Community locomotion is threatened when older individuals are required to negotiate obstacles, which place considerable stress on the musculoskeletal system. The vulnerability of older adults during challenging locomotor tasks is further compromised by age-related strength decline and muscle atrophy. The first study in this investigation determined the relationship between the major muscle groups of the lower body and challenging locomotor tasks commonly found in the community environment of older adults. Twenty-nine females and sixteen males aged between 62 and 88 years old (68.2 ±6.5) were tested for the maximal voluntary contraction (MVC) strength of the knee extensors and 1-RM for the hip extensors, flexors, adductors, abductors, knee extensors and flexors and ankle plantar flexors. Temporal measurements of an obstacle course comprising four gait tasks set at three challenging levels were taken. The relationship between strength and the obstacle course dependent measures was explored using linear regression models. Significant associations (p≤0.05) between all the strength measures and the gait performances were found. The correlation values between strength and obstructed gait (r = 0.356-0.554) and the percentage of the variance explained by strength (R2 = 13%-31%), increased as a function of the challenging levels, especially for the stepping over and on and off conditions. While the difficulty of community older adults to negotiate obstacles cannot be attributed to a single causal pathway, the findings of the first study showed that strength is a critical requirement. That the magnitude of the association increased as a function of the challenging levels, suggests that interventions aimed at improving strength would potentially be effective in helping community older adults to negotiate environmental gait challenges. In view of the findings of the first study, a second investigation determined the effectiveness of a progressive resistance-training program on obstructed gait tasks measured under specific laboratory conditions and on an obstacle course mimicking a number of environmental challenges. The time courses of strength gains and neuromuscular mechanisms underpinning the exercise-induced strength improvements in community-dwelling older adults were also investigated. The obstructed gait conditions included stepping over an obstacle, on and off a raised surface, across an obstacle and foot targeting. Forty-three community-living adults with a mean age of 68 years (control =14 and experimental=29) completed a 24-week progressive resistance training program designed to improve strength and induce hypertrophy in the major muscles of the lower body. Specific laboratory gait kinetics and kinematics and temporal measures taken on the obstacle course were measured. Lean tissue mass and muscle activation of the lower body muscle groups were assessed. The MVC strength of the knee extensors and 1-RM of the hip extension, hip flexion, knee extension, knee flexion and ankle plantar flexion were measured. A 25% increase on the MVC of the knee extensors (p≤0.05) was reported in the training group. Gains ranging between 197% and 285% were recorded for the 1-RM exercises in the trained subjects with significant improvements found throughout the study (p≤0.05). The exercise-induced strength gains were mediated by hypertrophic and neural factors as shown by 8.7% and 27.7% increases (p≤0.05) in lean tissue mass and integrated electromyographic activity, respectively. Strength gains were accompanied by increases in crossing velocity, stride length and reductions in stride duration, stance and swing time for all gait tasks except for the foot targeting condition. Specific kinematic variables associated with safe obstacle traverse such as vertical obstacle heel clearance, limb flexion, horizontal foot placements prior to and at post obstacle crossing and landing velocities resulted in an improved crossing strategy in the experimental subjects. Significant increases in the vertical and anterior-posterior ground reaction forces accompanied the changes in the gait variables. While further long-term prospective studies of falls rates would be needed to confirm the benefits of lower limb enhanced strength, the findings of the present study provide conclusive evidence of significant improvements to gait efficiency associated with a systematic resistance-training program. It appears, however, that enhanced lower body strength has limited effects on gait tasks involving a dynamic balance component. In addition, due to the larger strength-induced increases in voluntary activation of the leg muscle compared to relatively smaller gains in lean tissue mass, neural adaptations appear to play a greater contributing role in explaining strength gains during the current resistance training protocol.

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.

