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At least 1,009 records · Page 56Linked to original sources
PubMed2005

Associations among knee adduction moment, frontal plane ground reaction force, and lever arm during walking in patients with knee osteoarthritis.

The adduction moment about the knee during walking gait has been proposed as an indirect measure of dynamic knee joint load. However, the relative contributions of the variables primarily used to calculate the knee adduction moment have not been investigated. The objectives of this paper were to: (1) describe and compare the magnitude and temporal characteristics of the knee adduction moment, frontal plane lever arm, and frontal plane ground reaction force (GRF) during gait in patients with knee osteoarthritis (OA) and, (2) examine the associations among these variables. Results indicated that both the knee adduction moment and the frontal plane GRF varied considerably throughout stance and exhibited the characteristic "double-hump" pattern, while the frontal plane lever arm magnitude varied only slightly during stance. Knees with OA had significantly greater peak knee adduction moments and frontal plane lever arms, but significantly less peak frontal plane GRF than knees without OA. Pearson product moment correlations indicated a higher association between peak knee adduction moment and peak frontal plane lever arm than between peak knee adduction moment and peak frontal plane GRF, particularly in knees with OA. These results suggest that the frontal plane lever arm assessed during walking is an important variable in the examination of knee OA, and warrants further investigation.

Adult↗
PubMed2005

On hydrodynamics of drag and lift of the human arm.

The work presents results on drag and lift measurement conducted in a low speed wind tunnel on a replica of the entire human arm. The selected model positions were identical to those during purely rotational front crawl stroke in quasi-static conditions. A computational fluid dynamics model using Fluent showed close correspondence with the experimental results and confirmed the suitability of low speed wind tunnel for the drag and lift measurement in quasi-static conditions. The obtained profiles of the hydrodynamic forces were similar to the dynamic data presented in an earlier study suggesting that shape drag is a major contributing factor in propulsive force generation. The aim of this study was to underline the importance of the entire arm analysis, the elbow angle and a newly defined angle of attack representing the angle of shoulder rotation. It was found that both the maximum value of the drag force at 160 degrees elbow flexion angle and the momentum generated by it exceed the respective magnitudes for the fully extended arm. The latter is underlined by a prolonged plateau of near maximum drag that was obtained at shoulder angle range of 50-140 degrees suggesting that optimal arm configuration in terms of propulsive force generation requires elbow flexion. Furthermore it was found that drag trend is not consistent with the widely assumed and used sinus wave profile. A gap in the existing experimental research was filled as for the first time the entire arm lift and drag was measured across the entire stroke range.

Air Movements↗
PubMed2004

Quantifying the contribution of arm postural tremor to the outcome of goal-directed pointing task by displacement measures.

A method for quantifying the outcome of goal-directed postural pointing was presented and used for relating the tremor output to the oscillations of single arm landmarks. The displacement of reflective markers placed on shoulder, upper arm, forearm, and hand were measured by an optoelectronic motion capture system in nine subjects holding a laser penlight pointed at a target. The high signal-to-noise ratio of the measured displacement series (from 7:1 for shoulder marker to 30:1 for hand marker) demonstrated the feasibility of the proposed system to carry out tremor analysis. The track of the laser emission on the target, reconstructed from penlight displacements, was studied as the outcome of the pointing task. By measuring the length and the dispersion of the path covered by the target track in 30 s, a significant and comparable tremor amplitude was found in vertical and lateral directions. The correlation between target track and arm tremor was stronger for distal than for proximal markers. Spectral and cross-spectral analyses evidenced the presence of a dominant low frequency oscillation (1.5 Hz), along with a high frequency one (5-7 Hz), in the displacement of the target track. These two components were significantly linked to the oscillations of the hand, the forearm and the upper arm but not to those of the shoulder, suggesting that the oscillations in the overall tremor output during the pointing task are mainly generated by the arm segments.

