Force Platform (force + platform)

Distribution by Scientific Domains


Selected Abstracts


Control of the triceps surae during the postural sway of quiet standing

ACTA PHYSIOLOGICA, Issue 3 2007
C. D. Tokuno
Abstract Aim:, The present study investigated how the triceps surae are controlled at the spinal level during the naturally occurring postural sway of quiet standing. Methods:, Subjects stood on a force platform as electrical stimuli were applied to the posterior tibial nerve when the center of pressure (COP) was either 1.6 standard deviations anterior (COPant) or posterior (COPpost) to the mean baseline COP signal. Peak-to-peak amplitudes of the H-reflex and M-wave from the soleus (SOL) and medial gastrocnemius (MG) muscles were recorded to assess the efficacy of the Ia pathway. Results:, A significant increase in the Hmax : Mmax ratio for both the SOL (12 ± 6%) and MG (23 ± 6%) was observed during the COPant as compared to the COPpost condition. The source of the modulation between COP conditions cannot be determined from this study. However, the observed changes in the synaptic efficacy of the Ia pathway are unlikely to be simply a result of an altered level of background electromyographic activity in the triceps surae. This was indicated by the lack of differences observed in the Hmax : Mmax ratio when subjects stood without postural sway (via the use of a tilt table) at two levels of background activity. Conclusions:, It is suggested that the phase-dependent modulation of the triceps surae H-reflexes during the postural sway of quiet standing functions to maintain upright stance and may explain the results from previous studies, which, until now, had not taken the influence of postural sway on the H-reflex into consideration. [source]


Development of dynamic stability in children's rhythmic movement

DEVELOPMENTAL PSYCHOBIOLOGY, Issue 6 2009
Eric G. James
Abstract This study examined the hypothesis that the stability of rhythmic motor patterns increases with developmental age in children. Children aged 6 and 10 years and adults (18- to 23-year-olds) rocked back and forth at their preferred amplitude and frequency while seated on a wooden box placed atop a force platform. Participants performed the seated rocking task with their feet supported and unsupported. There was an age-related decrease in rocking frequency and variability of the rocking cycle period, while the stability of the rocking dynamics increased, as indexed by the standard deviation of the phase angle of center of pressure motion. The presence of foot support decreased the stability of the rocking dynamics and reduced cycle period variability in the children, but not the adults. The results revealed that increments of age are associated with an increase in the stability of rhythmic motor patterns even when environmental conditions are altered. © 2009 Wiley Periodicals, Inc. Dev Psychobiol 51: 465,473, 2009 [source]


Mechanisms of Postural Control in Alcoholic Men and Women: Biomechanical Analysis of Musculoskeletal Coordination During Quiet Standing

ALCOHOLISM, Issue 3 2010
Edith V. Sullivan
Background:, Excessive sway during quiet standing is a common sequela of chronic alcoholism even with prolonged sobriety. Whether alcoholic men and women who have remained abstinent from alcohol for weeks to months differ from each other in the degree of residual postural instability and biomechanical control mechanisms has not been directly tested. Method:, We used a force platform to characterize center-of-pressure biomechanical features of postural sway, with and without stabilizing conditions from touch, vision, and stance, in 34 alcoholic men, 15 alcoholic women, 22 control men, and 29 control women. Groups were matched in age (49.4 years), general intelligence, socioeconomic status, and handedness. Each alcoholic group was sober for an average of 75 days. Results:, Analysis of postural sway when using all 3 stabilizing conditions versus none revealed diagnosis and sex differences in ability to balance. Alcoholics had significantly longer sway paths, especially in the anterior,posterior direction, than controls when maintaining erect posture without balance aids. With stabilizing conditions the sway paths of all groups shortened significantly, especially those of alcoholic men, who demonstrated a 3.1-fold improvement in sway path difference between the easiest and most challenging conditions; the remaining 3 groups, each showed a ,2.4-fold improvement. Application of a mechanical model to partition sway paths into open-loop and closed-loop postural control systems revealed that the sway paths of the alcoholic men but not alcoholic women were characterized by greater short-term (open-loop) diffusion coefficients without aids, often associated with muscle stiffening response. With stabilizing factors, all 4 groups showed similar long-term (closed loop) postural control. Correlations between cognitive abilities and closed-loop sway indices were more robust in alcoholic men than alcoholic women. Conclusions:, Reduction in sway and closed-loop activity during quiet standing with stabilizing factors shows some differential expression in men and women with histories of alcohol dependence. Nonetheless, enduring deficits in postural instability of both alcoholic men and alcoholic women suggest persisting liability for falling. [source]


