Judging time-to-contact with a target is an important criterion for avoiding harm in everyday walking and running tasks, and maximizing performance in high-velocity sporting tasks. The information-based regulation of step length and duration during target-directed locomotion was examined in relation to gait mode, approach velocity, target task, expertise, and sporting performance during a series of four experiments. The first three experiments examined novice performers (Each n=12, 6 males, 6 females), whilst the last experiment examined expert gymnasts (n=5). Two reference strips with alternating 50cm black and white intervals were placed on either side of the approach strip for all of the experiments. One 50Hz-panning video camera filmed the approach from an elevated position. In Experiment 4, two stationary 250Hz cameras filmed the post-flight performance of the gymnastic vaults and, in addition, two qualified judges provided a performance score for each vaulting trial. The panning video footage in each experiment was digitized to deduce the gait characteristics. In Experiment 4, the high-speed video footage was analyzed three-dimensionally to obtain the performance measures such as post-flight height. The utilization of visual stimulus in target-directed locomotion is affected by the observer's state of motion as characterized by the mode of locomotion and also often the speed of locomotion. In addition, experience plays an important role in the capacity of the observer to utilize visual stimulus to control the muscular action of locomotion when either maintaining or adjusting the step mechanics. The characteristics of the terrain and the target also affect the observer's movement. Visual regulation of step length decreases at higher approach speeds in novice performers, where as expert performers are capable of increasing visual regulation at higher approach speeds. Conservatism in final foot placement by female participants accounts for the observed increase in distance from the critical boundary of the obstacle relative to toe placement. Behavioural effects of gender thus affect the control of final foot placement in obstacle-directed locomotion. The visual control of braking in target-directed locomotion is described by a tau-dot of-0.54. When tau-dot is below -0.54 a hard collision with the obstacle will occur, however, when tau-dot is above -0.54, a soft collision with the target will occur. It is suggested that the tau-dot margin defining the control of braking reveals the braking capacity of the system. In the target-directed locomotion examined a tau-dot greater than -0.70 would possibly exceed the braking capacity of the system, thus, leading to injury if performed. The approach towards the take-off board and vaulting horse in gymnastics is an example of target-directed locomotion in sport. Increased visual regulation of the timing and length of each step is a requirement for a fast running approach, a fundamental building block for the execution of complex vaults in gymnastics. The successful performance of complex vaults in gymnastics leads towards a higher judge's score. Future research suggestions include an investigation of visual regulation of step length in curved target-directed locomotion.

The kinematic motor redundancy of the human legs provides more local degrees of freedom than are necessary to achieve low degree of freedom performance variables like leg length and orientation. The purpose of this dissertation is to investigate how the neuromuscular skeletal system simplifies control of a kinematically redundant system to achieve stable locomotion under different conditions. I propose that the neuromuscular skeletal system minimizes step to step variance of leg length and orientation while allowing segment angles to vary within the set of acceptable combinations of angles that achieves the desired leg length and orientation. I find that during human hopping, control of the locomotor system is organized hierarchically such that leg length and orientation are achieved by structuring segment angle variance. I also found that leg length and leg orientation was minimized for a variety of conditions and perturbations, including frequency, constrained foot placement, and different speeds. The results of this study will give valuable information on interjoint compensation strategies used when the locomotor system is perturbed. This work also provides evidence for neuromuscular system strategies in adapting to novel, difficult tasks. This information can be extended to give insight into new and different areas to focus on during gait rehabilitation of humans suffering from motor control deficits in movement and gait.

Thesis (Ph. D.)--University of Oregon, 2001. / Includes vita and abstract. Includes bibliographical references (leaves 191-196). Also available for download via the World Wide Web; free to University of Oregon users.

Not available / text

published_or_final_version / Orthopaedic Surgery / Master / Master of Philosophy

The purpose of this study was to compare selected kinematic characteristics of distance runners over a twenty year period. The subjects in the investigation were 14 long distance runners who at the time of the first observation were considered highly trained (running more than 50 miles per week). The second observation occurred approximately 20-23 years after the first observation. At this time the average weekly mileage per runner had decreased to 37 miles per week. The first observation's data were collected with a Locam camera at film speeds ranging from 60 to 120 frames/second. The film data were digitized at the same time as the second observation's data. The second observation's data were collected with a Panasonic 5000 shutter video camera. The Peak Performance Motion Measurement System video interface allowed a 60 frame/second field rate. Ten subjects ran at a speed of 3.4 m/s; two subjects at the speeds of 3.1 and 3.6 m/s; and one subject at each of the following speeds: 4.0, 4.5, and 4.9 m/s. Statistical analyses (ANOVA) of the stride length, stride frequency, support and non-support time, and joint angular displacement indicated no significant difference (p > .05) between the first observation and the second observation. The results of this study indicated that the kinematics of continually active long distance runners do not change with an increase in age. / School of Physical Education

