Your central nervous system, or CNS, is the primary messenger system of your body, consisting of your brain and spinal cord. You cannot exercise it directly, but exercise affects various aspects of many messenger systems, including the peripheral nervous system, or PNS, which consists of nerves and nerve cells outside the CNS. The CNS and PNS work together to affect your ability to perform tasks, including exercises. Consult your physician before beginning any diet or exercise program.
Skill
Learning a movement takes practice, and learning it well is called skill. Skills are patterns recorded in your central nervous system and utilized on an as-needed basis. Coordinating multiple functions simultaneously, such as retracting the shoulder blades while engaging multiple muscles of your body to push a barbell overhead, is a very complex activity. Your muscles must fire in the right order, and your muscle fibers are usually recruited from smallest to largest. Elite weightlifters display a significantly higher ratio of larger muscle fibers than nontrained individuals, showing the result of specific, heavy training.
Motor Unit
Each muscle fiber is activated by a motor unit, and a motor unit might be responsible for many fibers. When a motor unit signals a fiber, the fiber contracts, and this generates power within your muscles. Multiple fibers contracting generate more power and require greater motor unit activation, which is increased by training with weights close to your maximum on a specific lift. Like fibers, motor units are activated on an as-needed basis, and the motor units that recruit the largest fibers require the most work to activate.
Rate Coding
The rate at which motor units are activated is called rate coding. While some people start out faster than others, this is a trainable reflex. Rate coding is improved by training to generate maximal force. This is not done with heavy weights, as the weights move too slowly. Rate coding is not improved by training with very light weights, as the weight is too light to exhibit a training response. Training with weights in the 40 percent to 60 percent of maximum strength range is optimal. To improve rate coding by training in this range, you need to lower the weight under control but attempt to accelerate it on the way up as fast as you can. This method is normally used by more advanced powerlifters, and this also serves to increase the number of larger muscle fibers.
Coordination
Coordination is not just for gymnastics, as the ability to coordinate the specific firing of muscle fibers in the proper order to generate maximal power is a complex event. Coordination of the fibers within a muscle is referred to as intra-muscular coordination. Coordination of multiple muscles is inter-muscular coordination. Both occur in simple tasks, but for optimal results, these skills are best trained using heavy weights. According to Dr. Vladimir Zatsiorsky in "The Science and Practice of Strength Training," you need to train with at least 90 percent of your one-repetition maximum on each exercise. This will allow you to improve both inter-muscular coordination and intra-muscular coordination.
References
- "Journal of Strength and Conditioning Research"; "Muscle Fiber Characteristics and Performance Correlates of Male Olympic-style Weightlifters"; A.C. Fry et al; November 2003
- "Journal of Physiology"; "Selective Recruitment of High-threshold Human Motor Units During Voluntary Isotonic Lengthening of Active Muscles"; A. Nardone et al; February 1993
- "Journal of Strength and Conditioning Research"; "Muscle Fiber Characteristics of Competitive Powerlifters"; A.C. Fry et al; May 2003
- "Science and Practice of Strength Training (second edition"; Vladimir Zatsiorsky; 2006
- "Theoretical Neuroscience: Computational and Mathematical Modeling of Neural Systems"; Peter Dayan; 2001
