Force Plate Recordings Research Articles

Improving the estimation of countermovement jump height from force plate recordings by considering the interaction between multiple procedural steps: An optimisation approach

ABSTRACT Force plates are used as standalone measurement systems in research and practice to evaluate metrics such as jump height. Calculating jump height involves multiple procedural steps, but previous investigations aiming to improve calculation procedures have only considered the influence of a single procedural step in isolation. The purpose of this study was to investigate if considering the interacting influence of multiple procedural steps in conjunction would impact the accuracy of jump height calculated from force plate recordings. An optimisation procedure was used to determine the combination of filter type, filter order, filter cut-off, integration start point and instant of take-off, that would minimize the root mean squared difference between force plate calculated jump height and a kinematic criterion. The best filter approach was a fifth order Butterworth filter with a 6 Hz cut-off frequency or a third order Chebyshev filter with a 5 Hz cut-off frequency. The best starting point for integration was approximately 0.25 s prior to the onset of the jump and the instant of take-off was best identified by finding the first instant that the force-time signal decreased by the magnitude of system weight. The presented optimisation technique provides an improved quantitative approach to develop standard procedures.

Evaluation of the Margin of Stability during Gait Initiation in Young Healthy Adults, Elderly Healthy Adults and Patients with Parkinson's Disease: A Comparison of Force Plate and Markerless Motion Capture Systems.

Gait initiation (GI) is a functional task classically used in the literature to evaluate the capacity of individuals to maintain postural stability. Postural stability during GI can be evaluated through the "margin of stability" (MoS), a variable that is often computed from force plate recordings. The markerless motion capture system (MLS) is a recent innovative technology based on deep learning that has the potential to compute the MoS. This study tested the agreement between a force plate measurement system (FPS, gold standard) and an MLS to compute the MoS during GI. Healthy adults (young [YH] and elderly [EH]) and Parkinson's disease patients (PD) performed GI series at spontaneous (SVC) and maximum velocity (MVC) on an FPS while being filmed by a MLS. Descriptive statistics revealed a significant effect of the group (YH vs. EH vs. PD) and velocity condition (SVC vs. MVC) on the MoS but failed to reveal any significant effect of the system (MLS vs. PFS) or interaction between factors. Bland-Altman plot analysis further showed that mean MoS biases were zero in all groups and velocity conditions, while the Bayes factor 01 indicated "moderate evidence" that both systems provided equivalent MoS. Trial-by-trial analysis of Bland-Altman plots, however, revealed that differences of >20% between the two systems did occur. Globally taken, these findings suggest that the two systems are similarly effective in detecting an effect of the group and velocity on the MoS. These findings may have important implications in both clinical and laboratory settings due to the ease of use of the MLS compared to the FPS.

Movement Onset Detection Methods: A Comparison Using Force Plate Recordings

Computational approaches for movement onset detection can standardize and automate analyses to improve repeatability, accessibility, and time efficiency. With the increasing interest in assessing time-varying biomechanical signals such as force-time recordings, there remains a need to investigate the recently adopted 5 times the standard deviation (5 × SD) threshold method. In addition, other employed methods and their variations such as the reverse scanning and first derivative methods have been scarcely evaluated. The aim of this study was to compare the 5 × SD threshold method, 3 variations of the reverse scanning method, and 5 variations of the first derivative method against manually selected onsets, in the countermovement jump and squat. Limits of agreement with respect to onsets, manually selected from unfiltered data, were best for the first derivative method using a 10-Hz low-pass filter (limits of agreement: -0.02 to 0.05s and -0.07 to 0.11s for the countermovement jump and squat, respectively). Thus, even when the onset of unfiltered data is of primary interest, filtering before calculating the first derivative is necessary as it reduces the amplification of high frequencies. The first derivative approach is also less susceptible to inherent variation during the quiet phase prior to the onset compared to the other approaches investigated.

