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Jianning Wu and Jue Wang

In this technical note, we investigate a combination PCA with SVM to classify gait pattern based on kinetic data. The gait data of 30 young and 30 elderly participants were recorded using a strain gauge force platform during normal walking. The gait features were first extracted from the recorded vertical directional foot– ground reaction forces curve using PCA, and then these extracted features were adopted to develop the SVM gait classifier. The test results indicated that the performance of PCA-based SVM was on average 90% to recognize young– elderly gait patterns, resulting in a markedly improved performance over an artificial neural network–based classifier. The classification ability of the SVM with polynomial and radial basis function kernels was superior to that of the SVM with linear kernel. These results suggest that the proposed technique could provide an effective tool for gait classification in future clinical applications.

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Stephen P. Messier, Walter H. Ettinger Jr, Thomas E. Doyle, Timothy Morgan, Margaret K. James, Mary L. O'Toole and Robert Burns

The purpose of our study was to examine the association between obesity and gait mechanics in older adults with knee osteoarthritis (OA). Subjects were 101 older adults (25 males and 76 females) with knee OA. High-speed video analysis and a force platform were used to record sagittal view lower extremity kinematic data and ground reaction forces. Increased body mass index (BMI) was significantly related to both decreases in walking velocity and knee maximum extension. There were no significant relationships between BMI and any of the hip or ankle kinematic variables. BMI was directly related to vertical force minimum and maximum values, vertical impulse, and loading rate. Increases in braking and propulsive forces were significantly correlated with increased BMI. Maximum medially and laterally directed ground reaction forces were positively correlated with BMI. Our results suggests that, in subjects with knee OA, obesity is associated with an alteration in gait.

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Clare B. Johnson, Shannon L. Mihalko and Karl M. Newell

The study reported had three purposes, namely, to analyze the effect of aging (cohort groups 20–29, 60–69, 70–79, and 80–89 years of age), step length, and self-efficacy on the time to reacquire stability after the execution of a step. The analysis of force-platform data showed that the time to reacquire a stable posture after taking a step increased with increments of age. Correlation analysis showed that older adults were less confident in their ability to complete daily activities without falling or losing balance and that participants with lower levels of balance-related efficacy required a longer time to reacquire stability. These findings provide evidence that aging imposes temporal limitations in the regaining of postural stability that are related to individuals’ perceptions of balance and falls efficacy.

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Telassin Silva Homem, Fernando Silva Guimarães, Maurício Santos Soares, Leandro Kasuki, Mônica Roberto Gadelha and Agnaldo José Lopes

Advances in the knowledge of acromegaly are leading to an increase in the survival rate of acromegalic subjects. This study was conducted to evaluate balance control, risk of falls, and peripheral muscle function in acromegalic older adults. Seventeen older subjects with acromegaly (67 [63–73] years) and 20 paired control subjects were evaluated with balance scales, force platform, and knee isokinetic dynamometry tests. There were significant differences between the groups on several balance and gait scales, with a worse performance and greater risk of falls in the acromegalic older adults. Acromegalic older adults had lower values for peak torque, maximum repetition of the total work, and total work during extension at 240°/s. The acromegalic older adults had higher values in the medial-lateral range. Acromegaly subjects had lateral instability that compromises their body balance and increases the risk of falls. Moreover, there was a propensity for muscle fatigue in these individuals.

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Alexander S. Aruin and Gil L. Almeida

The hypothesis that persons with Down syndrome are likely to trade mechanical efficacy of motor patterns for safety was tested in a study of postural adjustments associated with fast voluntary movements. Control subjects and subjects with Down syndrome performed bilateral shoulder flexion and extension movements “as fast as possible” while standing on a force platform. Anticipatory changes in the background activity of postural muscles were seen in both groups of subjects. Subjects with Down syndrome demonstrated simultaneous EMG bursts in postural “agonist-antagonist” pairs. Subjects with Down syndrome also demonstrated patterns of deviations in the major postural joints, suggesting that they were using a different strategy which may be a correlate of “clumsiness.” It was concluded that practice in conditions of changing components of a motor task is the most promising way to encourage the central nervous system of persons with Down syndrome to search for alternative strategies and improve these individuals' ability to solve everyday motor problems.

