An analysis of sit-to-stand movements

A Feasible Low-Cost System for Kinematic and Kinetic Analysis of Sit-to-Stand Movement

The sit-to-stand (STS) movement is a common activity essential for independence and mobility. Traditional methods for assessing STS often involve costly laboratory equipment, limiting their accessibility. This study introduced an economic alternative to the standard motion capture setup. The system presented in this study used an Azure Kinect and a plantar pressure sensor mat to acquire kinematic and kinetic data simultaneously during the STS. The Kinect provided noncontact motion capture, while the pressure sensor array measured ground reaction forces. To address the Kinect's inherent limitations in capturing extremity movements and the sensor array's inability to measure tangential forces, algorithms for the correction of lower limb joints and a multisource fusion model were developed. The accuracy of the proposed system was evaluated against a gold standard Vicon motion capture system. The results indicated that the system delivered estimates comparable to reference values for joint angles (r ranging from 0.85 to 0.99), antero-posterior and vertical ground reaction forces (r ranging from 0.81 to 0.98), joint reaction forces of knee and ankle (r ranging from 0.83 to 0.90), and joint moments of hip and ankle (r ranging from 0.77 to 0.82), suggesting that the proposed system can provide vital kinematic and kinetic data for efficient STS analysis. This study offered an accessible and practical solution for monitoring and assessing mobility in various settings.

Swetha, Prasanth G., Sakthi Sangeetha V., V. Gangadharan. Correlation between six-minute walk test and sit-to-stand test in COPD patients

Introduction and Aim: Six Minute Walk Test (6MWT) and spirometry are commonly used tests to assess the functional status of the Chronic Obstructive Pulmonary Diseases (COPD) patients. However, many other simpler tests like Sit to Stand Test (STST) are also available. This study is done to assess the utility of STST in comparison to 6MWT to evaluate the functional status of COPD patients in our hospital.   Materials and Methods: This study is a prospective and an observational study conducted on 50 COPD patients. Each patient underwent spirometry and subjected to 6MWT and STST. Quadriceps femoris muscle powers are measured for every patient before start of study. During the test, dyspnoea grade, Pulse rate, respiratory rate, saturation and blood pressure were measured.   Results: In this study group mean age was 60.38±11.09 years, mean FEV1 55.24% ±16.18% and then 6MWT and STST were correlating with each other. On comparing parameters hemodynamic parameters before and after performing 6MWT and STST for 30 seconds. There is significant correlation between 6MWT and STST using Pearson’s correlation. However, there is a negative correlation between FEV1 and both 6MWT and  STST.   Conclusion: Sit to stand test is less time consuming, repeatable and easy to perform. STST can also determine the functional status of COPD patient similar to Spirometry and Six-minute walk test. Hence, STST can be an alternative test for Spirometry and 6MWT in COPD patients in a limited resource facility.

An Embodied Sonification Model for Sit-to-Stand Transfers

Interactive sonification of biomechanical quantities is gaining relevance as a motor learning aid in movement rehabilitation, as well as a monitoring tool. However, existing gaps in sonification research (issues related to meaning, aesthetics, and clinical effects) have prevented its widespread recognition and adoption in such applications. The incorporation of embodied principles and musical structures in sonification design has gradually become popular, particularly in applications related to human movement. In this study, we propose a general sonification model for the sit-to-stand (STS) transfer, an important activity of daily living. The model contains a fixed component independent of the use-case, which represents the rising motion of the body as an ascending melody using the physical model of a flute. In addition, a flexible component concurrently sonifies STS features of clinical interest in a particular rehabilitative/monitoring situation. Here, we chose to represent shank angular jerk and movement stoppages (freezes), through perceptually salient pitch modulations and bell sounds. We outline the details of our technical implementation of the model. We evaluated the model by means of a listening test experiment with 25 healthy participants, who were asked to identify six normal and simulated impaired STS patterns from sonified versions containing various combinations of the constituent mappings of the model. Overall, we found that the participants were able to classify the patterns accurately (86.67 ± 14.69% correct responses with the full model, 71.56% overall), confidently (64.95 ± 16.52% self-reported rating), and in a timely manner (response time: 4.28 ± 1.52 s). The amount of sonified kinematic information significantly impacted classification accuracy. The six STS patterns were also classified with significantly different accuracy depending on their kinematic characteristics. Learning effects were seen in the form of increased accuracy and confidence with repeated exposure to the sound sequences. We found no significant accuracy differences based on the participants' level of music training. Overall, we see our model as a concrete conceptual and technical starting point for STS sonification design catering to rehabilitative and clinical monitoring applications.

Pulmonary function testing in COPD: looking beyond the curtain of FEV1

Chronic obstructive pulmonary disease (COPD) management remains challenging due to the high heterogeneity of clinical symptoms and the complex pathophysiological basis of the disease. Airflow limitation, diagnosed by spirometry, remains the cornerstone of the diagnosis. However, the calculation of the forced expiratory volume in the first second (FEV1) alone, has limitations in uncovering the underlying complexity of the disease. Incorporating additional pulmonary function tests (PFTs) in the everyday clinical evaluation of COPD patients, like resting volume, capacity and airway resistance measurements, diffusion capacity measurements, forced oscillation technique, field and cardiopulmonary exercise testing and muscle strength evaluation, may prove essential in tailoring medical management to meet the needs of such a heterogeneous patient population. We aimed to provide a comprehensive overview of the available PFTs, which can be incorporated into the primary care physician's practice to enhance the efficiency of COPD management.

Cultural bias in motor function patterns: Potential relevance for predictive, preventive, and personalized medicine

Background

Quantification of motor performance has a promising role in personalized medicine by diagnosing and monitoring, e.g. neurodegenerative diseases or health problems related to aging. New motion assessment technologies can evolve into patient-centered eHealth applications on a global scale to support personalized healthcare as well as treatment of disease. However, uncertainty remains on the limits of generalizability of such data, which is relevant specifically for preventive or predictive applications, using normative datasets to screen for incipient disease manifestations or indicators of individual risks.

Objective

This study explored differences between healthy German and Japanese adults in the performance of a short set of six motor tests.

Methods

Six motor tasks related to gait and balance were recorded with a validated 3D camera system. Twenty-five healthy adults from Chiba, Japan, participated in this study and were matched for age, sex, and BMI to a sample of 25 healthy adults from Berlin, Germany. Recordings used the same technical setup and standard instructions and were supervised by the same experienced operator. Differences in motor performance were analyzed using multiple linear regressions models, adjusted for differences in body stature.

Results

From 23 presented parameters, five showed group-related differences after adjustment for height and weight (R ² between .19 and .46, p<.05). Japanese adults transitioned faster between sitting and standing and used a smaller range of hand motion. In stepping-in-place, cadence was similar in both groups, but Japanese adults showed higher knee movement amplitudes. Body height was identified as relevant confounder (standardized beta >.5) for performance of short comfortable and maximum speed walks. For results of posturography, regression models did not reveal effects of group or body stature.

