Investigation of Effects of Physioherapy Interventions on Mechanical Properties of Muscle in Head and Neck Cancer

As the HNC survival rate has increased and therefore, the focus of post-treatments is to improve the quality of patients' life by decreasing the side effects. Treatment of HNC leads to acute and chronic soft tissue damage, and functional loss. However, patients with HNC need having rehabilitation throughout the post-treatment phase so as to improve functional outcomes because of the long term side effects. Chronic shoulder morbidity (70% of patients) is one of the common complications after surgery, whereas 84% of survivors complain of their physical appearance due to the remaining head and neck lymphedema (HNL) after radiotherapy. Moreover, pain, dysphonia, and musculoskeletal impairments are observed in the individuals after the treatments and the patients also have trouble swallowing problems, loss of taste, dry mouth, trismus, nausea, vomiting, and fatigue during and after therapy.

Materials might behave in different stress-strain relationships, and it is represented by a stress-strain curve, a basic descriptor of material.Thanks to the stress-strain diagram, differences between materials can be determined such as stiffness, hardness and toughness. Several concepts describe material properties in addition to a stress-strain diagram. For instance, a homogeneous material is one whose properties are not affected by location within the material, anisotropic material is one whose properties are free of direction, and incompressible material retains its volume during deformation. However, the behaviour of soft tissue is anisotropic due to its fibre contents, its constitutive behaviour is nonlinear and incompressible, and it is heterogeneous material owing to its composition, but it can be homogenized under macroscopic analysis. Due to the complexity of soft tissue, its mechanical behaviour is highly affected by density, collagen and elastin's structural arrangement, topographical site, function, and hydrated matrix of proteoglycans. In other words, mechanical properties of soft tissues are related to shape, genetics, age , physical and chemical environmental conditions like strain rate, osmotic pressure and Ph, temperature, which affects skeletal muscle's contractile properties.

It is known that deformable-body changes shape when it is exposed to an external force. In general, several constitutive relations govern the stress and strain relations, for example, plasticity, viscoelasticity, linear elastic, hyperelasticity so on. It is common to use hyperelastic models (i.e. time-independent) so as to determine the association of the stress-strain of soft tissue, even though the biological soft tissues mechanical behaviour is time-dependent . These models are based on the strain energy density which is the energy stored by a system undergoing deformation.

Disuse and immobilization influence muscle fibres harmfully including decreased muscle strength and neural activation of muscle fibre, muscle atrophy, loss of force production and endurance due to decrease in cross-sectional area (CSA). Jones et al., found that immobilization leads to muscle atrophy by decreasing protein synthesis and increasing protein impairment and loss of muscle mass after two weeks of immobilization. Muscle atrophy can exist in the following injury, during an illness such as cancer, sepsis and long term hospitalization. Shortening of myosin and actin filaments alters mechanical properties of muscle because of length-dependent force production. Moreover, the energy production of skeletal muscles is affected during the disuse period by decreasing fat oxidation and enhancing glycolysis, which is a source of muscle energy. Furthermore, muscle composition is impacted due to disuse and inactivity, mainly in type 1 fibre, which maintains postural control. Since radiotherapy and surgery impact negatively on muscle. For instance, after neck dissection, trapezius muscle atrophy seems to be due to SAN injury. It is found that atrophied trapezius muscle's stiffness was significantly lower because of physiological and intrinsic alterations associated with fatty infiltration and atrophy of muscle It is known that physical training affects muscle architecture, such as fibre type distribution, fascicle length, pennation angle and CSA, and force production. Since physical activity contributes to improving the CSA of skeletal muscle, muscle strength and bulk are increased. Moreover, exercise contributes to increased neural activity, contractile tissue and differentiating fibre type. Muscle mechanical properties may change.

Myofascial techniques are one of the manual therapy interventions which focus on treating fascia. It comprises various techniques and interventions such as acupuncture, dry needling, wet needling with pharmaceuticals, and traditional technical approaches such as strain-counter strain, muscle energy technique, positional release, ischemic compression and myofascial release (MFRT). The effectiveness of MFRT has been shown in various trials in different fields. For instance, MFRTs improve outcomes in individuals having shoulder pain, ankle joint restriction, fibromyalgia and lateral epicondylitis. On the other hand, in the cancer field, since MFRTs perform in addition to a standard rehabilitation program, the effect mechanism of MFRT is unclear in cancer . However, it impacts positively on pain, emotions and cancer-related fatigue.