Numerous mathematical models have been developed to investigate the high incidence of low back pain associated with lifting activities. These mainly consider the muscle forces required to support the spine, and few have considered the additional role of curvature. One previous model which represented the spine as an arch (Aspden 1987) indicated the curvature to have a significant effect on both loading and stability of the spine. However this model included collective loading patterns for body weight and muscle forces, and only partial representation of the spine. On the basis that the level of anatomic detail of a model affects the accuracy of its predictions (McGill and Norman, 1987), this thesis describes the development of a model which provides greater detail for investigating spinal stability in the sagittal plane. The curvature of the whole spine, a distributed loading pattern for body weight, and the activity of individual spinal muscle groups have been considered. Comparison with the previous arch model has shown these to be necessary features for determining the loading and stability associated with a given posture. In particular, application of individual muscle forces provide greater control of stability at each vertebral level. By considering the force requirements of the individual muscle groups and the consequent loads at each intervertebral joint, possible areas of tissue over load can be identified.

Abstract not available.

Olympic weightlifting has been subject to rigorous academic and applied sporting research for over 40 years. Biomechanists have concerned themselves with Olympic weightlifting due to the complex coordination requirements coupled with high levels of full-body muscular activity. Motivated by Enoka's (1988) research on load- and skill-related changes; we used modern three-dimensional motion capture to assess selected mechanical characteristics of the snatch lift across varied lifting intensities. Our research variables included peak moment powers about the joints of the lower extremity, bilateral shoulder symmetry, and range of anterior-posterior system centre of mass (COM) movement as barbell load was varied across 80, 85, and 90% of each lifter's maximum. The five subjects were elite-level Olympic weightlifters (mean age 23 +/- 4.18 years, mean mass 77.6 +/- 5.81 kg). Multiple dependent t-tests (one for each joint pair) with Bonferroni corrections were applied between left and right peak powers to assess symmetry in the lower extremities. No significant differences were found, t(df =14) = 0.068, 0.038, and 0.039. Significance statistics wereall > p (alpha/n) = 0.0167 about the ankle, knee, and hip joint pairs, respectively. This confirmed assumptions of previous researchers that peak moment powers in elite-level lifters were symmetrical between joint pairs of the lower extremity. Exploiting the symmetry results, we simplified further analyses by considering only the left side of the body. Repeated-measures ANOVA revealed no significant differences in average peak moment power in three dimensions about the joints of the left lower extremity across barbell intensities. In the flexion extension plane of motion, left ankle F (2, 8) = 2.594, p = 0.135, knee F (2,8) = 0.133, p = 0.878, and hip F (2, 8) = 0.420, P = 0.671). Similar results followed for motion about the y and z axes of motion. Results indicated between 80-90% of maximal barbell load, no differences existed in average peak moment powers about the joints of the lower extremity. These results confirmed the findings of Enoka (1988) and showed lifters do not accommodated heavier barbell loads through increased peak moment powers in the lower extremities. Shoulder symmetry was assessed through graphical and numerical methods. All trials showed Pearson's correlations of r > 0.95, which indicated strong similarity between left and right shoulder trajectories. Bilateral shoulder position remained highly stable across barbell intensities, as participants did not modify shoulder symmetry across the tested intensity range. Range of anterior-posterior system COM movement showed no significant differences across barbell intensities (F (2, 4) = 0.765, P = 0.523). While the range of anterior-posterior system COM motion did not vary across barbell intensities, various motion trends were observed. The anterior-posterior range of system COM motion was quite small, but perturbations in system COM trajectory could be detrimental to subsequent lift phases as the barbell load approaches maximum. In conclusion, peak moment powers about the joints of lower extremities did not vary significantly across snatch lifts of 80-90% maximal capacity. Thus, training programs designed to improve athletic power through the use of weightlifting movements should not exceed the 80% limit for snatch based exercises. Statistical tests revealed no significant differences between average peak moment powers between left and right joint pairs of the lower extremities. The peak moment powers during the snatch lift were not asymmetrical. Our research demonstrated elite-level weightlifters exhibiting strong linear correlation in shoulder position across the 8090% range of barbell loads. System COM showed no significant variation in anterior-posterior range of motion across barbell intensities. This research confirmed the results previously established by Enoka (1988) regarding power response to load variation.

