Use Of Force Platform Research Articles

Comparison of Two Contact Detection Methods for Ground Reaction Forces and Moment Estimation During Sidestep Cuts, Runs, and Walks.

Force platforms often limit the analysis of human movement to the laboratory. Promising methods for estimating ground reaction forces and moments (GRF&M) can overcome this limitation. The most effective family of methods consists of minimizing a cost, constrained by the subject's dynamic equilibrium, for distributing the force over the contact surface on the ground. The detection of contact surfaces over time is dependent on numerous parameters. This study proposes to evaluate two contact detection methods: the first based on foot kinematics and the second based on pressure sole data. Optimal parameters for these two methods were identified for walking, running, and sidestep cut tasks. The results show that a single threshold in position or velocity is sufficient to guarantee a good estimate. Using pressure sole data to detect contact improves the estimation of the position of the center of pressure (CoP). Both methods demonstrated a similar level of accuracy in estimating ground reaction forces.

Using Wearable Accelerometers to Develop a Vertical Ground Reaction Force Prediction Model during Running: A Sensitivity Study

The estimation of vertical ground reaction forces (VGRFs) during running is necessary to understand running mechanisms. For this purpose, the use of force platforms is fundamental. However, to extend the study of VGRFs to real conditions, wearable accelerometers are a promising alternative to force platforms, whose use is often limited to the laboratory environment. The objective of this study was to develop a VGRF model using wearable accelerometers and a stepwise regression algorithm. Several models were developed and validated using the VGRFs and acceleration signals collected during 100 stances performed by one participant. The validated models were tested on eight participants. In a sensitivity study, the strongest correlations were observed at cut-off frequencies of ≤25 Hz and in models developed with 30 to 90 stances. After the validation phase, the 10 best models had, on average, low relative differences (≤10%) in the estimation of discrete VGRF parameters, i.e., the passive peak (εpp=6.26%), active peak (εap=2.22%), and loading rate (εlr=2.17%). The results indicate that the development of personalized models is more suitable for achieving the best estimates. The proposed methodology opens many perspectives for monitoring VGRFs under real conditions using a limited number of wearable sensors.

Postural stability measures in healthy miniature Dachshunds obtained using a pressure mat and a force platform: a validity and reliability study

BackgroundMiniature Dachshunds have a high prevalence of neurological and musculoskeletal diseases potentially affecting their balance. The postural stability of dogs in quiet standing is an indicator of postural control and can aid in diagnosing and monitoring lameness and other pathologies affecting balance. Measures of centre of pressure (CoP) can be obtained from force and pressure platform systems to evaluate postural stability, however the two systems have not been compared and the latter has not been validated in dogs. The aims of this study were to assess the validity and reliability of using a pressure mat compared to a force platform and report normative values of CoP measures in healthy miniature Dachshunds. Forty two healthy miniature Dachshunds of smooth, long and wire-haired breed types stood still on a pressure mat (Tekscan MatScan®) placed on a force platform and the two systems were synchronised. Maximum anterior-posterior (AP) and medial-lateral (ML) ranges, sway path and 95% area of a best-fit ellipse were computed. Bland-Altman plots and coefficients of correlation assessed validity; intra-class correlation coefficients (ICC) assessed inter-test reliability for both systems. Non-linear regression analyses were used to describe the relationship between CoP and demographic measures.ResultsStrong correlations for AP range, ML range and 95% ellipse area and moderate correlation for sway path were found between the two devices. ICC showed good reliability (0.75–0.90) for AP range and moderate (0.5–0.75) for ML range and the 95% ellipse area for both devices. Sway path reliability was excellent (> 0.90) with the force platform but moderate with the pressure mat. Age was positively correlated with balance (inversely correlated with all measures except sway path), while weight explained 94% (force platform) and 27% (pressure mat) of the variance in sway path.ConclusionsPressure mats can be used to obtain valid and reliable measures of CoP and replace use of force platforms. Older (non-senior) and heavier (non-obese) dogs show better postural stability. Clinical examinations should include the use of a range of CoP measures when assessing postural balance, while accounting for the effects of age and body weight.