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

[Truncated abstract] Limitation of sagittal plane dorsiflexion, or hallux limitus (HL), represents the second most commonly encountered pathomechanical disorder affecting the first metatarsophalangeal joint, after hallux valgus (HV). The kinematic role of the first metatarsophalangeal joint represents an integral component of the gait cycle. It has often been reported that for adequate leverage and propulsion to occur during normal gait, the hallux must be able to dorsiflex approximately 65° on the head of the first metatarsal. Secondary gait compensation mechanisms have often been observed clinically as a result of HL. The effect of HL on gait can be reflected in transverse plane alteration of the foot in relation to the line of progression during gait, defined as the angle of gait (AOG). The first purpose of this study served to investigate potential differences in dynamic angle of gait AOG in subjects with HL compared to a control group. A validated technique using coloured powdered footprints was used to quantify AOG. Furthermore, it was required to establish whether the relative amount of transverse plane motion observed in the AOG was related to factors intrinsic or extrinsic to the foot. Intrinsic factors such as the amount of forefoot to rearfoot abduction was considered, and achieved by measuring the rearfoot to forefoot axis (RFA) angle using a weight bearing composite (COMP) view radiograph. The remaining objectives of the study served to investigate other common aetiological factors associated with HL and their potential influence on AOG in subjects with HL ... Results further indicated that the amount of first metatarsophalangeal joint dorsiflexion did not appear to influence AOG in the two groups, and that AOG did not reflect the iii amount of forefoot to rearfoot abduction in a foot with HL compared to the control group. When comparing foot type, as indicated by CIA, it appeared AOG did not significantly alter between the HL and control groups. Finally, the results indicated AOG did not differ significantly between subjects with unilateral HL. This thesis study indicated that with the current sample population, the wide variability in AOG prevented detection of any subtle differences that may exist in subjects with HL. Results also emphasised the need to incorporate other variables such as symptomology and foot dominance when considering the effects first metatarsophalangeal joint pathology might have on HL, such as AOG.

[Truncated abstract] Hallux valgus (HV) is one of the most common foot deformities encountered in clinical practice. This complex deformity primarily affects the first metatarsophalangeal joint (MPJ), leading to altered foot structure and function. By virtue of the lateral displacement of the hallux on the first metatarsal, HV has the potential to influence adjacent joints of the foot. In doing so, function of the foot may be altered, and clinically this may result in abduction of the foot during the stance phase of gait. However the relationship between an abducted angle of gait (AOG) and HV has never been substantially examined. The purpose of this study is to investigate the relationship between HV and AOG, and determine if specific radiographic features are associated with the deformity or with a particular AOG. Such information would assist in understanding aetiological factors and the effects of intervention to treat the deformity ... Length and elevation of the first metatarsal were associated in subjects with HV, implying that length of the metatarsal may be related to whether or not it becomes elevated (R: 0.50, CI: 0.21, 0.71, P< 0.05). Similarly, an association was found between length of the first metatarsal and the amount of first MPJ dorsiflexion, suggesting perhaps length of the metatarsal has implications for first MPJ range of motion (R: -0.37, CI: -0.62, -0.04, P<0.05). However the amount of first MPJ dorsiflexion did not influence the AOG in HV subjects when compared to the control group. First MPJ dorsiflexion was also associated with the first intermetatarsal angle. Interestingly, the HV group alone did not show an association between the hallux abductus angle and the first intermetatarsal angle. The findings of this study are contrary to those suspected in clinical practice and alluded to in the literature. Despite the documented support for the biomechanical causes of HV, an abducted AOG was not significantly different in HV subjects when compared to controls. Possible explanations may have related to limitations of the present study including the size and gender demographics of the sample population, and greater variability in normal AOG ranges than reported in the literature. The present study indicated a possible need to gather information regarding foot dominance and leg length; factors extrinsic to the foot capable of influencing transverse plane orientation of the foot; and, the influence of symptoms and subsequent compensatory mechanisms adopted during gait.

Thesis (M.S.)--University of Delaware, 2008. / Principal faculty advisor: David A. Barlow, Dept. of Health, Nutrition, & Exercise Sciences. Includes bibliographical references.

Thesis (Ph. D)--University of Oregon, 2005. / Includes bibliographical references (leaves 94-101). Also available online (PDF file) by a subscription to the set or by purchasing the individual file.

Thesis (Ph. D.)--University of Oregon, 2005. / Includes bibliographical references (leaves 115-119). Also available online (PDF file) by a subscription to the set or by purchasing the individual file.

Thesis (Ph. D.)--University of Oregon, 2005. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 94-101). Also available for download via the World Wide Web; free to University of Oregon users.