No / Motion at the midfoot joints can contribute significantly to overall foot motion during gait. However, there is little information regarding the kinematic coupling relationship at the midfoot. The purpose of the present study was to determine whether the coupling relationship at the midfoot and subtalar joints was affected when step width was manipulated during running. Twelve subjects ran over-ground at self-selected speeds using three different step widths (normal, wide, cross-over). Coupling at the midfoot (forefoot relative to rearfoot) and subtalar (rearfoot relative to shank) joints was assessed using cross-correlation techniques. Rearfoot kinematics were significantly different from normal running in cross-over running (P < 0.05) but not in wide running. However, coupling between rearfoot eversion/inversion and shank rotation was consistently high (r > 0.917), regardless of step width. This was also the case for coupling between rearfoot frontal plane motion and forefoot sagittal plane (r < 0.852) and forefoot transverse plane (r > 0.946) motion. There was little evidence of coupling between rearfoot frontal plane motion and forefoot frontal plane motion in any of the conditions. Forefoot frontal plane motion appeared to have little effect on rearfoot frontal plane motion and thus, had no effect on motion at the subtalar joint. The strong coupling of forefoot sagittal and transverse plane motions with rearfoot frontal plane motion suggests that forefoot motion exerts an important influence on subtalar joint kinematics.

A number of parameters have been identified as characteristic of the walking pattern in patients with INPH. Most of these have been identified through qualitative surveys and manually conducted test batteries. In order to obtain quantitative, standardized and objective measures, which enable studies based on larger patient populations and comparable results, there is a need for a user-friendly system that can measure specific key parameters over time in a reliable manner in everyday clinical work. Step height, width and the variability in the gait cycle are such parameters which are interesting research areas for this group of patient. Problems with balance and gait are very common in other patient groups as well, particularly in neurological diseases such as Parkinson's disease, multiple sclerosis and stroke. This is the reason that the development of this gait analyzer is performed. Giving access to a simple and objective method for estimating gait and balance ability in clinical routine investigations would increase the ability to provide the right kind of treatment, confirm treatment results, and conducting larger research studies. Therefore, this equipment can contribute to the assessment of diseases which contain impaired gait. As a first test of the usability and for the validation of accuracy and repeatability of the equipment a group of healthy volunteers was used. Results from tests on healthy subjects show god repeatability between measurements, for step width at normal gait the difference was -0,2 ±0,34 cm (mean, ±SD) and step height 0,69 ±3,34 cm. The stride time variability in the healthy group where very small 0,00048 ±0,00028 s2 with a difference between test of 0,000019 ±0,00038 s2. Three pilot patients have been tested where we have clearly seen indications of increased stride time variability and reduced step height.

Falling 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. / text

The best results in a sprint running are based upon covering the distance in the shortest possible time, and therefore performance has to be maximized. To achieve the best performance, the sprinter has to develop the greatest forward acceleration, reach his/her maximal speed, and keep it over the run. The greatest anteroposterior acceleration is generated in the first stance of a sprint due to the greatest propulsive force production. Thus, the first step was selected to study induced accelerations by the main muscles of the lower limb. Since a wider step width was founded out to help with force generation during long foot-ground contacts, an elite sprinter with a wide step width was selected. Ankle plantarflexors were the main contributors to body propulsion and support, while knee extensors decelerated forward propulsion but induced medial accelerations. Hip extensors and hip adductors did not offer a remarkable contribution to body COM acceleration in any direction.

Falls and their consequences among older people are a serious medical and public health problem. Identifying individuals at risk of falling is therefore a major concern. The purpose of this thesis was to evaluate measurement tools of balance control and their predictive value when screening for fall risk in physically dependent individuals ≥65 years old living in residential care facilities, and physically independent individuals ≥75 years old living in the community. Following baseline assessments falls were monitored during six months in physically dependent individuals based on staff reports, and during one year in physically independent individuals based on self reports. In physically dependent individuals test-retest reliability of the Timed Up&amp;Go test (TUG) was established in relation to cognitive impairment. Absolute reliability measures exposed substantial day-to-day variability in mobility performance at an individual level despite excellent relative reliability (ICC 1.1 &gt;0.90) regardless of cognitive function (MMSE ≥10). Fifty-three percent of the participants fell at least once during follow-up. Staff judgement of their residents’ fall risk had the best prognostic value for ruling in a fall risk in individuals judged with ‘high risk’ (positive Likelihood ratio, LR+ 2.8). Timed, and subjective rating of fall risk (modified Get Up&amp;Go test, GUG-m) were useful for ruling out a high fall risk in individuals with TUG scores &lt;15 seconds (negative LR, LR- 0.1) and GUG-m scores of ‘no fall risk’ (LR- 0.4), however few participants achieved such scores. In physically independent individuals balance control was challenged by dual-task performances. Subsequent dual-task costs in gait (DTC), i.e. the difference between single walking and walking with a simultaneous second task, were registered using an electronic mat. Forty-eight percent of the participants fell at least once during follow-up. A small prognostic guidance for ruling in a high fall risk was found for DTC in mean step width of ≤3.7 mm with a manual task (LR+ 2.3), and a small guidance for ruling out a high fall risk with DTC in mean step width of ≤3.6 mm with a cognitive task (LR- 0.5). In cross-sectional evaluations DTC related to an increased fall risk were associated with: sub-maximal physical performance stance scores (Odds Ratio, OR, 3.2 to 3.8), lower self-reported balance confidence (OR 2.6), higher activity avoidance (OR 2.1), mobility disability (OR 4.0), and cautious walking out-door (OR 3.0). However, these other measures of physical function failed to provide any guidance to fall risk in this population of seemingly able older persons. In conclusion – Fall risk assessments may guide clinicians in two directions, either in ruling in or in ruling out a high fall risk. A single cut-off score, however, does not necessarily give guidance in both directions. Staff experienced knowledge is superior to a single assessment of mobility performance for ruling in a high fall risk. Clinicians need to consider the day-to-day variability in mobility when interpreting the TUG score of a physically dependent individual. DTC of gait can, depending on the type of secondary task, indicate a functional limitation related to an increased fall risk or a flexible capacity related to a decreased fall risk. DTC in mean step width seems to be a valid measure of balance control in physically independent older people and may be a valuable part of the physical examination of balance and gait when screening for fall risk as other measures of balance control may fail to provide any guidance of fall risk in this population.