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J. Morris The Effects of Immobilization on the Musculoskeletal System, International Journal of Therapy and Rehabilitation, Vol 6. Iss. 8, Aug 1999, pp 390 – 393:
Immobilization, both general and regional, has marked adverse effects on all systems of the body and, in some people, can prove to be life threatening. The resulting deterioration occurs within days, but takes many months to reverse.
R. Gotlin, Sports Injuries Guidebook: Understanding Functional Conditioning
Simply put, function is the outcome of any activity. Everyday functional movements include running, biking, throwing, walking, carrying a child, tying shoelaces, getting out of bed, and even switching from sitting to a standing position. Thus the benefits of functional conditioning are not limited to athletics. Its movements occur in some form in work, home, and sport environments. To perform these tasks, a chain reaction involving muscles, nerves, and joints occurs. If this chain is interrupted because of inadequate flexibility or lack of strength in part of the chain, a breakdown results, leading to a decrease in performance and to possible injury.
Exercises to help condition the body for functional improvements must meet all four of these criteria:
1. They must include movements in all three planes (sagittal, frontal, and transverse).
2. They must properly condition the body’s nerves and muscles to develop memory and help make movements “automatic.”
3. They must condition for responding to external forces, allowing the body to make best use of outside influences such as gravity, ground reaction forces, and momentum.
4. They must condition biomotor abilities (flexibility, strength, power, endurance, agility or coordination.
A quick look at these four criteria confirms that functional conditioning works beyond the realm of physical fitness and benefits the body during the activities that most people, athletes and non-athletes alike, do every day.
Conditioning the Neuromuscular System
Functional conditioning requires training of the nervous system. For example, when bending down to pick up an object off the ground, you are unaware of the intricate coordination it takes for your body to execute this movement. The actions involved in the flexion and rotation of your spine, hips, knees, and ankles are not premeditated. The nervous system plays an integral role in this process. The body’s nerves send messages to the muscles, which direct the timing, means, and speed of movement. To clarify how this occurs, let's take a closer look at the neurological mechanisms of the nervous system that are used during movement and their relation to functional conditioning and injury prevention.
The brain learns movement by developing motor programs. According to Physical Therapist, Gray Cook, motor programs are ways that the brain stores information about movement. Every time someone learns how to shoot a basketball or ride a bike, the brain creates a motor program that allows the athlete to repeat this activity without relearning the mechanics each time. (Cook 2003) This is the nervous system’s method for running efficiently. Conditioning the neural network through repeated functional movements improves the way the body develops motor programs and helps the neuromuscular system operate to its highest potential .
Conditioning the nervous system through repetitive functional movements improves the proprioceptive feedback to the muscles in the body. Proprioceptors are sensory receptors located within the joints, muscles, and tendons. They receive input about the physical state of the body, constantly informing the central nervous system about muscle tone and the coordination of certain movements. Likewise, the way the body senses both touch and movement is referred to as proprioception, which means “sense of self.”
It is through proprioception that the body communicates with itself at a subconscious level. For example, you do not have to think about maintaining a particular posture or how to position your various body parts during a familiar movement. Your proprioceptors govern the spatial and temporal relations of your body and limbs in space, freeing your conscious mind to focus on other matters.
With conditioned proprioceptors, an athlete is in a better position to react, as joints and muscles respond automatically to protect the body from injury and other physical problems. (Cook 2003) For example, someone with a highly conditioned proprioception can slip on ice and land on the ground without turning an ankle. Essentially, to improve the nervous system’s response to movement, it is necessary to implement a conditioning program.
K. Pearson, J. Gordon, Introduction to Sensory Motor Systems, University of Texas: Reflexes
DURING NORMAL MOVEMENTS the central nervous system uses information from a vast array of sensory receptors to ensure the generation of correct pattern of muscle activity. Sensory information from muscles, joints, and skin, for example, is essential for regulating movement. Without this somatosensory input, gross movements tend to be imprecise, while tasks requiring fine coordination are impossible.
Reflexes have been viewed as stereotyped movements in response to the stimulation of peripheral receptors. This view arose primarily from early studies on reduced animal preparations in which reflexes were examined under a set of standard conditions. However, as investigators extended their studies to measure reflexes during normal behavior, our concept of reflexes changed substantially. We now know that under normal circumstances reflexes can be modified to adapt to a task.
Three important principles are involved in the adaptation process. First, transmission in reflex pathways is set according to motor task. The state of the reflex pathways for any task is referred to as functional set.
Second, sensory input from a localized source generally produces reflex responses in many muscles, some of which may be distant from the stimulus. These multiple responses are coordinated to achieve an intended goal. Third, supraspinal centers play an important role in modulating and adapting spinal reflexes, even to the extent of reversing movements when appropriate.