Validation of a client-based clinical metrology instrument for the evaluation of canine elbow osteoarthritis

JOURNAL OF SMALL ANIMAL PRACTICE, Issue 6 2009
C. A. Hercock
Objective: To validate a disease-specific client-based clinical metrology instrument (questionnaire) for dogs with chronic osteoarthritis of the elbow joint. Materialsand Methods: This was a prospective cohort study involving 26 dogs with chronic osteoarthritis of the elbow with 24 associated clients. Validity (face and criterion), reliability and responsiveness of the metrology instrument (named "Liverpool Osteoarthritis in Dogs [elbow]") were tested in a sequence of studies. Face validity involved use of international peer review. Reliability was assessed using a test-retest scenario with a two week interval; peak vertical force as measured by a force platform was used as an external standard measure. Responsiveness was tested with a two week, single-blinded placebo-controlled intervention using a licensed non-steroidal anti-inflammatory drug. Results: The reliability of Liverpool Osteoarthritis in Dogs (elbow) in the test-retest scenario was good; intraclass correlation coefficient is 0·89, 95 per cent confidence interval 0·75 to 0·95, compared with intraclass correlation coefficient 0·92, 95 per cent confidence interval 0·74 to 0·98, for peak vertical force. Responsiveness testing indicated that the "net" effect size (allowing for placebo effect) for Liverpool Osteoarthritis in Dogs (elbow) was 0·13 compared with (,)0·18 for the force platform. Criterion validity for Liverpool Osteoarthritis in Dogs (elbow) against peak vertical force was poor; Spearman's rank correlation is ,0·24 (P=0·30). Clinical Significance: Liverpool Osteoarthritis in Dogs (elbow) was considered reliable with satisfactory responsiveness. The poor criterion validity suggests a mismatch between force platform peak vertical force and client perceptions of lameness. This instrument requires further validation in larger studies with alternative client groups and alternative therapeutic interventions, but this initial validation suggests that Liverpool Osteoarthritis in Dogs (elbow) is worthy of continued investigation. [source]


Visual judgements of steadiness in one-legged stance: reliability and validity

PHYSIOTHERAPY RESEARCH INTERNATIONAL, Issue 3 2000
Travis Haupstein
Abstract Background and Purpose There is a paucity of information about the validity and reliability of clinicians' visual judgements of steadiness in one-legged stance. Such judgements are used frequently in clinical practice to support decisions about treatment in the fields of neurology, sports medicine, paediatrics and orthopaedics. The aim of the present study was to address the validity and reliability of visual judgements of steadiness in one-legged stance in a group of physiotherapists. Method A videotape of 20 five-second performances was shown to 14 physiotherapists with median clinical experience of 6.75 years. Validity of visual judgement was established by correlating scores obtained from an 11-point rating scale with criterion scores obtained from a force platform. In addition, partial correlations were used to control for the potential influence of body weight on the relationship between the visual judgements and criterion scores. Inter-observer reliability was quantified between the physiotherapists; intra-observer reliability was quantified between two tests four weeks apart. Results Mean criterion-related validity was high, regardless of whether body weight was controlled for statistically (Pearson's r=0.84, 0.83, respectively). The standard error of estimating the criterion score was 3.3 newtons. Inter-observer reliability was high (ICC (2,1) = 0.81 at Test 1 and 0.82 at Test 2). Intra-observer reliability was high (on average ICC (2,1) = 0.88; Pearson's r = 0.90). The standard error of measurement for the 11-point scale was one unit. Conclusions The finding of higher accuracy of making visual judgements than previously reported may be due to several aspects of design: use of a criterion score derived from the variability of the force signal which is more discriminating than variability of centre of pressure; use of a discriminating visual rating scale; specificity and clear definition of the phenomenon to be rated. Copyright © 2000 Whurr Publishers Ltd. [source]


The interplay between speed, kinetics, and hand postures during primate terrestrial locomotion

AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 2 2010
Biren A. Patel
Abstract Nonprimate terrestrial mammals may use digitigrade postures to help moderate distal limb joint moments and metapodial stresses that may arise during high-speed locomotion with high-ground reaction forces (GRF). This study evaluates the relationships between speed, GRFs, and distal forelimb kinematics in order to evaluate if primates also adopt digitigrade hand postures during terrestrial locomotion for these same reasons. Three cercopithecine monkey species (Papio anubis, Macaca mulatta, Erythrocebus patas) were videotaped moving unrestrained along a horizontal runway instrumented with a force platform. Three-dimensional forelimb kinematics and GRFs were measured when the vertical force component reached its peak. Hand posture was measured as the angle between the metacarpal segment and the ground (MGA). As predicted, digitigrade hand postures (larger MGA) are associated with shorter GRF moment arms and lower wrist joint moments. Contrary to expectations, individuals used more palmigrade-like (i.e. less digitigrade) hand postures (smaller MGA) when the forelimb was subjected to higher forces (at faster speeds) resulting in potentially larger wrist joint moments. Accordingly, these primates may not use their ability to alter their hand postures to reduce rising joint moments at faster speeds. Digitigrady at slow speeds may improve the mechanical advantage of antigravity muscles crossing the wrist joint. At faster speeds, greater palmigrady is likely caused by joint collapse, but this posture may be suited to distribute higher GRFs over a larger surface area to lower stresses throughout the hand. Thus, a digitigrade hand posture is not a cursorial (i.e. high speed) adaptation in primates and differs from that of other mammals. Am J Phys Anthropol 2010. © 2009 Wiley-Liss, Inc. [source]


Comparison of biomechanical gait parameters of young children with haemophilia and those of age-matched peers

HAEMOPHILIA, Issue 2 2009
D. STEPHENSEN
Summary., Quality of life for children with haemophilia has improved since the introduction of prophylaxis. The frequency of joint haemorrhages has reduced, but the consequences of reduced bleeding on the biomechanical parameters of walking are not well understood. This study explored the differences in sagittal plane biomechanics of walking between a control group (Group 1) of normal age-matched children and children with haemophilia (Group 2) with a target ankle joint. A motion capture system and two force platforms were used to collect sagittal plane kinematic, kinetic and temporal,spatial data during walking of 14 age-matched normal children and 14 children with haemophilia aged 7,13 years. Group differences in maximum and minimum flexion/extension angles and moments of the hip, knee and ankle joints, ground reaction forces and temporal,spatial gait cycle parameters were analysed using one-way anova. Significant changes (P < 0.05) in kinematic and kinetic parameters but not temporal,spatial parameters were found in children with haemophilia; greater flexion angles and external moments of force at the knee, greater ankle plantarflexion external moments and lower hip flexion external moments. These results suggest that early biomechanical changes are present in young haemophilic children with a history of a target ankle joint and imply that lower limb joint function is more impaired than current clinical evaluations indicate. Protocols and quantitative data on the biomechanical gait pattern of children with haemophilia reported in this study provide a baseline to evaluate lower limb joint function and clinical progression. [source]


Proposed model of botulinum toxin-induced muscle weakness in the rabbit

JOURNAL OF ORTHOPAEDIC RESEARCH, Issue 6 2005
D. Longino
Abstract Osteoarthritic patients show only a weak association between radiographic signs of joint disease and joint pain and disability. Conversely, muscle weakness is one of the earliest and most common symptoms of patients with osteoarthritis (OA). However, while many experimental models of osteoarthritis include a component of muscular weakness, no model has isolated this factor satisfactorily. Therefore, the purpose of this study was to develop and validate an experimental animal model of muscle weakness for future use in the study of OA. Botulinum Type-A toxin (BTX-A) was uni-laterally injected into the quadriceps musculature of New Zealand white rabbits (3.5 unit/kg). Isometric knee extensor torque at a range of knee angles and stimulation frequencies, and quadriceps muscle mass, were quantified for control animals, and at one- and six-months post-repeated injections, in both, the experimental and the contralateral hindlimb. Ground reaction forces were measured in all animals while hopping across two force platforms. Isometric knee extension torque and quadriceps muscle mass was systematically decreased in the experimental hindlimb. Vertical ground reaction forces in the push off phase of hopping were also decreased in the experimental compared to control hindlimbs. We conclude that BTX-A injection into the rabbit musculature creates functional and absolute muscle weakness in a reproducible manner. Therefore, this model may be used to systematically study the possible effects of muscle weakness on joint degeneration, either as an isolated intervention, or in combination with other interventions (anterior cruciate ligament transection, meniscectomy) known to create knee joint degeneration. © 2005 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved. [source]