Conclusions

Our results support the existence of a population-specific bias in motor function patterns in young healthy adults. This needs to be considered when motor function is assessed and used for clinical decisions, especially for personalized predictive and preventive medical purposes. The bias affected only the performance of specific items and parameters and is not fully explained by population-specific ethnic differences in body stature. It may be partially explained as cultural bias related to motor habits. Observed effects were small but are expected to be larger in a non-controlled cross-cultural application of motion assessment technologies with relevance for related algorithms that are being developed and used for data processing. In sum, the interpretation of individual data should be related to appropriate population-specific or even better personalized normative values to yield its full potential and avoid misinterpretation.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13167-021-00236-3.

Effects of different vibration frequencies on muscle strength, bone turnover and walking endurance in chronic stroke

This randomized controlled trial aimed to evaluate the effects of different whole body vibration (WBV) frequencies on concentric and eccentric leg muscle strength, bone turnover and walking endurance after stroke. The study involved eighty-four individuals with chronic stroke (mean age = 59.7 years, SD = 6.5) with mild to moderate motor impairment (Fugl-Meyer Assessment lower limb motor score: mean = 24.0, SD = 3.5) randomly assigned to either a 20 Hz or 30 Hz WBV intervention program. Both programs involved 3 training sessions per week for 8 weeks. Isokinetic knee concentric and eccentric extension strength, serum level of cross-linked N-telopeptides of type I collagen (NTx), and walking endurance (6-min walk test; 6MWT) were assessed at baseline and post-intervention. An intention-to-treat analysis revealed a significant time effect for all muscle strength outcomes and NTx, but not for 6MWT. The time-by-group interaction was only significant for the paretic eccentric knee extensor work, with a medium effect size (0.44; 95% CI: 0.01, 0.87). Both WBV protocols were effective in improving leg muscle strength and reducing bone resorption. Comparatively greater improvement in paretic eccentric leg strength was observed for the 30 Hz protocol.

The Association of Obesity With Quadriceps Activation During Sit-to-Stand

OBJECTIVE

Obesity reduces voluntary recruitment of quadriceps during single-joint exercises, but the effects of obesity on quadriceps femoris muscle activation during dynamic daily living tasks, such as sit-to-stand (STS), are largely unknown. The purpose of this study was to determine how obesity affects quadriceps muscle recruitment during STS.

METHODS

In this cross-sectional study, 10 women who were lean and 17 women who were obese completed STS from a chair with arms crossed over the chest. Three-dimensional motion analysis was used to define 3 distinct phases (I-III) of the STS cycle. The electromyographic (EMG) activity of the vastus medialis, vastus lateralis, and semitendinosus was measured.

RESULTS

STS duration was greater (3.02 [SD = 0.75] seconds vs 1.67 [SD = 0.28] seconds) and peak trunk flexion angle was lower (28.9 degrees [SD = 10.4 degrees] vs 35.8 degrees [SD = 10.1 degrees]) in the women who were obese than in the women who were lean. The mean EMG activity of the knee extensors increased from phase I to phase II in both groups; however, the mean EMG activities of both the vastus medialis (32.1% [SD = 16.6%] vs 47.3% [SD = 19.6%] maximal voluntary isometric contraction) and the vastus lateralis (31.8% [SD = 19.4%] vs 47.5% [SD = 19.6%] maximal voluntary isometric contraction) were significantly lower during phase II in the women who were obese. The mean EMG activity of the semitendinosus increased throughout STS but was not significantly different between the 2 groups. Coactivation of the semitendinosus and knee extensors tended to be greater in the women who were obese but failed to reach statistical significance.

CONCLUSIONS

Knee extensor EMG amplitude was reduced in women who were obese during STS, despite reduced trunk flexion.

IMPACT

Reduced knee extensor recruitment during STS in obesity may redistribute forces needed to complete this task to other joints. Functional movement training may help improve knee extensor recruitment during STS in people who are obese.

LAY SUMMARY

People with obesity often have low quadriceps muscle strength and impaired mobility during daily activities. This study shows that women who are obese have lower voluntary recruitment of quadriceps when rising from a chair than women who are lean do, which could increase workload on hip or ankle muscles during this important daily task. Quadriceps strengthening exercises might improve the ability to rise from sitting to standing.

Chronic nerve health following implantation of femoral nerve cuff electrodes

BACKGROUND

Peripheral nerve stimulation with implanted nerve cuff electrodes can restore standing, stepping and other functions to individuals with spinal cord injury (SCI). We performed the first study to evaluate the clinical electrodiagnostic changes due to electrode implantation acutely, chronic presence on the nerve peri- and post-operatively, and long-term delivery of electrical stimulation.

METHODS

A man with bilateral lower extremity paralysis secondary to cervical SCI sustained 5 years prior to enrollment received an implanted standing neuroprosthesis including composite flat interface nerve electrodes (C-FINEs) electrodes implanted around the proximal femoral nerves near the inguinal ligaments. Electromyography quantified neurophysiology preoperatively, intraoperatively, and through 1 year postoperatively. Stimulation charge thresholds, evoked knee extension moments, and weight distribution during standing quantified neuroprosthesis function over the same interval.

RESULTS

Femoral compound motor unit action potentials increased 31% in amplitude and 34% in area while evoked knee extension moments increased significantly (p < 0.01) by 79% over 1 year of rehabilitation with standing and quadriceps exercises. Charge thresholds were low and stable, averaging 19.7 nC ± 6.2 (SEM). Changes in saphenous nerve action potentials and needle electromyography suggested minor nerve irritation perioperatively.

CONCLUSIONS

This is the first human trial reporting acute and chronic neurophysiologic changes due to application of and stimulation through nerve cuff electrodes. Electrodiagnostics indicated preserved nerve health with strengthened responses following stimulated exercise. Temporary electrodiagnostic changes suggest minor nerve irritation only intra- and peri-operatively, not continuing chronically nor impacting function. These outcomes follow implantation of a neuroprosthesis enabling standing and demonstrate the ability to safely implant electrodes on the proximal femoral nerve close to the inguinal ligament. We demonstrate the electrodiagnostic findings that can be expected from implanting nerve cuff electrodes and their time-course for resolution, potentially applicable to prostheses modulating other peripheral nerves and functions.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01923662 , retrospectively registered August 15, 2013.

Intraoperative Responses May Predict Chronic Performance of Composite Flat Interface Nerve Electrodes on Human Femoral Nerves

Peripheral nerve cuff electrodes (NCEs) in motor system neuroprostheses can generate strong muscle contractions and enhance surgical efficiency by accessing multiple muscles from a single proximal location. Predicting chronic performance of high contact density NCEs based on intraoperative observations would facilitate implantation at locations that maximize selective recruitment, immediate connection of optimal contacts to implanted pulse generators (IPGs) with limited output channels, and initiation of postoperative rehabilitation as soon as possible after surgery. However, the stability of NCE intraoperative recruitment to predict chronic performance has not been documented. Here we report the first-in-human application of a specific NCE, the composite flat interface nerve electrode (C-FINE), at a new and anatomically challenging location on the femoral nerve close to the inguinal ligaments. EMG and moment recruitment curves were recorded for each of the 8 contacts in 2 C-FINE intraoperatively, perioperatively, and chronically for 6 months. Intraoperative measurements predicted chronic outcomes for 87.5% of contacts with 14/16 recruiting the same muscles at 6 months as intraoperatively. In both 8-contact C-FINEs, 3 contacts elicited hip flexion and 5 selectively generated knee extension, 3 of which activated independent motor unit populations each sufficient to support standing. Recruitment order stabilized in less than 3 weeks and did not change thereafter. While confirmation of these results will be required with future studies and implant locations, this suggests that remobilization and stimulated exercise may be initiated 3 weeks after surgery with little risk of altering performance.