Two experiments were undertaken. The objective of Experiment One was to identify the lower limb muscles that were most frequently active during the early period of a step turning task for further testing in Experiment Two. In Experiment Two participants undertook multiple trials of a step-turning task, 30 and 60° to the left and right of midline, at a self-selected pace in response to a visual cue. There were five objectives to Experiment Two. Firstly, to identify the predominant order in the onset of foot movement so that anticipatory muscle activity could be defined for this task. Secondly, to identify whether there is a consistent temporal order in movement onset between the head and the feet. Thirdly, to identify whether and how consistently anticipatory lower limb muscle activity is present bilaterally. Fourthly, to assess whether there is a consistent sequence in the onset of anticipatory muscle activity among muscles active in at least 80% of trials. The final objective was to identity whether there was a consistent temporal relationship in the onset of the anticipatory muscle activity present in at least 80% of trials, with the onset of head and foot movement. Study Design: A repeated measures design was used. Background: Anticipatory lower limb muscle activity in gait initiation and forward stepping studies has been reported to be consistently present, and associated with initial and important balance responses. Falls during turning are associated with a high incidence of hip fractures in the elderly population. The presence of anticipatory lower limb muscle activity turning has not been previously reported. Participants: There were five participants in Experiment One, and ten in Experiment Two. All were between 18 and 40 years of age and did not have neurological or musculoskeletal disorders, or severe visual loss. Results: In Experiment One, four muscles were consistently active bilaterally, during the early period of step-turning and were: tibialis anterior, gastrocnemius, biceps femoris and gluteus medius. In Experiment Two the ipsilateral foot moved before the contralateral foot in 68% of trials towards the left, and 79% of trials towards the right. The onset of head movement consistently occurred before the onset of foot movement during turns towards both directions. The percentage of trials in which the four muscles were active in an anticipatory manner was low bilaterally, ranging from 12 to 38% of trials. Objectives that involved the further analysis of muscles active in at least 80% of trials were unable to be completed. Conclusions: During a step-turning task young healthy adults predominantly move their ipsilateral foot before their contralateral foot. The consistent onset of head movement prior to that of the feet, indirectly suggests that the visual system might influence the temporal onset of the feet. The low levels of anticipatory muscle activity during step-turning suggest that the lower limbs are not involved with the initial balance responses for this task thus making it inherently different to gait initiation and forward stepping.

[Truncated abstract] Previous research has found that full recovery of knee function following arthroscopic partial meniscectomy (APM) is often not achieved, and in the long-term, over 50% of these patients will develop knee osteoarthritis (OA). Mechanical factors are believed to contribute largely to the development of knee OA. High frequency loading has been shown to lead to degenerative joint changes in animal models. In human gait, the knee adduction moment during stance phase, which tends to load the medial articular surface of the tibiofemoral joint, has been associated with the presence, severity and progression of knee OA. Quadriceps weakness, which is common in people with knee pathology, has been associated with abnormal sagittal plane knee moments during gait, yet no studies have investigated the effect of knee strength on frontal plane kinetics. This work aimed to investigate gait mechanics in a post-APM population, determine the influence of neuromuscular factors on gait, and assess recovery of function over 12 months while examining factors associated with recovery. One hundred and six APM subjects were examined between one and three months postsurgery. Data were compared to an age-matched control group of 49 healthy adults. Subjects were aged 20 to 50 years and had been screened for: clinical and radiographic evidence of knee OA; previous or current knee joint disease or injury (other than the current meniscus pathology); or any other previous or existing disease or injury that may have an effect on gait, or predispose to joint disease. Three-dimensional gait analysis was performed at a freely-chosen walking velocity, using a 50 Hz VICON three-dimensional motion analysis system, instrumented with two force platforms and 10-channel electromyography system. Subjects also underwent knee strength testing on a Biodex isokinetic dynamometer. Information was collected regarding subject’s physical activity levels, general health and knee function, as well as patient’s surgery specifics and rehabilitation regime.

[Truncated abstract] Unicondylar knee arthroplasty (UKA) has re-emerged as a successful treatment option for isolated single compartment tibio-femoral joint osteoarthritis. However despite its increasing use, controversy still remains over fixed or mobile bearing tibial components, as there is a lack to prospective randomised studies reported in the literature. In addition, the theoretical advantages of the mobile bearing for knee kinematics, kinetics and clinical outcome have not been evaluated in vivo. The aim of this research study was to explore the clinical and biomechanical outcomes of the fixed and mobile bearing UKA. . . . When the results for the both studies were combined, utilising the Preservation and MG fixed bearing prostheses, there was a significant relationship between knee adduction moment, and a poor prognosis predicted from RSA. Those patients with translation or rotation of the tibial component in any direction above 1mm and 1.5 degrees respectively were considered to have a poor prognosis for long term fixation. Of the 28 patients, the 8 patients considered to have a poor prognosis, had increased knee adduction moments post-surgery (mean difference = 1.66Nm.kg-1, p = 0.007). There was no difference between the groups for knee flexion moment (mean difference 0.16Nm.kg-1, p = 0.844). Pre-surgery gait was unable to predict the post-surgery outcome, due to the significant changes in gait from pre- to post-surgery. Care must taken when implanting the Preservation mobile bearing prosthesis, as long term outcome is questionable. The mobile bearing prosthesis also produced the worst clinical outcome, however the theoretical advantages of the mobile bearing does not affect gait. Gait analysis is a useful tool to identify patient who are overloading their prosthesis, leading to potential early failure. Identification of these gait patterns can allow for early intervention to reduce joint load, and possible extend the longevity of the prosthesis.

Thesis (M.S.)--University of Texas at El Paso, 2007. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.