Adult↗
PubMed2005

Improvement and generalization of arm motor performance through motor imagery practice.

This study compares the improvement and generalization of arm motor performance after physical or mental training in a motor task requiring a speed-accuracy tradeoff. During the pre- and post-training sessions, 40 subjects pointed with their right arm as accurately and as fast as possible toward targets placed in the frontal plane. Arm movements were performed in two different workspaces called right and left paths. During the training sessions, which included only the right path, subjects were divided into four training groups (n = 10): (i) the physical group, subjects overtly performed the task; (ii) the mental group, subjects imagined themselves performing the task; (iii) the active control group, subjects performed eye movements through the targets, (iv) the passive control group, subjects did not receive any specific training. We recorded movement duration, peak acceleration and electromyographic signals from arm muscles. Our findings showed that after both physical and mental training on the right path (training path), hand movement duration and peak acceleration respectively decreased and increased for this path. However, motor performance improvement was greater after physical compared with mental practice. Interestingly, we also observed a partial learning generalization, namely an enhancement of motor performance for the left path (non-training path). The amount of this generalization was roughly similar for the physical and mental groups. Furthermore, while arm muscle activity progressively increased during the training period for the physical group, the activity of the same muscles for the mental group was unchanged and comparable with that of the rest condition. Control groups did not exhibit any improvement. These findings put forward the idea that mental training facilitates motor learning and allows its partial transfer to nearby workspaces. They further suggest that motor prediction, a common process during both actual and imagined movements, is a fundamental operation for both sensorimotor control and learning.

Adult↗
PubMed2002

Bimanual circle drawing in children with spastic hemiparesis: effect of coupling modes on the performance of the impaired and unimpaired arms.

The present study examined the effect of interlimb coupling on the performance of the impaired and unimpaired arm in children with spastic hemiparesis during bimanual circle drawing. The following questions were addressed: (1) does coupling positively influence the performance of the impaired arm compared to single-hand performance and (2) is such an effect dependent on mode of coordination (i.e., symmetric versus asymmetric). Twelve children with spastic hemiparesis produced circle drawings on a digitizer under different task conditions. Spatiotemporal characteristics and quality of movement of pen trajectories of the individual limbs as well as interlimb relative phase were analysed. Coupling in a symmetric coordination mode resulted in a decrease of temporal variability and an increase of smoothness of circle drawing movements in the impaired arm compared to single-handed performance. Coupling in an asymmetric coordination mode resulted in an increase of spatial and temporal variability in the unimpaired arm. It is concluded that coupling may enhance the performance of the impaired arm in children with spastic hemiparesis, but only during symmetric bimanual coordination. A possible underlying neural mechanism that might explain these findings is discussed.

Adolescent↗
PubMed1998

Neuromuscular control model of the arm including feedback and feedforward components.

A neuromusculoskeletal model of the human arm was developed which contains both feedforward and feedback control, and thereby accounts for motor control of fast movements as well as interaction with external forces. The feedforward control component forms an approximate representation of the inverse dynamics of the arm and its interaction with the environment. The feedback control component compensates for errors in the representation of the inverse dynamics and for unexpected forces acting on the arm. Moreover, the control system provides a solution for the redundancy of the muscles. The system performance is adapted in a learning procedure according to a specified goal function. It is shown in the paper that good control of the nonlinear musculoskeletal model and neural control signals which are similar to electromyographic (EMG) data, are attained. The response of the arm to external forces is analysed and compared with experimental data on arm impedance.

Arm↗
PubMed1995

Exercise-induced hypertension in the arms due to impaired arterial reactivity after successful coarctation resection.