Knee extensor torque and BMI differently relate to sit-to-stand strategies in obesity

BACKGROUND

Obesity alters whole body kinematics during activities of daily living such as sit-to-stand (STS), but the relative contributions of excess body mass and decreased relative strength are unknown.

METHODS

Three-dimensional motion analysis data was collected on 18 obese subjects performing sit-to-stand (chair height: 52 cm). Isometric knee extensor strength was measured at 90⁰ knee flexion. Forward stepwise linear regression was used to determine the association between the independent variables BMI and the knee extensor torque with the dependent variables: foot position and trunk kinematics.

FINDINGS

BMI, but not knee extensor torque, was inversely related to shank angle and positively related to stance width. Relative knee extensor torque, but not BMI, was inversely associated with initial trunk angle, peak trunk flexion angle, and peak trunk extension velocity (r² = 0.470-0.495). BMI was positively associated with peak trunk flexion velocity, but no other parameters of trunk kinematics. In the final regression model, BMI was the primary predictor (r² = 0.423) and relative knee extensor strength served as a secondary predictor (r² = 0.118) of peak trunk flexion velocity.

INTERPRETATION

BMI and knee extensor strength differently contribute to sit-to-stand performance strategies in obese subjects. Muscle strength may be an important determinant of whole-body kinematics during activities of daily living such as STS.

Relationship between movement time and hip moment impulse in the sagittal plane during sit-to-stand movement: a combined experimental and computer simulation study

Background

The association between repetitive hip moment impulse and the progression of hip osteoarthritis is a recently recognized area of study. A sit-to-stand movement is essential for daily life and requires hip extension moment. Although a change in the sit-to-stand movement time may influence the hip moment impulse in the sagittal plane, this effect has not been examined. The purpose of this study was to clarify the relationship between sit-to-stand movement time and hip moment impulse in the sagittal plane.

Methods

Twenty subjects performed the sit-to-stand movement at a self-selected natural speed. The hip, knee, and ankle joint angles obtained from experimental trials were used to perform two computer simulations. In the first simulation, the actual sit-to-stand movement time obtained from the experiment was entered. In the second simulation, sit-to-stand movement times ranging from 0.5 to 4.0 s at intervals of 0.25 s were entered. Hip joint moments and hip moment impulses in the sagittal plane during sit-to-stand movements were calculated for both computer simulations.

Results and conclusions

The reliability of the simulation model was confirmed, as indicated by the similarities in the hip joint moment waveforms (r = 0.99) and the hip moment impulses in the sagittal plane between the first computer simulation and the experiment. In the second computer simulation, the hip moment impulse in the sagittal plane decreased with a decrease in the sit-to-stand movement time, although the peak hip extension moment increased with a decrease in the movement time. These findings clarify the association between the sit-to-stand movement time and hip moment impulse in the sagittal plane and may contribute to the prevention of the progression of hip osteoarthritis.

New estimation model of the initial lower limb angle to improve angle estimation during the extension phase of standing-up movement

[Purpose] An estimation model of the knee and ankle joint angles during the extension phase was proposed in the previous study. However, it had limited use because of the fixed initial lower limb angle before standing up. This study aimed to propose a new estimation model of the initial lower limb angle to improve the angle estimation during extension phase. [Subjects and Methods] Seven healthy male volunteers were enrolled. The new estimation model approximated the initial lower limb angle using a force sensor plate that measured the plantar pressure of the subjects. The estimated angle and force were compared to those obtained by a motion capture system and force plate. [Results] The new estimation model of initial lower limb angle showed no significant difference compared with the true values obtained by motion capture, except for the subject who had a greater foot-pressure measurement error compared with the force plate measurement, with maximum errors of 5.98° and 6.31°, respectively. [Conclusion] The proposed model in this study can estimate the initial lower limb angle before standing and can be applied to the angle estimation model during the extension phase of the standing-up movement.

External loading alters trunk kinematics and lower extremity muscle activity in a distribution-specific manner during sitting and rising from a chair

BACKGROUND

Excess body mass alters gait biomechanics in a distribution-specific manner. The effects of adding mass centrally or peripherally on biomechanics during sitting and rising from a chair are unknown.

METHODS

Motion analysis and lower extremity EMG were measured for fifteen healthy, normal weight subjects during sit-to-stand (SitTS) and stand-to-sit (StandTS) from a chair under unloaded (UN), centrally loaded (CL), and peripherally loaded (PL) conditions.

RESULTS

Compared to UN, PL significantly increased support width (SitTS and StandTS), increased peak trunk flexion velocity (SitTS), and trended to increase peak trunk flexion angle (SitTS). During StandTS, CL significantly reduced peak trunk flexion compared to UN and PL. EMG activity of the semitendinosus, vastus lateralis and/or medialis was significantly increased in CL compared to UN during SitTS and StandTS.

CONCLUSIONS

Adding mass centrally or peripherally induces contrasting biomechanical strategies to successfully sit or rise from a chair. CL limits trunk flexion and increases knee extensor muscle activity whereas; PL increases support width and trunk flexion, thus preventing increased EMG activity.

Rising from Sitting in Elderly People, Part 1: Implications of Biomechanics and Physiology

Rising from a sitting position is arguably the most frequently performed component of activities of daily living and is a prerequisite to functional mobility and subsequent meaningful activity. A difficulty with rising, commonly observed in elderly people, may either be a nuisance factor or have a serious impact on independence and quality of life; thus the occupational therapist seeks to maintain and improve this function.

This literature review is in two parts. Part 1 discusses the functional implications and importance of rising from sitting and provides a biomechanical analysis of sit-to-stand that focuses on balance and momentum. It considers the dynamic relationship between the centre of mass and the centre of pressure, the phases of rising and the factors that affect ease of rising, such as initial body position, speed of rising and age-related physiological changes. Part 2 will offer movement, environmental and motivational strategies based on the findings presented in part 1. These strategies are designed to help elderly people to compensate for difficulties in rising. The analysis and strategies proposed are also applicable to younger clients with balance or muscle strength impairments.

Evoked EMG versus muscle torque during fatiguing functional electrical stimulation-evoked muscle contractions and short-term recovery in individuals with spinal cord injury

This study investigated whether the relationship between muscle torque and m-waves remained constant after short recovery periods, between repeated intervals of isometric muscle contractions induced by functional electrical stimulation (FES). Eight subjects with spinal cord injury (SCI) were recruited for the study. All subjects had their quadriceps muscles group stimulated during three sessions of isometric contractions separated by 5 min of recovery. The evoked-electromyographic (eEMG) signals, as well as the produced torque, were synchronously acquired during the contractions and during short FES bursts applied during the recovery intervals. All analysed m-wave variables changed progressively throughout the three contractions, even though the same muscle torque was generated. The peak to peak amplitude (PtpA), and the m-wave area (Area) were significantly increased, while the time between the stimulus artefact and the positive peak (PosT) were substantially reduced when the muscles became fatigued. In addition, all m-wave variables recovered faster and to a greater extent than did torque after the recovery intervals. We concluded that rapid recovery intervals between FES-evoked exercise sessions can radically interfere in the use of m-waves as a proxy for torque estimation in individuals with SCI. This needs to be further investigated, in addition to seeking a better understanding of the mechanisms of muscle fatigue and recovery.

