Lumbar Spine Rehabilitation
Spinal rehabilitation is the discipline of medicine that guides the physical, psychological, and social recovery of individuals who have become partially or totally disabled because of spinal disease or injury. Because the muscles and joints of the spine are not easily observed, the need for rehabilitation from spinal disorders has been recognized slowly and rehabilitation gains have been more difficult to measure by objective standards.1 Manual or manipulative therapy may be effective for the treatment of pain and restoration of movement in the short term, but it has not been shown to be effective in the long term.2-5 On the other hand, core strengthening programs may improve function and decrease pain, but the effectiveness in the long term management of lower back pain has been hotly debated.6-9 Despite this, strengthening programs continue to be recommended.9-11
With persistent reported findings, strengthening programs will still continue to be recommended.9-11 With the consideration that some strengthening programs have been reported to be beneficial, it should be noted that outcome measures often have to do with return to work and not whether the client’s pain quality has improved. Strengthening programs are often included in “functional programs” combined with behavioral models, or so ill-defined that positive effects cannot be separated from the strengthening exercise components.12 There is rarely any follow up monitoring to see if any benefits are maintained or if the person has subsequent changes in work status. We also note that there may be significant improvements in symptoms or a variable return to work regardless whether any interventions are given or not.13,14 Regardless of this, it does seem logical that the neuromuscular system can be rehabilitated when there is a musculoskeletal injury or neuromuscular dysfunction.
Muscle Physiological Contributions
Muscles are composed of many minute fibers organized into motor units. A motor unit is composed of the motor neuron and muscle fiber that it innervates. Human muscles are composed of predominantly two muscle fiber types: slow (tonic/aerobic, Type I) or fast (phasic/ anaerobic, Type II). Skeletal muscles vary in metabolic characteristics and between individuals, which appears to be due to variable genetic differences. Therefore, the maximal contraction speed, strength, and fatigability of each muscle depends predominantly on the individual proportion of these fiber types, and how they are reinforced to increase their proportions to fit each individual person’s needs.15 The key characteristics of these motor units are as follows: slow motor units (slow speed of contraction, aerobic/oxidative metabolism, low contraction force, and fatigue-resistant) and fast motor units (fast speed of contraction, anaerobic/glycolytic metabolism, high contraction force, and fatique-nonresistant). Due to these individual characteristics, the recruitment of slow motor fibers would optimize postural holding or antigravity function and the recruitment of fast motor fibers would be optimal for the production of high force or when rapid movements are required.16
The definition of strength is the maximum force or tension generated by a muscle, and that the force generated is considered during specific movements.17,18 Muscle hypertrophy is a local adaptation to the demands placed on the muscles and is the result of overload training.15 Various factors are involved in muscle hypertrophy. Myofibrils thicken and increase in number. Additional sarcomeres are created by accelerated protein synthesis and corresponding decreases in protein breakdown, with proliferation of connective tissue cells and small satellite cells. This proliferation thickens and strengthens the muscle’s connective tissue structure and improves the structural and functional integrity of both tendons and ligaments. These in turn may provide some protection from joint and muscle injury and therefore provides justification for using resistance exercise in prevention and rehabilitation programs.17
Spinal Stability Dysfunction
While there is no current measure of spinal instability nor a gold standard definition, Panjabi has introduced a model for spinal instability which has gained widespread popular acceptance.19-22 The model is based on the concept that the majority of lower back pain is caused by mechanical derangement of the spine (i.e., clinical spinal instability).23 He further categorized the stability of the spine to be dependent on three subsystems: passive (spinal column), active (spinal muscles), and control (neural influence). Panjabi stated that the three subsystems were interdependent and were capable of compensating for each other’s limitations.19,20 Therefore, lower back pain may occur as a consequence of these deficits in the control of the spinal segment when stresses on the spine cause excessive compression or stretch on neural structures or abnormal deformation of ligaments and pain sensitive structures. In turn, these deficits may potentially be caused by a dysfunction in any of the subsystems that cannot be compensated by the other subsystems. Further, clinical instability is a significant decrease in the capacity of the stabilizing system of the spine to maintain the intervertebral neutral zones within physiological limits so that there is no major deformity, no neurological dysfunction, or no incapacitating pain.
The link between muscle function, spinal stiffness, and a neutral zone of displacement provides the basis of the possible conservative management, through therapeutic exercise, of low back pain or spinal instability. By increasing the strength in the muscles that function to stabilize or mobilize the spinal column they will in turn maintain a neutral spine throughout work and leisure activities, as well as post-surgically. When considering dynamic stabilization, it is useful to consider the classification of muscles in relation to function. Stabilizer muscles are described as primarily monoarticular or segmental, deep, working to control movement, and having static holding capacities. Mobility muscles are described as biarticular or multisegmental, superficial, working concentrically with acceleration of movement and producing power. Based on this concept, the new model of functional muscle classification has been proposed.16,24,25 This model includes local stability muscles, global stability muscles, and mobility muscles. These three groups of muscles that provide spinal stabilization are further categorized as Local Stability Muscles, Global Stability Muscles, and Global Mobilizer Muscles1,26 (see Table 1).