Balance represents an ability to stabilize and maintain a desired body position. Balance can also be thought of as correct, or efficient, positioning of a body part or the entire body.
Natural and functional movement is directly related to the harmonious work of joints, muscles and the neurological system. The neurological system interacts with the musculoskeletal system in a coordinated and complex manner. Using stability or balance training, and CCE, is the perfect way to stimulate and train this complex interaction of the body. Think about common activities and it quickly becomes apparent that most movements are dependent on coordinated balance and changing force output throughout the body.
Demands placed on the body during stability training, balance training and closed chain exercise vary dramatically, but replicate daily life and sport situations. From moment to moment, the body strives to maintain balance and to integrate the responses into safe, skilled movement. This mirrors daily activities where one must constantly perform in many planes of movement.
A number of components represent key building blocks that contribute to safe, effective and functional movement, as well as skilled performance. The concept of body equilibrium includes:
Note: The term kinesthesis is used to define a person's awareness of motion or position as it pertains to his/her limbs. Proprioception is defined as one's sense of movement as it relates to movement of the body and how it is oriented in space. Today, current literature uses the terms as though they are synonymous (Plowman and Smith 1997).
3. Gradation of force. An ability to control muscular force production and maintain an equalized, though dynamic, position regardless of the physical task at hand, is critical to any type of human movement. Correct application of force is complex, learned and under the direct influence of neural control. The regulatory control of muscular force is referred to as “gradation of force.”
These three components of body equilibrium are important to consider, and train, when used in the context of sport performance and daily movement requirements. Balance, kinesthetic sense, proprioception, body symmetry and proper force application are key aspects of any activity that requires a dynamic, integrated, coordinated and skilled response. Being able to change one's center of gravity to compensate for required movement is the key to moving skillfully. Agility is the technical term for this developed sense that incorporates proprioception and balance, and allows a person to move efficiently, confidently, gracefully and smoothly, while wasting little motion. The smooth fusion and training of all of these elements can represent skillful or functional movement, and reflect the athletic qualities that everyone should seek to develop.
science foundation behind balance training
Balance and stability training have been studied for many years and continue to grow as a mainstay of cuttingedge conditioning training programs. The scientific foundation behind this type of training has a longstanding history that is well researched and documented (Plowman and Smith 1997; Wilmore and Costill 1994; McArdle et al. 1991; Jackson, J.H. 1931).
Postural stability as it relates to balance revolves around the body's ability to maintain center of mass (COM) within specific stability and balance limits. This capacity is the foundation for all movement activity and has become increasingly recognized in the realm of sport and rehabilitation (Anderson, Gregory 2004, unpublished manuscript; Anderson et al. 2005). The benefits of training controlled instability on unstable surfaces are many.
Skilled movement is epitomized by athletes who perform tasks requiring complex degrees of coordination, balance, strength and power – and make them look easy! Yet, skill cannot be developed without a “sharp” neuromuscular system, which only occurs with practice, rehearsal, training and experience. The most basic element of human movement relies solely on the nervous system. Muscles do not get the signal to “go” unless the nervous system directs them to do so!
the nervous system and movement
The brain, spinal cord and nerves make up the basic elements of the nervous system. The nervous system represents the control tower for communication and directs movement for the entire body. In a basic sense, movement occurs because information is received and forwarded via the nervous system and its specialized messengers, the sensory organs, to the skeletal muscles of the body. Quite simply, the brain controls muscular movement and “thinks” in terms of whole motions to attain a synchronized movement pattern (Jackson 1931; Korr 1976; reported in Wolf 2001).
Understanding human movement becomes easier with a realization that “exercise is muscle contraction.” More specifically, movement relates to muscular force production rather than muscle contraction. Why? Because not all muscular force development refers to a tension building process of “contraction,” which results in a shortening of the muscle and is referred to as a “concentric contraction.” A muscle can also produce force where the length of the muscle does not change (isometric force production), where the “contraction” produces an increase in tension but does not cause significant movement at the joint, or where the muscle exerts tension while lengthening, which represents eccentric force production (Plowman and Smith 1997).
Traditional approaches to conditioning, as well as functional types of training incorporate concentric, eccentric and isometric types of force production. One type of training or force production is not superior to the other, but all are essential to a wellrounded program that meets all the requirements of a forwardlooking program. In turn, a progressive and complete training program will meet all the requirements that contribute to proficient human movement.
neural control of human movement
The study of neuromuscular control in human movement provides the science that backs functional balance training, and explains why it is important. As mentioned, all human movement, skilled or unskilled, is dependent on muscle contraction or force production, which in turn is one hundred percent dependent on receiving a signal from the nervous system. A muscle that is not activated by the nervous system is a muscle that does not contribute to movement. This fact implies that muscles must “learn” how to contribute to skilled movement patterns through training and repetition that is specific to the movement(s) being undertaken. Activity like this is usually referred to as “skill practice,” “sport specific training” or “rehearsal.” The principle of skillrehearsal encompasses specificity – specific practice and repetition – and is the most important fundamental aspect related to motor learning and highlevel performance.
As a result of training in a specific manner, for given activities, the nervous system is able to call on and activate groups of muscle fibers (motor units) at the precise moment needed, as well as call into play the correct number of motor units to develop the appropriate amount of force needed for the activity. As an example, removing an eyelash from the surface of the cornea requires a different amount of muscle force production when compared to slamdunking a basketball or pressing a 1 RM (repetition maximum) amount of weight. An ability to mediate muscular force development is called “rate coding,” or as referred to earlier, as a “gradation of force” (Plowman and Smith 1997).
