Thesis (Ph. D.)--Brigham Young University. Dept. of Exercise Sciences, 2008. / Includes bibliographical references.

Surface electromyography (SEMG) has been widely used in functional measurement of lumbar muscles, which can be applied for low back pain (LBP) rehabilitation assessment. Previous study has reported the application of SEMG topographic analysis for obtaining an objective and quantitative assessment of LBP. However, the previous SEMG topographic analysis was performed manually and offlined, which was time consuming and with big inter-observer variations. This will limit the use of this technique for practical assessment of LBP and rehabilitation. Therefore, the objectives of this thesis are to design and develop an automatic and online SEMG topographic analysis system, and to verify its potential uses in clinical tests. Current problems in the process of SEMG topographic analysis include noise removal and signal segment. The recording of SEMG on lumbar area is usually contaminated with a lot of noises, while electrocardiography (ECG) is a main source of influences to mislead the characteristics of SEMG. Previous study proved the use of independent components analysis (ICA) to be a useful tool to eliminate ECG from raw SEMG signals, but it was not implemented in current available SEMG system. The second problem is the automatic identification of SEMG signals in different motion phases, i.e. trunk flexion and extension during forward-bending motion. To achieve an automatic and online SEMG topographic analysis, the present study will develop the system with three unique functional components: 1) an automated feature cognition and identification for ECG artifact removal, 2) an automatic segmentation algorithm for signal processing, and 3) a quantitative analysis of SEMG topographic characteristics. Four topographic parameters, namely relative area (RA), relative width (RW), relative height (RH) and relative width-to-relative height (W/H), are employed for quantifying the characteristics of SEMG topograph. A clinical test, enlisting twenty healthy subjects and forty-one LBP patients, was conducted to verify the functionality and reliability of the developed system based on these four parameters. In addition, the dynamic variation of these four topographic parameters with respect to time was also studied by asking the subjects to perform forward-bending movements. Results showed that the developed system is highly reliable. From the results, it was also found that the time-based changing patterns of the four topographic parameters in healthy subjects can be used as a reference indicator for distinguishing between normal subjects and LBP patients. The applicability of the developed system was further verified and demonstrated by studying the effect of wearing soft lumbar corsets (SLCs) on low back neuromuscular function in elderly patients with acute LBP. In conclusion, the developed real-time SEMG topographic analysis system can be used for detecting lumbar muscle function and producing quantitative assessment results for various rehabilitation applications. / published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

No description available.

No description available.

Empirical and simulation studies are described which assess the form of central control signals for human limb movement. Recent claims about the complexity of control signals are addressed using a mathematical model of two-joint planar arm movement. The model is based on the lambda version of the equilibrium point hypothesis and includes neural control signals, reflexes, reflex delays, muscle mechanical properties, realistic musculo-skeletal geometry, limb dynamics and external loads. It is shown that ostensibly "complex" features of limb motion such as the "2/3 power law" and non-monotonic patterns of limb impedance are predicted using simple constant-rate equilibrium shifts which do not explicitly encode these movement properties. In addition it is shown that simulated limb impedance using the A model both during movement and in statics matches empirically estimated values of impedance reported in the literature. / Empirical studies assessed the control of muscle coactivation by measuring tonic levels of electromyographic activity in shoulder and elbow muscles at the end of reaching movements in a horizontal plane. Shoulder muscle coactivation was related to the amplitude and velocity of shoulder motion, and unrelated to elbow motion whereas elbow and double-joint muscle activity was related to elbow motion, and unrelated to shoulder motion. It is suggested that muscle coactivation at the shoulder and elbow may be controlled independently. / Other experiments addressed the extent to which control signals are adjusted to account for interaction torques---torques arising at one joint due to the motion of limb segments about adjacent joints. Electromyographic activity of limb muscles was measured during single- and multi-joint movements in which the magnitude or direction of interaction torque was systematically varied. During single-joint movements, phasic activity which preceded motion and varied in magnitude with interaction torque was observed in muscles acting at the stationary joint. During multi-joint movement EMG activity in muscles at one joint was modulated to offset interaction torque arising from limb motion about an adjacent joint. It is suggested that control signals to muscles are adjusted to offset interaction torques arising from limb dynamics. Schemes for incorporating information about dynamics into the position control framework proposed in the equilibrium point hypothesis are discussed.

