The objective of this work was threefold: 1) to assess how local dynamic spinal stability is affected by various factors including: the personal lift-assist device (PLAD), different loads when lifting, and prolonged repetitive work; 2) to establish the between-day reproducibility of local dynamic stability and kinematic variability measures; and 3) to directly compare local dynamic spinal stability to quasi-static mechanical spinal stability. The first study was an investigation into the effects of the PLAD on local dynamic spinal stability during repetitive lifting. Short- (λmax-s) and long-term (λmax-l) maximum finite-time Lyapunov exponents were calculated from measured trunk kinematics to assess stability. PLAD use did not change λmax-s, but significantly reduced λmax-l; indicating increased local dynamic spinal stability when lifting with the device. The second study was a report on the effects of lifting two different loads (0% and 10% maximum back strength) on local dynamic spinal stability and kinematic variability, expressed as the mean standard deviation (MeanSD) across cycles. It was determined that increasing the load that was lifted significantly reduced λmax-s, but not λmax-l or MeanSD. Thus, as muscular and moment demands increased with load so did subjects’ spinal stability. The third study was designed to look at changes in local dynamic spinal stability and kinematic variability resulting from 1.5 hours of repetitive automotive manufacturing work, as well as the between-day reproducibility of the measures. Operators performed a repetitive dynamic trunk flexion task immediately pre- and post-shift, as well as at the same pre-shift time on the following day. Despite significant increases in back pain scores, operators were able to maintain their stability and variability post-shift. Moreover, λmax-s was the most reproducible measure. The final study was structured to directly compare lumbar spine rotational stiffness (quasi-static mechanical spinal stability), calculated with an EMG-driven biomechanical model, to local dynamic spine stability, during a series of dynamic lifting challenges. Results suggest that spine rotational stiffness and local dynamic stability are positively associated, as they provided similar information when lifting rate was controlled. However, both models provide unique information and future research is required to fully understand their relationship. In general, the results of these studies illustrate the potential for Lyapunov analyses of kinematic data to be used to assess local dynamic spinal stability in a variety of situations. / Thesis (Ph.D, Kinesiology & Health Studies) -- Queen's University, 2012-07-31 15:34:01.804

Proximal stability, or the ability to stabilize and actively control the spine, pelvis and trunk, has been reported to influence sport performance. Traditional training practices for the proximal segments have had little success improving sport performance. The purpose of this dissertation was to investigate the effects a sport specific proximal stability training program can have on throwing velocity and measures of muscular endurance and power which target the proximal segments of the pelvis, spine and trunk. A stratified randomized clinical trial was implemented with a pre- to post-intervention design. Forty-six healthy, Division III collegiate female softball (n=17) and male baseball (n=29) players were randomly assigned to one of two training groups for 7 weeks; a traditional endurance training group (ET) (n=21) or a power stability training group (PS) (n=25). The primary outcome measures were the change in peak throwing velocity/Kg of body weight in mph. Mean throwing velocity, power outputs from a one-repetition maximum chop test and lift test (watts/Kg body weight), and muscular endurance plank tests. Student’s independent t-tests were used to compare differences between change scores of all dependent variables. Peak throwing velocity change scores were significantly faster (ET= .21 ±.55 mph, PS= 3.4 ±1.1 mph, p< .001) in the PS at post-intervention when compared to the ET group. Change scores were significantly greater in the PS group for mean throwing velocity, (ET= 1.1 ±1.6 mph vs. PS= 3.7 ±1.8 mph, p< .001), chop (watts), (ET= 20 ±78 watts vs. PS= 105 ±68 watts, p< .001), and lift, (ET= 49 ±62 watts vs. PS= 114 ±73 watts, p= .003). There were no change score differences for the side and prone plank endurance measures in seconds (p≥ .60). The PS group increased primary outcome measures over the ET program, indicating a more sport specific training regimen targeting the proximal segments is beneficial to both the power measures and throwing performance.

Title of thesis: Influence of intra-abdominal pressure on the stability of the lumbar spine Definition of the problem: This thesis addresses the problem of the stabilization mechanism of the lumbar spine and the influence of intra-abdominal pressure on the stability of the lumbar spine. Objectives: The aim of my thesis is to locate, evaluate and process all available resources and to bring up the issue of IAP and its influence on the lumbar spine. The work should provide the widest possible insight into the problems of IAP effects on the stability of the lumbar spine, summarize differing opinions, and allow easier orientation in the isme. Method: The work is treated as a search, focusing on the processing and retrieval of literature concerning the issue. Studies included range from 1953 to present. To which I will use a variety of sources of literature, internet and consultation with the head of my thesis. Results: The increase in IAP, which is provided by a synchronous contraction of the diaphragm, pelvic floor muscles and m. transversus abdominis, can effectively stabilize the spine. But you can not determine with certainty whether this mechanism to support the stability of the lumbar spine is indeed used or the stability is provided by contraction of muscles, leading to an increase in IAP, and...

