Proprioceptive sensations are those having to do with the physical state of the body, including position sensations, tendon and muscle sensations, pressure sensations from the bottom of the feet and even the sensation of equilibrium, which is generally considered to be a "special" sensation rather than a somatic sensation. Although not considered proprioceptive organs, the term visual proprioception has been given to the ambient vision function of the eyes. This term was given because the eyes are very valuable for determining one’s position in space relative to other objects.
The brain monitors proprioceptive input from several sources in the body (Table 1). Proprioceptive input is part of a complex system for determining the spatial and temporal relationships of our body and limbs in space. This information allows you to close your eyes and touch your nose every time you try. In fact, if you can’t, you may have a proprioceptive deficit or altered proprioceptive information reaching the brain from either the spine or one or more joints of your arm.
TABLE 1. IMPORTANT PROPRIOCEPTORS OF THE BODY
||Monitor muscle length
|Golgi Tendon Organs
||Monitor muscle tension. Can cause reflex inhibition in a working muscle/tendon unit. On occasion, this can be seen in weight lifters attempting maximum lifts.
||Pressure sensors found in skin and fascia. They are fast adapting receptors that inform the brain of rapid mechanical deformation of their respective tissues.
|Free Nerve Endings (type IV)
* Also called C Fibers
|Unmyelinated fibers carrying pain, itch, temperature, and crud touch sensations.
||Low threshold, slowly adapting static and dynamic mechanoreceptors. Tonic reflexogenic effects on neck, limb, jaw and eye muscles. Postural and kinesthetic sensation. Pain suppression. Facilitate the tonic muscle system.
||Fast adapting, low threshold dynamic mechanoreceptors. Phasic reflexogenic effects on the neck, limb, jaw, and eye muscles as well as pain suppression. Facilitate the phasic muscle system.
||High threshold, very slow adapting receptors. Have the same characteristics as a golgi tendon organ.
||High threshold, nonadapting pain provoking nerve fibers. These fibers have tonic reflexogenic effects on the neck, limb, jaw and eye muscles. They also induce cardiovascular reflexogenic effects. Facilitation can cause guarding in the tonic muscle system.
|Senses motion and speed of movement of the head on all three planes of motion. Highly integrated with the cervical and ocular systems.
IMPROVING THE PROPRIOCEPTOR SYSTEM FOR OPTIMAL FUNCTIONAL OUTCOMES
The proprioceptor system includes many types of receptors, several of which have not been mentioned here to keep the article from becoming impractical. These receptors work as part of a complex neural net (see Figure 1) to constantly inform the brain of the intrinsic environment of the body. Proprioceptive information is integrated with extroceptive information to give the brain a real time image of the body’s current status and to facilitate the appropriate response in all systems of the body.
The concept of a neural net is very important for the rehabilitation or conditioning specialist to grasp because it has a tremendous amount to do with how the brain processes sensory information to create both wanted and unwanted motor actions. For example, it is hypothesized that since muscle spindles are connected to each other via secondary muscle spindle afferents (sensory fibers projecting to gamma motoneurons of other spindles), the fusimotor muscle spindle system may constitute a neural network in which each neuron (i.e., each individual muscle spindle) is influenced by the activity of the entire network.
When teaching a client an exercise, you are informing the brain, through the proprioceptors, about the position, pressure, tension, torsion, compression and motion dynamics of every joint as well as the length, rate of length change and tension of every muscle at any given instant the exercise is performed. Because exercise selection is critical to achieving a functional outcome in any exercise program, careful analysis must be utilized or the neural programming will be of little benefit in the work or sports environment.
From a conditioning perspective, the concept of the neural net makes it clear that isolation of muscles as traditionally performed in bodybuilding will do little to enhance function of the motor system. Therefore, it is no surprise that there are hundreds of studies showing that such exercises as knee extensions, hamstring curls, leg press, biceps curls and the like have almost no significant carryover to functional activities. This is evident in studies showing that isolation exercises, particularly those performed on machines, does little to improve such activities as driving a golf ball further, throwing a baseball or football faster and further or even improving squat performance!
