This study developed a three-dimensional biomechanical model to investigate the internal loads on the human neck that result from isometrically generated loads resisted by a force on the head. The first goal was to apply the double-optimization (DOPT) method, the EMG-based method, and the EMG assisted optimization (EMGAO) method to the neck model, calculating muscle forces and C4/5 cervical joint loads for each method. The second goal was to compare the results of the different methods, and the third was to determine maximum exertion forces in the cervical spine for isometric contractions. To formulate the EMG-based model, electromyographic signals were collected from 10 male subjects. EMG signals were obtained from 8 sites around the C4/5 level of the neck by surface electrodes, while the subject performed near maximum, isometric exertions. The mean maximum values (±SD) calculated for C4/5 joint compressive forces during peak exertions were 1654 (±308) N in flexion by the EMG method, 1674 (±319) N in flexion by the EMGAO method, and 1208 (±123) N in extension by the DOPT method. In contrast to the DOPT method, the EMG and EMGAO methods showed activation of all the muscles, including the antagonists, and accommodated various load distribution patterns among the agonist muscles during generation of the same magnitude of moments, especially in lateral bending. The EMG and EMGAO methods predicted higher cervical spinal loads than previously published results by the DOPT method. These results may be helpful to engineers and surgeons who are designing and using cervical spine implants and instrumentation.
Hyeonki Choi and Ray Vanderby Jr.
David T. Corr, Ray Vanderby Jr. and Thomas M. Best
An existing rheological model of skeletal muscle (Forcinito et al., 1998) was modified with a nonlinear Maxwell fluid element to provide a phenomenological model capable of analyzing the strain-stiffening behavior typically found in passive, and occasionally observed in active, skeletal muscle. This new model describes both active and passive muscular behavior as a combination of the behavior of each model component, without requiring prior knowledge of the force-length or force-velocity characteristics of the muscle.
Todd C. Phillips, Sean S. Kohles, John F. Orwin, Lori Thein Brody, Ronald P. McCabe and Ray Vanderby Jr.
An impulse-momentum exercise system was instrumented for collection of kinematic and kinetic data during shoulder exercise. The objective of this study was to quantify the dynamics of an exercise system that utilizes a weighted shuttle (22.2 N) traveling on a rail system and evaluate its efficacy as an exercise and rehabilitative tool. Two healthy adults (mean age. 30.0 years) were tested utilizing 2 protocols. The first protocol required the subject to maintain tension in the system while externally rotating the upper arm from neutral to 90° relative to the shoulder and then internally rotating back to the initial position. In me second protocol, the range of motion was similar, but each subject was instructed to carry out the exercise as rapidly as possible without regard to the tension in the rope, thus creating an impulsive load. Average peak loads up to 87.9 and 137.0 N were recorded using the first and second protocols. respectively. Average maximum loads using the second protocol were approximately 50 N greater than those using the first protocol (p < .05). Representative calculations demonstrated that less mechanical work was performed during the first protocol (−3.8 to −45.9%). Qualitatively the shuttle acceleration curves appear dramatically different, although similar average peak accelerations are achieved during use (4.12 vs. 3.47 m/s2, protocol I vs. protocol 2, respectively).