Neuromechanical interference of posture on movement: evidence from Alexander technique teachers rising from a chair

While Alexander technique (AT) teachers have been reported to stand up by shifting weight gradually as they incline the trunk forward, healthy untrained (HU) adults appear unable to rise in this way. This study examines the hypothesis that HU have difficulty rising smoothly, and that this difficulty relates to reported differences in postural stiffness between groups. A wide range of movement durations (1–8 s) and anteroposterior foot placements were studied under the instruction to rise at a uniform rate. Before seat-off (SO) there were clear and profound performance differences between groups, particularly for slower movements, that could not be explained by strength differences. For each movement duration, HU used approximately twice the forward center-of-mass (CoM) velocity and vertical feet-loading rate as AT. For slow movements, HU violated task instruction by abruptly speeding up and rapidly shifting weight just before SO. In contrast, AT shifted weight gradually while smoothly advancing the CoM, achieving a more anterior CoM at SO. A neuromechanical model revealed a mechanism whereby stiffness affects standing up by exacerbating a conflict between postural and balance constraints. Thus activating leg extensors to take body weight hinders forward CoM progression toward the feet. HU's abrupt weight shift can be explained by reliance on momentum to stretch stiff leg extensors. AT's smooth rises can be explained by heightened dynamic tone control that reduces leg extensor resistance and improves force transmission across the trunk. Our results suggest postural control shapes movement coordination through a dynamic “postural frame” that affects the resistive behavior of the body.

Perception of weight-bearing and effort distribution during sit-to-stand in individuals post-stroke

The objectives were to assess whether individuals who are poststroke can rate their perceived knee effort distribution during sit-to-stand tasks in various foot positions, to quantify their errors of perception and to compare these to their errors in weight-bearing perception. Weight-bearing distribution was assessed in hemiparetic participants (N = 19) using a force platform. Electromyographic (EMG) data normalized to maximal EMG values were used to quantify knee effort distribution. The difference between participants' real weight bearing and knee effort and the perceived values rated on a visual analog scale defined their errors of weight-bearing and effort perception. The perception of effort and weight bearing, and the errors therein, were compared among the four foot positions. Participants perceived only the changes induced by the different foot positions on their weightbearing distribution, not on their knee effort distribution, and they made greater perception errors with the knee effort distribution than with the weight-bearing distribution.

Muscle weakness, fatigue, and torque variability: effects of age and mobility status

INTRODUCTION

Whereas deficits in muscle function, particularly power production, develop in old age and are risk factors for mobility impairment, a complete understanding of muscle fatigue during dynamic contractions is lacking. We tested hypotheses related to torque-producing capacity, fatigue resistance, and variability of torque production during repeated maximal contractions in healthy older, mobility-impaired older, and young women.

METHODS

Knee extensor fatigue (decline in torque) was measured during 4 min of dynamic contractions. Torque variability was characterized using a novel 4-component logistic regression model.

RESULTS

Young women produced more torque at baseline and during the protocol than older women (P < 0.001). Although fatigue did not differ between groups (P = 0.53), torque variability differed by group (P = 0.022) and was greater in older impaired compared with young women (P = 0.010).

CONCLUSIONS

These results suggest that increased torque variability may combine with baseline muscle weakness to limit function, particularly in older adults with mobility impairments.

Knee efforts and weight-bearing asymmetry during sit-to-stand tasks in individuals with hemiparesis and healthy controls

The asymmetrical weight-bearing distribution of individuals with hemiparesis rising from a chair might be used to produce similar muscular efforts at the lower limbs. The aim of this study was to determine if individuals with hemiparesis have symmetrical levels of effort at the knee during spontaneous sit-to-stand transfers. Nineteen subjects with hemiparesis and 16 healthy controls participated. Their weight-bearing (WB) distribution during sit-to-stand was assessed with a force platform setup while the knee effort distribution was quantified using electromyographic (EMG) data normalized to maximal EMG values then expressed relative to the sum of the bilateral efforts. The healthy individuals presented symmetrical weight-bearing and knee effort distributions during the sit-to-stand transfer. The participants with hemiparesis, classified in three subgroups based on knee extensors' strength asymmetries (mild, moderate and severe), yielded different results. The mild group (n = 6) behaved like the controls, with almost symmetrical WB and knee efforts. The moderate group (n = 7) had similar WB and effort asymmetries while the severe group (n = 6) exhibited a WB distribution difference between sides but had almost symmetrical knee effort. These results for the severe group suggest that a control is exerted on the levels of effort when rising from a chair, which might be required when a certain threshold of effort is reached on the nonparetic side.

Perception of weight-bearing distribution during sit-to-stand task in healthy young and elderly individuals

The first objective was to assess whether healthy individuals could accurately estimate their weight-bearing distribution in sit-to-stand transfers. The second was to evaluate the effect of age on weight-bearing perception. 16 young participants (11 women, 5 men; M age 29 yr., SD = 8.7) and 15 elderly participants (7 women, 8 men; M age 65 yr., SD = 3.8) were recruited. Verbal instructions and visual feedback referring to different percentages of weight-bearing distribution to execute were used to quantify weight-bearing perception in sit-to-stand tasks. For the feedback approach, the perception was assessed with a visual analog scale. For the verbal task, the weight-bearing distribution produced was assessed with force plates. Both young and elderly participants had good perception of weight-bearing distribution, with mean absolute errors of 6.4%. Moreover, their perceived and real weight-bearing distribution showed good agreement (ICC > or = .79).

[Differences in biomechanical parameters during sit to stand transfer between elderly with and without history of frequent falls]

INTRODUCTION

The phenomenon of frequent falls (FF) is a health problem in the older population, and is a reason why tools need to be designed for the objective assessment of the risk of FF. In this sense the use of biomechanical parameters could be of use in designing these. The aim of this work was to describe the biomechanical differences registered during a sit to stand transfer (STS) between subjects with and without a history of frequent falls.

MATERIAL AND METHOD

A sample of sixty voluntary older adults were assessed, divided in two groups of thirty subjects. The first group was composed of older adults without history of frequent falls (WoHFF) and the other group with history of frequent falls (WHFF). In both groups the velocity of the mass centre, the anterior flexion of the trunk, the joint and support moments of the lower extremity and the time of execution during the TSB was assessed.

RESULTS

The subjects WHFF generate a slower vertical velocity (P<0.001), lower slope (P<0.001), greater anterior trunk flexion (P<0.0001), lower support moment (P=0.001) and took longer in executing the STS (P=0.0001) than the group WoHFF.

CONCLUSIONS

Differences exist in the biomechanical parameters registered during the STS between the elderly WHFF and WoHFF. The results indicate that the function of the hip extensor muscles could have an important role in the execution of the STS in subjects WHFF. The biomechanical parameters assessed during the STS should be considered as useful tools to distinguish between subjects WHFF and WoHFF, and should be considered in the design of tools to determine the risk of frequent falls.

