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Ricky Anderson, Carol Courtney and Eli Carmeli

The purpose of this study was to see if vastus medialis oblique/vastus lateralis (VMO:VL) ratios could be increased by widening the squat stance and if the VMO activity increases with deeper ranges of knee flexion. Fifteen healthy subjects performed unloaded narrow and wide stance squats through three ranges of knee flexion: 30°, 60°, and 90°. The two squat stances were compared using a 2 × 3 ANOVA to see if the wide-stance squat had any significant difference in EMG activity for VMO: VL ratios compared to the narrow-stance squat. The difference in EMG activity of the VMO between the various angles for both squat stances was also compared. The ANOVA revealed no significant differences between the squat stances for VMO:VL ratios but did show the VMO:VL ratios to be significantly higher with increasing knee flexion angles. These findings suggest that the VMO is active throughout the 90° range and that increasing knee flexion angles can elicit greater activity of the VMO relative to the VL.

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Jack R. Engsberg, Kathy G. Tedford, James A. Harder and Jocelyn P. Mills

This investigation compared stance, swing, and double support times of a recent below-the-knee amputee (BKA) child’s gait with the gait of normal children and with that of experienced BKA children. Kinematic data were collected for 11 normal children, 2 experienced BKA children, and a novice BKA child. Results indicated there were significant differences between the steps of prosthetic and nonprosthetic limbs and between normals and BKAs. Initially the gait of the novice BKA differed from that of experienced BKAs. After 94 days the gait of the novice BKA was not significantly different from that of the experienced BKAs. It was concluded that since the structure and function of the prosthetic limb is not the same as normal, (a) it may be appropriate for the BKA child to have an asymmetrical gait pattern, and (b) rehabilitation may be directed toward teaching the recent BKA child to walk more like experienced BKAs than like normal children.

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Stephen C. Cobb, Mukta N. Joshi, David M. Bazett-Jones and Jennifer E. Earl-Boehm

The effect of time-to-boundary minima selection and stability limit definition was investigated during eyes open and eyes closed condition single-limb stance postural stability. Anteroposterior and mediolateral time-to-boundary were computed using the mean and standard deviation (SD) of all time-to-boundary minima during a trial, and the mean and SD of only the 10 absolute time-to-boundary minima. Time-to-boundary with rectangular, trapezoidal, and multisegmented polygon defined stability limits were also calculated. Spearman’s rank correlation coefficient test results revealed significant medium-large correlations between anteroposterior and mediolateral time-to-boundary scores calculated using both the mean and SD of the 10 absolute time-to-boundary minima and of all the time-to-boundary minima. Friedman test results revealed significant mediolateral time-to-boundary differences between boundary shape definitions. Follow-up Wilcoxon signed rank test results revealed significant differences between the rectangular boundary shape and both the trapezoidal and multisegmented polygon shapes during the eyes open and eyes closed conditions when both the mean and the SD of the time-to-boundary minima were used to represent postural stability. Significant differences were also revealed between the trapezoidal and multisegmented polygon definitions during the eyes open condition when the SD of the time-to-boundary minima was used to represent postural stability. Based on these findings, the overall results (i.e., stable versus unstable participants or groups) of studies computing postural stability using different minima selection can be compared. With respect to boundary shape, the trapezoid or multisegmented polygon shapes may be more appropriate than the rectangular shape as they more closely represent the anatomical shape of the stance foot.

