Large Force Plate Research Articles

Manual wheelchair users gradually face fewer postural stability and control challenges with increasing rolling resistance while maintaining a rear-wheel wheelie

Teaching manual wheelchair users to perform wheelies using various rolling resistances is expected to facilitate learning of this advanced wheelchair skill. However, limited scientific evidence is available to support this approach. This study aimed to measure and compare postural stability and control requirements when maintaining a stationary wheelie on different rolling resistances. Eighteen manual wheelchair users with a spinal cord injury performed in a random order and maintained four 30-second wheelies on four rolling resistances: natural hard floor (NAT), 5-cm thick soft foam (LOW), 5-cm thick memory foam (MOD), and rear wheels blocked by wooden blocks (HIGH). All wheelies were performed over a large instrumented force plate to continuously record the center of pressure (CoP). To quantify postural stability, resultant and directional time- and frequency-domain CoP measures were computed and compared across all four rolling resistances. All resultant time-domain measures confirmed increased postural stability from NAT to LOW and from MOD to HIGH rolling resistances. Most time-domain measures confirmed a shift in postural control from an anticipatory to a predominantly compensatory strategy, accompanied by increased reliance on proprioceptive feedback, especially from NAT to LOW and from MOD to HIGH rolling resistances. Postural stability gradually increased with various rolling resistances while maintaining a stationary wheelie, whereas the postural control strategy shifted from an anticipatory to a reactive strategy. Blocking the rear wheels is recommended when first teaching this advanced wheelchair skill. Rapid progression on foam and natural surfaces is advocated to refine learning and enhance proper postural control strategies.

Postural adaptation during arm raising in children with and without unilateral cerebral palsy

Postural sway during arm movements were related to the size of the base of support (BOS) and the limits of stability (LOS) of children with unilateral cerebral palsy (USCP) and typically developing (TD) children. For half of the trials the mechanical disturbance due to the rapid arm movement was increased by attaching small weights at the wrists. The participants stood with both feet on a large force plate, which recorded the displacements of the center of pressure (CoP). The results showed that in the children with USCP the LOS forward and toward the non-dominant (more-affected) side were smaller than in the TD children whereas the LOS backward and toward the dominant (less-affected) side did not differ between the two groups. When rapidly moving the arms the children with USCP swayed over a larger portion of their base of support in the forward direction and toward their more-affected side. In addition, the maximal sway toward the more-affected side during arm movement exceeded the LOS while balance was maintained. These effects increased when the movements were performed with the weights at the wrists. These results show that an area of permissible sway, which was not spontaneously explored during the leaning task, was required to maintain balance during the supra-postural task. Training to enlarge the LOS that includes weight shifts toward the more-affected side might reduce the area of the BOS that is self-perceived as less secure.

Performance and Postural Interactions during Synchronous Pointing and Leg Flexion

When several tasks are superimposed in a sequence, their associated postural dynamics interact, being either in opposition or in adequacy. The aim of this study was to test the influence of these postural interactions on the performance of each elementary task composing a sequence. Seven subjects performed the following experimental conditions: pointing to a target; right leg flexion; left leg flexion; right leg flexion and pointing (ipsilateral leg sequence, IS); and left leg flexion and pointing (contralateral leg sequence, CS). Movements were performed on a large force plate. Wrist and trunk accelerations were detected with accelerometers. Analysis of the postural dynamics along the lateral axis showed that the direction of the anticipatory postural adjustments (APA) for the pointing was the same as for the contralateral leg flexion, and that it was opposite to that for the ipsilateral leg flexion; that is, APA of the elementary tasks were compatible or in opposition. The performance of the pointing (maximal wrist velocity) was higher in the isolated pointing than in both sequences, and it was higher in CS than in IS. The performance of the leg flexion (maximal vertical velocity of the center of gravity) was higher in both sequences than in the isolated leg flexion, and body weight transfer toward the stance leg was facilitated in CS as compared with IS. These results show that the performance of a task depends whether it is done in isolation or in combination with an associated task, and that there exists favorable combinations for task performance. These results are interpreted in terms of compatibility between the postural dynamics associated with each task of the sequence.