Intraoperative demonstration of selective stimulation of the common human femoral nerve with a FINE

We have tested the hypothesis that the Flat Interface Nerve Electrode (FINE) can selectively stimulate each muscle innervated by the common femoral nerve of the human, near the inguinal ligament in a series of intraoperative trials. During routine vascular surgeries, an 8-contact FINE was placed around the common femoral nerve between the inguinal ligament and the first branching point. The efficacy of the FINE to selectively recruit muscles innervated by the femoral nerve was determined from electromyograms (EMGs) recorded in response to electrical stimulation. At least four of the six muscles innervated by the femoral nerve were selectively recruited in all subjects. Of these, at least one muscle was a hip flexor and two muscles were knee extensors. Results from the intraoperative experiments were used to estimate the potential for the electrode to restore knee extension and hip flexion through Functional Electrical Stimulation (FES). Normalized EMGs and biomechanical simulations were used to estimate joint moments and functional efficacy. Estimated knee extension moments exceed the threshold required for the sit-to-stand transition.

Selective stimulation of the human femoral nerve with a flat interface nerve electrode

In humans, we tested the hypothesis that a flat interface nerve electrode (FINE) placed around the femoral nerve trunk can selectively stimulate each muscle the nerve innervates. In a series of intraoperative trials during routine vascular surgeries, an eight-contact FINE was placed around the femoral nerve between the inguinal ligament and the first nerve branching point. The capability of the FINE to selectively recruit muscles innervated by the femoral nerve was assessed with electromyograms (EMGs) of the twitch responses to electrical stimulation. At least four of the six muscles innervated by the femoral nerve were independently and selectively recruited in all subjects. Of these, at least one muscle was a hip flexor and at least two were knee extensors. Results from the intraoperative experiments were used to estimate the potential for the electrode to restore knee extension and hip flexion through functional electrical stimulation. Normalized EMGs and biomechanical simulations were used to estimate joint moments and functional efficacy. Estimated knee extension moments exceed the threshold required for the sit-to-stand transition.

Musculoskeletal biomechanics in sit-to-stand and stand-to-sit activities with stroke subjects: a systematic review

INTRODUCTION: Sit-to-stand and stand-to-sit are two of the most mechanically demanding activities undertaken in daily life and which are usually impaired in stroke subjects. OBJECTIVES: To determine the distinguishing characteristics in musculoskeletal biomechanical outcomes of the sit-to-stand and stand-to-sit activities with stroke subjects, with an emphasis on the clinical management of stroke disabilities, in a systematic review. MATERIAL AND METHODS: An extensive literature search was performed with the MEDLINE, CINAHL, EMBASE, PEDro, LILACS, and SciELO databases, followed by a manual search, to select studies on musculoskeletal biomechanical outcomes in both activities with stroke subjects, without language restrictions, and published until December/2007. RESULTS: Out of the 432 studies, only 11 reported biomechanical outcomes of both activities and none reached the total score on the selected quality parameters. The majority of the experimental studies which compared groups did not achieve acceptable scores on their methodological quality (PEDRo). The investigated conditions and interventions were also restricted. Only one study compared biomechanical outcomes between the activities, but only evaluated the time spent to perform them. Few musculoskeletal biomechanical outcomes have been investigated, being weight bearing on the lower limbs and duration of the activities the most investigated. CONCLUSION: There is little information regarding musculoskeletal biomechanical outcomes during these activities with stroke subjects and no definite conclusions can be drawn regarding the particularities of these outcomes on their performance with stroke survivors.

Biomechanical analysis of the relation between movement time and joint moment development during a sit-to-stand task

Background

Slowness of movement is a factor that may cause a decrease of quality of daily life. Mobility in the elderly and people with movement impairments may be improved by increasing the quickness of fundamental locomotor tasks. Because it has not been revealed how much muscle strength is required to improve quickness, the purpose of this study was to reveal the relation between movement time and the required muscle strength in a sit to stand (STS) task. Previous research found that the sum of the peak hip and knee joint moments was relatively invariant throughout a range of movement patterns (Yoshioka et al., 2007, Biomedical Engineering Online 6:26). The sum of the peak hip and knee joint moment is an appropriate index to evaluate the muscle strength required for an STS task, since the effect of the movement pattern variation can be reduced, that is, the results can be evaluated purely from the viewpoint of the movement times. Therefore, the sum of the peak hip and knee joint moment was used as the index to indicate the required muscle strength.

Methods

Experimental kinematics data were collected from 11 subjects. The time at which the vertical position of the right shoulder fell outside three standard deviations of the vertical positions during the static initial posture was regarded as the start time. The time at which the vertical position fell within three standard deviations of the vertical positions during static upright standing posture was regarded as the finish time. Each movement time of the experimental movements was linearly lengthened and shortened through post-processing. Combining the experimental procedure and the post-processing, movements having various movement patterns and a wide range of movement times were obtained. The joint moment and the static and inertial components of the joint moment were calculated with an inverse dynamics method. The static component reflects the gravitational and/or external forces, while the inertial component reflects the acceleration of the body.

Results

The quantitative relation between the movement time and the sum of the peak hip and knee joint moments were obtained. As the STS movement time increased, the joint moments decreased exponentially and converged to the static component (1.51 ~ 1.54 N.m/kg). When the movement time was the longest (movement time: 7.0 seconds), the joint moments (1.57 N.m/kg) closely corresponded to the minimum of 1.53 N.m/kg as reported by Yoshioka et al..

Conclusion

The key findings of this study are as follows. (1) The minimum required joint moment for an STS task is essentially equivalent to the static component of the joint moment. (2) For fast and moderate speed movements (less than 2.5 seconds), joint moments increased exponentially as the movement speed increased. (3) For slow movements greater than 2.5 seconds, the joint moments were relatively constant. The results of this STS research has practical applications, especially in rehabilitations and exercise prescription where improved movement time is an intended target, since the required muscle strength can be quantitatively estimated.

Chronic stability and selectivity of four-contact spiral nerve-cuff electrodes in stimulating the human femoral nerve

This study describes the stability and selectivity of four-contact spiral nerve-cuff electrodes implanted bilaterally on distal branches of the femoral nerves of a human volunteer with spinal cord injury as part of a neuroprosthesis for standing and transfers. Stimulation charge threshold, the minimum charge required to elicit a visible muscle contraction, was consistent and low (mean threshold charge at 63 weeks post-implantation: 23.3 +/- 8.5 nC) for all nerve-cuff electrode contacts over 63 weeks after implantation, indicating a stable interface with the peripheral nervous system. The ability of individual nerve-cuff electrode contacts to selectively stimulate separate components of the femoral nerve to activate individual heads of the quadriceps was assessed with fine-wire intramuscular electromyography while measuring isometric twitch knee extension moment. Six of eight electrode contacts could selectively activate one head of the quadriceps while selectively excluding others to produce maximum twitch responses of between 3.8 and 8.1 N m. The relationship between isometric twitch and tetanic knee extension moment was quantified, and selective twitch muscle responses scaled to between 15 and 35 N m in tetanic response to pulse trains with similar stimulation parameters. These results suggest that this nerve-cuff electrode can be an effective and chronically stable tool for selectively stimulating distal nerve branches in the lower extremities for neuroprosthetic applications.