Usefulness of Mobile Devices in the Diagnosis and Rehabilitation of Patients with Dizziness and Balance Disorders: A State of the Art Review.

ObjectiveThe gold standard for objective body posture examination is posturography. Body movements are detected through the use of force platforms that assess static and dynamic balance (conventional posturography). In recent years, new technologies like wearable sensors (mobile posturography) have been applied during complex dynamic activities to diagnose and rehabilitate balance disorders. They are used in healthy people, especially in the aging population, for detecting falls in the older adults, in the rehabilitation of different neurological, osteoarticular, and muscular system diseases, and in vestibular disorders. Mobile devices are portable, lightweight, and less expensive than conventional posturography. The vibrotactile system can consist of an accelerometer (linear acceleration measurement), gyroscopes (angular acceleration measurement), and magnetometers (heading measurement, relative to the Earth’s magnetic field). The sensors may be mounted to the trunk (most often in the lumbar region of the spine, and the pelvis), wrists, arms, sternum, feet, or shins. Some static and dynamic clinical tests have been performed with the use of wearable sensors. Smartphones are widely used as a mobile computing platform and to evaluate the results or monitor the patient during the movement and rehabilitation. There are various mobile applications for smartphone-based balance systems. Future research should focus on validating the sensitivity and reliability of mobile device measurements compared to conventional posturography.ConclusionSmartphone based mobile devices are limited to one sensor lumbar level posturography and offer basic clinical evaluation. Single or multi sensor mobile posturography is available from different manufacturers and offers single to multi-level measurements, providing more data and in some instances even performing sophisticated clinical balance tests.

Post-stroke hip fracture in older people: A narrative review

Background/Aims: A hip fracture is a serious and common complication after stroke. Individuals often experience particular gait problems post-stroke and may have difficulty with everyday activities such as walking. Therefore, the interventions for falls prevention in older patients should be re-examined when applied to the post-stroke population. This study reviews the risk factors for falls and hip fractures that are specific to the post-stroke population and the measures that may be taken to prevent hip fractures and/or falls in this patient group. Method: A narrative review of articles written in English in the scientific literature on the risk factors, natural history and prevention of hip fractures in post-stroke patients. Results: The interventions that were reviewed showed some benefit to post-stroke patients. These included interventions designed to increase physical activity, water-based exercise, general falls prevention programmes, and the use of force platforms and body weight supported treadmills. More solid evidence was found to support strategies such as the symmetrical use of limbs, which provides appropriate support and an environment where an individual can regain more normal movement patterns. This can be achieved by training in a low-gravity environment using water-based exercises or a body-weight supported treadmill. To perform more symmetrical movements, biofeedback (visual feedback) or a force platform can be used in addition to symmetrical exercises. Conclusions: In a post-stroke population, it is better to pay special attention to the prevention of falls and hip fracture than to rehabilitate after a fracture has occurred. Evaluation and management of the risk factors that contribute to falls should be a priority in post-stroke rehabilitation, focusing on as many risk factors as possible in hip fracture prevention programmes. A variety of techniques should be used to facilitate functional recovery, emphasising symmetry and optimal movement patterns.

Biomechanic characteristics of gait of four breeds of dogs with different conformations at walk on a treadmill

Principle of ‘dynamic similarity’ is frequently applied in biomechanic research as a tool to extrapolate data between animals from the same species, but, in dogs, different breeds entail different conformations. For that reason, comparison of dynamic parameters among dogs of different breeds should not be only based in weight and relative velocity. By means of the use of force platform and high-speed videography in 12 dogs corresponding with four breeds of different conformations, we showed how most of kinetic and kinematic variables are highly independent of weight or relative velocity and other factors as morphometric values and ratios are determinant.

Assessment of standing balance in patients after ankle fractures.