The efficacy of training for three manual handling strategies based on the observation of expert and novice workers

Objectives. To evaluate the efficacy of training for three manual handling strategies, i.e. load tilting/hands positioning, shoulders positioning and feet orientation based on the observation of the contrasted strategies of expert and novice workers and free practice using a search approach. Design. Ten novice male workers were tested at pre-training (one trial) and post-training with homogeneous boxes (three trials) and heterogeneous boxes (two trials) sampled from two sessions. Training took place with homogeneous boxes whereas heterogeneous boxes were new situations. Background. The effectiveness of training programs in safe handling and the repetition of specified techniques are contested; they should rather be based on expert workers’ strategies. Methods. Pre-training and post-training trials were analyzed with five video cameras and a large force plate. The biomechanical variables included three safety criteria: net 3D resulting moments at L5/S1, asymmetry of posture/efforts at L5/S1 and mechanical work on load; kinematics and ergonomic variables were used as explicative variables. Results. Training produced safer strategies by reducing mechanical work and back extensor moments; this occurred in both load conditions, an indication of the transfer of knowledge. These strategies consisted of changes in load maneuvers (tilting/hand positioning) and feet orientation. Conclusions. Training programs should be based on observations of workers. Relevance These results may guide the specialists involved in training programs. Training based on a search approach by the learner and anchored on observations of contrasted strategies (load tilts/hands positioning and feet orientation) by experts and novices appears promising for safe handling.

Biomechanical differences between best and worst performances in repeated free asymmetrical lifts

The purpose of the study was to evaluate, in 10 novice workers, the effect of the free practice of asymmetrical lifts with 3 different 15-kg containers. Practice effects were evaluated during one session (trials 1, 25 and 49), and also one month later (trial 50); containers effects were evaluated for homogeneity (2 boxes: homogeneous vs. heterogeneous) and for format (homogeneous box and cylinder). Each subject performed 150 lifts (50 practice trials and 3 containers per trial) but only 12 lifts were first analyzed. The data were obtained from 4 video cameras and a large force plate. A 3D dynamic rigid body model was used to evaluate low-back kinetics and kinematics. There were not any significant differences between the practice trials nor the boxes but there was high variability of performance within and between subjects. The main objective was then to evaluate the variability of these trials by contrasting the worst and best trials using three safety criteria: mechanical work, back efforts and asymmetry. The best strategies of reduced mechanical work (mean difference: 31%) was mainly associated with reduced knee flexion at take-off; strategies of reduced low-back moments at take-off (27%) were associated with smaller knee flexion and asymmetrical trunk efforts but larger feetspacings; finally, strategies of reduced back asymmetry at take-off (155%) were associated with reduced asymmetry of posture i.e. a better parallelism between shoulders/pelvis/handgrips and shoulders more parallel to the ground. Conclusions based on analyses of single trials or even means may be misleading. Relevance to industry Analyses of handling strategies including best and worst performances on the basis of specific safety criteria may help to better understand risk factors and suggest potential solutions for safer handling.

Gait intiation in bilateral vestibular loss

Objective: Gait initiation is a transient procedure between orthostatic posture and steady-state locomotion and includes anticipatory anteroposterior (AP) and lateral movements. Commands for this task are located in some levels of brain stem, which modulates activity of central pattern generator in the spinal cord. The purpose of this work was to explore the role of the vestibular system in this voluntary stepping. Methods: Six patients with chronic bilateral vestibular loss (BVL) were measured by means of a large force plate (70 cm×120 cm ) and the displacement of the center of pressure (COP) during gait initiation was calculated. Measurement parameters comprised maximum distance (MD), velocity (MV) in the AP and lateral direction as well as for pre-, first- and second-step stages, and the angle of the COP trajectory. Results: For all stages, BVL patients registered lower values for both MD and MV in the AP direction than did normal subjects. In the lateral direction, however, neither MD nor MV in BVL patients showed any difference from those of normals. The step angle of the COP trajectory was obviously reduced. Conclusion: These results suggest that in the AP direction, the vestibulospinal pathway can influence the locomotor related neural circuits, including the central pattern generator and supraspinal levels, by means of modifying the velocity and step length in order to stabilize the trunk. On the other hand, the control mechanism in the lateral direction may be different from that in the AP direction.

