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Matthew Brodie, Alan Walmsley and Wyatt Page

A fusion integration algorithm is used to estimate the one-dimensional center of mass (COM) trajectory from force platform data. The resulting COM trajectory combines the best attributes of several established algorithms used to estimate the COM trajectory, and it appears to have the advantage of being robust, accurate, continuous in its higher derivatives, and fast to obtain. In current research projects, variations of the fusion integration algorithm have been adapted by the authors for the analysis of postural balance and the sensing of limb orientations with inertial measurement units.

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Zohreh Meshkati, Mehdi Namazizadeh, Mahyar Salavati and Masood Mazaheri

Context:

Although reliability is a population-specific property, few studies have investigated the measurement error associated with force-platform parameters in athletic populations.

Objective:

To investigate the skill-related differences between athletes and nonathletes in reliability of center-of-pressure (COP) summary measures under eyes-open (EO) and eyes-closed (EC) conditions.

Design:

Test–retest reliability study.

Setting:

COP was recorded during double-leg quiet standing on a Kistler force platform before and after a fatiguing treadmill exercise, with EO and EC.

Participants:

31 male participants including 15 athletes practiced in karate and 16 nonathletes.

Main Outcome Measures:

Standard deviation (SD) of amplitude, phase-plane portrait, SD of velocity, mean total velocity, and area were calculated from 30-s COP data. Intraclass correlation coefficient (ICC), standard error of measurement, and coefficient of variation (CV) were used as estimates of reliability and precision.

Results:

Higher ICCs were found for COP measures in the athlete (compared with the nonathlete) group, postfatigued (compared with prefatigued) condition, and EC (compared with EO) tests. CVs smaller than 15% were obtained for most of the COP measures. SD of velocity in the anteroposterior direction showed the highest reliability in most conditions.

Conclusions:

Tests with EC and to a lesser extent tests performed in the athlete group and in the postfatigued condition showed better reliability.

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Marko T. Korhonen, Harri Suominen, Jukka T. Viitasalo, Tuomas Liikavainio, Markku Alen and Antti A. Mero

Eighteen young (23 ± 4 yr) and 25 older (70 ± 4 yr) male sprinters were examined for ground reaction force (GRF) and temporal-spatial variables. The data were collected during maximum-speed phase, and variability and symmetry indices were calculated from a total of 8 steps. There was little variation (CV < 6%) in vertical and resultant GRF and kinematic variables, while impact loading had high variability (CV: 10–21%). Overall, the pattern of variability was similar in both groups. Yet, a small but significant age-related increase in CV was evident in horizontal GRFs. There was a variable-specific asymmetry between legs but it was not related to leg dominance. No age differences existed in the symmetry indices. Results indicate that only selected force platform variables are symmetric and repeatable enough so that their use for comparison purposes is appropriate. Data also suggest that aging may increase variability in certain biomechanical measures, whereas symmetry is not affected by age.

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Juan V. Durá, Juan M. Belda, Rakel Poveda, Álvaro Page, José Laparra, José Das, Jaime Prat and Ana C. García

The effect of walking velocity on force platform measures is examined by means of functional regression and nonfunctional regression analyses. The two techniques are compared using a data set of ground reaction forces. Functional data analysis avoids the need to identify significant points, and provides more information along the waveform.

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Mary Emily Littrell, Young-Hui Chang and Brian P. Selgrade

Multicamera gait analysis systems and force platforms are used to measure the kinematics and kinetics of locomotion. 1 – 5 Although 3-dimensional analysis provides valuable insights, these systems are difficult to transport and prohibitively expensive for widespread clinical use. However, the

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Katherine L. Hsieh, Yaejin Moon, Vignesh Ramkrishnan, Rama Ratnam and Jacob J. Sosnoff

also been linked to a greater fall risk. 13 , 14 In these studies, VTC was determined based on COP derived from force platforms or COM derived from high-speed motion capture cameras. Although these techniques of measuring VTC are generally considered the gold standard for postural stability, they are

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Patrice R. Rougier and Samir Boudrahem

Past studies have emphasized the beneficial effect of additional visual feedback (VFB) on the capacity of healthy adults to decrease the amplitudes of the center-of-pressure minus center-of-gravity (CP-CGv) movements. To better assess these capacities, 56 subjects were asked to stand still on a force platform and to use the visual information provided. Dependency coefficients, based on their capacity to lower their CP-CGv movements and therefore relax their lower limb muscles, as well as parameters aimed at characterizing their postural strategies were measured across VFB conditions including (1) CP displacements in real time (VFBCP0), (2) CP displacements with a 600-ms delay (VFBCP600), and (3) CP-CGv displacements with a 600-ms delay (VFBCP-CG600). A non-VFB condition (eyes open) was also included. Several linear correlations were used to specify the relation between subjects’ capacity to relax, compared with the VFBCP0 condition, across the three remaining conditions. The data highlight the complementary nature of the VFB conditions and establish the postural control behaviors necessary to use these VFB protocols efficiently.