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Sean Clark, Peter W. Iltis, Crystal J. Anthony and Andrea Toews

Despite widespread use of the functional-reach (FR) and limits-of-stability (LOS) tests, comparisons of postural strategies and postural limits for these tests have not been previously reported. The purpose of this study was to compare postural strategies as determined by cross-correlation analyses of trunk and lower leg angular displacements and postural limits as assessed by maximum center-of-gravity (COG) excursions as older adults at low fall risk completed the FR and LOS tests. Fourteen older adults completed three FR and LOS trials while standing on a Balance Master® force platform. Results indicated that despite relatively similar instructions to reach or lean as far as possible without losing balance or altering the base of support, their performance differed with regard to postural strategies employed and maximum COG excursions produced. These findings suggest that because of differences in task constraints, FR and LOS tests should not be used interchangeably.

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Kathy J. Simpson, Eugene G. Jameson and Susan Odum

Patellofemoral dysfunctions due to abnormal force loading are significant problems for dancers. Increased jump length was predicted to require increased quadriceps force during landing, which would increase patellofemoral forces and pressures. Six female dancers performed 10 traveling jumps each at 30, 60, and 90% maximum jump displacements (JDs). A sagittal view of the landing onto a force platform (500 Hz) was filmed (100 fps). Repeated-measures ANOVA (JD) and Scheffé post hoc analyses (p < .05) showed that greater peak patellofemoral pressures occurred at longer JDs and the corresponding times to these events decreased and knee flexion increased. Previous research and these findings indicate that different regions of the patella may endure higher loads at greater JDs even though the contact areas increase with greater patellofemoral forces. However, greater knee flexion and velocity could indicate more rapid distribution of load to various patellar regions, which would reduce the time any given patellofemoral region would be subjected to high loads.

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Patrice Rougier and Mélanie Garin

To determine the relationship between eye movement and postural control on an undisturbed upright stance maintenance protocol, 15 young, healthy individuals were tested in various conditions. These conditions included imposed blinking patterns and horizontal and vertical saccadic eye movements. The directions taken by the center of pressure (CP) were recorded via a force platform on which the participants remained in an upright position. The CP trajectories were used to estimate, via a low-pass filter, the vertically projected movements of the center of gravity (CGv) and consequently the difference CP-CGv. An analysis of the frequency shows that regular bilateral blinking does not produce a significant change in postural control. In contrast, performing saccadic eye movements induces some reduced amplitude for both basic CGv and CP-CGv movements principally along the antero-posterior axis. The present result supports the theory that some ocular movements may modify postural control in the maintenance of the upright standing position in human participants.

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George Vagenas and T. Blaine Hoshizaki

The sprint starts of 15 skilled sprinters were filmed and their sprinting times recorded while they were performing four 20-meter sprinting trials. They employed their natural hand-block spacings with alternative leg placements in the front starting block. The subjects were tested for dynamic strength on a force platform and their stronger leg was determined. Selected qualitative variables concerning certain perceived characteristics of lateral dominance and preferred leg for some basic motor skills were identified using a questionnaire. Significantly greater takeoff velocities and faster sprinting times were found when the stronger leg was placed in the front block. Previous empirical methods used in determining the best front leg in the start were found unreliable. Even some experienced sprinters fail to use their optimal leg in the forward position. Dynamic lower limb strength asymmetry was established as the key determinant in optimizing leg placement in the sprint start.

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John B. Cronin, Eadric Bressel and Loren Finn

Context:

Frequency and magnitude of ground reaction forces (GRF) have been implicated in causing injuries such as “jumpers knee.”

Objective:

To investigate whether a single session of augmented feedback concerning landing technique would decrease GRF.

Design:

Pretest posttest experimental design.

Setting:

University biomechanics laboratory.

Participants:

Fifteen female Division 1 intercollegiate volleyball players.

Intervention:

Participants were required to land on a force platform after spiking a volleyball from a four-step approach before and after an intervention involving visual and aural augmented feedback on correct jumping and landing technique.

Main Outcome Measures:

Mediolateral (ML), anterioposterior (AP), and vertical (V) GRF normalized to body weight (BW).

Results:

Augmented feedback was found to significantly (P = 0.01) decrease VGRF by 23.6% but not ML (25%, P = 0.16) and AP (4.9%, P = 0.40) peak GRF.

Conclusions:

A single session of augmented feedback may be effective in reducing VGRF in collegiate athletes.