The authors would like to thank the ANRT and the LADAPT.

The authors have no competing interests.

The goal of this paper was to provide scholars, clinicians, and higher education students information on the method (the &#34;global&#34; method) used in our laboratory to investigate the biomechanical organization of gait initiation (GI). Critical steps of the protocol, limitations of the method, and alternative methods and applications are discussed below.
A critical step in the protocol is the detection of the timing events of GI (i.e., APA onset, swing heel-off and toe-off, and rear foot-off). The values of both the temporal and the spatial variables related to the organization of GI depend on the correct detection of these events. For each of them, several methods of detection were proposed (these proposed methods are not exhaustive). It is recommended to use the same method throughout data analysis to ensure consistency across trials and experimental conditions and to allow comparison across studies in the literature. However, it is also recommended to use at least two different methods to ensure that the correct timing events are properly detected (only slight differences in the temporal features values are expected across these methods). Furthermore, for each timing event, automatic detection might be applied (e.g., with a MATLAB routine). This routine can be programmed easily through the methods provided in this article. It is strongly recommended to visually check the coherence and &#34;credibility&#34; of the data automatically obtained with these routines. For example, the amplitude of anticipatory center of pressure displacement should not exceed the base of support size. It is expected to be directed backward and toward the swing leg side (except for specific experimental populations); swing toe-off time is expected to occur after swing heel-off; APA onset should not occur sooner than 150 ms before the departure signal or 300 ms afterward (in a reaction time condition). In other words, it is believed that automatic detection alone is not sufficient to properly and &#34;safely&#34; analyze the data; it is essential to have an in-depth knowledge of i) the global time course of the biomechanical plots expected from the force platform and ii) the typical values expected from healthy participants. We believe that, in addition to the ability to program automatic routines, this knowledge is of strong didactic value for higher education students in biomechanics. This is why these two elements are provided in this article.
It is acknowledged that the &#34;global&#34; method has at least two limitations. First, this method does not provide data on the participants&#39; initial posture (i.e., on the relative position of body segments) but provides data on the initial center of pressure and center of gravity position (the relative position of which determines the condition of balance). The same initial center of pressure and center of gravity position could theoretically be reached with an infinite number of postures. In other words, the initial postural conditions under which the participants initiate gait may not be fully controlled with the global method. Visual checking of the participants&#39; initial posture by an experimented researcher or clinician is therefore important if the relative position of the body segments cannot be recorded (e.g., with a camera). Second, the method does not provide information on the contribution of each body segment acceleration (or &#34;local&#34; accelerations) to whole-body center of gravity acceleration. It follows that it is theoretically possible that the acceleration of certain body segments might be compensated by a deceleration of some distant body segments, resulting in a null whole-body center of gravity acceleration during APA31. Thus, the use of accelerometers positioned over several body segments (e.g., trunk, hips, legs) might be relevant to complete the force platform data.
An alternative and popular method to compute the whole-body center of gravity during GI is the kinematic method, which is based on recordings using a motion capture system of reflective markers glued to whole-body joint segments. The signals provided by these reflective markers allow the reconstitution of the whole-body skeleton. Based on the size of each body segment thus reconstituted and information provided by anthropometrical tables (e.g., mass and density of bones), the 3D position of the center of gravity of each segment can be computed with the camera software. With these data, it is then possible to compute the 3D position of the whole-body center of gravity. With successive derivation of the position signal, the velocity and acceleration of the whole-body center of gravity can be obtained. To compute the kinematics of the whole-body center of gravity, 53 reflective markers are required32. However, a simplified model with 13 markers was recently proposed by Tisserand et al.33.
The advantages of the global method (which can be assimilated into a kinetic method since it is based on the recording of forces and moments) over the kinematic method to investigate the postural organization of GI are the following: i) it requires no preparation of the participants, thus saving time, which is particularly important in cases of frail or pathological patients participating in the experiment; ii) it avoids potential errors in the computation of whole-body center of gravity acceleration due to cumulative small errors on marker positioning made by the experimenter, since the global method provides a direct measure of this quantity; iii) the center of pressure position cannot be computed using motion capture systems. The main disadvantage of the global method over the kinematic method was raised above - it does not allow the investigation of posture or segmental coordination.
Now, it is noteworthy that results from the current literature suggest both methods provide equivalent measure of center of gravity kinematics and event timing during locomotor tasks. For example, Langeard et al.34 reported that estimating the center of gravity braking (the &#34;braking index&#34; (BI)) using the global method or the kinematic method during GI was highly reliable. During compensatory stepping reactions, Maki and McIlroy35 reported that the anteroposterior velocity and displacement of the center of gravity computed at foot contact with both methods provided reasonably good agreement in both young healthy adults and the elderly. Similarly, during straight walking on level ground in people with transfemoral amputation, Lansade et al.36 showed that the estimation of center of gravity velocity from force platform data integration was acceptable. Finally, Caderby et al.24 and Yiou et al.25 showed that these two methods provided a similar estimation of swing heel off event and step length/width, respectively, during GI.
The global method was initially applied to the GI paradigm in young healthy adults to obtain basic knowledge on normal postural control during a functional motor task requiring simultaneous whole-body propulsion and stability maintenance10. It has since been extended widely to investigate many other dynamic whole-body motor tasks, such as lunging in fencing37, jumping38, sit to stand39, and lower limb flexion40. It is worth mentioning that the method has also been applied to investigate postural control during the termination of various motor tasks, including single stepping41 and pointing42, and may potentially be applied to investigate gait termination as it has previously been done with the kinematic method43. Finally, the method has also been widely used in patients with neurological conditions and in the elderly to better understand the pathopsychophysiological mechanisms affecting dynamic postural control2,3,4,5 and, more recently, in patients with Parkinson&#39;s disease to test the effectiveness of various non-pharmacological interventions (such as ankle stretching44 and functional electrical stimulation3) in enhancing postural control.
In conclusion, this article has presented a detailed method designed to investigate postural control during gait initiation. For each variable, normative values obtained in young healthy adults were provided. The method has a strong biomechanical background, since it is based on the laws of mechanics to compute the kinematics of the center of gravity and the center of pressure. Analysis of the interaction between these two virtual points is a key point of this method, since it determines the conditions of stability and whole-body progression. Because the performance of most of our daily motor tasks (including sports and work) requires safe (stable) whole-body progression, the method is highly appropriate to obtain insight into the posturo-dynamic mechanisms underlying motor efficiency/deficiency in both healthy and pathological populations. It therefore has strong applications in human movement science, sport science, ergonomics, and clinical science.