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Gavin L. Moir, Alberto Garcia and Gregory B. Dwyer

Purpose:

To investigate the intersession reliability of selected kinematic and kinetic variables during countermovement vertical jumps (CMJs).

Methods:

Thirty-five men and 35 women performed CMJs on a force platform during four testing sessions each separated by 1 wk. Kinematic variables included time in the air (TIA), take-off velocity (TOV), total vertical displacement of the center of mass (TJH). and countermovement depth, whereas kinetic variables included positive impulse, negative impulse, vertical stiffness, and rates of force development. Systematic bias was assessed by calculating the 90% confidence interval of the change in the mean between consecutive testing sessions and between the first and final testing session for each variable. Coefficients of variation (CV) and intraclass correlation coefficients (ICC) were also calculated.

Results:

Systematic bias was observed only for peak rate of force development during the concentric phase of the movement. For TIA, TOV, and TJH, CV values ranged from 1.7% to 6.6%, with ICC values ranging from 0.82 to 0.97. The other variables showed greater variation (CV range: 1.7% to 39.9%; ICC range: 0.04 to 0.99). Only slight gender differences were found in the reliability statistics, and the reliability of most of the variables was diminished as the time between the testing sessions was increased.

Conclusion:

Even though practitioners can expect good reliability for jump height measured from a force platform in men and women, other kinematic and kinetic variables often assessed during vertical jumps may not be reliable.

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Stephen J. Kinzey, Mitchell L. Cordova, Kevin J. Gallen, Jason C. Smith and Justin B. Moore

Objective:

To determine whether a standard 20-min ice-bath (10°C) immersion of the leg alters vertical ground-reaction-force components during a 1 -legged vertical jump.

Design:

A 1 × 5 factorial repeated-measures model was used.

Setting:

The Applied Biomechanics Laboratory at The University of Mississippi.

Participants:

Fifteen healthy and physically active subjects (age = 22.3 ± 2.1 years, height = 177.3 ± 12.2 cm, mass = 76.3 ± 19.1 kg) participated.

Intervention:

Subjects performed 25 one-legged vertical jumps with their preferred extremity before (5 jumps) and after (20 jumps) a 20-min cold whirlpool to the leg. The 25 jumps were reduced into 5 sets of average trials.

Main Outcome Measures:

Normalized peak and average vertical ground-reaction forces, as well as vertical impulse obtained using an instrumented force platform.

Results:

Immediately after cryotherapy (sets 2 and 3), vertical impulse decreased (P = .01); peak vertical ground-reaction force increased (set 2) but then decreased toward baseline measures (P= .02). Average vertical ground-reaction force remained unchanged (P >.05).

Conclusions:

The authors advocate waiting approximately 15 min before engaging in activities that require the production of weight-bearing explosive strength or power.

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Brad Hodgson, Laurie Tis, Steven Cobb and Elizabeth Higbie

Objective:

To examine the effects of external ankle support on vertical ground-reaction forces (VGRF) and kinematic data.

Methods:

Subjects completed 2 braced and 2 nonbraced 0.61-m hanging drop landings onto a force platform. Kinematic data were collected with 8 digital-optical cameras sampling at 120 Hz.

Subjects:

12 Division I female volleyball players.

Statistical Analysis:

A repeated-measures ANOVA with Bonferroni correction (P < .05) was used to determine whether significant differences existed between test conditions for peak VGRF, loading rate, hip angle, knee angle, and ankle angle at right-foot contact for peak 1 and peak 2 of the VGRF curve over the first 100 milliseconds of the landing phase, as well as total hip range of motion (ROM), total knee ROM, and total ankle ROM for the entire landing phase.

Results:

There were significant increases in peak P1 and LR1 and a significant decrease in ankle-angle change at right-foot contact in braced trials compared with the nonbraced condition.