CARTILAGE THICKNESS, SUBCHONDRAL BONE MINERAL DENSITY, AND AMBULATORY LOADING ARE CORRELATED IN NON-OSTEOARTHRITIC FEMORAL CONDYLES

A few studies have reported correlations between structural and functional parameters in healthy knees, and sometimes alterations of these correlations with OA. These observations suggested a new concept where knee OA could be related to a maladaptation between joint features. However, studies analyzing multiple features from different domains simultaneously are missing, which makes it difficult to fully understand the importance of relationships in maintaining joint homeostasis and their role in the development of OA. To assess the correlations among cartilage thickness (CTh), subchondral bone mineral density (sBMD), and ambulatory loading in non-OA femoral condyles. As commonly done, ambulatory loading was quantified using the peak knee adduction moment during walking (pKAM), which is a proxy for the distribution of load between medial and lateral compartments. To analyze comparable data, CTh and sBMD were expressed as medial-to-lateral (M/L) ratios. Therefore, this study tested the hypothesis that CTh M/L ratios, sBMD M/L ratios, and pKAM are positively correlated in non-OA femoral condyles. This study analyzed a subgroup of 48 young (25.7 ± 4.8 years; 22 males) asymptomatic volunteers with healthy knees enrolled in the HIPPA-compliant IRB-approved Lausanne Knee Study. This study aims at characterizing the structure and function of the knee, with a particular emphasis on the relationships among knee features The study protocol included clinical evaluation, radiographic imaging (weight-bearing Schuss and lateral radiographs of both knees), CT imaging (calibrated by a solid calcium hydroxyapatite-based bone mineral reference phantom) and 3T MRI of one randomly selected knee. 3D gait recordings were performed using a 16-camera motion capture system and force plates. CTh was obtained by manually segmenting the cartilage and bone on the DESS images, building 3D mesh models of bone and cartilage, and calculating the distance between the models. sBMD was obtained by registering the bone models from the DESS segmentation to the CT images and calculating the average CT intensity in the 3 mm of bone adjacent to cartilage. Mean CTh and sBMD were then calculated for six common regions of interest (ROIs) in the medial and lateral condyles and expressed as M/L ratios. pKAM was obtained following a standard inverse dynamics procedure applied to the marker-based motion capture and force plate recordings. Data processing was done using in-house software and algorithms previously validated. The relationship among CTh M/L ratios, sBMD M/L ratios and pKAM were assessed using Pearson correlation, with an α-level set a priori at 5%. All statistically significant correlations were positive, indicating larger CTh M/L ratios in knees with larger sBMD M/L ratios and larger pKAM, and vice versa. Specifically, CTh and sBMD M/L ratios were correlated in 5 of the 6 ROIs (0.31 ≤ r ≤ 0.53; 0.001 ≤ p ≤ 0.035), CTh M/L ratios in 4 ROIs were correlated with pKAM (0.29 ≤ r ≤ 0.33; 0.021 ≤ p ≤ 0.047), and sBMD M/L ratio in one ROI was correlated with pKAM (r = 0.31; p = 0.032). The hypothesis was supported, confirming the idea that structural and mechanical features of the knee are positively correlated, or adapted, in non-OA knees. This first study to show correlations among bone, cartilage, and mechanical loading provided insight into the functioning of the joint and underlined the potential of evaluating knee health based on relationships among features rather than on individual features in isolation. The analyses in this study will be extended to OA knees in future studies in order to determine the alterations of the relationships between knee features with OA.

Effects of experimentally induced cervical spine mobility alteration on the postural organisation of gait initiation

Gait initiation (GI), the transient period between quiet standing and locomotion, is a functional task classically used in the literature to investigate postural control. This study aimed to investigate the influence of an experimentally-induced alteration of cervical spine mobility (CSM) on GI postural organisation. Fifteen healthy young adults initiated gait on a force-plate in (1) two test conditions, where participants wore a neck orthosis that passively simulated low and high levels of CSM alteration; (2) one control condition, where participants wore no orthosis; and (3) one placebo condition, where participants wore a cervical bandage that did not limit CSM. Centre-of-pressure and centre-of-mass kinematics were computed based on force-plate recordings according to Newton’s second law. Main results showed that anticipatory postural adjustments amplitude (peak backward centre-of-pressure shift and forward centre-of-mass velocity at toe-off) and motor performance (step length and forward centre-of-mass velocity at foot-contact) were altered under the condition of high CSM restriction. These effects of CSM restriction may reflect the implementation of a more cautious strategy directed to attenuate head-in-space destabilisation and ease postural control. It follows that clinicians should be aware that the prescription of a rigid neck orthosis to posturo-deficient patients could exacerbate pre-existing GI deficits.