Standing after spinal cord injury with four-contact nerve-cuff electrodes for quadriceps stimulation

This paper describes the performance of a 16-channel implanted neuroprosthesis for standing and transfers after spinal cord injury including four-contact nerve-cuff electrodes stimulating the femoral nerve for knee extension. Responses of the nerve-cuffs were stable and standing times increased by 600% over time-matched values with a similar eight-channel neuroprosthesis utilizing muscle-based electrodes on vastus lateralis for knee extension.

Estimations of relative effort during sit-to-stand increase when accounting for variations in maximum voluntary torque with joint angle and angular velocity

The main purpose of this study was to compare three methods of determining relative effort during sit-to-stand (STS). Fourteen young (mean 19.6+/-SD 1.2 years old) and 17 older (61.7+/-5.5 years old) adults completed six STS trials at three speeds: slow, normal, and fast. Sagittal plane joint torques at the hip, knee, and ankle were calculated through inverse dynamics. Isometric and isokinetic maximum voluntary contractions (MVC) for the hip, knee, and ankle were collected and used for model parameters to predict the participant-specific maximum voluntary joint torque. Three different measures of relative effort were determined by normalizing STS joint torques to three different estimates of maximum voluntary torque. Relative effort at the hip, knee, and ankle were higher when accounting for variations in maximum voluntary torque with joint angle and angular velocity (hip=26.3+/-13.5%, knee=78.4+/-32.2%, ankle=27.9+/-14.1%) compared to methods which do not account for these variations (hip=23.5+/-11.7%, knee=51.7+/-15.0%, ankle=20.7+/-10.4%). At higher velocities, the difference in calculating relative effort with respect to isometric MVC or incorporating joint angle and angular velocity became more evident. Estimates of relative effort that account for the variations in maximum voluntary torque with joint angle and angular velocity may provide higher levels of accuracy compared to methods based on measurements of maximal isometric torques.

Side difference in the hip and knee joint moments during sit-to-stand and stand-to-sit tasks in individuals with hemiparesis

BACKGROUND

No study has reported the differences between sides in the net muscular moment of lower limbs of subjects with hemiparesis during sit-to-stand and stand-to-sit tasks in various foot positions. Moreover, the asymmetry of lower-joint moments has not yet been related to muscular weakness of the lower limbs in this population.

METHODS

A convenience sample of 12 individuals (mean age (standard deviation): 49.7 (9.0) years) with chronic hemiparesis due to stroke were asked to stand up and sit down at their natural speed in four foot positions. The joint moments at the hip and knee on both sides during the tasks were estimated with an inverse dynamic approach while the dynamic concentric strength in extension at the hip and knee was assessed with a Biodex dynamometric system. Statistical analyses (paired t-tests and ANOVAs) were used to assess the effects of sides and foot position factor on the asymmetry in the hip and knee joint moments. The level of association between muscle weakness and the asymmetry in the joint moments was quantified with Pearson correlation coefficients (r).

FINDINGS

At the knee, the extensor moments were significantly lower on the affected side (P<0.05) and were affected by the foot position. At the hip, the moments were not significantly different between sides and were slightly modified by the foot positions. There were also strong correlations (0.70<r<0.89; P<0.05, for symmetrical foot position) between the asymmetry in knee extensor moments and the asymmetry in strength. No relation was established at the hip.

INTERPRETATION

The sit-to-stand and stand-to-sit tasks are characterized by a marked asymmetry in the knee extensor moments, which is associated with knee extensor weakness.

Computation of the kinematics and the minimum peak joint moments of sit-to-stand movements

Background

A sit-to-stand (STS) movement requires muscle strength higher than that of other daily activities. There are many elderly people, who experience difficulty when standing up from a chair. The muscle strength required (or the load on the joints) during a STS task is determined by the kinematics (movement pattern). The purpose of this study was to evaluate the kinematics and resultant joint moments of people standing up from a chair in order to determine the minimum peak joint moments required for a STS task.

Methods

This study consisted of three steps. In the first step, kinematic data of lower extremity joint angles (hip, knee and ankle) during STS movements were experimentally collected from human subjects. Eighty-five sets of STS kinematic data were obtained. In the second step, the experimentally collected kinematic data and a link segment model of the human body were used to generate more than 5,000,000 computed STS movements. In the third step, using inverse dynamics method, joint moments of the lower extremity were calculated for all movements obtained through the preceding steps. From the outputs of the third step, the optimal kinematics (movement pattern) in terms of minimized peak joint moment for the hip, knee and ankle was determined.

Results

The peak hip joint moment ranged from 0.24 to 1.92 N.m/kg. The peak knee joint moment ranged from 0.51 to 1.97 N.m/kg, and the peak ankle joint moment ranged from -0.11 to 1.32 N.m/kg. The optimal movement patterns differed depending on which minimized joint moment index was selected (hip, knee or ankle). However, the sum of the peak hip joint moment and peak knee joint moment was always approximately 1.53 N.m/kg regardless of which minimized joint moment index was selected.

Conclusion

The most important finding of this study was that the relation between the peak joint moments at the hip and knee joints was complementary and the sum of those moments needed to be greater than 1.53 N.m/kg in order to perform a successful STS. A combined hip-knee value of 1.5 N.m/kg or lower may indicate the need for physical rehabilitation and/or exercise to increase muscular force.

Investigating joint kinematics during a hoist-assisted sit-to-stand activity

Assisting individuals to stand up from a chair, or sit-to-stand (STS), is a physically demanding task restricted by manual handling regulations. If a hoist was able to produce a normal STS movement pattern this would offer a safe option for both therapist and patient, satisfying both therapeutic and manual handling criteria.

Twenty-two healthy subjects participated in the study. Each subject completed STS with and without hoist assistance. Two hoists were used: the Sara 3000 and the Encore. The STS movements were captured on digital camera and the knee and trunk angles were calculated at point of seat-off for unassisted STS, Sara 3000 STS and Encore STS. Data were analysed using a repeated measures ANOVA.

Trunk angles during STS using both hoists were found to be different (P < 0.001) from that seen during normal STS. Knee angles measured when using the Sara 3000 hoist were different to those seen during unassisted (or normal) STS; however, knee angles at seat-off for the Encore hoist were similar to those seen during normal STS.

This study analysed the movement patterns re-created by two hoists used in the clinical setting. Results showed that the Encore hoist is effective at re-creating normal knee angles at seat-off during the STS transfer, however, neither hoist is able to encourage the required normal trunk angle for independent STS.

Maximum voluntary joint torque as a function of joint angle and angular velocity: model development and application to the lower limb

Measurements of human strength can be important during analyses of physical activities. Such measurements have often taken the form of the maximum voluntary torque at a single joint angle and angular velocity. However, the available strength varies substantially with joint position and velocity. When examining dynamic activities, strength measurements should account for these variations. A model is presented of maximum voluntary joint torque as a function of joint angle and angular velocity. The model is based on well-known physiological relationships between muscle force and length and between muscle force and velocity and was tested by fitting it to maximum voluntary joint torque data from six different exertions in the lower limb. Isometric, concentric and eccentric maximum voluntary contractions were collected during hip extension, hip flexion, knee extension, knee flexion, ankle plantar flexion and dorsiflexion. Model parameters are reported for each of these exertion directions by gender and age group. This model provides an efficient method by which strength variations with joint angle and angular velocity may be incorporated into comparisons between joint torques calculated by inverse dynamics and the maximum available joint torques.