Experimental Analysis of Force Moment about Body Center of Mass during Level Walking Using Force Plates.

In this paper we report the characteristics of force moment about the center of mass (COM) of a human body during level walking at a steady pace, using two large force plates by which the three-dimensional floor reaction force components can be measured. The displacements of COM in the three directions are obtained from the Fourier series of the reaction force components by double integration. The following results are obtained : although the three-dimensional reaction force components are large, the moment of force about the COM becomes very small, which suggests that a human walks producing as small a moment as possible about the COM of his / her body. In other words, only a negligible rotation about the COM occurs ; the magnitude of the external moment applied at the sole is remarked in the moment of force about the vertical axis.

Characteristics of Reaction Force from the Floor in Stair Walking. Transient Characteristics in Stair Walking from or to Level Walking.

We report the dynamic characteristics of the reaction force from the floor, its application point, and the velocity and the displacement of the center of gravity of human body in stair walking when transferring from or to level walking. The reaction force and its application point are obtained using two large force plates, on one of which a stair model with five stairs is fixed, and the velocity and the displacement of the C. G. of the body are calculated by integrating the force once or twice. Discussions of these dynamic characteristics and their transient properties are given. One of the remarkable transient characteristics in stair walking is observed in the sagittal components of three physical quantities: reaction force, the velocity of the C. G. of the body and its displacement.

Analysis of Motion of Body Center during Human Stair Gait Using Force Plate

This paper reports the kinematic characteristics of the mass center of the entire human body while ascending and descending stairs, using large force plates which can measure both three-dimensional force components between the feet and the stair and the point of application of the force. Kinematic characteristics in terms of the velocity and the displacement of the body center in the three-dimensional space can be obtained by numerical integration of the force components with respect to time after proper calibration of measured data. For the calibrations, two methods were use: the first one compensates the measured force according to the sensitivity of the force plates due to their size were large; the second one tunes integration constants to avoid drifting features in integrated data. The following results are obtained: our new method, i.e., obtaining kinematic characteristics for stair gait using force plates, gives reliable results in the three orthogonal directions in space; characteristics in the sagittal and the vertical directions change depending on gait cadence; characteristics in the lateral direction are similar to those observed in level walking.

Analysis of Human Stair Walking Using Force Plate. Characteristics during Starting and Stopping Compared with Level Walking.

This paper reports the dynamic characteristics of human stair walking, particularly the transient during starting and stopping phases. The transient characteristics in human walking, especially in stair walking, has rarely been studied because of the difficulty of experimental measurement. Large force plates, on which two staircase models having 5 stairs are set, were used for measuring both three orthogonal components of the reaction force and its point of application in four different walking modes. In this paper, experimental results in stair walking are compared with those in level walking to make the distinct characteristics of stair walking clear. The velocity and the displacement of the mass center of the entire human body are obtained by numerical integration of the reaction force components, once or twice, respectively. The following results are obtained : the behaviors of the reaction force and the motion of its point of application in stair walking are more complicated than those in level walking ; this finding suggests that the stress appearing at joints is bigger in stair walking.

Analysis of Motion of Body Center during Human Stair Gait Using Force Plate.