Dual vs single force plate analysis of human drop jumping

The aim was to develop a Drop Jump (DJ) protocol on dual force plate recordings (Dual Force Plate method: DFPM) to assess lower limb power production and quantify impact loading, and range of body center of mass (BCM) excursion during human DJ, and to examine if single-plate analysis (Reverse Integration Method: RIM) was a valid alternative. Nineteen male subjects performed DJs from an elevated platform (48 cm). Kinematic (BCM displacement and velocity, rebound jump height) and kinetic (BCM power, work, rate of force development (RFD), lower limb stiffness (LLS)) variables were obtained by force plate recording during the drop take-off phase (DFPM) and rebound phase (RIM, DFPM). DFPM and RIM did not differ at the group level for any outcome parameter. However, large intra-individual differences in BCM displacement were observed between DFPM and RIM (CV 9-10%) as well as for rebound jump height, LLS, and work performed on BCM (CV 9.8-14%). A majority of the remaining variables demonstrated low intra-individual variability between the two methods (r= 0.73-0.96, CV 1-5%). In conclusion, No systematic differences were revealed between DFPM and RIM, suggesting that RIM is a valid approach for assessing DJ performance. Substantial between-method intra-individual variability was noted for key outcome parameters.

Video System Correlated with Force Plate Recordings for Vertical Jump Biomechanics Analysis

The main idea is the biomechanical analysis of human body movements vertical on the spot, or free-fall jumps in order to assess the movements’ anatomical and physiological limits in subjects with and without sustained motor activity. The complex movement in vertical jump is defined by a fixed coordinate system of the recording system and also a mobile system attached to the entire human body. The assessment of the jump biomechanics is determined in relation to the measurement of the contact force between the plantar surface of both legs and the surface of a Kistler type plate. The research methodology is based on experimental system consisting of a calibrated motion video analyser, with dedicated software, based on a high-speed video cameras set synchronized and targeted on three main axes. Subjects participating in this experiment were selected on the principle of normal health, the same gender and similar anthropometric dimensions, but practicing sports or not. The results of the investigations have materialized in knee joint paths data set during the vertical jump but also the variation of the angles measured between the lower limb segments during jumping. Lower limb movements were recorded and determined for leg plantar base of support (BOS) on a large basis and using equipment and shoes specific to sports activities. The determinations highlighted a number of important aspects of the configuration required for this type of investigation and allowed identification of mechanisms for rapid assessment of how the human body was positioned during vertical jump in the goal of finding the best ways to improve performance. Also the coefficients of flexion/extension of the lower limbs, as well as those of impact on the contact with the force plate type Kistler, were used in relation to the human subjects’ anthropometric dimensions.

Adaptation to Coriolis force perturbations of postural sway requires an asymmetric two-leg model.

In the companion paper (Bakshi A, DiZio P, Lackner JR. J Neurophysiol. In press, 2019), we reported how voluntary forward-backward sway in a rotating room generated medial-lateral Coriolis forces that initially deviated intended body sway paths. Pure fore-aft sway was gradually restored over per-rotation trials, and a negative aftereffect occurred during postrotation sway. Force plate recordings showed that subjects learned to compensate for the Coriolis forces by executing a bimodal torque, the distribution of which was asymmetric across the two legs and of opposite sign for forward vs. backward sway. To explain these results, we have developed an asymmetric, nonparallel-leg, inverted pendulum model to characterize upright balance control in two dimensions. Fore-aft and medial-lateral sway amplitudes can be biomechanically coupled or independent. Biomechanical coupling occurs when Coriolis forces orthogonal to the direction of movement perturb sway about the ankles. The model includes a mechanism for alternating engagement/disengagement of each leg and for asymmetric drive to the ankles to achieve adaptation to Coriolis force-induced two-dimensional sway. The model predicts the adaptive control underlying the adaptation of voluntary postural sway to Coriolis forces. A stability analysis of the model generates parameter values that match those measured experimentally, and the parameterized model simulations reproduce the experimentally observed sway trajectories. NEW & NOTEWORTHY This paper presents a novel nonparallel leg model of postural control that correctly predicts the perturbations of voluntary sway that occur in a rotating environment and the adaptive changes that occur to restore faithful movement trajectories. This engaged leg model (ELM) predicts the asymmetries in force distribution and their patterns between the two legs to restore accurate movement trajectories. ELM has clinical relevance for pathologies that generate postural asymmetries and for altered gravitoinertial force conditions.