Gait initiation (GI), the transient phase between orthograde posture and steady-state locomotion, is a functional task and an experimental paradigm that is classically used in the literature to investigate postural control during a complex motor task requiring simultaneous whole-body propulsion and stability1. Patients with neurological conditions, such as Parkinson&#39;s disease2, stroke3, progressive supranuclear palsy4, and &#34;higher level gait disorders&#34;5, are known to have difficulty initiating gait, which exposes them to an increased risk of falling. It is therefore important for both basic and clinical sciences to develop concepts and methods to gain insight into the postural control mechanisms in play during gait initiation, to gain scientific knowledge and a better understanding of the pathophysiology of gait and balance disorders and be able to remediate them through adequate interventions.
The concept of biomechanical organization of gait initiation is described below, and the classical method designed to investigate this organization is detailed in the protocol section. GI can be subdivided into three successive phases: the &#34;anticipatory postural adjustments&#34; (APA) phase corresponding to the dynamic phenomena occurring in the whole body before swing heel-off, the &#34;unloading&#34; phase (between swing heel-off and toe-off), and the &#34;swing&#34; phase that ends at the time of swing foot contacting the support surface. This classical subdivision of the GI process originates from the pioneering studies of Belenkii et al.6 and others7,8, focusing on the coordination between posture and movement during voluntary arm raising to horizontal in the erect posture. In this paradigm, the body segments that are directly involved in the arm raising correspond to the &#34;focal&#34; chain, while the body segments that are interposed between the proximal part of the focal chain and the support surface correspond to the &#34;postural&#34; chain9. These authors reported that raising the arm was systematically preceded by dynamic and electromyographical phenomena in the postural chain, which they called &#34;anticipatory postural adjustments&#34;. For GI, swing heel-off (or swing toe-off, depending on the authors) is considered as the onset of gait movement10. Consequently, the dynamic phenomena occurring before this instant correspond to APA, and the swing limb is considered to be a component of the focal chain11. This statement is in agreement with the classical conception of movement biomechanical organization, according to which any motor act must involve a focal and a postural component12,13.
From a biomechanical point of view, APA associated with GI manifests as a backward and mediolateral (swing leg side-oriented) displacement of the center of pressure, which acts to propel the center of gravity in the opposite direction - forward and toward the stance leg side. The larger the anticipatory backward center of pressure displacement, the higher the motor performance in terms of the forward center of gravity velocity at foot contact10,14. In addition, by propelling the center of gravity toward the stance leg side, APA contribute to maintain mediolateral stability during the swing phase of GI1,15,16,17. The current literature stresses that alteration in this anticipatory control of stability is a major source of falls in the elderly1. Stability during GI has been quantified in the literature with an adaptation of the &#34;margin of stability&#34;18, a quantity that takes into account both the velocity and the position of the center of gravity within the base of support. In addition to the development of APA, the fall of the center of gravity during the swing phase of GI under the effect of gravity has been reported to be actively braked by the triceps surae of the stance leg. This active braking facilitates stability maintenance after foot contact, allowing a smooth foot landing on the support surface4.
The goal of this paper is to provide scholars, clinicians, and higher education students information on the material and method developed in our laboratory to investigate the postural organization of GI via a biomechanical approach. This &#34;global&#34; method (which can also be assimilated to a &#34;kinetic&#34; method for the reasons detailed below) was initiated by Breni&#232;re and collaborators10,19. It is based on the direct principle of mechanics to calculate both the acceleration of the center of gravity, as well as the instantaneous positions of the center of pressure. Each of these points is a global expression specific to the movement.
One is the instantaneous expression of the movements of all body segments related to the purpose of the movement (the center of gravity; e.g., the progression velocity of the body during GI); the other (the center of pressure) is the expression of the support conditions necessary to reach this objective. The instantaneous positions of these two points reflect the posturo-dynamic conditions to be satisfied for gait initiation. The force platform is the appropriate instrument for this model because it allows the direct measurement of the external forces and moments acting at the supporting surface during movement. It also allows the performance of natural movements and requires no special preparation.
Many factors are known to influence the postural organization of GI, including biomechanical, (neuro)physiological, psychological, environmental, and cognitive factors1,20. This paper focuses on the influence of two factors - velocity of GI and temporal pressure - and provides typical values obtained in healthy young adults.