Exercise-induced hypertension of the arms is a well-known late complication after coarctation repair. Residual narrowing at the anastomosis site as well as abnormalities of the precoarctation arterial system may be the cause of this problem. Blood pressure response to exercise and flow-mediated arterial dilatation of the arms and legs were studied in 29 young adults after successful coarctectomy in childhood and compared with 13 control subjects. Peak exercise systolic blood pressure was significantly higher in patients than in control subjects: 238 versus 199 mm Hg (p = 0.007). Both groups had a positive systolic arm-leg gradient during exercise: 59 versus 37 mm Hg (p = 0.05). Flow-mediated dilatation of the brachial artery was significantly reduced in patients compared with that in control subjects: 4.2% (range 0% to 9.4%) versus 9.4% (range 3.7% to 16%) (p < 0.0001). Flow-mediated dilatation of the femoral artery was similar in both groups. Dilatation of the brachial artery was inversely correlated to peak exercise systolic pressure in the study patients (r = -0.427, p = 0.02). A positive arm-leg exercise gradient partly represents physiologic circulatory adaptation to ergometry and is therefore not appropriate for evaluation of residual narrowing. Exercise-induced hypertension of the arms late after coarctation repair is caused by impaired arterial reactivity, which results from structural or functional abnormality, or both.

Adolescent↗
PubMed2003

Hand orientation for grasping and arm joint rotation patterns in healthy subjects and hemiparetic stroke patients.

We previously demonstrated that the hand orientation for grasping (azimuth) is strongly coupled to arm movement direction in the horizontal plane. The question is whether this coupling is directly controlled or secondary to a regulation of the arm angular configuration. To this purpose, we quantified hand orientation and arm joint rotations during unconstrained reaching movements in healthy subjects and in patients with hemiparesis due to stroke since they use altered joint rotation patterns for reaching. Seven healthy subjects and eight patients with a right hemiparesis participated (four had a moderate and four had a mild disorder). Four electromagnetic sensors were used to measure hand orientation and to compute the wrist, elbow and shoulder joint angles. Hand azimuth at the time of grasping was correlated to arm movement direction in all the healthy and hemiparetic individuals. In healthy subjects, a regression analysis of the arm joint rotations suggested that the coupling between hand azimuth and movement direction was not due to a correlation with a particular degree of freedom. Patients used different hand orientations for grasping and different joint rotation patterns that varied according to their level of disability and the use of compensatory strategies. The findings observed in both healthy subjects and patients with stroke show that the coupling of hand azimuth for grasping to movement direction was controlled independently of the set of joint rotations used for reaching. This suggests that it is a basic synergy directly controlled by the motor system.

Adult↗
PubMed1999

Neural mechanisms of soleus H-reflex depression accompanying voluntary arm movement in standing humans.

This study have investigated the changes in soleus (Sol) H-reflexes by arm movement during freely standing (FS) and back-supported standing (BS) in healthy subjects. Before the arm movement, there is an anticipatory phase, which includes increased electromyographic (EMG) activity in the biceps femoris (BF) and decreased EMG activity of the Sol muscle. The Sol H-reflex appeared to be inhibited during the anticipatory phase as well as during the time of arm movement. However, the inhibition appeared to be larger in FS than in BS conditions. Vibration applied to the tendon of the BF muscle depressed the Sol H-reflex. This inhibition was attributed to presynaptic inhibition and was reduced during the anticipatory phase, and was not very much changed during arm movements. It is suggested that the depression of the Sol H-reflex induced by voluntary arm movement has two inhibitory components of different origins. Descending motor commands generate the early inhibitory component, while the late component is produced by the presynaptic inhibition that results from peripheral inputs. The inhibition related to anticipatory postural adjustment (APA) indicates that a new-setting of the spinal mechanisms is required and responsible in order to stabilize body equilibrium which is dependent upon different postural conditions.

Adult↗
PubMed2000

Kinematics of human arm reconstructed from spatial tracking system recordings.

