by Developing the Core
Kinetic Select June 2017
The following is an exclusive excerpt from the book Developing the Core, published by Human Kinetics. All text and images provided by Human Kinetics.
The nervous system determines the specific combination and intensity of core muscle activation to stabilize the spine, and it also enables the dynamic transfer of torque and angular velocity between skeletal segments. The nervous system orchestrates a perfectly integrated steering of muscular torque through the skeletal linkages (i.e., kinetic chain), enabling efficient and powerful movement patterns.
The optimal performance of sports skills is not solely dependent on absolute muscular torque production (i.e., strength). If this were the case, then the strongest men and women in the world would also be ideal draft picks for sports such as baseball and basketball. However, the strongest men and women in the world cannot necessarily, for example, throw a 100-mile-per-hour fastball. Absolute muscular torque production is not useful without the neurologically orchestrated steering of torque that enables optimal storage and recovery of muscular elasticity. The muscles possess an elastic property that allows for the storage and recovery of energy; the contractile force of the muscles is enhanced through the elastic recoil (think of a rubber band) of the muscles in the performance of sports skills. However, the ability to harness this elastic recoil is dependent on movement efficiency. In other words, technique is more important than absolute strength for successful sports performance.
This is why isolated muscle training methods don’t necessarily transfer to better sports performance. Resistance training for dynamic sports must involve ground-based movements that incorporate the coordinated stabilizing and dynamic functions of multiple muscles. With this approach, there is greater likelihood of promoting successful transfer between movements performed in the weight room and sports skill performance. The central nervous system (i.e., brain and spinal cord) receives a constant stream of sensory feedback from proprioceptors (e.g., muscle spindles, Golgi tendon organs, free nerve endings) regarding muscle length, muscle tension, joint position, and the rate of joint rotation (Holm, Indahl, and Solomonow 2002). A key point is that the nervous system must simultaneously meet spinal stability requirements and breathing requirements. The rhythmic action of breathing may compromise spinal stability through the transient relaxation of the core muscles; this is why during performance of maximal lifts, breathing may transiently cease altogether with the Valsalva maneuver, whereby lifters attempt to exhale against a closed airway. For healthy people without cardiovascular limitations such as high blood pressure, this maneuver can be advantageous by increasing intra-abdominal pressure and thus increasing the compressive forces between adjacent vertebrae to preserve spinal stability.
However, in most training scenarios, repeated submaximal torque production necessitates the complementary blending of breathing and core muscle activation to meet spinal stability requirements. Traditionally, the instruction for breathing has been to inhale during the lowering phase and exhale during the lifting phase. However, breathing during exertion rarely involves such a neatly coordinated pattern. Therefore, coaches should instruct athletes to breathe freely while focusing on the maintenance of constant tension (abdominal bracing) within the core muscles. As the prescription of resistance exercises progresses from simple to complex movement patterns, the nervous system adapts to effectively meet breathing and spinal stability requirements.
The specific combination and intensity of core muscle activation during the execution of any given task is dependent on both feed-forward and feedback mechanisms (Nouillot, Bouisset, and Do 1992). Feed-forward mechanisms involve the anticipatory activation of the core musculature, based on muscle memory from prior performance (Nouillot, Bouisset, and Do 1992). Feedback mechanisms play a role as sports skills are repeatedly practiced and refined; the nervous system stores sensory feedback regarding the appropriate combination and intensity of core muscle activation necessary to create sufficient spinal stability and also enable efficient movement.
For example, before a baseball shortstop reacts to field a ground ball, rapid anticipatory activation of the core muscles takes place (i.e., feed-forward mechanism) to create a stable spine and also allow for forceful and dynamic actions of the hip musculature in moving the body laterally to field the ball. The practice of fielding ground balls in preparation for a game promotes the storage and refinement of sensory feedback (i.e., feedback mechanism) that later enables anticipatory core muscle activation for effective fielding performance during a game.
The intervertebral discs, vertebral ligaments, and facet joint capsules are well equipped with proprioceptors such as free nerve endings that relay sensory feedback to the central nervous system regarding position and movement of the vertebral column. This sensory feedback is crucial to stimulate specific neural recruitment patterns of the core muscles to meet task demands. During performance of any given task, the core musculature must be activated sufficiently to create a stable spine, but not to the point of restricting movement. Therefore, a trade-off exists between stiffness and mobility; the nervous system regulates the activation of the core musculature to allow for sufficient stiffness without compromising movement capability (McGill 2006). Through proper movement training (addressed in later chapters), athletes can enhance the regulation of core muscle activation to improve performance.
The National Strength and Conditioning Association (NSCA), the world’s leading sport conditioning organization, offers its unrivaled expertise in a book perfect for any athlete seeking to strengthen the core and improve athletic performance. Featuring 11 ready-to-use sport-specific programs, Developing the Core provides more than 50 of the most effective exercises along with science-based assessments to help athletes understand their individual needs. The book is available in bookstores everywhere, as well as online at the NSCA Store.