Sprint mechanics evaluation using inertial sensor-based technology: A laboratory validation study.

Advances in micro-electromechanical systems have turned magnetic inertial measurement units (MIMUs) into a suitable tool for vertical jumping biomechanical evaluation. Thus, this study aimed to determine whether appropriate reliability and agreement reports could also be obtained when analyzing 20-m sprint mechanics. Four bouts of 20-m sprints were evaluated to determine whether the data provided by a MIMU placed at the lumbar spine could reliably assess sprint mechanics and to examine the validity of the MIMU sensor compared to force plate recordings. Maximal power (P0 ), force (F0 ), and velocity (V0 ), as well as other mechanical determinants of sprint performance associated with the force-velocity, power-velocity, and ratio of forces-velocity, such as applied horizontal force loss (Sfv ) and decrease in ratio of forces (Drf ), were calculated and compared between instrumentations. Extremely large-to-very large correlation levels between MIMU sensor-based sprint mechanics variables and force plate recordings were obtained (mean±SD, force plate vs MIMU; V0, 8.61±0.85 vs 8.42±0.69; F0 , 383±110 vs 391±103; P0 , 873±246 vs 799±241; Sfv, -44.6±12.7 vs -46.2±10.7), ranging from 0.88 to 0.94, except for Drf, which showed weak-to-moderate correlation level (r=.45; -6.32±1.08 vs -5.76±0.68). Step-averaged force values measured with both systems were highly correlated (r=.88), with a regression slope close to the identity (1.01). Bland and Altman graphical representation showed a no random distribution of measured force values. Finally, very large-to-extremely large retest correlation coefficients were found for the intertrial reliability of MIMU measurements of sprint performance variables (r value ranging from .72 to .96). Therefore, MIMUs showed appropriate validity and reliability values for 20-m sprint performance variables.

Estimation of the centre of mass from motion capture and force plate recordings: A study on the elderly

The estimation of the centre of mass position in humans is usually based on biomechanical models developed from anthropometric tables. This method can potentially introduce errors in studies involving elderly people, since the ageing process is typically associated with a modification of the distribution of the body mass. In this paper, an alternative technique is proposed, and evaluated with an experimental study on 9 elderly volunteers. The technique is based on a virtual chain, identified from experimental data and locating the subject's centre of mass. Its configuration defines the location of the centre of mass, and is a function of the anatomical joint angles measured on the subject. This method is a valuable investigation tool in the field of geronto-technology, since it overcomes some of the problems encountered with other CoM estimation methods.

Visual Data Exploration for Balance Quantification in Real-Time During Exergaming.

Unintentional injuries are among the ten leading causes of death in older adults; falls cause 60% of these deaths. Despite their effectiveness to improve balance and reduce the risk of falls, balance training programs have several drawbacks in practice, such as lack of engaging elements, boring exercises, and the effort and cost of travelling, ultimately resulting in low adherence. Exergames, that is, digital games controlled by body movements, have been proposed as an alternative to improve balance. One of the main challenges for exergames is to automatically quantify balance during game-play in order to adapt the game difficulty according to the skills of the player. Here we perform a multidimensional exploratory data analysis, using visualization techniques, to find useful measures for quantifying balance in real-time. First, we visualize exergaming data, derived from 400 force plate recordings of 40 participants from 20 to 79 years and 10 trials per participant, as heat maps and violin plots to get quick insight into the nature of the data. Second, we extract known and new features from the data, such as instantaneous speed, measures of dispersion, turbulence measures derived from speed, and curvature values. Finally, we analyze and visualize these features using several visualizations such as a heat map, overlapping violin plots, a parallel coordinate plot, a projection of the two first principal components, and a scatter plot matrix. Our visualizations and findings suggest that heat maps and violin plots can provide quick insight and directions for further data exploration. The most promising measures to quantify balance in real-time are speed, curvature and a turbulence measure, because these measures show age-related changes in balance performance. The next step is to apply the present techniques to data of whole body movements as recorded by devices such as Kinect.