The kinematics of the human arm in terms of angles of rotations in the joints is reconstructed from the spatial tracking system (Fastrack() Polhemus) recordings. The human arm is modeled by three rigid bodies (the upper arm, the forearm and the hand) with seven degrees of freedom (three in the shoulder, two in the elbow and two in the wrist). Joint geometry parameters (orientations of the axes relative to the arm segments, the angles and the distances between the axes) have been calculated on the basis of passive rotations in the joints. The calculated parameters have been used to solve the direct kinematics problem for the reaching movements in different directions. The difference between calculated and recorded positions and accelerations of the hand has been used to assess the accuracy of the proposed method of kinematics reconstruction. The error analysis showed that spatial tracking system recordings and human arm kinematics reconstruction could reliably be used to accurately analyze multijoint movement in humans.

Adult↗
PubMed2002

Analysis of a swimmer's hand and arm in steady flow conditions using computational fluid dynamics.

Propulsive forces generated by swimmers' hands and arms have, to date, been determined strictly through experimental testing. As an alternative to these complex and costly experiments, the present research has applied the numerical technique of computational fluid dynamics (CFD) to calculate the steady flow around a swimmer's hand and arm at various angles of attack. Force coefficients computed for the hand and arm compared well with steady-state coefficients determined experimentally. The simulations showed significant boundary layer separation from the arm and hand, suggesting that Bernoulli's equation should not be used to mathematically describe the lift generated by a swimmer. Additionally, "2D" lift was shown to be inaccurate for the arm at all angles of attack and for the hand near angles of attack of 90 degrees. Such simulations serve to validate the chosen CFD techniques, and are an important first step towards the use of CFD methods for determining swimming hydrodynamic forces in more complex unsteady flow conditions.

Adult↗
PubMed1998

Three-dimensional modelling of the motion range of axial rotation of the upper arm.

Computer simulation of human movements and postures suffers generally from the lack of reliable data, such as data on joint limits. In this paper, the motion range of axial rotation of the upper arm was investigated. An original surface regression fitting method using an orthogonal homogeneous polynomial basis has been presented. The method was used to fit both maximum internal and external upper arm axial rotation surfaces based on the experimental data from seven male subjects of ages 23-34. Under the assumption of normal distribution, the sample mean and the confidence limits for population mean of both internal and external upper arm axial rotation limits were derived. It has been shown that the axial motion range of the upper arm depends strongly on the position of the upper arm in the shoulder sinus cone and varies on average from 94 to 157 degrees. The present work can be considered as an extension of the shoulder kinematic data base established by Engin and Chen (1986), Journal of Biomechanical Engineering 108, 215-221.

Adult↗
PubMed2004

Adaptive behavior of cortical neurons during a perturbed arm-reaching movement in a nonhuman primate.

This chapter provides evidence of spatial and temporal changes in the behavior of neurons within Areas 5 and 4 of the sensorimotor cortex of a nonhuman primate while it was executing a perturbed arm-reaching task. Chronically implanted electrode arrays were used to record simultaneously from 37 to 58 neurons. Also measured were the trajectory of arm movement, EMG activity in selected arm muscles and the perturbation force applied to the arm. The adaptation in Area 4 neurons' behavior usually involved a reduction in the latency from the onset of the perturbation to the peak-firing rate of the cell. In contrast, Area 5 neurons exhibited no such adaptive change in this latency. In each cortical area, the adaptation was not uniform across all neurons, and the spatial pattern of neuronal population behavior changed over the period of behavioral adaptation. We also found that the direction of arm movement and its configuration were important in determining which control strategy (predictive trajectory compensation or stiffness control) the animal used to overcome the externally applied perturbation for an improved performance of the reaching task.

Adaptation, Physiological↗
PubMed2003

Reconstruction of complex parotidectomy defects using the lateral arm free tissue transfer.

