Proporioceptive sense, and consequently balance, is available largely because of muscle spindles and other sensory organs or proprioceptive receptors. Sensory organs relay information via the central nervous system, and provide a sense of body or limb position in space. This is also referred to as kinesthetic awareness. Sensory organs, located in muscles, tendons or joints, for example, allow a person to predict the degree of elbow flexion or extension even if the individual does not have the advantage of visual feedback. Therefore, balance training should include drills that both allow and discourage the use of sight, as this will challenge the somatic receptors of the body in different ways, which will challenge the body as whole, in a different manner.
The muscle spindle plays an important role in daily posture and has important implications for balance needs in general, for all movement. Muscle spindles are located in skeletal muscles, and lie parallel to and are imbedded in muscle fibers or muscle cells (Plowman and Smith 1997, pg. 491). They are sensitive to the resting length of the muscle, changes in the length of the muscle and the speed at which lengthening occurs, and thus are stimulated by stretch. Information from the spindle is sent directly to the central nervous system via a reflex arc. This sensory feedback loop (the reflex arc) is made up of a sensory receptor (the muscle spindle and afferent neuron) and spinal nerve (efferent neuron). This reflex arc allows a person to regularly adjust body position based on immediate physical demands, as presented by current stimuli, and to do so with little thought. Muscle spindles help the body maintain tone, posture, alignment and balance.
Additionally, when muscle spindles are activated because of changes in the length of the muscle (i.e. when attempting to maintain balance on an unstable surface), associated muscles will alternately contract and relax as a result of muscle spindle activation. This reaction, in turn, directly affects body position, balance and center of gravity. Muscle spindles are involved in both sensory and motor functions. Challenging this automatic “correction factor” through functional balance practice and participation in a specific sport or activity, lays critical groundwork that leads to efficient, functional movement.
In summary, the muscle spindle is an important sensory feedback mechanism of the body. Not only does the spindle normally emit lowlevel sensory nerve signals that assist in maintaining muscle tone and affect constant postural adjustments throughout the day, feedback from the spindle also helps the muscles and body adjust movement requirements based on load or degree of effort required. Spindles influence skilled movement capabilities because of the spindle's dampening affect on skeletal muscles' agonist/antagonist relationship, which contributes to “smooth” movement (Plowman and Smith 1997).
golgi tendon organ
The golgi tendon organ (GTO) represents the last key sensory organ that impacts somatic reflexes. The GTOs are located within the tendonous attachment area of muscles and are stimulated by stretch or muscle contraction. GTOs transmit information about muscle tension, and if activated, cause associated muscle(s) to relax. This reflex inhibition of the muscle is called the inverse myotatic response.
This reflex action that results in a relaxed muscle is important to movement for several reasons. First, this reflex inhibition can be called into play when the GTOs “sense” that excessive tension in the muscle could cause the tendonous attachment(s) of the muscle to tear away, or rupture, from its bony attachment point. GTOs are responsible for a “muscle giving out” when under too much duress. Finally, sensory information gathered by the GTOs about tension development in the muscle allows for adjustments during movement that require only the needed tension, or force development, to successfully begin and finish movements with smooth transitions (Plowman and Smith 1997).
automatic integration of sensory systems
Many of the responses made by the body to balance challenges (external stimulus, visual affect, points of contact and movement) are referred to as automatic postural reactions. These responses occur before voluntary movement and after reflexes, yet have commonalities with both (Anderson, et al. 2005).
Just as highlevel sport performance represents a picture of extraordinary neuromuscular accomplishment, at even its simplest level, so does balance training and its maintenance. The key difference in perspective is that balance training is accessible to all, easy to do, fun and selfgratifying! Yet any skill level, as it relates to movement, is dependent on the intricate and precise participation of the central nervous system as it acts upon muscles, after receiving information. It is only through a complex, automatic integration of several sensory systems of the body, that one can accurately position the body, perceive where and how the body is positioned in space, and easily adjust how much force is developed in the muscles to maintain precise performance boundaries, assure safe execution of the movement and maintain or recover alignment and center of gravity without a second thought.
The neuromuscular system's motor output – maintenance or recovery of body equilibrium – is directly influenced by the somatosensory, visual and vestibular systems. Training the various nervous and sensory receptor systems of the body with functional, balance and sport/activity specific training can lead to more efficient, accurate and highly skilled movement patterns. Skilled movement is more energy efficient, safer and it feels better. Moving gracefully and performing better are just two reasons why functional training is important to all who want to move efficiently and with purpose.
The importance of a broad-ranged plan of attack that includes functional, traditional and specific exercise/practice is apparent. A complete approach should:
1. Teach the nervous system how to regulate muscular force production.
2. Improve proprioception or awareness of the body's position, or any of its parts, and how they are positioned.
3. Develop more skillful and energy efficient movement patterns.
4. Train flexibility, cardiorespiratory endurance, stabilizing strength, muscular strength and endurance – and
develop power, which combines an element of strength with speed of movement.
Functional training incorporates the concepts of balance/stability training and closed chain exercise (CCE) by
requiring the body's natural motor reflexes to react as an integrated unit. In other words, the whole body is challenged
to participate in order to maintain correct posture and balance while moving. The inclusion of activities that involve the
entire body in a dynamic and coordinated fashion represents the development of functional fitness. This type of fitness is
easily transferred to daily tasks, recreation and sport. Stabilization and functional training can both be integrated
into closed chain and open chain exercise. But, remember that functional training ultimately trains movement, not just
stabilizing contractions that contribute to effective movement. Stability and balance training represent two aspects of
training that fit under the “functional training umbrella.”