Implementation of machine learning for classifying prosthesis type through conventional gait analysis.

Current forecasts imply a significant increase in the quantity of lower limb amputations. Synergizing the capabilities of a conventional gait analysis system and machine learning facilitates the capacity to classify disparate types of transtibial prostheses. Automated classification of prosthesis type may eventually advance rehabilitative acuity for selecting an appropriate prosthesis for a given aspect of the rehabilitation process. The presented research utilized a force plate as a conventional gait analysis device to acquire a feature set for two types of prosthesis: passive Solid Ankle Cushioned Heel (SACH) and the iWalk BiOM powered prosthesis. The feature set consists of both temporal and kinetic data with respect to the force plate signal during stance. Intuitively a passive prosthesis and powered prosthesis generate distinctively different force plate recordings. A support vector machine, which is type of machine learning application, achieves 100% classification between a passive prosthesis and powered prosthesis regarding the feature set derived from force plate recordings.

The role of task constraints in relating laboratory and clinical measures of balance

This study tested the hypothesis that age-related postural control deficits are more clearly detected from force plate recordings when using postural control tasks with an explicitly defined goal as opposed to the frequently used quiet stance task. Eighteen older adults (over 65) and seventeen younger adults (under 30) stood on a force plate with visual feedback (VFB) of the center of pressure (COP) and without such visual feedback with eyes open (NVFB). In the VFB condition, online visual feedback about the COP was provided and participants maintained that feedback on a stationary visual target for 80s. We hypothesized that age-related difference in COP variability (standard deviation of COP position and average absolute maximum COP velocity; AAMV) would be more pronounced in the VFB than in the NVFB condition. In addition, we hypothesized that Berg balance scale (BBS) scores for older adults would correlate more strongly with the COP measures in the VFB condition than in the NVFB condition. Results showed that VFB enhanced age-related differences only for AAMV in anterior–posterior direction. Both age groups decreased postural sway when using VFB. Older adults increased AAMV with VFB while young adults did not, indicating that the task modified their postural control strategy stronger than in younger adults. BBS scores were correlated with the AAMV in both feedback conditions, while COP position variability was more clearly correlated with BBS in the VFB condition. These results suggest that the quiet stance task is sufficient to index balance function if velocity-based COP variables are utilized in the analysis.

Postural disturbances resulting from unilateral and bilateral diaphragm contractions: a phrenic nerve stimulation study.

Thoracoabdominal breathing movements are a complex source of postural disturbance, but there are contradictory reports in the literature with inspiration described as having either a backward or a forward disturbing effect. To elucidate the mechanisms underlying this phenomenon, the present study studied the postural disturbance caused by isolated contractions of the diaphragm. Eight male and four female healthy subjects followed an original paradigm of phrenic nerve stimulation (bilateral and unilateral) and "diaphragmatic" voluntary sniff maneuvers in the seated and standing postures. Center of gravity (CG) acceleration was calculated from force plate recordings, and respiratory kinematics were assessed with thoracic and abdominal sensor belts. CG and respiratory signals revealed that, while seated, bilateral phrenic stimulation and sniff maneuvers consistently produced expansion of the abdomen associated with a forward peak of CG acceleration. In the standing posture, the direction of the CG peak was reversed and always directed backward. Unilateral phrenic stimulation induced an additional medial-lateral acceleration of the CG, directed toward the nonactive side while seated, but in the opposite direction while standing. These results suggest that isolated diaphragmatic contractions produce a constant disturbing pattern for a given posture, but with opposite effects between standing and seated postures. This could be related to the different biomechanical configuration of the body in each posture, corresponding to distinct kinematic patterns of the osteoarticular chain. In addition, the lateral component of the CG acceleration induced by unilateral diaphragm contractions could be clinically relevant in patients with hemidiaphragm paralysis.