This paper reports the kinematic characteristics of the center of mass of the entire human body while ascending and descending stairs, using large force plates which can measure both three-dimensional force components between the feet and the stair and the point of application of the force. Kinematic characteristics in terms of the velocity and displacement of the body center in the three-dimensional space can be obtained by numerical integration of the force components with respect to time after proper calibration of measured data. For the calibrations, two methods were used : the first one compensates the measured force according to the sensitivity of the force plates due to their size were large ; the second one tunes integration constants to avoid drifting features in integrated data. The following results are obtained : our new method, i. e., obtaining kinematic characteristics for stair gait using force plates, gives reliable results in the three orthogonal directions in space ; characteristics in the sagittal and vertical directions change depending on gait cadence ; characteristics in the lateral direction are similar to those observed in level walking.

階段昇降時の床反力特性解析

Human motions during steady-state gait have been extensively investigated and their average characteristics are well understood. In recent years, studies of transient gaits, such as initiation and stopping or turning during steady gait, have attracted the interest of some researchers. But most of these studies have been done with level walking. Going up and down stairs is a common activity of daily living. From the mechanical viewpoint, stair gait is quite different from level walking, because the vertical motion of the body is added. A study of the characteristics of the ground reaction forces during stair gait is an important step toward the understanding of the motion of the stair gait. In this study, the characteristics of both the reactions and the points of application during ascending and descending stairs were investigated, and the differences between them are discussed. The initiation and stopping of the stair gait were investigated also. These results are compared with the data on level walking. In experiments, two large force plates and two staircase models composed of five steps were used. Each model had standard dimensions in height and depth for an indoor staircase, and both were set on the large force plate. The results of this study showed many interesting characteristics. In the steady stair gait, the peak-to-peak transition in the longitudinal reaction force diagram was not monotonous, as it is in level walking. The value of the peak in the vertical force diagram was generally larger than that for level walking. It was produced in the double support phase in going up stairs, and in the single support phase in going down stairs. The point of application in the longitudinal direction moved backward once in the single support phase. The reason for this is that the first contact with floor is not the heel but the toe. In the initiation and stopping of the stair gait, the most remarkable characteristics was that the magnitude of the peak of the vertical force component during the first single support phase in initiation differed from that of the last single support phase in stopping. This difference was closely related to the vertical driving and breaking forces, which were produced at the time of initiation and stopping, respectively.

Relation between Peak Values of Floor Reaction Forces and Cadence in Human Transient Walking: Starting, Stopping, and Turning.

Human walking has been actively studied in such fields as biomechanics and rehabilitation engineering. Steady characteristics for a normal person walking at a constant speed are predictable based on these research results. Transient characteristics, for example, speed change in starting or stopping phase, however, have not been studied in detail due to difficulties in experimental data acquisition and processing. In this research, two large force plates are used to measure both the reaction force applied to each foot separately and their point of application in three modes of transient walking, that is, starting, stopping, and turning. The relations between the cadence and each wave peak value, which characterizes the walking motion, are shown. Experimental procedures and results will be presented. Transient characteristics to or from the steady walking state will be discussed.

Experimental Analysis of Reaction Forces and Motion of Center of Gravity during Human Gait Initiation. Characteristics of Transferring from Transient Phase to Steady-State Phase.

Two large force plates were used to measure the ground reaction force components in three directions. They can measure five steps in one trial. The characteristics of forces, velocities and displacements were investigated in relation to the walking speed. Velocities and displacements of CG (Center of Gravity) in three directions were obtained by integrating the reaction force components numerically. The results indicate that most of the driving force in the forward direction, which is closely related to the mean walking velocity in the steady-state phase, is generated during the first double support phase and successive single support phases. It is also found that the transient motion in gait initiation transfers the steady-state motion at the second or third time of heel contact.