Comparison of the Sit-to-Stand Test with 6 min walk test in patients with chronic obstructive pulmonary disease

OBJECTIVE

To discuss the utility of Sit-to-Stand Test (STST) compared to the 6min walking test (6MWT) for the evaluation of functional status in patients with chronic obstructive pulmonary disease (COPD).

MATERIAL-METHOD

SUBJECTS

Fifty-three patients with stable COPD (mean forced expiratory volume in 1s (FEV(1)) 46+/-9% predicted, mean age 71+/-12 year) and 15 healthy individuals (mean FEV(1) 101+/-13% predicted and mean age 63+/-8) were included.

INTERVENTIONS

Functional performance was evaluated by STST and 6MWT. During the tests, severity of dyspnea (by Modified Borg Scale), heart rate, pulsed oxygen saturation (SpO(2), by Modified Borg Scale) (by pulse oxymeter), blood pressure were measured. The pulmonary function (by spirometry), quadriceps femoris muscle strength (by manual muscle test) and quality of life (by Nottingham Health Profile Survey) were evaluated.

RESULTS

The STST and 6MWT results were lower in COPD group than the healthy group (P<0.05). During the 6MWT the rise in the heart rate, systolic blood pressure and the decrease in SpO(2) were statistically significant according to STST in COPD groups (P<0.05). The STST and 6MWT were strongly correlated with each other in both groups (P<0.05). Similarly, they were correlated with age, quality of life, peripheral muscle strength and dyspnea severity in COPD groups (P<0.05).

CONCLUSION

Similar to 6MWT, STST is also able to determine the functional state correctly. Additionally, it produces less hemodynamical stress compared to the 6MWT. In conclusion, STST can be used as an alternative of the 6MWT in patients with COPD.

Predicting Caregiver Assistance Required for Sit-to-Stand Following Rehabilitation for Acute Stroke

OBJECTIVE/METHODS

The objective of this case series was to determine the relationship between impairments identified at hospital admission and a reduced need for sit-to-stand (STS) assistance during an inpatient rehabilitation hospital stay. Fifty- five inpatients with a diagnosis of acute stroke were retrospectively studied. Demographic information and the following admission and discharge measures were collected from a chart review: bilateral dorsiflexion PROM, strength of the unaffected leg, Motricity Index (MI), presence of hemi-neglect, gait velocity, and Functional Independence Measure (FIM) scores for STS, ambulation, and cognition. Sit to stand improvement was determined by a change of at least one Caregiver Assistance Level (CAL) in STS performance between hospital admission and discharge. CAL 1 = STS FIM score of 7 or 6; CAL 2 = STS FIM score of 5; CAL 3 = STS FIM score of 4, 3, 2, or 1.

RESULTS

Unaffected knee extension strength, Motricity Index (MI) score, FIM cognition scores, and bilateral ankle dorsiflexion PROM were each univariate, age-adjusted predictors of improvement in STS CAL. A multivariate, 3 main-effect model that included admission FIM cognitive scores and ankle PROM correctly predicted 90.6% (48 out of 53) of the possible sit to stand improvement outcomes. Admission gait velocity and MI differentiated extent of functional change in those who improved.

CONCLUSIONS

Cognition and bilateral ankle dorsiflexion PROM most strongly predicted STS CAL improvement during an inpatient rehabilitation stay. Caregivers of patients with significant impairments may benefit from early and intensive training on how to assist their family member in the STS task.

Strength and endurance of knee extensors in subjects after paralytic poliomyelitis

PURPOSE

To compare the strength and endurance of knee extensors in subjects after paralytic poliomyelitis as well as to extend the comparison to healthy subjects.

METHOD

Twenty subjects after poliomyelitis with new symptoms (SYM group), 10 without new symptoms (ASYM group) and 15 healthy controls were included. To determine strength, isometric maximal voluntary contraction (MVC) torque of knee extensors in both legs was determined by Biodex dynamometer at 60 degrees knee angle. To determine endurance, the subjects were asked to maintain force in the knee extensors in the same position, in the range between 40-45% of MVC torque, as long as possible. The 'tensiomyography' method was applied to measure the radial displacement of m. rectus femoris during submaximal continuous electrical stimulation until recording a flat response.

RESULTS

No significant difference in MVC torque and endurance was found between SYM and ASYM group, as well between the duration of m. rectus femoris response of both groups to submaximal electrical stimulation. MVC torque and endurance of knee extensors with 'normal' strength was significantly lower in post-polio subjects compared to healthy controls.

CONCLUSION

Endurance of knee extensor muscles in post-polio subjects is generally and significantly lower than that of knee extensors in healthy subjects, regardless of the implication of normal strength and subjective observations of post-polio subjects.

The Chitranjan Ranawat Award: in vivo knee forces after total knee arthroplasty

Tibial forces were measured in vivo during the first year after total knee arthroplasty in a 66 kg, 80-year-old man. Forces were measured during activities of daily living, rehabilitation, and exercise. Peak tibial forces recorded during walking increased up to 12 months postoperatively (2.8 times body weight). Tibial forces correlated with increasing speed during treadmill walking. Rising from a chair generated peak forces of 2.6 times body weight. Stair descent generated higher peak forces than stair ascent (3.3 versus 2.9 times body weight, respectively). Exercising on a stair-climbing machine generated forces close to two times body weight whereas stationary bicycling generated even lower forces, near one times body weight. In general, the tibial forces recorded during walking and stair climbing were lower than most predicted values. These measurements can be used to validate in vitro and mathematical models of the knee. This should lead to refined surgical techniques and to enhanced prosthetic designs that will improve patient function, patient quality of life, and longevity of total knee arthroplasty implants.

Transition from sitting to standing after trans-femoral amputation

Standing up is an important and common daily activity. It is essential for independence and a prerequisite for walking. Many elderly and many subjects with impairments have problems with transition from sitting to standing. The aim of the present study was to determine whether there was any difference between the characteristics of standing up in trans-femoral amputees and healthy subjects. Five young trans-femoral amputees and five healthy subjects were included in the study. They were asked to stand up. The body motion was recorded using an Optotrak contactless optical system. The force and moment vectors exerted on the seat were recorded by a JR3 six-axis robot wrist sensor. The force under the feet was recorded by two AMTI force plates. The trans-femoral amputees were found to stand up more slowly than the healthy subjects. The angles of the hip, knee, and ankle joints on the amputated side were different from the angles on the healthy side or in the healthy subjects. There was also a great difference in loading between the healthy and the prosthetic foot. It can be concluded that there are differences in standing up between the trans-femoral amputees and the healthy subjects. These differences may indicate a reason for problems many elderly trans-femoral amputees face when standing up.