Surgery to correct cam femoroacetabular impingement (FAI) is increasingly popular. Despite this, no known study has used motion analysis and ground reaction forces to quantify the outcome of surgery for FAI. The goal of this study was to compare the preoperative and postoperative lower-extremity joint kinematic and kinetic measurements of cam FAI patients during activities of daily living with use of a high-speed motion capture system and force platforms. We hypothesized that the lower-extremity joint mechanics of FAI patients during level walking and maximal squatting would resemble more those of healthy control subjects, after surgery. Ten patients with unilateral symptomatic cam FAI, who underwent corrective surgery using an open or combined technique, performed walking and maximal depth squatting trials preoperatively and postoperatively. Thirteen healthy control subjects, matched for age, sex and body mass index, provided normative data. Results showed that postoperatively, FAI patients had reduced hip ROM in the frontal and sagittal planes, produced smaller peak hip abduction and external rotation moments, and generated less peak hip power compared to the control group during level walking. During maximal squatting, postoperative FAI patients squatted to a greater depth, and had larger knee flexion and ankle dorsiflexion angles, as well as the sum of all joint angles of the affected limb at maximal depth compared to the preoperative values. The lower-extremity joint and pelvic mechanics of FAI patients did not fully return to normal after surgery. Although surgery seemed to reduce hip pain and restore a normal femoral head-neck offset, it further impaired muscle function as a result of muscle incisions. More research is needed to determine the effects of muscle incisions, which could help improve surgical techniques and develop better rehabilitation programs for FAI patients.

Introduction: Understanding the relationship between muscle loads crossing the knee joint and knee joint mechanics is critical for understanding knee stability and the effects of altered muscle forces on healthy and ACL injured knees. In vitro measurement can be used to elucidate this if the simulation is biofidelic, allowing the physiological levels of applied loads to dictate the tibiofemoral kinematics in all degrees of freedom (DoF). The objectives of this study were to describe and apply the University of Ottawa knee simulator as well as measure the reliability of the device. In addition, this device was used to quantify the effect of muscle loads and anterior cruciate ligament (ACL) resection on contact mechanics and kinematics of the tibiofemoral joint. Methods: Muscle forces were determined from an electromyography-driven musculoskeletal model of a healthy male during gait. Six knee specimens were loaded into the simulator and subjected to 100%, 75% and 50% in vivo muscle forces applied through the 6 simulated muscles, in addition to a quadriceps weakness and a hamstring weakness condition. Tibiofemoral mechanics were measured with all 5 loading conditions before and after ACL transection. Results: With the ACL intact, very high reliability in contact area and pressures among loading conditions were observed as the intra-class correlation coefficients (ICC) ranged from 0.932 to 0.99. After ACL transection, reliability remained very high as ICCs ranged from 0.926 to 0.99. In all simulated conditions, muscle forces maintained the knee joint in a stable position resulting in minimal kinematic differences, but altered contact mechanics in both the ACL and non-ACL condition. Removal of the ACL significantly reduced both the medial and lateral contact areas in all loading conditions compared to the ACL intact condition. Conclusion: In summary, the UOKS has demonstrated high reliability within repeated measures. Additionally, small, normally undetectable alterations in joint kinematics resulted in significant alterations to contact mechanics, which can be linked to the degenerative process.

An aging population and rising prevalence in obesity, arthritis and diabetes are resulting in a great number of elders that are suffering from mobility challenges. Walking assist exoskeletons have the potential to help preserve mobility in elders. The most common type of exoskeleton relies on heavily, complex and expensive components to help their user walk effortlessly. Recent research on walking assist exoskeletons has shifted towards the creation of an entirely mechanical system called passive walking assist exoskeleton. This research aims to design, model and test a passive walking assist exoskeleton that reduces the felt weight of the user during gait. The assist is achieved by the action of a seat mechanism which constantly produces an upward force on the pelvis of the user. This thesis details the entire composition and assembly of such device. The proposed device was modelled in order to predict the assistance provided by the seat mechanism when standing and walking with the device. A human-sized prototype was built and tested in order to mechanically validate the proposed design. The test results validated the proposed seat mechanism which produces the desired upward force, but the use of the exoskeleton in its current state hindered the natural gait pattern of the user.

As the number of total knee arthroplasty (TKA) procedures increases annually, the patient demographic is shifting to include younger patients with higher expectations for post-operative function. The aim of this study was to compare movement patterns during activities of daily living among TKA patients and a healthy, age-matched group using 3D motion analysis. Specifically, this analysis looked at walking on level and inclined surfaces, as well as sitting up and down from a chair. It was predicted that (1) TKA patients would exhibit reduced knee extension moments at the operated limb and increased adduction moments at the contralateral limb during gait, (2) walking downhill would result in greater differences between TKA and control groups, compared to level walking, and (3) TKA participants would have greater flexion angles, moments and power values at the hip, compared to controls, during the sit-stand tasks. Seventeen participants (age=62±6 years, BMI=30±3 kg/m2, time after surgery=11±5 months) were recruited from the Ottawa Hospital, having undergone unilateral TKA by the same surgeon. An age-matched control group was composed of 17 individuals (age=63±8 years, BMI=27±4 kg/m2) who were recruited from the local community. Three dimensional (3D) biomechanical assessment was conducted with all participants performing five trials of walking on level and inclined surfaces, stair ascent and descent as well as sit-stand tasks. Results from this study were focused on gait and sit-stand transitions, showing that TKA participants exhibited altered gait patterns on both walking surfaces, with significantly smaller knee flexion angles and moments, as well as reduced peak power at the knee. The TKA group also experienced reduced knee extension moments; however, this was only significant for downhill walking. Consistent with our hypothesis, downhill walking resulted in greater discrepancies between the groups compared to level walking. Contrary to our third hypothesis, TKA participants exhibited significantly smaller peak hip flexion angles and moments during the sit-stand task, along with reduced hip abduction angles and knee abduction moments. The reduced knee flexion kinematics and kinetics observed during gait tasks, combined with the differences in frontal plane mechanics observed during the sit-stand task suggest that altered loading patterns persist six to twelve months after surgery. This may be a result of continued pre-operative movement patterns as well as the surgery itself, and should be kept in mind when developing rehabilitation programs for this patient population.