Proprioceptive Reflexes Play an Important Role in Regulation of Both Voluntary and Automatic Movements
All movements activate receptors in the muscles, joints, and skin. These sensory signals generated by the body’s own movements were referred to as proprioceptive by Sherrington, who proposed that they control important aspects of normal movements. A good example is the Hering-Breuer reflex, which regulated the amplitude of inspiration. Stretch receptors in the lungs are activated during inspiration, and the Hering-Breuer reflex eventually triggers the transition from inspiration to expiration when the lungs are expanded. A similar situation exists in the walking systems of many animals; sensory signals generated near the end of the stance phase initiate the onset of the swing phase.
The primary function of proprioceptive reflexes in regulating voluntary movement is to adjust motor output according to the biomechanical state of the body and limbs. This ensures a coordinated pattern of motor activity during an evolving movement, and it provides a mechanism for compensating for the intrinsic variability of motor output.
An Overall View
Reflexes are coordinated involuntary motor responses initiated by a stimulus applied to peripheral receptors. Some reflexes initiate movements to avoid potentially hazardous situations, whereas others automatically adapt motor patterns to maintain, or achieve, a behavioral goal. The purposeful responses evoked by reflexes depend on mechanisms that set the strength and pattern of responses according to the task and behavioral state (known as functional set).
Many groups of interneurons in the reflex pathways of the spinal cord are also involved in producing complex movements such as walking and transmitting voluntary commands from the brain. In addition, some components of the reflex responses, particularly components of reflexes involving the limbs, are mediated via supraspinal (brain stem nuclei, cerebellum, and motor cortex). The convergence of afferent signals onto spinal supraspinal interneuronal systems involved in initiating movements provides the basis for the smooth integration of reflexes into centrally generated motor commands.
D. Berger, K.Kain, Orienting and Defensive Responses: A Motor Development Perspective:
Motor reflexes, which provide for optimal self-protective responses, may be disrupted as a result of trauma, but may also be disturbed in the course of otherwise normal motor development. These developmental disturbances may then be intertwined with disruptions caused by traumatic incidents. Proper functioning of the sensory systems is another critical element in the overall mechanism of self protection. As with motor reflexes, sensory systems may be disrupted due to trauma, or via disturbances in the original development process for these systems.
Orienting and defensive responses cannot be completely separated (e.g., orienting is a primary part of our capacity to defend). Likewise, the sensory and motor functions which are critical for self-protection often serve to support both orienting and defense.
In order for the threat response cycle to function properly, the sensory systems and motor functions that contribute to the ability to orient and defend must be integrated, functional, and available. Interruption of the normal development of the sensory systems or early protective reflexes may leave the person with an impaired capacity for defensive movements that predates the current traumatic event. Fortunately, the techniques for restoration of developmental reflexes parallel those for restoration of orienting and defensive responses. The essential repair process for each is similar: gently increase the demand for the missing reflexes until the body brings the appropriate movements into play.
The body systems related to orienting and defense must have the appropriate level of function available in order to meet the challenges to those systems. If there has been serious physical damage to any of the systems or orienting and defense, there may be a limit to how fully the orienting and defensive responses can return to full function.
Finally, the person must have an appropriate level of self-regulation in the autonomic nervous system (“ANS”) to accomplish the work of orienting and defensive response repair. It is the nature of orienting and defending that the triggering of these body responses happens when there is an experience of threat, or potential threat. By extension, these will be more activation of the sympathetic system when the perceived need for orienting and defense arises. If the person has limited self-regulatory capacity in ANS function, the increase activation associated with perceived threat will sometimes overwhelm rather than encourage orienting and defense responses. Ironically, when orienting and defense are perceived as being successful, it invariably leads to a calming of the sympathetic activation.
Proprioceptors are nerve endings that give information about where different parts of the body are in relation to each other and how fast they are moving. The proprioceptive system supports three main functions: muscle tone, body image, and control of effort. These functions provide the foundation for learning motor patterns which become the skilled movements we call coordination.
Physical repair of orienting systems is a common focus in body therapy modalities. It is standard practice, for example, to do proprioceptive repair and re-training in a classical physical therapy treatment, using hands-on techniques, balance boards, and movement exercise.
Impairment of Orienting and Defensive Responses
Our capacity to gather information about our surroundings, to correctly process that information, and to respond appropriately depends upon proper functioning of all of the orienting systems. If one of our “paying attention” systems is deficient, we will likely be predisposed to poor assessment and response to potential threat. In addition, lack of healthy ANS self-regulation and poor protective reflex development often means that our ability to choose appropriate defensive strategies is impaired. This combination of insufficient orienting and poor defensive response almost guarantees greater likelihood of injury. The irony is that traumatic injury often further impairs the orienting and defensive systems. It is common in both Failure of Physical Defense and Physical Injury categories to trauma to see this cycle of disruption of orienting and defensive responses, followed by further injury, repeated again and again. After each cycle, the capacity to orient and defend is more limited. When proper orienting and defensive responses are restored, this cycle is interrupted and the person is able to meet future physical challenges appropriately and successfully.