The objective of the study is to evaluate the degree of balance disorders in patients with surgical treatment of ankle fractures with the use of stabilometric examinations. The subjects in the study were 21 patients with ankle fractures treated surgically, within one year of the procedure. The control group comprised 20 healthy subjects. The balance was evaluated with the use of force platform in standing posture in both single and double limb stance. The parameters analysed were the transition area of the centre of feet pressure (COP), the length of the COP path and the COP velocity. The range of movement in the ankle joint and the intensification of pain were also measured. In the balance evaluation in double limb stance, there were no statistically significant differences. A significant difference was found in the attempts of single limb-stance. An average value of COP transition area in the study group was 261.2 mm2 in single stance (on the right operated limb) and in the control group--93.2 mm2, so the difference was statistically significant (p = 0.0096). The presence of pain, the presence or the removal of anastomosis had no significant influence on the balance of the subjects under study. Also a significant correlation between the balance of the subjects and their age was found. The balance in single limb stance after an instable ankle fracture within one year of the surgical procedure is significantly poorer in comparison with healthy subjects. Elderly persons have significantly poorer balance control.

Walking Through the Impulse-Momentum Theorem

Modern force platforms are handy tools for investigating forces during human motion. Earlier they were very expensive and were mostly used in research laboratories. But now even platforms that can measure in two directions are quite affordable. In this work we used the PASCO 2-Axis Force Platform. The analysis of the data can serve as a nice illustration of qualitative or quantitative use of the impulse-momentum theorem p - p0 = ∫t0t Fdt = I. The most common use of force platforms is to study the force from the base during the push-off period of a vertical jump. I think this is an activity of great value, and I would recommend it. The use of force platforms in teaching is well documented in research literature.1–4

Comparison of two methods of postural control analysis during upright and quiet stance

The goal of this study was to compare two methods of analysis, the use of force platform and based on video system, to investigate the postural control of young adults during upright stance on three bases of support. Fifteen young adults (30±4.96 years old) were asked to maintain an upright and quiet stance on a force platform for 30 s on bipedal, semi-tandem stance, and reduced bipedal bases of support. One reflective marker was placed on their back to acquire the space coordinates. Mean sway amplitude and mean velocity in anterior-posterior (AP) and medial-lateral (ML) directions and the area of stabilogram were calculated and used to compare the two methods of analysis and the effects of bases of support. Coefficient of correlation values indicated strong relation between trajectories of center of pressure and reflective marker in both directions (AP and ML), and statistical analysis of both methods indicated similar results in terms of effects of base of support. According to these results it might be suggested that both methods of analysis to investigate the control of upright and quiet stance in young adults can be used.

Relationships Between Standing Balance and Symmetry Measurements in Patients Following Recent Strokes (≤3 Weeks) or Older Strokes (≥6 Months)

The Functional Standing Balance (FSB) Scale was designed to obtain measurements of standing balance and to identify the problems typically faced by people with stroke. The purpose of this study was to investigate the validity of measurements obtained with the FSB Scale for use in the acute and chronic phases of stroke by comparing the measurements obtained with the FSB Scale with those obtained for postural sway and lateral symmetry by use of a force platform. Measurements were obtained for 26 people with recent strokes (ie, strokes within 3 weeks of data collection) and for 28 people with long-standing strokes (ie, strokes of 6 months' duration or older). The FSB Scale consists of 3 components: weight distribution, balance without movement, and balance with movement. Measurements of balance performance were compared with measurements of anteroposterior and lateral sway velocity obtained on a force platform. The weight distribution on 2 digital scales was compared with the lateral symmetry measured on the force platform. The highest correlations were found between the FSB Scale balance measurements and the measurements of anteroposterior sway velocity obtained on the force platform with feet apart and eyes open. The correlations (r) were -.68 and -.67 for the group with recent strokes and -.74 and -.91 for the group with long-standing strokes. The correlations (r) between weight distribution measured on the digital scales and lateral symmetry measured on the force platform were.44 for the group with recent strokes and.52 for the group with long-standing strokes. The subjects whose results on the FSB Scale were poor had higher sway velocities on the force platform than the subjects whose results on the FSB Scale were good. The results of this study suggest that the FSB Scale provides the same kind of information as that obtained for sway velocity and lateral symmetry as measured with the use of force platforms in both patients with recent strokes and patients with long-standing strokes.

