Browsing by Subject "Dynamic stability"
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Item Dynamic stability of human walking during perturbations and voluntary gait changes(2011-05) Young, Patricia Mary; Dingwell, Jonathan B.; Barr, Ronald; Grabiner, Mark; Markey, Mia; Neptune, RichardFalling during walking leads to millions of emergency room visits every year for all age groups and is a significant medical concern. While gait training has shown some promise for fall prevention, we know relatively little about how humans maintain stability, how we can quantify it and how we can use this knowledge to increase the success of fall prevention training. In this dissertation, I studied how human stability responds to continuous, small magnitude perturbations and to voluntary changes in gait characteristics by examining movement variability and long-term and instantaneous dynamic stability. In the first set of experiments, participants were exposed to continuous, pseudo-random external perturbations of the visual field and support surface in a Computer Assisted Rehabilitation ENvironment (CAREN). Participants exhibited increased step widths, shorter step lengths and increased step variability, orbital and short-term local instability. Despite this, mean instantaneous lateral stability remained approximately constant. In the second set of experiments, participants voluntarily adopted changes in their step widths and step lengths. Wider steps were associated with increased step width variability, decreased nonlinear stability, decreased anterior-posterior margins of stability and increased instantaneous lateral stability. Shorter steps were associated with decreased short-term and orbital stability but did not affect mean instantaneous stability. When instantaneous stability was examined between steps, as opposed to as an average over many steps, results from both studies indicated a relationship between each step’s stability and the stability of the immediately preceding step. From these studies, we now know that unpredictable, continuous perturbations during human walking applied in a given direction can be used to elicit predictable responses in motion variability and stability in that same direction. We know that the type of stability examined can influence the conclusions drawn about an individual’s stability during perturbed walking. For example, an individual’s variability may indicate increased risk of falling while he or she simultaneously demonstrates increased orbital stability and instantaneous lateral stability. A challenge faced in this area of research will be to understand how quantitative measures of stability relate to how we perceive our stability.Item The effects of walking speed and an uneven surface on dynamic stability margins in young adult subjects with and without traumatic unilateral trans-tibial amputations(2009-12) Scott, Shawn James; Dingwell, Jonathan B.; Abraham, Larry; Jensen, Jody; Wilken, Jason M.; Childs, JohnDynamic stability is commonly defined as the ability to maintain balance through center of mass control during locomotion. Patients with locomotor impairments are especially challenged when walking over uneven surfaces (Richardson 2004). We studied dynamic stability margins in young healthy adults and in adults with unilateral traumatic trans-tibial amputations (TTA). To date, studies have not controlled for walking speed over an uneven surface in a patient population. We hypothesized that: 1) DSMs would increase over the uneven rocky surface (URS) for both groups, 2) DSMs would be greater on the involved side at faster walking speeds for subjects with TTA and, 3) DSMs would increase more for the involved limb when on the URS. 17 (4 females, 13 males) young healthy military service members (22.8 ± 6.4 years) and 12 (1 female, 11 males) service members (27.2 ± 4.7 years) with traumatic unilateral trans-tibial amputations participated in two study designs. A 15-segment model was used to estimate whole body COM motions. All subjects walked at 5 dimensionless speeds over a flat level surface (FLS) and an URS. Subjects completed 6-10 trials over each surface at each speed. Minimum frontal plane DSM values were extracted for each stride for statistical analyses. For young healthy subjects a two factor (speed x surface) ANOVA was used to test significance (p<.05). The DSMs were not greater over the URS (p=.307), but a main effect due to speed was found (p<.001) for young healthy subjects. In contrast, DSMs were significantly larger when subjects with TTA walked on the URS compared to the FLS (p = 0.011). For subjects with unilateral TTA, a three-factor ANCOVA ((amputation) side x speed x surface) with residual limb length (p=.029) and time in prosthesis (p=.741) as covariates was used for hypothesis testing. When limb length and time in prosthesis were accounted for there was no significant within subjects effect due to speed (p=.656). There were no significant differences between involved and uninvolved limbs (p = 0.211). There were no significant interaction effects. In conclusion, there was a difference in DSMs due to speed in unimpaired subjects and due to surface and residual limb length in subjects with unilateral TTAs. In subjects with unilateral TTA side-to-side symmetry was found for DSM measures, which was in contrast to an earlier study of subjects with unilateral trans-femoral amputations (Hof 2006). It appears that symmetry and dynamic stability are reasonable expectations for young adults with isolated TTAs.