Musculoskeletal Theory Of The Physical Stress Theory

Muscle activity, including generating force and moving limbs through lengthening and shortening, is an important influence on beneficial tissue stress. Muscles adapt quickly to periods of lower or higher stress and demonstrate obvious visual and functional changes. At a tissue level, the Physical Stress Theory (PST) states that muscle adaptations are consistent with other high and low strain tissue adaptation models. Low stress/activity associated with immobilization results in decreases in contractile protein, fiber diameter, peak tension and power. Evidence supports the idea that tissues within the musculoskeletal system atrophy and become less tolerant of physical stress if stress on the tissue diminishes below a baseline level.3 In addition,

Although joint movement is a very important source of physical stress on connective tissues, isometric muscle contractions can assist with applying therapeutic levels of stress to immobilized structures. Muscle tissue benefits from the force generated by an isometric contraction and may reduce the loss of proteins and muscle fiber diameter, and help maintain tension and power of fibers during immobilization. Isometric contractions across the wrist will help minimize the effects of immobilization. As noted in earlier sections, this can be achieved with making a fist, and with other gripping activities with objects of various size and density. Active muscle contractions are encouraged throughout the 6 week period of immobilization. Active range of motion and resistive exercises of the non-immobilized joints of the upper extremity will also be of great benefit. Use of resistance bands are a convenient way to progress resistance of upper extremity exercises while the arm is still in a cast. Pain from the bone fracture will be the likely guide in the progression of these exercises during the 6 weeks of

Controlled increases in physical stress through progressive resistive exercise cause muscle fibers to hypertrophy and become capable of generating greater force.3 Early emphasis is on restoring joint range of motion and muscle flexibility, however, resistive exercises are not delayed. The initial emphasis of muscle loading should be on endurance, accomplished with lower loads and higher repetitions. Progressive resistive exercises are initiated at the available range and progressed to new positions as wrist range of motion returns in all planes. Both the overload principle and the SAID Principle (Specific Adaptation to Imposed Demands) are important considerations in therapeutic exercise dosing.1,3,11 Within pain tolerance, dosing progressive resistive exercises that maintain a therapeutic stress level will encourage muscle tissue hypertrophy. Finding activities that produce the correct force and repetition, without injury, is the goal of the remobilization period. Starting with low force, moderate to high repetitions, and encouraging therapeutic rest following induced stress is important to both the overload principle and the SAID Principle. Additionally, it is important to prevent dosing resistive exercises that exceed optimal stress, which may result in injury. The patient’s response to therapeutic exercise should be assessed during, immediately following,