Tissue Adaptation and Remodeling
The presence of physical stress causes adaptive responses in all tissues of the human body including the spine. Physical stress is defined as the force applied to a given area of biological tissue. The level of stress required to initiate an adaptive response varies between each tissue. The fundamental principles of tissue adaptation to physical stress can be used to help guide multidisciplinary spinecare, physical rehabilitation and the development of exercise programs.
Chiropractic physicians and physical therapists have particular expertise in the application of non-operative therapeutic approaches which promote favorable tissue adaptation and remodeling. This includes exercise, activity modification, postural therapy, modalities, braces and the use of orthotic devices. There are numerous physiological and biochemical factors which influence a tissues response to physical stress, but these are not always easy to modify. Certain medications can influence the ability of tissues to favorably adapt to physical stress. For example, corticosteroids can cause a reduction of inflammation in one tissue and cause atrophy in other tissues such as skin, bone, and muscle.
Age is another important variable which can influence a tissues ability to adapt and remodel to physical stressors. In general aging has a negative effect on tissue adaptation. The true effect is not entirely obvious for some of the apparently negative effects felt to be secondary to aging may actually be due to an age-related reduction in physical activity.
A mild to moderate degree of physical stress can have a very positive effect on adaptation within the musculoskeletal system. A high level of physical stress can cause injury to supportive tissues. The magnitude as well as the duration of physical loads and strain both play a role 9in adaptation and injury. Musculoskeletal tissues such as cartilage, bone, ligaments, muscles and tendons exposed to levels of physical stress that are higher than normal respond by adapting and remodeling in a manner that makes them stronger and more resistant to injury. For tissue to respond favorably the recovery period has to be adequlety. If the recovery periods are to short the tissue cannot repair itself and it remain in a vulnerable state susceptible to be injured if the loads placed upon them become to high.
Controlled and gradual use of resistive exercise can be used to make muscles stronger and more capable of performing work. This approach causes muscle fibers to enlarge or hypertrophy. Higher-than-normal physical loads placed on bone will stimulate the remodeling process in bone. There are specialized cells in bone called osteoblasts which lay down for more bone under the adequate stimulus. This process is described well by Wolff Law which states that with the proper level of stress the supportive pillars in bone called trabeculae will increase in number, become thicker and stronger. The structural changes occur along the orientation of the physical stress which is placed upon the bone. This is also true of other musculoskeletal tissues. The tissue adaptation and remodeling process will correspond with the orientation of the higher than normal stress. Tendons and ligaments respond to exercise-induced stress with increases in their cross-sectional area, stiffness, and ability to withstand tensile loads.
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