<table><tbody><tr><td>Force platform(s)</td><td>AMTI</td><td></td><td>One large [120 cm x 60 cm] or two small [60 cm x 40 cm] force platform(s)</td></tr><tr><td>Python or Matlab</td><td>Python or MathWorks</td><td></td><td>Programming language for the computation of experimental variables</td></tr><tr><td>Qualisys track manage</td><td>Qualisys</td><td></td><td>Software for the synchronization of the force platform(s), the recording and the on-line visualization of raw biomechanical traces (3D forces and moments)</td></tr><tr><td>Visual3D</td><td>C-Motion Inc</td><td></td><td>Software for the processing of raw biomechanical traces (low-pass filtering)</td></tr></tbody></table>

postural organization of gait initiation for biomechanical analysis using force platform recordings

Gait initiation (GI), the transient phase between orthograde posture and steady-state locomotion, is a functional task and an experimental paradigm that is classically used in the literature to obtain insight into the basic postural mechanisms underlying body motion and balance control. Investigating GI has also contributed to a better understanding of the physiopathology of postural disorders in elderly and neurological participants (e.g., patients with Parkinson&#39;s disease). As such, it is recognized to have important clinical implications, especially in terms of fall prevention.
This paper aims to provide scholars, clinicians, and higher education students information on the material and method developed to investigate GI postural organization via a biomechanical approach. The method is based on force platform recordings and the direct principle of mechanics to compute the kinematics of the center of gravity and center of pressure. The interaction between these two virtual points is a key element in this method since it determines the conditions of stability and whole-body progression. The protocol involves the participant initially standing immobile in an upright posture and starting to walk until the end of an at least 5 m track.
It is recommended to vary the GI velocity (slow, spontaneous, fast) and the level of temporal pressure - gait may be initiated as soon as possible after the deliverance of a departure signal (high level of temporal pressure) or when the participant feels ready (low level of temporal pressure). Biomechanical parameters obtained with this method (e.g., duration and amplitude of anticipatory postural adjustments, step length/width, performance, and stability) are defined, and their computation method is detailed. In addition, typical values obtained in healthy young adults are provided. Finally, critical steps, limitations, and significance of the method with respect to the alternative method (motion capture system) are discussed.

