Viscous Elastic Properties of Superficial Back Muscles in Individuals With Hyperkyphosis

Thoracic hyperkyphosis is a frequently observed spinal deformity characterized by an excessive posterior curvature of the thoracic spine. Increased kyphotic posture is associated with altered biomechanical loading, postural imbalance, reduced functional capacity, and changes in muscle performance. Although previous studies have largely focused on muscle tightness and postural alignment, limited evidence exists regarding the viscoelastic mechanical properties of trunk muscles in individuals with hyperkyphosis. The mechanical behavior of skeletal muscle-including tone, stiffness, elasticity, and relaxation properties-reflects neuromuscular adaptation and tissue integrity. Changes in spinal curvature may lead to asymmetrical loading patterns between the anterior and posterior trunk muscles, potentially resulting in measurable differences in muscle viscoelastic characteristics. Understanding these adaptations may provide insight into rehabilitation strategies targeting both anterior and posterior muscle groups. This comparative study is designed to evaluate and compare the viscoelastic properties of selected trunk muscles in individuals with thoracic hyperkyphosis and healthy controls. Participants are classified into two groups based on thoracic kyphosis angle measurements: individuals with a kyphosis angle of 50 degrees or greater are assigned to the hyperkyphosis group, while those with an angle below 50 degrees form the control group. The thoracic kyphosis angle is assessed using a flexible ruler method. Muscle mechanical properties of the upper trapezius, erector spinae, and pectoralis major muscles are assessed bilaterally using a handheld myotonometer device. Parameters recorded include muscle tone (frequency), stiffness, elasticity, and relaxation time. In addition, participants' perception of spinal appearance is evaluated using a kyphosis-specific spinal appearance questionnaire. The primary objective of the study is to determine whether individuals with hyperkyphosis demonstrate altered or asymmetric viscoelastic muscle properties compared to healthy individuals. A secondary objective is to explore the relationship between kyphosis severity and muscle mechanical characteristics. The results of this study are expected to provide further information regarding muscular adaptations associated with thoracic hyperkyphosis and to support the development of comprehensive rehabilitation approaches targeting anterior chest and posterior trunk musculature.