Friction Measurement in Tennis on the Field and in the Laboratory

Tennis movements are characterized essentially by lateral displacements, thus external load on the lower extremities is created predominantly by friction generated between shoes and playing surfaces. This study analyzed the behavior of frictional forces and torques produced during an open stance forehand using various playing surfaces and different sport shoes. The frictional data were obtained from 12 advanced players returning a tennis ball fired from a ball machine and hitting a large Kistler force plate located at the base line of the tennis court. Using statistical ANOVA techniques, friction was found to be more sensitive to the choice of playing surface than to the choice of tennis shoe. “Fluid” type surfaces displayed the lowest frictional values in most cases. Additionally, comparison of the frictional data collected during the forehand with the measurements from a standardized laboratory test demonstrated that extrapolation of friction results from laboratory to real field conditions may lead to erroneous conclusions.

Characteristics of Transient Human Gait. Experiments and Analysis by Large Force Plate.

The characteristics of floor reaction forces are investigated using two large force plates in the three phases of human gait, that is, initiation, stopping and turning, The time histories of the point of application and the center of the body mass in gait initiation and stopping are obtained. In gait initiation, the phenomena of inverse fluctuation are noticed not only in the point of application, but in the floor reaction forces as well. It becomes clear experimentally that inverse fluctuations occur when a person initiates walking. The following results are also described: gait stopping is roughly similar to the time-reverse motion of the gait initiation; gait turning is the continuous motion of gait stopping and gait initiation.

大型三次元床反力計を用いた歩行の解析 脳性麻ひ治療における適用に関して

There are various methods of gait analysis, and analysis of floor reaction force is one of useful methods. We have been using large three-dimentional force plate system since September 1988. This time we discuss about application of this system to cerebral palsied children and its problems. We observed two patterns of floor reaction force, and both of them seemed to be caused by slightly different pattern of insufficiency about the segmental motion of muscles of lumbar girdle and knee. We also discuss about usefulness of trace of the COP (center of pressure) and its relation to actual pattern of gait.

Analysis of the transition from upright stance to steady state locomotion in children with under 200 days of autonomous walking.

The aim of this paper was to study, from a developmental perspective, the transient phase of gait during the period between the standing posture and the achievement of steady state gait, using temporal and biochemical parameters. Eight children who had been walking autonomously for 90 to 200 days were observed. A total of 64 sequences of steps were analyzed. A sequence of steps began with the child standing still and was executed on a large force plate. From the determination of the instantaneous velocity of center of gravity results establish that, unlike adults, progression velocity in children end of the first step, but after two to four steps. The gait initiation process does not depend on the steady state velocity, but results from an initial fall. The duration of the movement up to the end of the first step is independent of the progression velocity but depends only upon the body mass and moment of inertia of the children.

An analysis of characteristics of normal walking using a large forceplate. (1st Report, The characteristics of the antero-posterior step forces).

Periodic step forces which were obtained from a large force plate were expanded in Fourier series. The relative velocities and the relative displacements of the center of gravity of a human body were obtained by integrating those Fourier series. It was emphasized that the walking state diagrams, that is, Lissajous' figures of those step forces, relative velocities and relative displacements were available to analyze the characheristics of waling. The even terms of the Fourier coefficients of antero-posterior step forces were large and implied symmetry of right and left step forces. The odd terms of those were small and implied nonsymmetry of right and left step forces. The ratio of the even-numbered Fourier coefficients to the total amplitudes of the relative velocities of the center of gravity in antero-posterior direction was linear to the walking speed.

Are Dynamic Phenomena Prior to Stepping Essential to Walking?

The aim of our research was to examine the function of the pre-gait weight shifts in generating the dynamic forces needed to start walking at different speeds. Five subjects participated in the experiment, and a total of 105 gait initiation movements, executed on a large force plate, for three speed conditions (slow, normal, and fast), were examined. Results, which related to durations of the anticipation and of the step execution phases and to biomechanical parameters (progression velocity of the center of gravity, backward shift of the center of foot pressure, and magnitude of propulsive forces at heel-off time), suggested that dynamic phenomena prior to stepping are essential to walking as far as they contribute to the creation of convenient conditions for progression. The configuration of the support basis prior to stepping limits the progression velocity reached at the end of the first step.