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Mansour Eslami, Mohsen Damavandi and Reed Ferber

There is evidence to suggest that navicular drop measures are associated with specific lower-extremity gait biomechanical parameters. The aim of this study was to examine the relationship between navicular drop and a) rearfoot eversion excursion, b) tibial internal rotation excursion, c) peak ankle inversion moment, and d) peak knee adduction moment during the stance phase of running. Sixteen able-bodied men having an average age of 28.1 (SD = 5.30) years, weight of 81.5 (SD = 10.40) kg, height of 179.1 (SD = 5.42) cm volunteered and ran barefoot at 170 steps/minute over a force plate. Navicular drop measures were negatively correlated with tibial internal rotation excursion (r = −0.53, P = .01) but not with rearfoot eversion excursion (r = −0.19; P = .23). Significant positive correlations were found between navicular drop and peak knee adduction moment (r = .62, P < .01) and peak ankle inversion moment (r = .60, P < .01). These findings suggest that a low navicular drop measure could be associated with increasing tibial rotation excursion while high navicular drop measure could be associated with increased peak ankle and knee joint moments. These findings indicate that measures of navicular drop explained between 28% and 38% of the variability for measures of tibial internal rotation excursion, peak knee adduction moment and peak ankle inversion moments.

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Andreia S. P. Sousa and João Manuel R. S. Tavares

This study aims to assess the influence of gait speed (manipulated through cadence) on muscle activity patterns and activation degree during stance.

Methods:

Thirtyfive healthy individuals participated in this study. Surface electromyographic activity from the gastrocnemius medialis (GM), gluteus maximus (GMax), biceps femoris (BF) and rectus femoris (RF) was acquired with subjects walking at three different speeds.

Results:

Speed influenced: (1) relative motor activity patterns at heel strike, midstance-propulsion transition and propulsion; (2) the activity level of RF, GMax, GM and BF, in decreasing order, with higher activity at the fastest and slowest speeds.

Conclusions:

In general, muscle activity was higher at the fastest and slowest speeds than at the self-selected speed and only the activity of the main actions in each subphase remained stable. These findings suggest that gait speeds different from the self-selected speed influence not only activity levels but also relative muscle activity patterns. As a result, caution is advised when choosing standard speeds in gait studies, as this can lead to increased variability in relative muscle activity patterns.

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Cameron Powden and Matthew Hoch

Context:

Currently, there are limited guidelines for the trial duration of quiet single-limb postural control tests. However, trial duration may influence the results of postural control assessments.

Objective:

To examine the effect of trial duration on instrumented measures of postural control in healthy adults.

Design:

Cross-sectional.

Setting:

Laboratory.

Patients or Other Participants:

Ten healthy adults (eight females, two males; age = 22.1 ± 1.5 years; 167.4 ± 9.3 cm; 67.4 ± 12.3 kg).

Interventions:

Static postural control was assessed using quiet single-limb stance on a force plate. With eyes open and closed, participants stood barefoot on one limb. Instructions were stand with hands on hips and remain as motionless as possible. A practice trial was performed before the collection of three 10 s trials on each limb for each visual condition. The data collected during each trial were analyzed as the initial 2.5 s, the initial 5 s, and 10 s.

Main outcome Measures:

The independent variables included vision, limb, and trial duration. The dependent variables included postural control examined using time-to-boundary (TTB) variables: mean of TTB minima (TTB-M) and the standard deviation of TTB minima (TTB-SD) in the anterior-posterior (AP) and medial-lateral (ML) directions.

Results:

No significant 3-way or 2-way interactions or limb main effects were identified. Main effects were identified for vision and trial duration in all TTB variables. Post hoc analysis revealed significant differences between all trial durations in all TTB variables.

conclusions:

Greater TTB values were exhibited during the 10 s trial durations compared with 5 s and 2.5 s, and 5 s trial durations compared with 2.5 s, indicating postural control improved with longer trial durations. This suggests differing aspects of postural control may be examined with different trial durations.

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Hana Debevec, Douglas R. Pedersen, Aleš Iglic̆ and Matej Daniel

It was shown in several clinical studies that static one-legged stance may be a relevant body position to describe the loads acting at the hip. However, the stress distribution averaged during movement may better describe hip load than hip contact stress distribution in the static body position. Using data on the resultant hip force during walking taken from the measurements of Bergmann (2001), spatial distribution of contact stress over the articular surface was calculated by the HIPSTRESS method and compared with the stress distribution in one-legged stance. It is shown, that the shape of the contact stress distribution during one-legged stance closely resembled the averaged contact stress distribution during the walking cycle (Pearson’s correlation coefficient R 2 = .986; p < .001). This finding presents a link between the hypothesis that the averaged contact stress distribution during a walking cycle is crucial for cartilage development and the results of clinical studies in which the calculated distribution of contact stress in one-legged stance was successfully used to predict the clinical status of the hip.