Leg-extension strength and chair-rise performance in elderly women with Parkinson's disease

The lower extremity performance in elderly female patients with mild to moderate Parkinson's disease (PD; n = 12) and controls (n = 16) was compared. Isometric dynamometry and force-plate measurements were used. PD patients had lower (p < .05) bilateral (BL) maximal isometric leg-extension force (MF), BL isometric MF relative to body mass, and maximal rate of isometric force development than control participants. BL strength deficit was greater (p < .05) in PD patients than in controls. A significantly longer chair-rise time and lower maximal rate of vertical-ground-reaction-force development while rising from a chair was found in PD patients than in controls. These findings suggest that elderly women with PD have lowered voluntary isometric force-generation capacity of the leg-extensor muscles. Reduced BL leg-extension strength might contribute to the difficulty of individuals with PD to rise from a chair.

Effects of a partially supervised training program in subjects over 75 years of age

BACKGROUND AND AIMS

Partially supervised training programs may be preferable than class-based ones in older subjects because the adherence rate is more likely to be good and they cost less. The main purpose of this investigation was to provide some evidence of the effectiveness of a 4-month partially supervised training program. We compared it with a class-based program focusing on the knee extensor (KE) and ankle plantar flexor (APF) muscles.

METHODS

We selected for the study 14 subjects over 75 years of age (75+), age range 75 to 83 years with a mean age of 77.8, and 14 subjects over 65 years of age (65+), age range 65 to 72 years, mean age 66.3 years. They were moderately physically active subjects, free from neurological, cardiovascular, metabolic or inflammatory diseases. The two groups underwent two 4-month training sessions 3 days a week, including: warm-up, aerobics, strength training, cool-down exercises. 65+ subjects underwent a class-based program three times a week. 75+ subjects underwent a partially supervised program consisting of two supervised sessions and one session at home. Strength training was carried out bilaterally with the "Leg Press" and "Sitting Calf" variable-resistance machines (Technogym, Italy). The subjects performed one set of 10 repetitions with a 2-min rest in between. At home, 75+ subjects were instructed to carry out the strength exercises with graded elastic bands (Theraband). Subjects were tested immediately before and after the 4-month training. In addition to weight-lifting ability (1RM), we measured the isometric maximum strength values of KE and APF with a Cybex Norm dynamometer at various angles.

RESULTS

Significant baseline differences between 75+ and 65+ were found at all KE angles except 30 degrees and -20 degrees APF. A significantly increased maximum load (1RM) was observed over the 4-month period. The baseline and post-training torque-angle relationships for APF and KE in the two groups showed higher post-training gains in 75+ at all angles except at -20 degrees APF, although a statistically significant difference (p < 0.005) between the groups was only found at 30 degrees KE.

CONCLUSION

Our baseline data confirm the decay in torque capacity in subjects aged 75+ compared with 65+. The partially supervised training for 75+ subjects showed better responses in terms of relative strength gain than for 65+ subjects, and it appears effective in counteracting the age-related physiological and functional decay which appears to be particularly evident around that age.

Performance of epimysial stimulating electrodes in the lower extremities of individuals with spinal cord injury

This study describes the performance of surgically-implanted epimysial stimulating electrodes in the muscles of the lower extremities for use in functional neuromuscular stimulation (FNS) systems for standing after spinal cord injury. A total of 86 epimysial electrodes were implanted in 13 volunteers with low tetraplegia or paraplegia receiving the Case Western Reserve University/Veteran Affairs (CWRU/VA)-implanted standing/transfer neuroprosthesis. The neuroprosthesis consisted of bilateral epimysial electrodes in the knee and hip extensors (vastus lateralis, gluteus maximus, and adductor magnus or semimembranosus) and intramuscular electrodes at the T12/L1 or L1/L2 spinal roots for trunk extension. Recruitment properties, stimulated knee and hip extension moments, standing performance, and mechanical integrity over time were measured for a period up to four years post-implantation. Stimulated thresholds were stable and recruitment was sufficient to generate joint moments adequate for standing, with up to 97% body weight supported by the legs. Four mechanical failures were observed, all in the posterior muscles of the thigh, leaving 95% of all electrodes operational at all followup intervals. Probability of 24-month survival is estimated to be 93% plateauing to a steady state of 90% at four years. These results indicate that epimysial designs are appropriate for long-term clinical use in the large muscles of the lower extremities with implanted motor system neuroprostheses.

Instant of chair-rise lift-off can be predicted by foot–floor reaction forces

OBJECTIVE

To develop a predictive model of the lift-off event during chair rise in healthy subjects, using foot-floor reaction forces.

BACKGROUND

An important event during chair rise is lift-off from the seat: the transition from the inherently stable three-point contact to the unstable two-point contact. There is no consistent or generally agreed upon method for estimating the time of lift-off when an instrumented seat is unavailable.

METHODS

Twenty healthy volunteers were divided into a testing set and training set. Each subject performed repeated chair rise trials at different speeds. Seat-floor and foot-floor forces, recorded with two force platforms, were used to develop a model of the lift-off event.

RESULTS

The magnitude of the vertical foot-floor reaction at lift-off (F0VF) was linearly related (R2 = 0.71, P < 0.001) to the peak vertical foot-floor reaction force (FMVF). A linear model was developed for the training group, which enabled prediction of lift-off time for the testing group with an absolute average error of 6 ms (about 1 data frame at 150 Hz). The linear model derived for the entire sample was: F0VF = 28.14 + FMVF * (0.6434).

CONCLUSIONS

The lift-off event for healthy subjects performing chair rise can be accurately predicted from foot-floor reaction forces, without requiring an instrumented seat.

Determinants of sit-to-stand capability in the motor impaired elderly

Among the healthy elderly, sit-to-stand (STS) movement largely depends on: (a) trunk bending momentum, (b) centre of gravity (CG) position before the body rises and (c) lower limb extensor muscle strength. Because determining whether (c) improvement would affect STS capability in the motor impaired elderly (MIE) has been recommended, we studied the relative importance of (a), (b) and (c) in determining a successful fast STS movement comparing the healthy elderly with MIE with orthopaedic disorders studied before and after a rehabilitation program. Force platform was used to measure body's posture and kinematics during a STS test and therefore to assess (a), (b) and maximum vertical velocity (VVpeak), assumed as outcome measurement. Knee extensor maximal isometric voluntary contraction normalized by body mass (nMVC) was an indicator of (c). A multiple regression model was built to predict VVpeak from the three determinants of STS movement. In both groups, the model significantly determined VVpeak, with (a) and (c) being significant predictors of VVpeak and (a) being the major predictor. Rehabilitation was effective in improving nMVC. This process resulted in a change of the relative importance of (a) and (c), strength becoming the major predictor of VVpeak. In conclusion the present study demonstrates that a rehabilitative intervention aimed at increasing strength is effective in improving STS capability in MIE.

Edge loading in third generation alumina ceramic-on-ceramic bearings: stripe wear

Alumina ceramic-on-ceramic bearings perform exceptionally well under standard hip simulator conditions, but in vivo some retrieved bearings have shown an unusual stripe pattern of wear. We studied 16 bearings retrieved from a series of 1,588 cementless hip arthroplasties with third generation alumina ceramic-on-ceramic bearings to characterize the mechanism of stripe wear formation. None of these bearings were retrieved for bearing failure. The average wear volume was 0.4 mm(3) per year in the heads and 0.3 mm(3) per year in the liners. Mapping of wear stripes on the heads and liners showed that the majority do not occur with normal walking; instead they probably occur with edge loading when the hip is flexed, such as with rising from a chair or with climbing a high step.