No description available.

This thesis is concerned with the investigation, in vitro, of the mechanical properties of the intact and injured human lumbar spine under general loading conditions, by both experimentation and use of a numerical simulation. / For the experimental investigation, a three dimensional loading apparatus and displacement transducer were constructed. In order to standardize the experiment, the influence of several secondary variables was investigated. The load deflection properties of intact and injured joints were then studied. Eight states of injury were considered. As well, the effect of various types of preloading upon joint response was determined. / Using the data generated by the experimental study and measurements of the surface geometry of the vertebra, a numerical simulation was devised. This simulation allowed the interpretation of the experimental results in terms of strains in the soft tissue elements and facet interaction. As well, the locations of the instant center of rotation and the foraminal gap dimensions could be determined.

Humans routinely make movements to targets that have different accuracy requirements in different directions. Examples extend from everyday occurrences such as grasping the handle of a coffee cup to the more refined instance of a surgeon positioning a scalpel. The attainment of accuracy in situations such as these might rest upon the nervous system's capacity to regulate the limb's resistance to displacement, or impedance. To test this idea, subjects made movements from random starting locations to targets that had shape dependant accuracy requirements. A robotic device was used to assess both limb impedance and patterns of movement variability just as the subject reached the target. Impedance was seen to increase in directions where required accuracy was high. Furthermore, independent of target shape patterns of limb stiffness were seen to predict spatial patterns of movement variability. The nervous system was thus seen to modulate limb impedance in wholly predictable environments to shape movement variability and achieve reaching accuracy.

The purposes of this study were to determine (1) how running kinematics varied across two different speeds (200 and 268m/min), (2) to what degree intense interval training sessions affected running mechanics and (3) whether these changes correlated to changes in running economy (RE). Eleven highly trained male endurance athletes (average VO2max = 72.5 +/- 4.3 ml/kg/min) performed three intense interval running workouts of 10 x 400m at an average running velocity of 357.9 +/- 9.0 m/min, with a minimum of 4 days between runs. Recovery duration between trials was randomly assigned at 60s, 120s, and 180s. The following biomechanical variables were used to assess running kinematics during the last 3 minutes prior to and following each workout at speeds of 200 and 268m/min: maximum knee flexion in support (KFLEX), minimum knee velocity during stance (KVEL), maximum plantar flexion angle at toe-off (PFLEX), shank angle at heel strike (SANG), mean trunk angle during stride cycle (TANG), mean vertical oscillation of center of mass (VOSC), and stride cycle length (SL). Results of this study affirmed our hypothesis that speed significantly impacts on some kinematic variables (KVEL, SANG, SL), and to a degree has shown that pre and post test and recovery conditions creating a fatigued state altered 2 of the kinematic variables (KVEL and VOSC). However, none of the other kinematic variables measured were altered by speed or fatigue in any substantial way, nor were there any clear correlations between changes in running economy and mechanics. Whether the significant kinematic changes that occurred reflect adaptations to fatigue, rather than a failure to compensate for it, is not clear. The interrelationship between metabolic and biomechanical markers of training and performance appears to be complex and somewhat individualistic.

The response of the human talocrural articulation to internal and external torques was investigated in an in vitro study. Experimental and theoretical methods were used to evaluate this response in terms of (1) displacement between the tibia and the talus, (2) tension in the major ligamentous structures of the joint, and (3) stresses in the bones of the talocrural joint mortise. The experimental investigation involved the design and fabrication of several testing and measurement instruments, including a three-dimensional joint loading apparatus, a six degrees-of-freedom displacement measuring device, and several implantable, non-destructive ligament tension transducers. The stress distribution in the talocrural mortise was estimated using a three-dimensional finite element model with simulated physiological loading conditions. / The effects of the talocrural joint flexion angle, the subtalar joint angle, and the amount of weightbearing across the joint were examined. The results showed a varying joint behavior for the same torque application across the range of variables studied. Based on the experimental and theoretical findings, a mechanism for the talocrural joint response to torque was proposed. In addition, the results have been discussed in terms of their clinical significance.