Trapezius muscle activity in using ordinary and economically designed dentistry chairs

Most dentists complain of musculoskeletal disorders which can be caused by prolonged static posture, lack of suitable rest and other physical and psychological problems, We evaluated a chair with a new ergonomic design which incorporated forward leaning chest and arm supports. The chair was evaluated in the laboratory during task simulation and EMG analysis on 12 students and subjectively assessed by 30 professional dentists using an 18-item questionnaire. EMG activity of right and left trapezius muscles for 12 male students with no musculoskeletal disorders was measured while simulating common tasks like working on the teeth of the lower jaw. Normalized EMG data showed significant reduction [p<0.05] in all EMG recordings of the trapezius muscle. Dentists also unanimously preferred the economically designed chair. Such economically designed chairs should be introduced as early as possible in student training before bad postural habits are acquired

[Review of finite element model studies in knee joint biomechanics]

Human knee joints experience very large loads and motions during regular daily, occupational and sport activities. Consequently, they are at high risk of being exposed to injuries and degeneration. Osteoarthritis and ligament injuries often inflict knee joints causing considerable pain and loss of productivity involving thus significant human and economic costs. Hence, biomechanics of human knee joints has been the focus of many investigations with the primary aim to improve understanding of joint function in normal and perturbed conditions. The existing prevention and treatment programs have been based on such studies. Due to inherent costs, limitations, difficulties and ethical concerns associated with in vivo and in vitro cadaveric studies, finite element model studies have been developed as effective, powerful and complementary tools to investigate knee joint biomechanics subject to internal and external mechanical conditions affecting its normal function. The advantage of finite element method in study of joint biomechanics lies in its robustness to incorporate complex 3D joint geometry, intricate boundary and loading conditions and materials with nonhomogeneous and nonlinear properties. This article reviews important model studies, presents their relevant results and discusses some of the promising future directions

effects of abdominal hollowing maneuver on thickness of lateral abdominal wall muscles

The Transversus Abdominis Muscle [TrA] is the deepest abdominal muscle which contributes to lumbosacral stability. Abdominal Hollowing [AH] maneuver is a clinical way to activate the TrA muscle in an isolated fashion. The aim of this study was to investigate the effects of AH maneuver on External Oblique [EO], Internal Oblique [IO], and Transversus Abdominis [TrA] muscles in supine and standing positions in both healthy men and women. This clinical trial study was conducted on 43 asymptomatic volunteers aged 19-44 years. After collecting demographic information, the participants were instructed to activate their TrA muscle in standing position. Then Rehabilitative Ultrasonic Imaging [RUSI] was performed for measuring thickness of all above muscles in both supine and standing positions and before and during doing AH. At the same time activation of the TrA was controlled by Pressure Biofeedback [PBF]. ANOVA, paired t-test and Pearson correlation tests were used to analyze the data. Values of p<0.05 were considered to be significant. During AH, the thickness of TrA increased significantly in both supine and standing positions [p<0.0001]. Also, thickness of the IO muscle increased in both men and women groups after AH [p<0.0001]. Generally, we observed that both IO and TrA thickness increased in standing position compared to supine position [p<0.003, p<0.0001] but advanced analysis indicated that TrA had increased only in its rest thickness [p<0.02]. There was no effect of AH or changing position on EO muscle's thickness [p<0.2]. It appears that performing AH in standing position can be effective on TrA thickness, although the PBF has been introduced as a clinical and available device for monitoring TrA activity, RUSI showed that both TrA and IO muscles were activated after AH. We recommend performing further investigations using electromyography and RUSI at the same time

Theoretical study of possible solutions for addressing the kinetic redundancy in lumbar spine by central nervous system

This is mainly achieved by the way that central nervous system [CNS] uses the redundancy in musculoskeletal system. The kinetic redundancy in human musculoskeletal systems is a significant property by which central nervous system achieves many complementary goals. In this study, by explaining the definition and role of uncontrolled manifold for movement kinematics, the kinetic redundancy concept is explored in mathematical terms. The null space of the kinetically redundant system when certain joint moment and/or stiffness are needed is derived and discussed. In this paper, the mathematical methods have been developed for a simpler planar biomechanical model with 3 muscles in which the explained concepts have been utilized

Co-activation of muscles in biomechanical modeling

Muscles co-activation is a significant concept often used in the studies of spine and knee joint biomechanics and rehabilitation. Researchers and clinicians use this measure to design rehabilitation strategies and/or evaluate clinical interventions. In this paper, biomechanical and physiological consequences of co-activation of muscles are discussed succinctly using a number of illustrative examples. The paper shall further demonstrate the need for more cooperation and interaction between clinicians and biomechanical engineers for development of better biomechanical models, assisting the development of new experimental designs and more precise methods of evaluating neuromuscular performance during functional tasks