How much does the human medial gastrocnemius muscle contribute to ankle torques outside the sagittal plane?

Ankle movements in the frontal plane are less prominent though not less relevant than movements in the plantar or dorsal flexion direction. Walking on uneven terrains and standing on narrow stances are examples of circumstances likely imposing marked demands on the ankle medio-lateral stabilization. Following our previous evidence associating lateral bodily sways in quiet standing to activation of the medial gastrocnemius (MG) muscle, in this study we ask: how large is the MG contribution to ankle torque in the frontal plane? By arranging stimulation electrodes in a selective configuration, current pulses were applied primarily to the MG nerve branch of ten subjects. The contribution of populations of MG motor units of progressively smaller recruitment threshold to ankle torque was evaluated by increasing the stimulation amplitude by fixed amounts. From smallest intensities (12–32mA) leading to the firstly observable MG twitches in force-plate recordings, current pulses reached intensities (56–90mA) below which twitches in other muscles could not be observed from the skin. Key results showed a substantial MG torque contribution tending to rotate upward the foot medial aspect (ankle inversion). Nerve stimulation further revealed a linear relationship between the peak torque of ankle plantar flexion and inversion, across participants (Pearson R>.81, p<.01). Specifically, regardless of the current intensity applied, the peak torque of ankle inversion amounted to about 13% of plantar flexion peak torque. Physiologically, these results provide experimental evidence that MG activation may contribute to stabilize the body in the frontal plane, especially under situations of challenged stability.

Muscle co-activation, knee joint kinematics, and ground reaction forces are altered in the operated leg of meniscectomized patients at high risk of knee osteoarthritis

Purpose: Every other meniscectomized patient develop knee osteoarthritis (OA) 10-15 years after surgery. Thus, meniscectomized patients constitute a useful model to study changes in neuromuscular activity and knee joint biomechanics, which are factors suggested to play a role in OA development. Recently, we were unable to detect differences in neuromuscular activity and knee joint kinetics/kinematics betweenmeniscectomized patients and controls during stair descent. Furthermore, only modest leg-to-leg differences were observed between the operated and contra-lateral leg of the patients. More demanding motor tasks may be needed to detect early changes in knee joint kinetics/kinematics and neuromuscular activity in meniscectomized patients at high risk of knee OA. The aim of this study was therefore to investigate knee joint kinematics, ground reaction force (GRF) kinetics and level of muscle co-activation during a standardized forward lunge maneuver in meniscectomized patients at high risk of knee osteoarthritis. We hypothesized that patients would display increased levels of muscle co-activation along with reduced knee joint range of motion (ROM) and altered GRF kinetics in the operated compared to the contra-lateral leg. Methods: Patients: Twenty-two patients meniscectomized uni-laterally for a medial meniscal tear in the posterior half of the meniscus (15 men and 7 women, 45.4 5.1 years, 174.3 7.1 cm, 77.3 15.4 kg, BMI 25.4 kg/ m2, values are mean SD) were investigated during a standardized forward lunge with synchronous electromyography (EMG), goniometer and force plate recording. In the analyseswe focusedon threedifferent phasesof the forward lunge; the loading phase (foot-strike to 80% peak GRF), the unloading phase (80% peak GRF to toe-off) and mean of the entire stance phase (foot strike to toe-off). Knee joint range of motion (ROM): Knee joint ROM during the loading phase (ROMload), unloading phase (ROMunload) and from foot strike to peak knee flexion (ROMpeakflex) were measured using a flexible electrogoniometer. Ground reaction forces (GRF): The vertical GRF signal during the forward lunge was used to calculate the rate of loading (Loadslope), rate of unloading (Unloadslope) and average magnitude of GRF during the entire stance phase (GRFmean). Co-activation: Thigh muscle co-activation in the above phases of the forward lunge was quantified using normalized EMG signals obtained in the vastus lateralis (VL), vastus medialis (VM), biceps femoris (BF) and semitendinosus (ST) muscles. Statistics: Paired t-test with 0.05 level of significance was used to assess differences between the operated and contra-lateral leg of the patients. Results: All results are reported as mean SE. Consistent differences were observed between the operated leg and contra-lateral leg during the impact phase (loading phase) of the forward lunge. These differences were manifested as increased levels of muscle co-activation (38.0 4.0 vs. 30.1 3.1 %MVC, p1⁄40.02), reduced ROM (23.4 2.9 vs. 29.7 2.7 degrees, p1⁄40.01) and a higher loading rate (Loadslope) (985 160 vs. 696 82 %BW s-1, p1⁄40.01). Furthermore, ROMpeakflex was reduced in the operated compared with the contra-lateral leg (59.4 2.3 vs. 64.9 2.0 degrees, p1⁄40.01). No differences were observed in ROMunload, Unloadslope or muscle co-activation during the unloading phase. In addition, no differences were observed in GRFmean and averagemuscle co-activation during the entire stance phase. Conclusions: The findings of increasedmuscle co-activation, reduced ROM and increased rate of loading during the loading phase between the operated and contra-lateral leg support the hypothesis that meniscectomized patients demonstrate early modulations in knee joint kinetics, kinematics and neuromuscular activity in the operated leg. Future studies should include more demanding motor tasks than stair walking. Representing such a task, the forward lunge test appears to provide a sensitive approach to identify leg-to-leg differences in relevant neuromuscular and biomechanical variables in middle-aged patients at risk of OA.