Description of representative biomechanical time plots obtained from the force platform during gait initiation 
Whatever the level of temporal pressure or the instruction on GI velocity, swing heel-off is systematically preceded by APA. These APA can be characterized by a backward and swing leg side shift of the center of pressure (Figure 2). This anticipatory center of pressure shift promotes the acceleration of the center of gravity in the opposite direction (i.e., forward and to the stance leg side). Along the anteroposterior direction, the velocity of the center of gravity increases progressively to peak shortly after swing foot contact. Along the mediolateral direction, the center of gravity velocity first peaks toward the stance leg side at around swing toe-off, then peaks toward the swing leg side shortly after foot contact. Along the vertical direction, the center of gravity velocity peaks downward at around mid-stance. It then reverses direction and reaches a value close to zero at around foot contact.
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/64088/64088fig02.jpg" /> 
Figure 2: Representative biomechanical time plots obtained from the force platform during gait initiation (one single trial) and selected spatio-temporal variables. Gait was initiated quickly in a reaction time condition. X&#39;&#39;G, y&#39;&#39;G, z&#39;&#39;G: acceleration of the center of gravity along the anteroposterior, mediolateral, and vertical directions, respectively. X&#39;G, y&#39;G, z&#39;G: velocity of the center of gravity along the anteroposterior, mediolateral, and vertical directions, respectively. xP, yP: displacement of the center of pressure along the anteroposterior and mediolateral directions, respectively. Timing events. t0ML, t0AP, tHO, tTO, tFC, tRFO: onset of APA along the mediolateral and anteroposterior directions, time of swing heel-off, time of swing toe-off, time of swing foot contact, and time of rear foot-off, respectively. Temporal variables. APA, UNL, SWING: time windows for APA, unloading phase, and swing phase of gait initiation, respectively. Spatial variables. X&#39;GFO, x&#39;GFC, xPMAX, yPMAX, L, W, z&#39;GMIN, z&#39;GFC: anteroposterior velocity of the center of gravity at foot-off and foot-contact, maximal anticipatory center of pressure displacement along the anteroposterior and mediolateral directions, step length, step width, peak downward center of gravity velocity, and vertical center of gravity velocity at swing foot contact time, respectively. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/64088/64088fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Representative values of experimental variables in young healthy adults: Influence of velocity and temporal pressure
Temporal variables
APA duration 
The duration of APA along the anteroposterior and mediolateral directions depends on the velocity of GI but in an opposite way. More specifically, APA duration along the anteroposterior direction increases with GI velocity, with typical values ranging between ~500 ms for slow GI, and ~700 ms for fast GI9. By contrast, APA duration along the mediolateral direction decreases with GI velocity. Typical values range between ~700 ms for slow GI and ~500 ms for fast GI21.
The duration of anteroposterior and mediolateral APA also depends on the temporal pressure (values provided above are for a self-initiated condition (i.e., a condition with a low temporal pressure level). Studies in the literature typically compare APA duration in a condition with low versus high temporal pressure, when gait is initiated in a fast condition1,28. Under these conditions, the duration of both anteroposterior and mediolateral APA decreases by approximately 20-30 ms in the reaction time condition compared to the self-initiated condition.
Unloading phase duration 
The unloading phase duration depends on the velocity of GI (i.e., it decreases when GI velocity increases). Typical durations range between ~200 ms for slow GI and ~70 ms for fast GI21. The unloading phase duration is not sensitive to temporal pressure, at least when gait is initiated in a fast condition29.
Swing phase duration 
The swing phase duration depends on the velocity of GI (i.e., it decreases when velocity increases). Typical durations range between ~500 ms for slow GI and ~300 ms for fast GI21. By contrast, this duration is not sensitive to temporal pressure, at least when gait is initiated in a fast condition29.
Spatial variables
Amplitude of APA 
The amplitude of APA depends on the velocity of GI. More specifically, in a self-initiated condition, the amplitude of APA along the anteroposterior direction increases when the velocity of GI increases9. Typical APA values range between ~7 cm and ~0.15 m/s (for the anticipatory center of pressure displacement and the center of gravity velocity, respectively) for slow GI, and ~13 cm and ~0.36 m/s for fast GI. The amplitude of APA along the mediolateral direction, in terms of center of pressure displacement, also increases with the velocity of GI21. Typical values range between ~3 cm for slow GI and ~4 cm for fast GI. By contrast, the maximal velocity of the center of gravity reached during APA (mediolateral direction) does not change with the velocity of GI. Typical values are ~0.13 m/s. The amplitude of APA is also sensitive to temporal pressure, at least when gait is initiated quickly28,29. More specifically, both the anteroposterior and mediolateral components of APA increase with temporal pressure.
Step length and step width 
Step length and step width both depend on the velocity of GI but not on temporal pressure. Step length typically reaches ~50 cm and ~90 cm when gait is initiated in a slow and a fast condition, respectively23. Step width typically reaches ~12 cm and ~14 cm when gait is initiated in a slow and a fast GI condition, respectively9.
Performance of gait initiation 
The peak of center of gravity velocity typically ranges between ~1 m/s for slow GI and ~2 m/s for fast GI10. For fast GI, temporal pressure does not affect this performance parameter29, although it may induce a small (~9%) alteration28.
Stability control parameters
Braking index 
The BI is sensitive to the velocity of GI. When gait is initiated in a slow condition with a step length less than ~43 cm, the BI is null because there is no need to brake the fall of the center of gravity. The need to brake the center of gravity fall occurs for step lengths greater than 43 cm. A typical value of BI is 0.08 m/s for gait initiated at 1 m/s and with a step length of 55 cm27.
Margin of stability 
The MOS is not sensitive to the velocity of GI or to temporal pressure21,30. Typical MOS values obtained during GI are ~5 cm21.
Supplemental Figure S1: Screenshots of the software (Qualisys Track Manager) showing 3D ground reaction forces during gait initiation. Left, the force platform axis, the center of pressure position (corresponding to the application point of the ground reaction force vector), and the ground reaction force vector in the initial posture; right, the time-course of the raw 3D ground reaction forces during gait initiation (one participant, one trial). Green, red, and blue traces represent the ground reaction force along the anteroposterior, mediolateral, and vertical direction, respectively. Ordinate: force amplitude in Newtons. Abscissa: time in ms. The participants initially stood at the left side of the force platform and initiated gait to the right side. Note that the participant left the force platform at time t = 3,200 ms. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/64088/screenshot 1.pdf" target="_blank">Please click here to download this File.</a>
Supplemental Figure S2: Screenshots of the software (Qualisys Track Manager) showing the raw center of pressure displacement traces. Left, the force platform axis, the center of pressure position (corresponding to the application point of the ground reaction force vector), and the action force vector exerted by the participant on the force platform in the initial posture; right, the time-course of the raw center of pressure displacement traces (one participant, one trial). Green and red traces represent the center of pressure displacement along the anteroposterior and mediolateral direction, respectively. Ordinate: displacement in millimeters. Abscissa: time in ms. The participants initially stood at the left side of the force platform and initiated gait to the right side. Note that the participant left the force platform at time t = 3,200 ms. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/64088/screenshot 2.pdf" target="_blank">Please click here to download this File.</a>

