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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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C. Collin Herb, Lisa Chinn, Jay Dicharry, Patrick O. McKeon, Joseph M. Hart and Jay Hertel

Chronic ankle instability (CAI) results in longstanding symptoms and subjective feelings of “giving way” following initial ankle sprain. Our purpose was to identify differences in joint coupling and variability between shank internal/external rotation and rearfoot inversion/eversion throughout the gait cycle of CAI subjects and healthy controls. Twenty-eight young adults participated (CAI, n = 15, control, n = 13). Kinematics were collected while walking and jogging on a treadmill. A vector coding method in which direction (θ) and magnitude of the angle-angle relationship and stride-to-stride variability (VCV) in shank-rearfoot coupling were calculated. In walking, the CAI group demonstrated lower θ, indicating a greater proportion of rearfoot-to-shank motion, compared with the control group in early and late swing. The CAI group had higher magnitude, indicating greater combined motion between the two segments, in early swing, but lower magnitude, indicating less combined motion, during late swing. The CAI group also had lower VCV measures, indicating less stride-to-stride variability during stance. In jogging, the CAI group had lower θ measures than the control group during stance and swing. Differences in shank-rearfoot coupling of the CAI group may be related to changes in sensorimotor control and lead to further instances of instability.

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Jay Hertel, Lauren C. Olmsted-Kramer and John H. Challis

A novel approach to quantifying postural stability in single leg stance is assessment of time-to-boundary (TTB) of center of pressure (COP) excursions. TTB measures estimate the time required for the COP to reach the boundary of the base of support if it were to continue on its instantaneous trajectory and velocity, thus quantifying the spatiotemporal characteristics of postural control. Our purposes were to examine: (a) the intrasession reliability of TTB and traditional COP-based measures of postural control, and (b) the correlations between these measures. Twenty-four young women completed three 10-second trials of single-limb quiet standing on each limb. Traditional measures included mean velocity, standard deviation, and range of mediolateral (ML) and anterior-posterior (AP) COP excursions. TTB variables were the absolute minimum, mean of minimum samples, and standard deviation of minimum samples in the ML and AP directions. The intrasession reliability of TTB measures was comparable to traditional COP based measures. Correlations between TTB and traditional COP based measures were weaker than those within each category of measures, indicating that TTB measures capture different aspects of postural control than traditional measures. TTB measures provide a unique method of assessing spatiotemporal characteristics of postural control during single limb stance.

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Gurtej S. Grewal, Rachel Baisch, Jacqueline Lee-Eng, Stephaine Wu, Beth Jarrett, Neil Humble and Bijan Najafi

Context:

Improvements in postural stability in figure skaters can play a significant role in performance, as well as reducing fall risk.

Objective:

To explore the effect of custom foot insoles on postural stability in advanced figure skaters.

Design:

Exploratory study.

Setting:

Out of laboratory.

Participants:

Nine advanced figure skaters were recruited and 7 completed the study (age 38 ± 18.5 y, body-mass index 25 ± 3.6 kg/m2).

Intervention:

Custom foot insoles.

Main Outcome Measures:

Primary outcome of changes in postural stability (PS) quantified by center-of-mass sway with secondary outcomes of ankleand hip-joint sway and joint range of motion. Sway measurements were assessed using body-worn sensors while participants wore skates on ice. PS was assessed in single-leg stance, as well as during gliding on the dominant foot.

Results:

A significant improvement in static PS was observed after 6-wk use of custom insoles. Center-of-mass sway reduced significantly on average by 48.44% (P = .023), and ankle-joint sway reduced by 45.7% (P = .05) during single-leg-stance balance measurements. During the gliding maneuver nonsignificant changes were observed for both ankle- and knee-joint range of motion.

Conclusion:

The results of this study suggest proof of concept toward benefits of custom insoles in improving postural stability in advanced figure skaters. To generalize the findings, randomized controlled trials with larger sample sizes are warranted.

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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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Erik B. Simonsen, Morten B. Svendsen, Andreas Nørreslet, Henrik K. Baldvinsson, Thomas Heilskov-Hansen, Peter K. Larsen, Tine Alkjær and Marius Henriksen

The aim of the study was to investigate the distribution of net joint moments in the lower extremities during walking on high-heeled shoes compared with barefooted walking at identical speed. Fourteen female subjects walked at 4 km/h across three force platforms while they were filmed by five digital video cameras operating at 50 frames/second. Both barefooted walking and walking on high-heeled shoes (heel height: 9 cm) were recorded. Net joint moments were calculated by 3D inverse dynamics. EMG was recorded from eight leg muscles. The knee extensor moment peak in the first half of the stance phase was doubled when walking on high heels. The knee joint angle showed that high-heeled walking caused the subjects to flex the knee joint significantly more in the first half of the stance phase. In the frontal plane a significant increase was observed in the knee joint abductor moment and the hip joint abductor moment. Several EMG parameters increased significantly when walking on high-heels. The results indicate a large increase in bone-on-bone forces in the knee joint directly caused by the increased knee joint extensor moment during high-heeled walking, which may explain the observed higher incidence of osteoarthritis in the knee joint in women as compared with men.

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Jeffrey M. Haddad, Jeff L. Gagnon, Christopher J. Hasson, Richard E.A. Van Emmerik and Joseph Hamill

Postural stability has traditionally been examined through spatial measures of the center of mass (CoM) or center of pressure (CoP), where larger amounts of CoM or CoP movements are considered signs of postural instability. However, for stabilization, the postural control system may utilize additional information about the CoM or CoP such as velocity, acceleration, and the temporal margin to a stability boundary. Postural time-to-contact (TtC) is a variable that can take into account this additional information about the CoM or CoP. Postural TtC is the time it would take the CoM or CoP, given its instantaneous trajectory, to contact a stability boundary. This is essentially the time the system has to reverse any perturbation before stance is threatened. Although this measure shows promise in assessing postural stability, the TtC values derived between studies are highly ambiguous due to major differences in how they are calculated. In this study, various methodologies used to assess postural TtC were compared during quiet stance and induced-sway conditions. The effects of the different methodologies on TtC values will be assessed, and issues regarding the interpretation of TtC data will also be discussed.

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Ferdous Wahid, Rezaul Begg, Noel Lythgo, Chris J. Hass, Saman Halgamuge and David C. Ackland

Normalization of gait data is performed to reduce the effects of intersubject variations due to physical characteristics. This study reports a multiple regression normalization approach for spatiotemporal gait data that takes into account intersubject variations in self-selected walking speed and physical properties including age, height, body mass, and sex. Spatiotemporal gait data including stride length, cadence, stance time, double support time, and stride time were obtained from healthy subjects including 782 children, 71 adults, 29 elderly subjects, and 28 elderly Parkinson’s disease (PD) patients. Data were normalized using standard dimensionless equations, a detrending method, and a multiple regression approach. After normalization using dimensionless equations and the detrending method, weak to moderate correlations between walking speed, physical properties, and spatiotemporal gait features were observed (0.01 < |r| < 0.88), whereas normalization using the multiple regression method reduced these correlations to weak values (|r| < 0.29). Data normalization using dimensionless equations and detrending resulted in significant differences in stride length and double support time of PD patients; however the multiple regression approach revealed significant differences in these features as well as in cadence, stance time, and stride time. The proposed multiple regression normalization may be useful in machine learning, gait classification, and clinical evaluation of pathological gait patterns.

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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.

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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.