The ability to gradually and progressively control muscular force output, up or down, for a given movement, is obviously a critical aspect of successful and skilled human movement. The ability to regulate force development depends on the nervous system, with the other key aspect being tied to mechanical factors (i.e., lengthtensionangle, forcevelocity and elasticityforce relationships, as well as architectural design of the muscle) that influence muscle contraction in the body (Plowman and Smith 1997). Human performance – balance responses included – is directly dependent on the correct application of force.
muscle fibers and motor units
The physiologic reason behind the ability to regulate force production lies in the fact that movement is based on contractions of motor units (force production output), and not single muscle fibers, nor entire muscles. A number of muscle fibers make up a motor unit, and many motor units are contained within each muscle. The body's muscles are comprised of both fast and slow twitch muscle fibers. Each type of fiber has a different threshold at which they will fire or activate. Slow twitch muscles have a lower stimulus threshold so they will fire or be called into action sooner, and will continue to perform the work load until the activity demands a more powerful contraction, at which time the fast twitch motor units will be activated (Brooks 2001; Brooks 1997).
Motor units, of which there are many in each muscle, are made up of either all fast or slow twitch fibers. When a motor unit is activated, or in other words the stimulus from the nervous system is great enough to cross its threshold, all of the muscle fibers associated with the motor unit will be called into action. This is known as the “allornone” principle of muscle contraction. Mistakenly, many people believe this means that a muscle fires allornone. It does not. What is true is that motor units and their associated fibers do fire allornone. Each type of motor unit – fast or slow twitch – has a different threshold or point at which it will activate in response to neural stimuli. These facts explain why an athlete can perform explosive physical movement in a skilled fashion, and can also delicately remove a speck of dirt from the eye. This complex and subtle interplay is developed through practice.
reflex control of movement
A discussion of coordinated movement must always include a reference to bodily reflexes, and the systems that govern motormovement reflex feedback. These systems obviously play an important role. A reflex is a rapid, involuntary response that results in a specific motor response (Plowman and Smith 1997), with that response being dependent on the type and duration of the stimulus received. Skilled movement depends a great deal upon the body's ability to respond to stimuli with an unconscious, or automatic, movement reaction.
Reflexes can be categorized into autonomic or somatic categories. Autonomic reflexes activate cardiac and smooth muscle and glands, whereas somatic (soma refers to the body) reflexes result in skeletal muscle contraction (Plowman and Smith 1997). Somatic reflexes are, of course, most important to a discussion that focuses on movement.
The spinal cord serves as the crucial link between the brain and peripheral nervous system (nerves that serve the extremities or limbs). The spinal cord is involved in both voluntary and involuntary movements, and besides serving as the information conduit between the brain and peripheral nervous system, it is also the site at which reflex integration occurs (Plowman and Smith 1997). In other words, information moves into and out of the spinal cord via spinal nerves that exit from each side and along the length of the cord. Information must be transmitted via the brain and the spinal nerves, and then must be integrated in a manner that results in useful or necessary movement. Along this information highway, data is carried up and down the spinal cord via a series of tracts, or bundles of fibers, in the central nervous system. Some tracts are responsible for transmitting sensory information (i.e., pressure, temperature, visual, sound, changes in equilibrium), whereas others carry motor, or movement information and regulate a continuum of movement that ranges from delicate or fine movement, to gross physical skills that require explosive and maximal force output.
the role of mechanoreceptors
Mechanoreceptors are specialized sensory cells which process a physical stimulus into a neurologic signal that can be interpreted by the central nervous system (CNS), with the end result being the ability to monitor and control joint position and movement. Mechanoreceptors have critical roles in not only providing feedback about joint position sense, but also in controlling muscle tone and impacting reflex response (Laskowski et al. 1997).
Each of four mechanoreceptor sites – currently thought to be key information receptors and to trigger dynamic joint stability – include cutaneous, joint capsule, muscle and ligamentous receptors. All are thought to contribute to joint position sense, and the muscle receptors which are found in the muscle spindle and Golgi tendon organ are important to both proprioception and motor control of the muscles (Laskowski et al. 1997). Mechanoreceptors can be stimulated by a variety of feedback or stimuli.
proprioception, equilibrium, balance and associated reflexes
Proprioception is a term that refers to the normal, ongoing awareness of body position or joint position sense. Automatic adaptations and responses to stimuli, that impact body position and stateofbalance, are everpresent and ongoing in the body. Sensory feedback, which helps discern how the body or a body part is positioned, is regulated by proprioceptors or sensory organs. All senses are important. A host of sensory receptors that include the eyes, ears and specialized sensory receptors located in muscles, tendons and joints provide a constant barrage of information about body motion, position of body parts and their interaction. This feedback gives the nervous system the information to make physical adjustments, if necessary.
Visual senses give immediate feedback about external stimuli, and are extremely important to skilled performance and balance. Try to stand on the Balance Trainer dome with the eyes closed, and it quickly becomes apparent that visual stimulus is very important to balance. Hearing is important as well. For example, the sound created by solid bat contact with a baseball gives information to fielders about the speed of the ball and even ground reaction conditions can be heard (i.e., wet, spongy playing surface or an athlete's shoe sliding and losing contact with the playing surface), which gives the performer insight and feedback into what adjustments will be necessary as movement is continued. It is easy to conclude that movement is complex and influenced by a number of factors.
the vestibular system
The inner ear is equipped with specialized equilibrium receptors and is called the vestibular apparatus. Turn the head one way, then the other, or tip an ear toward one shoulder to experience how sensory receptors in the inner ear attempt to preserve equilibrium and maintain a steady head position. Fluid filled structures and specially arranged semicircular canals in the vestibular apparatus allow information about head movement, and speed of head movement, to be transmitted to the brain via an inner ear nerve (vestibulochoclear nerve). This information is processed in the brain along with any information being received from the visual receptors and the somatic receptors located in the muscles, tendons and joints (Plowman and Smith 1997).