One must also consider that the Type I mechanoreceptors reflexively activate the tonic muscle system, which is primarily responsible for stabilization of joints. Inadequate stimulation of Type I receptors via unnatural stabilization as provided by machines leads to activation of prime mover muscles with inadequate stimulation of the receptors in the joints, supporting muscle actions throughout the motor system. Considering the tonic system is primarily responsible for postural stabilization, it becomes evident why many bodybuilders have very large muscles yet frequently demonstrate decreased motor skills and poor posture.
Another important consideration is that when the tonic muscle is primarily responsible for stabilization of joints. The spindle cell population of tonic muscles is higher than that of phasic muscles. Additionally, the more proximal the joint to the core, the greater the spindle cell population. Therefore, if large phasic muscles are exercised without concomitant activation of the tonic system, there is an ever-increasing chance that the working joint(s) will lose instantaneous axis of rotation. Loss of instantaneous axis of rotation always results in progressive derangement and/or destruction of joints.
To take advantage of this useful information, I suggest the following:
- Consider that you are programming the motor system when exercising any client. Always focus your attention toward selecting exercises that activate the tonic and phasic systems of the body in proportion to each other. Isolation exercises require less neurological demand and less skill. Therefore, it is critical that isolation exercises always follow those exercises that require greater demand of the neuromuscular system.
- Improving posture. Poor posture is commonly associated with ergonomic stress, aberrant adaptation to an exercise program (frequently sport specific in nature) and often injury. The exercise professional must always teach exercise with full comprehension of posture and integration of sound orthopedic principles. For example, forward protrusion of the head during a triceps press down or poor back position during a lunge or squat exercise leads the brain to believe that is "normal" for the exercise. The net result is degradation of soft tissues and faulty motor programming.
- Improving balance and coordination. Almost all activities performed in the work or sports environment require that the body perform in a three dimensionally unstable environment. Most sports require the application of force at high speeds and frequently from one leg and/or arm. The potential balance and coordination capabilities of any individual will be the sum of integration between tonic and phasic muscle systems or of the arthrokinematic and osteokinematic systems of the body. Put simply, to improve balance and coordination, we must put our clients in exercise situations that challenge those biomotor abilities!
- Preventing injury. Most athletes and clients in general don’t get the opportunity to learn how to exercise correctly until they have been injured. This is unfortunate, as we all know the body seldom returns to pre-injury levels after any significant injury, such as a torn ACL or a deranged lumbar disc.
Through the utilization of exercises that challenge the core and extremity stabilizers independently, and in concert with the phasic musculature, we can both improve the working foundation and power output. With the use of Swiss balls, the Fitter, balance boards and the balance beam, we can develop righting and tilting responses (see Figure 2).
Figure 2A - Side flexion over a Swiss Ball trains the righting response
Figure 2B - Kneeling on a Swiss Ball activates tilting reflexes
As the body becomes more proficient at utilizing a progressively reduced base of support, a neurological reserve is built and the motor vocabulary is expanded. Any athletic or work situation represents a task for the motor system. Solving the task efficiently is dependent on the ability and speed at which the motor system can produce appropriate responses. Such development cannot take place through traditional machine based or body building type exercise programs.
The human body is beautifully designed with efficient and highly effective extroceptors and proprioceptors. To enhance work and sport performance, our exercise programs must be methodically designed. For best results, we must support the neuromechanical system, providing an exercise environment that programs the body with sound postural and motor engrams. Exercise machines should never be used as a primary conditioning modality, instead being used to add volume after developing nervous system fatigue through functional compound exercises. By developing our ability to stabilize joints quickly, and by exposing our clients to a variety of exercise stimuli, we will serve to improve performance and reduce injury for the long term.
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- Chek, P. Scientific Back Training
- Guyton, A. C., Textbook of Medical Physiology, WB Saunders, 1986.
- Juhan, D. Job’s Body, Station Hill Press, 1987
- Rivard, J. and Grimsby, O., Joint Mechanoreceptor Update, Scientific Physical Therapy, Vol. 8 No. 4, 1998
- Schmidt, R. Motor Learning and Performance