Assessment, Restoration and Repair
Assessing the possible impairment of orienting and defensive responses is, in effect, the assessment of the different “paying attention” systems, in combination with the protective reflexes and responses. The restoration and repair process for these functions seems almost impossibly simple: demand that they function to do their job. Finding ways to demand the orienting responses, motor reflexes and responses to function is sometimes time-consuming and requires creativity in order to be specific enough about which reflex and which response is damaged––and which we are asking to function. The repair of these functions is a vast field of study in itself and is well beyond the scope of this paper.
: serving to protect the body or one of its parts from disease or injury <a protective reflex>.
A reflex is an inborn, involuntary, or automatic action that the body takes in response to something without conscious thought. There are many types of reflexes and every healthy person has them.
Reflexes protect the body from things that can harm it. For example, if your hand contacts a hot stove, a reflex causes it to immediately withdraw before a "Hey, this is hot!" message even makes it to your brain.
Similarly, when you trip and fall, a reflex causes your hands extend outward in an effort to cushion your impact with the ground. All protective reflexes involve the body’s proprioceptive reflex mechanisms.
Wolff’s Law of Bone Transformation:
Wolff's law states that bone in a healthy person or animal will adapt to the loads under which it is placed. If loading on a particular bone increases, the bone will remodel itself over time to become stronger to resist that sort of loading. The internal architecture of the trabeculae undergoes adaptive changes, followed by secondary changes to the external cortical portion of the bone, perhaps becoming thicker as a result. The inverse is true as well: if the loading on a bone decreases, the bone will become weaker due to turnover, it is less metabolically costly to maintain and there is no stimulus for continued remodeling that is required to maintain bone mass. Julius Wolff (1836–1902)
The Mechanostat Model
The Mechanostat is a model describing bone growth and bone loss. It was promoted by Harold Frost and described extensively in the Utah Paradigm of Skeletal Physiology in the 1960s. The Mechanostat is a refinement of Wolff's law described by Julius Wolff (1836–1902).
According to the Mechanostat bone growth and bone loss is stimulated by the local mechanical elastic deformation of bone. The reason for the elastic deformation of bone is the peak forces caused by muscles (e.g. measurable using mechanography). The Adaptation (feed-back control loop) of bone according to the maximum forces is considered to be a lifelong process. Hence bone adapts its mechanical properties according to the needed mechanical function – bone mass, bone geometry and hence bone strength (see also Stress-strain index, SSI) is adapted according to the every-day usage / needs.
Due to this control loop there is a linear relationship in the healthy body between muscle cross sectional area (as a surrogate for typical maximum forces the muscle is able to produce under physiological conditions) and the bone cross sectional area (as a surrogate for bone strength). These relations are of immense importance especially for bone loss situations like in osteoporosis, since an adapted training utilizing the needed maximum forces on the bone can be used to stimulate bone growth and hence prevent or help to minimize bone loss. An example for such an efficient training is vibration training or whole body vibration.
Davis' Law is used in anatomy to describe how soft tissue models along imposed demands. It is the corollary to Wolff's law. It is used in part to describe muscle-length relationships and to predict rehabilitation and postural distortion treatments as far as muscle length is concerned.
This is not necessarily describing myohypertrophy (muscle growth)—the shortening of muscle in response to resistance—but it explains also how a muscle will lengthen in response to stretching. Because most major muscles have an opposite, the protagonistic and antagonistic muscles (and their related synergistic and groups of muscles) will end up reciprocating each other's length. A strong and inflexible gastrosoleus complex (calf) will therefore result in a weak and flexible tibialis anterior (shin muscle).
The origin of the name Davis' law is unclear, but it may be a reference to Nathan Smith Davis, the first editor of the Journal of the American Medical Association.
Tendons are soft tissue structures that respond to changes in mechanical loading. Bulk mechanical properties, such as modulus, failure strain, and ultimate tensile strength, decrease over long periods of disuse as a result of micro-structural changes on the collagen fiber level. In micro-gravity simulations, human test subjects can experience gastrocnemious tendon strength loss of up to 58% over a 90-day period. Test subjects who were allowed to engage in resistance training displayed a smaller magnitude of tendon strength loss in the same micro-gravity environment, but modulus strength decrease was still significant.
Conversely, tendons that have lost their original strength due to extended periods of inactivity can regain most of their mechanical properties through gradual re-loading of the tendon, due to the tendon's response to mechanical loading. Biological signaling events initiate re-growth at the site, while mechanical stimuli further promote rebuilding. This 6-8 week process results in an increase of the tendon's mechanical properties until it recovers its original strength. However, excessive loading during the recovery process may lead to material failure, i.e. partial tears or complete rupture. Additionally, studies show that tendons have a maximum modulus of approximately 800 MPa; thus, any additional loading will not result in a significant increase in modulus strength. These results may change current physical therapy practices, since aggressive training of the tendon does not strengthen the structure beyond its baseline mechanical properties; therefore, patients are still as susceptible to tendon overuse and injuries.
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