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Neil E. Bezodis, Aki I.T. Salo and Grant Trewartha

Two-dimensional analyses of sprint kinetics are commonly undertaken but often ignore the metatarsal-phalangeal (MTP) joint and model the foot as a single segment. The aim of this study was to quantify the role of the MTP joint in the early acceleration phase of a sprint and to investigate the effect of ignoring the MTP joint on the calculated joint kinetics at the other stance leg joints. High-speed video and force platform data were collected from four to five trials for each of three international athletes. Resultant joint moments, powers, and net work at the stance leg joints during the first stance phase after block clearance were calculated using three different foot models. Considerable MTP joint range of motion (>30°) and a peak net MTP plantar flexor moment of magnitude similar to the knee joint were observed, thus highlighting the need to include this joint for a more complete picture of the lower limb energetics during early acceleration. Inclusion of the MTP joint had minimal effect on the calculated joint moments, but some of the calculated joint power and work values were significantly (P < .05) and meaningfully affected, particularly at the ankle. The choice of foot model is therefore an important consideration when investigating specific aspects of sprinting technique.

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Adrienne E. Hunt and Richard M. Smith

Three-dimensional ankle joint moments were calculated in two separate coordinate systems, from 18 healthy men during the stance phase of walking, and were then compared. The objective was to determine the extent of differences in the calculated moments between these two commonly used systems and their impact on interpretation. Video motion data were obtained using skin surface markers, and ground reaction force data were recorded from a force platform. Moments acting on the foot were calculated about three orthogonal axes, in a global coordinate system (GCS) and also in a segmental coordinate system (SCS). No differences were found for the sagittal moments. However, compared to the SCS, the GCS significantly (p < .001) overestimated the predominant invertor moment at midstance and until after heel rise. It also significantly (p < .05) underestimated the late stance evertor moment. This frontal plane discrepancy was attributed to sensitivity of the GCS to the degree of abduction of the foot. For the transverse plane, the abductor moment peaked earlier (p < .01) and was relatively smaller (p < .01) in the GCS. Variability in the transverse plane was greater for the SCS, and attributed to its sensitivity to the degree of rearfoot inversion. We conclude that the two coordinate systems result in different calculations of nonsagittal moments at the ankle joint during walking. We propose that the body-based SCS provides a more meaningful interpretation of function than the GCS and would be the preferred method in clinical research, for example where there is marked abduction of the foot.

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Nooranida Arifin, Noor Azuan Abu Osman and Wan Abu Bakar Wan Abas

The measurements of postural balance often involve measurement error, which affects the analysis and interpretation of the outcomes. In most of the existing clinical rehabilitation research, the ability to produce reliable measures is a prerequisite for an accurate assessment of an intervention after a period of time. Although clinical balance assessment has been performed in previous study, none has determined the intrarater test-retest reliability of static and dynamic stability indexes during dominant single stance. In this study, one rater examined 20 healthy university students (female = 12, male = 8) in two sessions separated by 7 day intervals. Three stability indexes—the overall stability index (OSI), anterior/posterior stability index (APSI), and medial/lateral stability index (MLSI) in static and dynamic conditions—were measured during single dominant stance. Intraclass correlation coefficient (ICC), standard error measurement (SEM) and 95% confidence interval (95% CI) were calculated. Test-retest ICCs for OSI, APSI, and MLSI were 0.85, 0.78, and 0.84 during static condition and were 0.77, 0.77, and 0.65 during dynamic condition, respectively. We concluded that the postural stability assessment using Biodex stability system demonstrates good-to-excellent test-retest reliability over a 1 week time interval.