Estimation of the centre of mass from motion capture and force plate recordings

The estimation of the centre of mass position in humans is usually based on biomechanical models developed from anthropometric tables. This method can potentially introduce errors in studies involv...

Estimation of the Centre of Mass From Motion Capture and Force Plate Recordings: A Study on the Elderly

The estimation of the centre of mass position in humans is usually based on biomechanical models developed from anthropometric tables. This method can potentially introduce errors in studies involving elderly people, since the ageing process is typically associated with a modification of the distribution of the body mass. In this paper, an alternative technique is proposed, and evaluated with an experimental study on 9 elderly volunteers. The technique is based on a virtual chain, identified from experimental data and locating the subject's centre of mass. Its configuration defines the location of the centre of mass, and is a function of the anatomical joint angles measured on the subject. This method is a valuable investigation tool in the field of geronto-technology, since it overcomes some of the problems encountered with other CoM estimation methods.

Assessed and distressed: White-coat effects on clinical balance performance

Objectives While balance in young and older adults is known to change with the threat of standing on elevated surfaces, the potential for social anxiety to influence emotional states and balance performance during a clinical assessment is currently unknown. Methods Nineteen young and 19 older healthy female adults volunteered for the study. The effects of age and clinical assessment on balance performance were examined using a 2×2 between- and within-subjects factorial design. Balance performance measures were derived from forceplate recordings of three different postural tasks. Psychological measures included fear of negative evaluation, state anxiety, and fear related to the completed balance tasks. Results There was a significant increase in state anxiety and fear when participants performed balance tasks while being assessed by an evaluator. Compared to the control condition, both age groups leaned significantly further forward during the functional reach task when being assessed. While being assessed, older adults had significantly larger amplitudes and frequencies of center of pressure (COP) displacement during two-legged stance with eyes closed (EC) and significantly less stance time during one-legged standing compared to the control condition. In contrast, balance performance in young adults during one-legged or two-legged stance tasks was unchanged by clinical assessment. Conclusions Social anxiety associated with the clinical assessment of balance can have a negative influence on both emotional states and balance control. As a result, clinicians need to recognize and account or control for potential social anxiety effects on clinical balance performance in young and older adults in particular.

Computational techniques for using insole pressure sensors to analyse three-dimensional joint kinetics

This study evaluated the feasibility of using insole pressure sensors together with whole body dynamics to analyse joint kinetics while running. Local affine transformations of shoe kinematics were first used to track the position of insole sensors during locomotion. Centre of pressure estimates derived from the insoles were within 10 mm of forceplate measures through much of stance, while vertical force estimates were within 15% of peak forceplate recordings. Insole data were then coupled with a least squares whole body dynamic model to obtain shear force estimates that were comparable to forceplate records during running. We demonstrated that these techniques provide a viable approach for analysing joint kinetics when running on uninstrumented surfaces.