Watch this Scientific Journal Video about Postural Organization of Gait Initiation for Biomechanical Analysis Using Force Platform Recordings at JoVE.com

Postural Organization of Gait Initiation for Biomechanical Analysis Using Force Platform Recordings

This paper describes the material and method developed to investigate the postural organization of gait initiation. The method is based on force platform recordings and on the direct principle of mechanics to compute center of gravity and center of pressure kinematics.

Gait initiation (GI), the transient phase between orthograde posture and steady-state locomotion, is a functional task and an experimental paradigm that ...

postural-organization-gait-initiation-for-biomechanical-analysis

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2.4K Views.  Centre de Soins de Suite et de Réadaptation. Deze methode maakt het mogelijk om anticiperende houdingsaanpassing of APA te verkrijgen. APA weerspiegelt de werking van het systeem op centraal niveau. Het maakt het dus mogelijk om de vraag in te voegen hoe de APA, de MOS en de BI eruit zien.Het belangrijkste voordeel van deze techniek is precisie. Bovendien is het een techniek die de mogelijkheid heeft om te worden aangepast, en minder vermoeiend voor patiënten die bijvoorbeeld motorische fixatie hebben. De implicatie van deze tec...

Video: Postural Organization of Gait Initiation for Biomechanical Analysis Using Force Platform Recordings

Substantiating Appropriate Motion Capture Techniques for the Assessment of Nordic Walking Gait and Posture in Older Adults

Nordic walking (NW) has become a safe and simple form of exercise in recent years, and in studying this gait pattern, various data collection techniques have been employed, each with positives and negatives. The aim was to determine the effect of NW on older adult gait and posture and to determine optimal use of different data collection systems in both short and long duration analysis. Gait and posture during NW and normal walking were assessed in 17 healthy older adults (age: 69 &#177; 7.3). Participants performed two trials of 6 Minute Walk Tests (6MWT) (1 with poles (WP) and 1 without poles (NP)) and 6 trials of a 5m walk (3 WP and 3 NP). Motion was recorded using two systems, a 6-sensor accelerometry system and an 8-camera 3-dimensional motion capture system, in order to quantify spatial-temporal, kinematic, and kinetic parameters.
With both systems, participants demonstrated increased stride length and double support and decreased gait speed and cadence WP compared to NP (p &#60;0.05). Also, with motion capture, larger single support time was found WP (p &#60;0.05). With 3-D capture, smaller hip power generation and moments of force were found at heel contact and pre-swing as well as smaller knee power absorption at heel contact, pre-swing, and terminal swing WP compared to NP, when assessed over one cycle (p &#60;0.05). Also, WP yielded smaller moments of force at heel contact and terminal swing along with larger moments at mid-stance of a gait cycle (p &#60;0.05). No changes were found for posture.
NW seems appropriate for promoting a normal gait pattern in older adults. Three-dimensional motion capture should primarily be used during short duration gait analysis (i.e. single gait cycle), while accelerometry systems should be primarily employed in instances requiring longer duration analysis such as during the 6MWT.

The aim was to substantiate optimal use of data collection techniques for Nordic walking gait and posture analysis. Three-dimensional motion capture should be used during short duration analysis (i.e. single gait cycle), while accelerometry should be employed for longer duration analysis (i.e. repeated cycles) like a 6 Minute Walk Test.

