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James W. Youdas, Erica F. Loder, Jody L. Moldenhauer, Christine R. Paulsen and John H. Hollman

Context:

Hip-abductor weakness is associated with many lower extremity injuries. A simple procedure to assess hip-abductor performance is necessary in patient populations.

Objective:

To describe the change in pelvic-on-femoral position of the stance limb before and after 45 seconds of resisted sidestepping.

Design:

Cross-sectional comparative.

Setting:

Laboratory.

Participants:

24 healthy women (24.6 ± 3.5 years) and 14 healthy men (24.5 ± 3.0 years).

Main Outcome Measures:

Pelvic-on-femoral position in degrees in single-leg stance before and after 45 seconds of resisted sidestepping.

Results:

The difference between the baseline and postexercise measurements for both men and women was significant (P < .05). The effect of the resisted-sidestepping exercise on the hip abductors was not statistically different between men and women.

Conclusions:

Forty-five seconds of resisted sidestepping using an elastic band produced a change in pelvic-on-femoral position in healthy adults. This test might be useful to detect impaired performance in hip abductors of patients with injury elsewhere in the musculoskeletal system.

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Daniel Maykranz, Sten Grimmer and Andre Seyfarth

The work-loop method is frequently used to determine the mechanical work performed by a system, for instance, when analyzing muscles or describing the work balance at the joint level. While for these examples usually only one-dimensional movements are investigated, for two- or three-dimensional movements, such as leg function during walking and running, the work-loop has to be adapted. In this paper, we present an analytical derivation that extends the work-loop method to two-dimensional sagittal plane movements. Three effects contribute to the mechanical work of the leg: (1) forces directed along the leg axis, (2) forces acting perpendicular to the leg axis, and (3) a shift of the center of pressure (COP) during stance. These three contributors to the mechanical work performed can be interpreted as three general tasks of the leg. To demonstrate the new work-loop method, we analyzed experimental data on hopping, running and walking. The results indicate that the proposed new generalized work-loop concept is suitable for describing the overall mechanical work performed on the COM during stance with energy consistent net work balances. Depending on the type of gait, specific contributions of each work term were found that characterize leg function during locomotion.

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Semyon Slobounov, Tao Wu and Mark Hallett

Human upright posture is a product of a complex dynamic system that relies on integration of input from multimodal sensory sources. Extensive research has explored the role of visual, vestibular, and somatosensory systems in the control of upright posture. However, the role of higher cognitive function in a participant’s assessment of postural stability has been less studied. In previous research, we showed specific neural activation patterns in EEG associated with recognition of unstable postures in young healthy participants. Similar EEG patterns have been recently observed in regulation of posture equilibrium in dynamic stances. This article evaluates participants’ postural stability in dynamic stances and neural activation patterns underlying visual recognition of unstable postures using event-related functional MRI (fMRI). Our results show that the “stable” participants were successful in recognition of unstable postures of a computer-animated body model and experienced egocentric motion. Successful recognition of unstable postures in these participants induces activation of distinct areas of the brain including bilateral parietal cortex, anterior cingulate cortex, and bilateral cerebellum. In addition, significant activation is observed in basal ganglia (caudate nucleus and putamen) but only during perception of animated postures. Our findings suggest the existence of modality-specific distributed activation of brain areas responsible for detection of postural instability.

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Kristof Kipp, Tyler N. Brown, Scott G. McLean and Riann M. Palmieri-Smith

The purpose of this study was to examine the combined impact of experience and decision making on frontal plane knee joint biomechanics during a cutting maneuver. Kinematic and kinetic data were collected from 12 recreationally active and 18 NCAA Division I female athletes during execution of anticipated and unanticipated single-leg land-and-cut maneuvers. Knee joint abduction angles and external knee joint abduction torques were calculated and discrete peak stance-phase variables were extracted. Angle and torque time-series data were also submitted to separate functional data analyses. Variables derived from the functional data analyses indicated that decision making influenced knee abduction angle and torque time series in the recreational group only. Specifically, these variables pointed to greater knee abduction at the end of stance as well as a greater, albeit delayed peak in knee abduction torque at the beginning of landing in the recreational athletes during the unanticipated condition. In addition, the recreational athletes displayed greater discrete peak knee abduction angles than the Division I athletes regardless of condition. Discrete peak knee abduction torque did not differ between groups or conditions.

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Heydar Sadeghi, Francois Prince, Karl F. Zabjek and Paul Allard

In this study, tasks of the hip in elderly and young gait were identified using principal-component analysis (PCA). Discrepancies between older and younger participants for hip-flexor and -extensor action during stance were also investigated. PCA was applied to the sagittal-hip-muscle-power curves of participants. Three principal components (PCs) were retained for further analysis. A t test revealed that all measures of gait spatiotemporal parameters were significantly lower in the older participants (p < .05). The first PC for both groups extracted the largest variation and described hip-power action during midistance. The second and third PCs in the older participants highlighted the role of the hip extensors and flexors during weight acceptance, late stance, and pull-off. The corresponding PCs for the younger participants were mainly associated with hip-extensor/flexor action during pull-off and weight acceptance. The results indicate that the hip-extensor/flexor muscles are mainly responsible for balance control in elderly gait but contribute to both balance control and propulsion in the gait of younger individuals.

