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James L. Croft, Vinzenz von Tscharner and Ronald F. Zernicke

Compliant surfaces are used to challenge postural stability, but assessments are frequently limited to summary measures of center of pressure that do not provide insights into the temporal dynamics of motor coordination. Here, we measured center-of-pressure changes on three surfaces (solid, foam, and air-filled disc) and quantified the relative timing of changes in joint angles and muscle activity with respect to center-of-pressure changes. Nine active male subjects (20–30 years old) performed ten 30-s trials of unipedal stance on each of the three surfaces. Sway range, mean sway, mean sway velocity, path length, and fitted ellipse area increased, monotonically, from solid surface to foam to air-filled disc. The number of significant cross-correlations was greater for the compliant surfaces compared with the solid surface. Muscle activity preceded changes in center-of-pressure displacement, with the type of surface affecting the magnitude of the lead in the mediolateral direction. Center of pressure was more constrained on less stable surfaces and in the mediolateral direction.

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Jong Hyun Yang and Young Suk Lee

The purpose of this study was to find the defensive stance and calculate an optimal defense position for goalkeepers while blocking forward jump shots made from a distance of 9 m. Nine men’s handball matches were recorded and 78 video clips were selected for analysis. These are the top class goalkeepers, which included players from the national team and reserve team of Korea. The goalkeeper’s actual defensive position was significantly different from instructional suggestions; the width of both feet of the goalkeeper was approximately 2.5 times the width of the shoulders, and the hands were at waist height. The goalkeeper’s actual defense position was about 1.10 (± 0.3) m from the goal line and also significantly different than instructional material (0.75 m). The optimal defense position, which was calculated from the goalkeeper’s actual movement, was 1.44 m from the goal line, because the ratio of goalkeeper’s defensive area in relation to the total area to be defended is highest at this point. In summary, we recommended that handball goalkeepers move forward, about a half step (0.34 m), when defending a forward jump shot made from 9 m, and instructional material should be modified according to the findings from this study.

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Jaap Swanenburg, Anne Gabrielle Mittaz Hager, Arian Nevzati and Andreas Klipstein

The purpose of this prospective cohort study was to determine whether the maximal width of the base of support (BSW) measure is able to predict the risk of multiple falls in community-dwelling women. Thirty-eight community-dwelling women (mean age of 72 ± 8 years old) participated. Falls were prospectively recorded during the following year. Overall, 29 falls were recorded; six (16%) women were multiple fallers and 32 (84%) were nonfallers. There was a significant difference in the BSW between the fallers and nonfallers (F[1, 37] = 5.134 [p = .030]). A logistic regression analysis indicated a significant contribution of the BSW test to the model (odds ratio = 0.637; 95% CI [0.407, 0.993]; p = .046 per 1 cm).The cut-off score was determined to be 27.8 cm (67% sensitivity and 84% specifcity). These results indicate that women with a smaller BSW at baseline had a significantly higher risk of sustaining a fall.

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Alison C. Novak and Brenda Brouwer

This study describes and contrasts the kinematics and kinetics of stair ambulation in people with chronic stroke and healthy control subjects. Three-dimensional motion data were collected from 10 persons with stroke (7 males) and 10 sex and age-matched older adults as they ascended and descended an instrumented staircase at self-selected speed with and without a handrail. Ankle, knee and hip joint angle and moment profiles were generated during stance and range of motion and peak moments were contrasted between groups, sides (stroke only) and condition. Cadence was lower in stroke than controls, although the kinematic profiles appeared similar during ascent and decent. Notable differences in joint kinetics were evident as the peak extensor moments were typically lower on the affected side in stroke compared with controls and the less affected side. These differences accounted for the lower magnitude net extensor support moment. The lower affected side hip abductor moments likely limited lateral stability. Handrail use tended to reduce the peak moments on the affected side only leading to more side-to-side differences than occurred without the handrail. The findings reveal differences in task performance between stroke and healthy groups that help inform rehabilitation practice.

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Thomas A. Stoffregen, M. Russell Giveans, Sebastien Villard, Jane Redfield Yank and Kevin Shockley

When two standing people converse with each other there is an increase in their shared postural activity, relative to conversation with different partners. We asked pairs of participants to converse with each other or with experimental confederates while standing on rigid and nonrigid surfaces. On the rigid surface, shared postural activity was greater when participants conversed with each other than when they conversed with confederates. In addition, the strength of interpersonal coupling increased across trials, but only when members of a dyad conversed with each other. On the nonrigid surface, postural sway variability increased, but we found no evidence that shared postural activity was different when participants conversed with each other, as opposed to conversing with confederates. We consider several possible interpretations of these results.