Nordic walking (NW) has become a safe and simple form of exercise in recent years, and in studying this gait pattern, various data collection techniques ...

Behavior

Simulation of Human-induced Vibrations Based on the Characterized In-field Pedestrian Behavior

For slender and lightweight structures, vibration serviceability is a matter of growing concern, often constituting the critical design requirement. With designs governed by the dynamic performance under human-induced loads, a strong demand exists for the verification and refinement of currently available load models. The present contribution uses a 3D inertial motion tracking technique for the characterization of the in-field pedestrian behavior. The technique is first tested in laboratory experiments with simultaneous registration of the corresponding ground reaction forces. The experiments include walking persons as well as rhythmical human activities such as jumping and bobbing. It is shown that the registered motion allows for the identification of the time variant pacing rate of the activity. Together with the weight of the person and the application of generalized force models available in literature, the identified time-variant pacing rate allows to characterize the human-induced loads. In addition, time synchronization among the wireless motion trackers allows identifying the synchronization rate among the participants. Subsequently, the technique is used on a real footbridge where both the motion of the persons and the induced structural vibrations are registered. It is shown how the characterized in-field pedestrian behavior can be applied to simulate the induced structural response. It is demonstrated that the in situ identified pacing rate and synchronization rate constitute an essential input for the simulation and verification of the human-induced loads. The main potential applications of the proposed methodology are the estimation of human-structure interaction phenomena and the development of suitable models for the correlation among pedestrians in real traffic conditions.

A protocol is presented for the characterization of the in-field pedestrian behavior and the simulation of the resulting structural response. Field-tests demonstrate that the in situ identified pacing rate and synchronization rate among the participants constitute an essential input for the simulation and verification of the human-induced loads.

For slender and lightweight structures, vibration serviceability is a matter of growing concern, often constituting the critical design requirement. With ...

Engineering

Sit-to-stand-and-walk from 120% Knee Height: A Novel Approach to Assess Dynamic Postural Control Independent of Lead-limb

Individuals with sensorimotor pathology e.g., stroke have difficulty executing the common task of rising from sitting and initiating gait (sit-to-walk: STW). Thus, in clinical rehabilitation separation of sit-to-stand and gait initiation - termed sit-to-stand-and-walk (STSW) - is usual. However, a standardized STSW protocol with a clearly defined analytical approach suitable for pathological assessment has yet to be defined.
Hence, a goal-orientated protocol is defined that is suitable for healthy and compromised individuals by requiring the rising phase to be initiated from 120% knee height with a wide base of support independent of lead limb. Optical capture of three-dimensional (3D) segmental movement trajectories, and force platforms to yield two-dimensional (2D) center-of-pressure (COP) trajectories permit tracking of the horizontal distance between COP and whole-body-center-of-mass (BCOM), the decrease of which increases positional stability but is proposed to represent poor dynamic postural control.
BCOM-COP distance is expressed with and without normalization to subjects&#39; leg length. Whilst COP-BCOM distances vary through STSW, normalized data at the key movement events of seat-off and initial toe-off (TO1) during steps 1 and 2 have low intra and inter subject variability in 5 repeated trials performed by 10 young healthy individuals. Thus, comparing COP-BCOM distance at key events during performance of an STSW paradigm between patients with upper motor neuron injury, or other compromised patient groups, and normative data in young healthy individuals is a novel methodology for evaluation of dynamic postural stability.

Here, we present a novel protocol to measure positional stability at key events during the sit-to-stand-to-walk using the center-of-pressure to the whole-body-center-of-mass distance. This was derived from the force platform and three-dimensional motion-capture technology. The paradigm is reliable and can be utilized for the assessment of neurologically compromised individuals.

Individuals with sensorimotor pathology e.g., stroke have difficulty executing the common task of rising from sitting and initiating gait (sit-to-walk: ...

Using Gold-standard Gait Analysis Methods to Assess Experience Effects on Lower-limb Mechanics During Moderate High-heeled Jogging and Running

A limited number of studies have explored lower-limb biomechanics during high-heeled jogging and running, and most studies have failed to clarify the wearing experience of subjects. This protocol describes the differences in lower-limb kinematics and ground reaction force (GRF) between experienced wearers (EW) and inexperienced wearers (IEW) during moderate high-heeled jogging and running. A three-dimensional (3D) motion analysis system with a configured force platform was used to synchronously capture lower-limb joint movements and GRF. 36 young females volunteered to participate in this study and were asked about high-heeled shoe-wearing experience, including frequency, duration, heel types, and heel heights. Eleven who had the experience of 3 to 6 cm heels for a minimum of three days per week (6 h per day) for at least two years and eleven who wore high heels less than twice per month participated. Subjects performed jogging and running at comfortable low and high speeds, respectively, with the right foot completely stepping onto a force platform when passing by along a 10 m walkway. EW and IEW adopted different biomechanical adaptations while jogging and running. IEW exhibited a generally larger range of joint movement, while EW showed a dramatically larger loading rate of GRF during running. Hence, further studies on the lower-limb biomechanics of high-heeled gait should strictly control the wearing experience of the subjects.