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Andrew W. Smith

The aims of the present study were to quantify lower limb kinetics and kinematics during walking and slow jogging of below-knee amputee athletes and to demonstrate the usefulness of the additional information provided by kinetic analyses as compared to that of kinematic assessments alone. Kinematic and force platform data from three amputee subjects were collected while the subjects walked and jogged in the laboratory. Results indicated that neither prosthesis (SACH and an energy-storing carbon fiber or ESCF) emulated the kinetics or the kinematics of so-called normal gait during walking. While the knee joint on the prosthetic side clearly tended to be biased toward extension during stance, the knee flexors were dominant and acted concentrically during this phase of the gait cycle. An examination of prosthetic limb hip and knee joint kinetics at both cadences revealed the functional role played by the hamstrings early in stance. The results indicated that with increasing cadence, less variability, measured by coefficients of variation, was evident in the kinematic data while the opposite was true for the kinetics.

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Tyler B. Weaver, Christine Ma and Andrew C. Laing

The Nintendo Wii Balance Board (WBB) has become popular as a low-cost alternative to research-grade force plates. The purposes of this study were to characterize a series of technical specifications for the WBB, to compare balance control metrics derived from time-varying center of pressure (COP) signals collected simultaneously from a WBB and a research-grade force plate, and to investigate the effects of battery life. Drift, linearity, hysteresis, mass accuracy, uniformity of response, and COP accuracy were assessed from a WBB. In addition, 6 participants completed an eyes-closed quiet standing task on the WBB (at 3 battery life levels) mounted on a force plate while sway was simultaneously measured by both systems. Characterization results were all associated with less than 1% error. R 2 values reflecting WBB sensor linearity were > .99. Known and measured COP differences were lowest at the center of the WBB and greatest at the corners. Between-device differences in quiet stance COP summary metrics were of limited clinical significance. Lastly, battery life did not affect WBB COP accuracy, but did influence 2 of 8 quiet stance WBB parameters. This study provides general support for the WBB as a low-cost alternative to research-grade force plates for quantifying COP movement during standing.

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Astrid Bergland, Hilde Sylliaas, Gun Britt Jarnlo and Torgeir Bruun Wyller

The aim of this study was to investigate walking and health among woman age 75 yr or older, in the associations between the highest step up performed without support by an individual and balance, walking, and health among women age 75+. Records of the highest step, balance, walking, and health were made for 307 women age 75–93 yr living in the community. Eighty percent managed to climb steps higher than 20 cm. There was a statistically significant negative relationship between age and stair-climbing capacity. The highest steps registered were significantly and independently associated with a short time on the timed up-and-go test, long functional reach, low body weight, lack of perceived difficulty walking outdoors, low number of “missteps” when walking in a figure of 8, longer time in one-leg stance, ability to carry out tandem stance, no walking aids outdoors, and not being afraid of falling. These variables together explained 67% of the variance in the step-height score.

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James W. Youdas, Sara T. Mraz, Barbara J. Norstad, Jennifer J. Schinke and John H. Hollman

Context:

Hip abductor muscle weakness is related to many lower extremity injuries. A simple procedure, the Trendelenburg test, may be used to assess hip abductor performance in patient populations.

Objective:

To describe the minimal detectable change (MDC) in pelvic-on-femoral (P-O-F) position of the stance limb during the Trendelenburg test.

Setting:

Laboratory.

Participants:

45 healthy women (28 ± 8 years) and 45 healthy men (33 ± 11 years).

Main Outcome Measures:

P-O-F position in degrees in single-leg stance. Results: Baseline P-O-F position (hip adduction) was 83° ± 3° with a range from 76° to 94°. The intratester reliability (ICC3,1 for measurement of P-O-F position using a universal goniometer was 0.58 with a standard error of measurement (SEM) of 2°. The minimal detectable change (MDC) was calculated to be 4°.

Conclusions:

If a person’s P-O-F position changes less than 4° between measurements, then the P-O-F position is within measurement error and it can be determined that there has been no change in the performance of the hip abductor muscles when examined by the Trendelenburg test.

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Kazuhiro Ishimura and Shinji Sakurai

This study investigates the potential asymmetries between inside and outside legs in determinants of curved running speed. To test these asymmetries, a deterministic model of curved running speed was constructed based on components of step length and frequency, including the distances and times of different step phases, takeoff speed and angle, velocities in different directions, and relative height of the runner’s center of gravity. Eighteen athletes sprinted 60 m on the curved path of a 400-m track; trials were recorded using a motion-capture system. The variables were calculated following the deterministic model. The average speeds were identical between the 2 sides; however, the step length and frequency were asymmetric. In straight sprinting, there is a trade-off relationship between the step length and frequency; however, such a trade-off relationship was not observed in each step of curved sprinting in this study. Asymmetric vertical velocity at takeoff resulted in an asymmetric flight distance and time. The runners changed the running direction significantly during the outside foot stance because of the asymmetric centripetal force. Moreover, the outside leg had a larger tangential force and shorter stance time. These asymmetries between legs indicated the outside leg plays an important role in curved sprinting.