There are many motor units within one muscle. The neuron of a motor unit excites its muscle fiber, and this, in turn, contracts or relaxes it. The force a muscle exerts depends on how many motor units are concurrently activated by the brain. The brain uses motor units to increase or decrease muscle force in three different ways. It can recruit more motor units when more force is necessary, and this is called recruitment. It can alter the firing rate of the motor unit, and this is called rate coding. And it can stimulate more motor units to fire simultaneously. Motor units typically fire asynchronously, and synchronized motor units permit a higher total muscle force than when they fire asynchronously. However, the smoothness and contraction of the muscle is lost, and the muscle will also be quicker to fatigue. So in this lesson, when you have completed it, you'll be able to discuss the difference between inter and intra muscular contribution to force production, describe a motor unit, explain how motor unit recruitment, rate coding, and synchronization contribute to force production. So let's get started.