Use of force platforms in physics and sport

The subject of biomechanics is growing as athletesturn to science to improve their performance. Biomechanicsinterests many students and is also a good area in which toinvestigate forces and Newton's laws. The use of forceplatforms can quantify such studies.

A quality control procedure for force platforms

A force platform is a technical method of quantitatively assessing balanceindirectly. The use of force platforms in physiotherapy departments has becomemore prominent over the last few years. However, the main drawback in the useof force platforms is the lack of comprehensive calibration procedures, whichcasts doubt on the results obtained with these systems. Existing calibrationtests are limited to testing the spatial accuracy of the force platform. Thispaper describes a comprehensive quality control test procedure which wasdeveloped. It is proposed that the developed quality control test procedurecould be used to test all types of force platform and it includes adescription of how the tests should be carried out, the frequency with whichthey should be carried out and the expected performance for each of the testsas recommended for the most part by the Association Francaise de Posturologie.

Plantar pressure assessment.

Measurements of plantar pressure provide an indication of foot and ankle functions during gait and other functional activities, because the foot and ankle provide both the necessary support and flexibility for weight bearing and weight shifting while performing these activities.1–3 Although plantar pressure data have been recognized as an important element in the assessment of clients with diabetes and peripheral neuropathy, information derived from plantar pressure data also can assist in determining and managing the impairments associated with various musculoskeletal, integumentary, and neurological disorders. The use of force platforms is the method most commonly used to assess the interaction of the foot and supporting surface. Although the force platform provides valuable information regarding both the vertical and shear components of the ground reaction force, it provides little information on how the planter surface of the foot is loaded with respect to the supporting surface. When evaluating patients, atypical amounts of loading or patterns of loading may be reflective of a systemic or localized lower-extremity pathology and may be indicators (risk factors) for or predictors of further pathology or worsening of the existing pathology.4 In addition, force platforms have very specific requirements for attachment to the supporting surface on which data collection will occur. Such is not the case with numerous commercially available systems for measuring plantar pressure (eg, Emed sensor platform, * Pedar insole system, * F-Scan system,† Musgrave footprint system‡). Thus, plantar pressure measurement systems offer the clinician a high degree of portability, permitting utilization among multiple clinic sites. Pressure (p) (also called “stress”) is defined as force (f) per unit area (a) (ie, p=f/a).5 Force , when measured using a force platform, is the net result of the 3 components of the ground reaction or resultant force acting on the foot. …

Opportunities and limitations in the use of force platforms in clinical applications

The purpose of this study was to assess the concurrent validity of center of pressure (COP) measurements during walking, comparing the Parotec System (an in-shoe pressure measurement device) to an Advanced Mechanical Technology Inc. (AMTI) force plate. Pearson correlation coefficients comparing COP displacement in the medial-lateral (ML) and anterior-posterior (AP) direction calculated from the two systems were greater than 0.70 for 52/67 trials (78%) in the ML direction and were greater than 0.90 for 67/67 trials (100%) in the AP direction. The mean root mean square (RMS) error for COP displacement in the ML direction was 0.56±0.3 cm and in the AP direction was 1.37±0.59 cm. Overall, the Parotec System showed good correlation and small RMS errors when compared to the AMTI force plate. Additional analysis to investigate sources of error pointed to the methods used for calculating the position and orientation of the subject’s foot on the force plate. Subsequent analysis to eliminate some of these errors, compared force calculated from the Parotec System and the AMTI plate and showed good to excellent correlation (>0.70) for 62/67 trials (93%). Additional data were collected that allowed for elimination of methodological errors. Again force calculated from the two systems was compared using Pearsons. These data showed excellent correlation (>0.90) for 20/20 trials (100%). This study provides evidence of the validity of the Parotec System for measuring COP during ambulation.