OBJECTIVES: The study goal was to show that the lateral arm flap is a viable reconstructive option for complex parotidectomy defects.Study design and setting We studied a case series at a tertiary care medical center from March 1997 to March 2002. The lateral arm flap was used to reconstruct parotidectomy defects that included a composite resection of adjacent tissue in 30 patients. There were 19 men and 11 women (mean age, 62 years; mean follow-up, 19 months). The mean flap area was 114 cm(2), and the mean flap volume was 172 cm(3). The posterior cutaneous nerve of the forearm (PCNF) was used as a facial nerve cable graft in 14 patients. Facial disability outcomes were measured using the Facial Clinimetric Evaluation scale. RESULTS: The major and minor complication rates with use of this reconstructive approach were low: 16.7% (5 of 30) and 26.7% (8 of 30), respectively. Donor site morbidity was minimal, with no patient having a major donor site complication and 23.3% (7 of 30) having minor complications. Functional recovery of the facial nerve occurred in 6 of 8 evaluable patients who underwent facial nerve grafting using the PCNF. Controlling for degree of facial nerve paralysis, Facial Clinimetric Evaluation scale scores of our patients were not statistically different than those of a historic population with a facial paralysis and no surgical defect. CONCLUSIONS: The lateral arm free flap effectively restores facial appearance when used for reconstruction of complex parotidectomy defects. The PCNF, a nerve harvested with the lateral arm flap, can be used as a facial nerve cable graft with a high rate of success. SIGNIFICANCE: The lateral arm flap is successful as a single donor site for reconstructing facial contour and the facial nerve after major ablative defects in the parotid region.

Adult↗
PubMed2002

Force measurements of postural sway and rapid arm lift in seated children with and without MMC.

OBJECTIVE: The aim was to investigate the horizontal ground reaction forces of seated postural sway and rapid arm lift in children with and without myelomeningocele. BACKGROUND; It is unclear whether children with myelomeningocele have limited control of body posture entirely caused by the impairment in the legs or also by other dysfunction. METHODS: 11 children with myelomeningocele, 10-13 years, and 20 children without physical impairment were investigated. Data were collected by force plate measurements during quiet sitting and during rapid arm lift. The forces were expressed as the corresponding acceleration of the centre of mass. The amplitude and the frequency of the centre of mass acceleration quantified the sway. Movement time, onset and anteroposterior peak acceleration were analysed during arm lift. RESULTS: The children with myelomeningocele had a low sway frequency under both conditions: eyes open and eyes closed. The movement time was longer for these children compared to the controls. The onset of initial anteroposterior centre of mass acceleration preceded the arm lift and was directed forward in both groups. The peak centre of mass acceleration was usually directed backward. CONCLUSIONS: The control of postural sway was different in children with myelomeningocele compared to children without disabilities and this could not be explained by the cele level. The children with myelomeningocele had a slow motor performance of the seated sway and during arm lift. RELEVANCE: Slow motor performance involves functional limitations in the individual child and is important for the therapy program.

Adolescent↗
PubMed2000

The synchronization of human arm movements to external events.

Previous research revealed the existence of coupling mechanisms (e.g. iso-directionality) at the level of perception and action. The present experiment investigated how the strength of the perception-action coupling affected synchronization performance. Arm movements were to be synchronized with a moving light that traveled back and forth from the left to the right side of a runway. Four experimental conditions were administered representing the orthogonal combination of two viewing conditions (intermittent vs. continuous) and two synchronization modes (in-phase, i.e. arm moving in the same direction as the light vs. anti-phase, i.e. arm moving in the opposite direction). Performance outcome measures, movement kinematics, and relative phase were used to examine the data. The results revealed a better synchronization performance when the arm and light traveled in the same direction (iso-directionality) during the continuous viewing condition. Apparently, the strength of the perception-action coupling has a severe impact on the quality of the synchronization of an arm movement to an external event.

Arm↗
PubMed1999

Liposuction of the arms.