Lacrosse, Canada’s national summer sport, is a sport anchored in first nations’ tradition. Its growing popularity in North America has not been reflected by a similar interest in the scientific literature more specifically on the biomechanics of the lumbar spine with its throwing motion. The aim of this study was to describe the motions, forces and muscle actions of the lumbar spine with the hybrid, overhand and sidearm throw. Twelve subjects were asked to throw at maximal speed while captured by a 3D motion analysis system. Flexion, extension and axial rotation angular velocities as well as positive and negative powers in the two planes were calculated. The first research question pertained to consistency in angular velocities and powers between trials of a given throwing technique. Subjects showed a fairly high variation on all variables but mostly with the angular velocities in extension and the peak positive power in flexion/extension which had high coefficient of variations (CVs). The contralateral rotation velocity and the positive rotation power had the lowest CVs. Overall the CVs for powers exceeded the angular velocities’. The second research question addressed if a difference in variables was present between the three throwing methods. A significant difference was observed in the peak negative power in flexion/extension and the peak positive power in rotation. The contralateral rotation angular velocity also showed a significant difference but the sphericity assumption failed. No other variable showed a significant difference but the observed power for those variables was also quite small. Due to the lack of power and the further need for controlling some unforeseen sources of error, this study can be used as a pilot study to further define and improve future studies in the field of lacrosse biomechanics.

Tooth cusp radius of curvature (RoC) has been hypothesized to play an important role in food item breakdown, but has remained largely unstudied due to difficulties in measuring and modeling RoC in multicusped teeth. We tested these hypotheses using a parametric model of a four cusped, maxillary, bunodont molar in conjunction with finite element analysis. When our data failed to support existing hypotheses, we put forth and tested the Complex Cusp Hypothesis which states that, during brittle food items breakdown, an optimally shaped molar would be maximizing stresses in the food item while minimizing stresses in the enamel. After gaining support for this hypothesis, we tested the effects of relative food item size on optimal molar morphology and found that the optimal set of RoCs changed as relative food item size changed. However, all optimal morphologies were similar, having one dull cusp that produced high stresses in the food item and three cusps that acted to stabilize the food item. We then set out to measure tooth cusp RoC in several species of extant apes to determine if any of the predicted optimal morphologies existed in nature and whether tooth cusp RoC was correlated with diet. While the optimal morphologies were not found in apes, we did find that tooth cusp RoC was correlated with diet and folivores had duller cusps while frugivores had sharper cusps. We hypothesize that, because of wear patterns, tooth cusp RoC is not providing a mechanical advantage during food item breakdown but is instead causing the tooth to wear in a beneficial fashion. Next, we investigate two possible relationships between tooth cusp RoC and enamel thickness, as enamel thickness plays a significant role in the way a tooth wears, using CT scans from hundreds of unworn cusps. There was no relationship between the two variables, indicating that selection may be acting on both variables independently to create an optimally shaped tooth. Finally, we put forth a framework for testing the functional optimality in teeth that takes into account tooth strength, food item breakdown efficiency, and trapability (the ability to trap and stabilize a food item).

Running has been a popular sport because of convenience and health benefits. Fatigue among recreational runners may alter running mechanics, thereby increasing the risk for injury. The purpose of this study was to evaluate changes in lower extremity biomechanics throughout a 3.1 mile (5K) run. Ten male and ten female participants wore reflective markers to capture contralateral pelvic drop, knee adduction, knee abduction, and hip adduction. Participants ran 3.1 miles (5K) on a treadmill at a self-determined pace. A two-way, repeated measures ANOVA was conducted to capture the within-subject data across time and between-subject comparing differences in gender. Females had significantly greater contralateral pelvic drop but it did not change over time. Knee abduction angles significantly declined over the five observations. Gender differences and effects of distance can alter the biomechanics in recreational runners. More research is needed to identify predisposing factors to the development of chronic running injuries. / North Dakota State University. Department of Health, Nutrition, and Exercise Sciences