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Stephanie L. Di Stasi, Erin H. Hartigan and Lynn Snyder-Mackler

Aberrant movement strategies are characteristic of ACL-deficient athletes with recurrent knee instability (non-copers), and may instigate premature or accelerate joint degradation. Biomechanical evaluation of kinematic changes over time may elucidate noncopers’ responses to neuromuscular intervention and ACL reconstruction (ACLR). Forty noncopers were randomized into a perturbation group or a strength training only group. We evaluated the effects of perturbation training, and then gender on knee angle and tibial position during a unilateral standing task before and after ACLR. No statistically significant interactions were found. Before surgery, the strength training only group demonstrated knee angle asymmetry, but 6 months after ACLR, both groups presented with similar knee flexion between limbs. Aberrant and asymmetrical tibial position was found only in females following injury and ACLR. Neither treatment group showed distinct unilateral standing strategies following intervention; however, males and female noncopers appear to respond uniquely to physical therapy and surgery.

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Musa L. Audu, Robert F. Kirsch and Ronald J. Triolo

Our long-term goal is to use a musculoskeletal modeling approach for developing controller algorithms to restore standing balance to individuals with lower extremity paralysis using functional electrical stimulation. This paper describes a technique that facilitates this approach by avoiding the numerical problems associated with modeling the closed kinematic chain formed by the two lower extremities and the ground while standing. Specifically, we propose an optimization technique to estimate the magnitude and origin of the ground reaction force (GRF) vector on one of the feet, resulting in an equivalent open-chain formulation. Using this technique, we performed a series of inverse dynamic computations to determine the GRF and center of pressure (COP) values for five standing postures: neutral, neutral with forward lean, neutral with backward lean, wide, and tandem. The optimization procedure elicited force results that satisfy equilibrium and result in COP locations that are consistent and physically reasonable.

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Chetan P. Phadke, Marc Klimstra, E Paul. Zehr, Floyd J. Thompson and Andrea L. Behrman

The purpose of this study was to test the effect of arm swing on modulation of soleus H-reflexes amplitudes during walking. Fifteen subjects walked (1.07 m/s) on a treadmill in 4 arm swing conditions: 1-natural arm swing (control), 2-active restraint, 3-passive restraint, and 4-passive-assisted. Tibial nerve was electrically stimulated and soleus EMG was recorded. H-reflex amplitude was significantly greater during active than during passive restraint (p = .013). Remaining arm swing conditions were not significantly different. We detected a subtle effect of arm swing on soleus H-reflex amplitude. Descending regulation may serve as a gating mechanism to control the effect of arm movements on reflex pathways for leg muscles. This gating mechanism may be impaired postneural injury, potentially enhancing the modulation of peripheral sensory inputs on reflexes in leg muscles during walking. Future experiments to test additional conditions and evoking reflexes in more phases of walking are recommended.

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Eryk P. Przysucha and M. Jane Taylor

The purpose of this study was to compare the postural sway profiles of 20 boys with and without Developmental Coordination Disorder (DCD) on two conditions of a quiet standing task: eyes open and eyes closed. Anterior-posterior (AP) sway, medio-lateral sway (LAT), area of sway, total path length, and Romberg’s quotient were analyzed. When visual information was available, there was no difference between groups in LAT sway or path length. However, boys with DCD demonstrated more AP sway (p < .01) and greater area of sway (p < .03), which resulted in pronounced excursions closer to their stability limits. Analysis of Romberg’s quotient indicated that boys with DCD did not over-rely on visual information.

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Pazit Levinger, Wendy Gilleard and Cliff Coleman

Use of a shank shell has been shown to estimate tibial transverse rotations better than skin-mounted markers. However, the day-to-day reliability of the transverse tibial rotations using an individually molded shank shell has not been previously investigated. This study examined the between-tests and trials reliability of an individually molded shank shell for measuring peak tibial internal and external rotations, time of peak values, and tibia range of motion during 5 walking trials. The trial-to-trial reliability of tibial transverse rotations was measured in 14 healthy individuals while the test-retest reliability was measured in 10 persons on two occasions. Trial-to-trial reliability for peak transverse rotations, time of peak values, and tibia range of motion ranged from ICC (3,1) 0.59–0.95. The PCA between trials showed that 88–99% of values were within 3° of agreement. Test-retest reliability for peak rotations, tibia range of motion, and time of peak values ranged from ICC (3,1) 0.70–0.89 with SEM 1.6–2.21°, 0.021%, and 0.034%, respectively. The PCA between tests showed that 70–100% of values were within 3° of agreement. The use of an individually molded shell and the close attachment of the shank shell to the individual's shank resulted in reliable test-retest and trial-to-trial data.