Liposuction of arms when properly performed with realistic expectations is almost always a "patient pleaser." Patients routinely marvel at the degree of skin contraction that typically occurs. Before and after photos, even as early as 1 week, routinely show dramatic skin contraction when significant volumes of fat are removed although textural changes may evolve for weeks to months (Figs. 14-19). Only the lower abdomen and neck consistently obtain such profound and predictable contraction. I am convinced that historically liposuction of the arms has been performed in a substandard fashion. Inadequate fat removal will often produce irregularity and will always result in less than maximal skin contraction. As I have performed progressively larger-volume cases, the indications for brachioplasty, in my opinion, are nearly nonexistent. My present approach, except in the most extreme cases, is to initially recommend liposuction and possibly even a second liposuction prior to performing or recommending brachioplasty. Even massive arms with good skin tone will usually obtain an aesthetically pleasing result when treated properly. Massive arms with poor skin tone, however, may not. One does not "burn bridges," however, by performing liposuction alone in these questionable candidates. If brachioplasty is subsequently desirable, in spite of the major drawback of the resultant scar, it can be performed at a later date. In summary, the key concepts for maximizing the potential of liposuction of the arms are to perform thorough but gentle fat removal and to avoid immediate subdermal fat removal or trauma to the underside of the dermis.

Anesthesia, Local↗
PubMed1997

Use of arm and lesser saphenous vein compared with prosthetic grafts for infrapopliteal arterial bypass: are they worth the effort?

PURPOSE: Arm and lesser saphenous veins (ALSVs) are generally considered to be the best alternative for infrapopliteal arterial bypass grafts when greater saphenous vein is not available. The need for additional incisions and repositioning of the patient, along with occasional use of general anesthesia for arm vein harvesting, led to our perception that the use of ALSVs increased operative time and possibly patient discomfort. Therefore, we compared the outcome of ALSVs with that of prosthetic infrapopliteal arterial bypass procedures performed at our hospital. METHODS: Between July 1, 1991, and Dec. 31, 1996, we performed 96 infrapopliteal arterial bypass procedures using 45 ALSVs (28 arm vein, 17 lesser saphenous) and 51 polytetrafluoroethylene (PTFE) grafts. Seventy grafts were single-length ALSV or PTFE bypass grafts, and 26 grafts were placed as the distal segment of a sequential or composite bypass graft. Every attempt was made to use ALSV and avoid the use of PTFE, even if a short segment of the vein graft measured less than 4.0 mm in diameter. There were no significant differences between patients with ALSV compared with PTFE grafts in terms of age, sex, indication for surgery, or number of previous revascularization procedures (2.1 vs 1.7), respectively (p > 0.05). However, ALSV grafts had more factors associated with an expected worse outcome: they were more commonly anastomosed to pedal arteries (17% [8 of 45] vs 0%; p = 0.0009), less commonly single-segment grafts (62% [28 of 45] vs 82% [42 of 51]; p = 0.03), had higher average runoff resistance values (2.3 vs 1.5; p = 0.001), and were less frequently treated with lifelong warfarin (65% [29 of 45] vs 95% [48 of 51]; p = 0.0001). RESULTS: The hospital mortality rate was 3.1% (3 of 96; 3 PTFE). All deaths were cardiac-related. Despite the potential factors associated with worse patency rates for ALSVs, 2-year assisted primary patency rates tended to be higher for arm veins (46%) than for lesser saphenous veins (23%) and PTFE grafts (26%), although this difference was not statistically significant. Limb salvage rates were similar between ALSV and PTFE grafts (76% vs 71%, respectively). The average operative time was significantly longer for ALSV bypass procedures (mean, 6.2 hours) than for PTFE bypass procedures (mean, 4.9 hours; p = 0.003), and for single-length conduits when revision of previously placed grafts was not attempted, the operative time was 4.0 hours for ALSV grafts and 2.5 hours for PTFE grafts. CONCLUSION: In our experience ALSV bypass grafts to infrapopliteal arteries do not function as well as reported by some others. In spite of the extra effort involved, arm vein grafts are preferred over PTFE grafts for their likely higher assisted primary patency rates and equivalent, if not better, limb salvage rates.

Aged↗