This study investigated lower-limb kinematics and ground reaction force (GRF) during moderate high-heeled jogging and running. Subjects were divided into groups of experienced wearers and inexperienced wearers. A three-dimensional motion analysis system with a configured force platform captured lower-limb joint movements and GRF.

A limited number of studies have explored lower-limb biomechanics during high-heeled jogging and running, and most studies have failed to clarify the ...

Clinical-oriented Three-dimensional Gait Analysis Method for Evaluating Gait Disorder

Three-dimensional gait analysis (3DGA) is shown to be a useful clinical tool for the evaluation of gait abnormality due to movement disorders. However, the use of 3DGA in actual clinics remains uncommon. Possible reasons could include the time-consuming measurement process and difficulties in understanding measurement results, which are often presented using a large number of graphs. Here we present a clinician-friendly 3DGA method developed to facilitate the clinical use of 3DGA. This method consists of simplified preparation and measurement processes that can be performed in a short time period in clinical settings and intuitive results presentation to facilitate clinicians&#39; understanding of results. The quick, simplified measurement procedure is achieved by the use of minimum markers and measurement of patients on a treadmill. To facilitate clinician understanding, results are presented in figures based on the clinicians&#39; perspective. A Lissajous overview picture (LOP), which shows the trajectories of all markers from a holistic viewpoint, is used to facilitate intuitive understanding of gait patterns. Abnormal gait pattern indices, which are based on clinicians&#39; perspectives in gait evaluation and standardized using the data of healthy subjects, are used to evaluate the extent of typical abnormal gait patterns in stroke patients. A graph depicting the analysis of the toe clearance strategy, which depicts how patients rely on normal and compensatory strategies to achieve toe clearance, is also presented. These methods could facilitate implementation of 3DGA in clinical settings and further encourage development of measurement strategies from the clinician&#39;s point of view.

In this study, a clinician-friendly three-dimensional gait analysis method, which was designed to be performed in the rehabilitation clinic, is presented. The method consists of a simplified measurement method and intuitive figures to facilitate clinicians&#39; understanding of the results.

Three-dimensional gait analysis (3DGA) is shown to be a useful clinical tool for the evaluation of gait abnormality due to movement disorders. However, ...

3D Kinematic Gait Analysis for Preclinical Studies in Rodents

The utility of three-dimensional (3D) kinematic motion analysis systems is limited in rodents. Part of the reason for this inadequacy is the use of complex algorithms and mathematical modeling that accompany 3D data collection and analysis procedures. This work provides a simple, user-friendly, step-by-step detailed methodology for 3D kinematic gait analysis during treadmill locomotion in healthy and neurotraumatic rats using a six-camera motion capture system. Also provided are details on 1) calibration of the system in an experimental set-up customized for quadrupedal locomotion, 2) data collection for treadmill locomotion in adult rats using markers positioned on all four limbs, 3) options available for video tracking and processing, and 4) basic 3D kinematic data generation and visualization and quantification of data using the built-in data collection software. Finally, it is suggested that the utility of this motion capture system be expanded to studying a variety of motor behaviors before and after neurotrauma.

Presented here is a protocol to collect and analyze three-dimensional kinematics of quadrupedal locomotion in rodents for preclinical studies.

The utility of three-dimensional (3D) kinematic motion analysis systems is limited in rodents. Part of the reason for this inadequacy is the use of ...

Lower-Limb Biomechanical Characteristics Associated with Unplanned Gait Termination Under Different Walking Speeds

Gait termination caused by unexpected stimulus is a common occurrence in everyday life. This study presents a protocol to investigate the lower-limb biomechanical changes that occur during unplanned gait termination (UGT) under different walking speeds. Fifteen male participants were asked to perform UGT on a walkway at normal walking speed (NWS) and fast walking speed (FWS), respectively. A motion analysis system and plantar pressure platform were applied to collect lower-limb kinematic and plantar pressure data. Paired-sampled T-test was used to examine the differences in lower-limb kinematics and plantar pressure data between two walking speeds. The results showed larger range of motion in the hip, knee, and ankle joints in the sagittal plane as well as plantar pressure in forefoot and heel regions during UGT at FWS when compared with NWS. With the increase in walking speed, subjects exhibited different lower-limb biomechanical characteristics that show FWS associated with greater potential injury risks.