Previous in-vivo studies showed that compressive force acting on the spine may exceed 2600 N. However, the ligamentous lumbar spine becomes unstable when subjected to compressive loads less than 100 N. It is generally accepted that the ligamentous spine itself is unstable but can be stabilized by muscle forces (MFs) in vivo. Nevertheless, normal spinal muscle contraction patterns remain unknown. In recent in vitro studies, when the direction of the applied load was controlled along the spinal curvature so that the internal spinal load became perfect compressive follower loads (CFLs) at all lumbar levels, the ligamentous lumbar spine was found to withstand large compressive load (up to 1200 N) without buckling while maintaining its flexibility in neutral or flexed postures. The results of in-vivo animal studies also have shown that shear stress has a more detrimental effect on the rate of disc degeneration compared to compressive stress. These results suggest CFLs in the lumbar spine would be a normal spinal load whereas the transverse (or shear) load abnormal. An initial test of this postulation would be to investigate whether the spinal muscles can create perfect internal CFLs in the lumbar spine in all 3-D postures. In addition, small intrinsic muscles (SIMs) are crucial for better control of the direction of the internal spinal load along the spinal axis was also proposed. A finite element (FE) model together with an optimization model were used for this study. Both models consist of the trunk, sacrolumbar spine and 244 spinal muscles. Different from other studies, 54 SIMs were also included in the models. The FE model was validated by comparing the ROM of the spine with the literature data. Minimization of the summation of the spinal loads and moments was used as the cost function for the optimization model. The geometrical data obtained from the FE model was used as the input for the optimization model; it was then used to calculate the MFs required for creating the CFLs at all lumbar spine levels. The MFs determined in the optimization model were then imported back to the FE model as input loads to check the stability of the spine under this loading condition. Five different postures were studied: neutral, flexion 40°, extension 5°, lateral bending 30° and axial rotation 10°. Many optimization solutions for spinal muscle force combinations creating pure CFLs in the lumbar spine were found available in each posture. However, FE analyses showed that only muscle forces and patterns solved at FLPs along the curve in the vicinity of the baseline curve stabilized the lumbar spine. Stability was determined by small displacement of the trunk (less or equal to 5mm) due to small deformation of the lumbar spine. The magnitudes of joint reaction forces (JRFs) predicted from the optimization model were comparable to those reported in the literature. When the SIMs were removed, optimization solutions were still feasible in all five postures, but JRFs and trunk displacement were increased. This suggests the need of SIM inclusion in future spine biomechanics studies and clinically, damages to the SIMs may have a high risk of future spinal problems, such as spinal instability, early disc degeneration, deformity and/or early failure of spinal fixation devices. The results from this study supported the hypothesis that the perfect CFLs at all lumbar levels could be the normal physiological load under which the lumbar spinal column could support large load without buckling while allowing flexibility. SIMs played an important role in creating CFLs as by including SIMs in the models, the JRFs at all lumbar spine levels were lowered and the stability of the spine was increased.

Low back pain is a common medical problem around the world afflicting 80% of the population some time in their life. Low back injury can result from a loss of torso stability causing excessive strain in soft tissue. This investigation seeks to apply existing methods to new applications and to develop new methods to assess torso stability. First, the time series averaged finite time Lyapunov exponent is calculated from data obtained during seated stability experiments. The Lyapunov exponent is found to increase with increasing task difficulty. Second, a new metric for evaluating torso stability is introduced, the threshold of stability. This parameter is defined as the maximum task difficulty in which dynamic stability can be maintained for the test duration. The threshold of stability effectively differentiates torso stability at two levels of visual feedback. Third, the state space distribution of the finite time Lyapunov exponent (FTLE) field is evaluated for deterministic and stochastic systems. Two new methods are developed to generate the FTLE field from time series data. Using these methods, Lagrangian coherent structures (LCS) are found for an inverted pendulum, the Acrobot, and planar wobble chair models. The LCS are ridges in the FTLE field that separate two inherently different types of motion when applied to rigid-body dynamic systems. As a result, LCS can be used to identify the boundaries of the basin of stability. Finally, these new methods are used to find the basin of stability from time series data collected from torso stability experiments. The LCS and basins of stability provide a richer understanding into the system dynamics when compared to existing methods. By gaining a better understanding of torso stability, it is hoped this knowledge can be used to prevent low back injury and pain in the future. These new methods may also be useful in evaluating other biodynamic systems such as standing postural sway, knee stability, or hip stability as well as time series applications outside the area of biomechanics. / Ph. D.

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