This study compared the biomechanical characteristics of the lower extremity during unplanned gait termination under different walking speeds. The lower-limb kinematic and kinetic data from fifteen subjects with normal and fast walking speeds were collected using a motion analysis system and plantar pressure platform.

Gait termination caused by unexpected stimulus is a common occurrence in everyday life. This study presents a protocol to investigate the lower-limb ...

Quantifying Arms and Legs Contributions during Repetitive Electrically-Assisted Sit-To-Stand Exercise in Paraplegics: A Pilot Study

Execution of Sit-to-Stand (SitTS) in incomplete spinal cord injury (SCI) patients involves motor function in both upper and lower extremities. The use of arm support, in particular, is a significant assistive factor while executing SitTS movement in SCI population. In addition, the application of functional electrical stimulation (FES) onto quadriceps and gluteus maximus muscles is one of the prescribed management for incomplete SCI to improve muscle action for simple lower limb movements. However, the relative contribution of upper and lower extremities during SitTS has not been thoroughly investigated. Two motor incomplete SCI paraplegics performed repetitive SitTS to fatigue exercise challenge. Their performance was investigated as a mixed-method case-control study comparing SitTS with and without the assistance of FES. Three sets of SitTS tests were completed with 5-min resting period allocated in between sets, with mechanomyography (MMG) sensors attached over the rectus femoris muscles bilaterally. The exercise was separated into 2 sessions; Day 1 for voluntary SitTS and Day 2 for FES-assisted SitTS. Questionnaires were conducted after every session to gather the participants&#39; input about their repetitive SitTS experience. The analysis confirmed that a SitTS cycle could be divided into three phases; Phase 1 (Preparation to stand), Phase 2 (Seat-off), and Phase 3 (Initiation of hip extension), which contributed to 23% &#177; 7%, 16% &#177; 4% and 61% &#177; 6% of the SitTS cycle, respectively. The contribution of arms and legs during SitTS movement varied in different participants based on their legs&#39; Medical Research Council (MRC) muscle grade. In particular, the applied arm forces start to increase clearly when the leg forces start to decline during standing. This finding is supported by the significantly reduced MMG signal indicating leg muscle fatigue and their reported feeling of tiredness.

Arms contribution in Sit-To-Stand (SitTS) is determined by the legs' muscle condition. Several compensating strategies were discovered in efforts to achieve complete SitTS cycles. These findings triangulate the spinal cord injury (SCI) persons' biomechanical measures with their subjective feeling of load borne by both their limbs throughout the SitTS approaches.

Execution of Sit-to-Stand (SitTS) in incomplete spinal cord injury (SCI) patients involves motor function in both upper and lower extremities. The use of ...

Experimental Methods to Study Human Postural Control

Many components of the nervous and musculoskeletal systems act in concert to achieve the stable, upright human posture. Controlled experiments accompanied by appropriate mathematical methods are needed to understand the role of the different sub-systems involved in human postural control. This article describes a protocol for performing perturbed standing experiments, acquiring experimental data, and carrying out the subsequent mathematical analysis, with the aim of understanding the role of musculoskeletal system and central control in human upright posture. The results generated by these methods are important, because they provide insight into the healthy balance control, form the basis for understanding the etiology of impaired balance in patients and the elderly, and aid in the design of interventions to improve postural control and stability. These methods can be used to study the role of somatosensory system, intrinsic stiffness of ankle joint, and visual system in postural control, and may also be extended to investigate the role of vestibular system. The methods are to be used in the case of an ankle strategy, where the body moves primarily about the ankle joint and is considered a single-link inverted pendulum.

This article presents an experimental/analytic framework to study human postural control. The protocol provides step-by-step procedures for performing standing experiments, measuring body kinematics and kinetics signals, and analyzing the results to provide insight into the mechanisms underlying human postural control.

Many components of the nervous and musculoskeletal systems act in concert to achieve the stable, upright human posture. Controlled experiments accompanied ...

Bioengineering

Lower Limb Biomechanical Analysis of Healthy Participants

Biomechanical analysis techniques are useful in the study of human movement. The aim of this study was to introduce a technique for the lower limb biomechanical assessment in healthy participants using commercially available systems. Separate protocols were introduced for the gait analysis and muscle strength testing systems. To ensure maximum accuracy for gait assessment, attention should be given to the marker placements and self-paced treadmill acclimatization time. Similarly, participant positioning, a practice trial, and verbal encouragement are three critical stages in muscle strength testing. The current evidence suggests that the methodology outlined in this article may be effective for the assessment of lower limb biomechanics.

This article introduces a comprehensive experimental methodology on two of the latest technologies available to measure the lower limb biomechanics of individuals.

Postural Organization of Gait Initiation for Biomechanical Analysis Using Force Platform Recordings

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