Abduction-adduction Movements Research Articles

Kinematic stabilization after the Latarjet procedure: beyond the triple blocking effect

BackgroundThe rationale for the Latarjet procedure was described as the “triple blocking” effect. Satisfactory surgical outcomes have been reported after surgery. However, it has been reported that the “triple blocking” effect increases joint stability, but it does not fully restore it. Moreover, the procedure is nonanatomic and concerns remain regarding the effects. The study of scapulohumeral rhythm, which is a clinical parameter used for the functional evaluation of shoulder kinematics, can offer new perspectives on the rationale for the procedure. This study aimed to compare the shoulder kinematics of patients after the Latarjet procedure to the shoulders of a healthy population using magnetic and inertial measurement units (MIMUs) with a motion analysis system. MethodsA retrospective study with prospective data collection was conducted on 28 patients who underwent the open Latarjet procedure for recurrent shoulder instability. At a minimum 12-month follow-up, each patient was evaluated by assessing the range of motion (ROM), the Rowe score, and the Constant-Murley score (CMS). Patients were examined using the ShowMotion 3D kinematic tracking system (NCS Lab, Modena, Italy), which uses wireless wearable noninvasive MIMUs sensors to assess the three-dimensional kinematics of the shoulder. For each plane of elevation (i.e., flexion and abduction), the scapulohumeral rhythm (SHR) was described by three scapulothoracic rotations (i.e., protraction–retraction, mediolateral rotation and posterior–anterior tilting) as a function of humeral anteflexion or humeral abduction. ResultsThe mean time from first shoulder dislocation to surgery was 6.6 ± 3 years (range, 1-12 years). No intraoperative complications occurred, and CT performed 3 months after surgery showed graft union in all patients. After a mean follow-up time of 32.4±20 months (range, 12-96), the mean CMS and Rowe scores were 94.5±4.8 (range, 84-100) and 96.7±3.5 (range, 90–100), respectively. All patients showed no signs of glenohumeral arthritis on X-ray examination. Scapular posterior tilt and scapular internal rotation were significantly greater in the patient group than in the healthy population for the flexion–extension and abduction–adduction movements along the whole shoulder range of motion (all p < 0.05); no differences were found in upward/downward scapular rotation. ConclusionA greater scapular posterior tilt and scapular internal rotation were observed after the Latarjet procedure. The modified position of the scapula was maintained during the entire ROM, suggesting a shoulder-stabilizing kinematic effect in addition to the bony, sling and bumper effects.

Bioimpedance Vector Analysis-Derived Body Composition Influences Strength and Power in Alpine Skiers

ABSTRACT Purpose: Alpine ski racing is a complex sport where no single factor can exclusively account for performance. We assessed body composition, using bioelectrical impedance vector analysis (BIVA), and our purpose was to study its influence on the strength and power profile of young alpine skiers. Methods: Anthropometric measurements and advanced BIVA parameters were recorded on eighteen alpine ski racers (6 females/12 males; 17.0 ± 1.3 years; 172.2 ± 9.3 cm; 68.5 ± 9.8 kg). Dynamic force and power were assessed using countermovement jumps (CMJ), while maximal isometric strength was evaluated for hip flexion-extension and abduction-adduction movements. Stepwise regression models examined the relationship between BIVA-derived parameters and strength/power variables. Results: Body cellular mass (BCM) positively related to jump height (p = .021, R 2 = 74%), jump momentum (p < .001, R 2 = 89%), reactive strength index modified (p = .026, R 2 = 75%) and peak concentric power (p < .001, R 2 = 82%), while intracellular water (ICW) related to peak eccentric (p < .001, R 2 = 76%) and concentric force (p < .001, R 2 = 77%) as well as to concentric rate of force development together with the phase angle (PhA) (p = .008, R2 = 79% and R2 = 0.015). Regarding isometric assessment, ICW was a significant predictor for all four movement directions, and PhA contributed to hip adduction strength. Conclusions: Body composition, particularly BCM and ICW, significantly predict force- and power-related factors in young alpine skiers.

Accuracy of measuring scapular position and motion with a novel motion capture system

Scapula kinematics is recognized to be a crucial variable in shoulder dysfunction. Nevertheless, quantitative scapula tracking and measurement are not part of the current clinical evaluation. The main concern is measurement accuracy. To assess the accuracy of the wearable sensor technology Showmotion a cadaver experiment was designed, allowing a direct comparison between sensors directly pinned to the scapula and superficial sensors. A measurement protocol was adopted to evaluate errors in measurement, mimicking the suggested invivo evaluation. Sensors were simultaneously placed above (supraspinal) and below (infraspinal) the scapular spine to determine if one placement resulted in fewer errors compared to the other. Mean and standard deviations of the supraspinal sensor root mean square error (RMSE) in flexion-extension movements resulted in 3.59° ± 2.36°, 4.73° ± 2.98°, and 6.26° ± 3.62° for upward-downward rotation (up-down), anterior-posterior tilt and internal-external (intra-extra) rotation, respectively, while 2.16° ± 1.21°, 2.20° ± 1.02°, and 4.46° ± 2.16° for the infraspinal sensor. In abduction-adduction movements, mean and standard deviations of the supraspinal sensor RMSE resulted in 4.26° ± 2.98°, 5.68° ± 4.22°, and 7.04° ± 4.36° for up-down rotation, anterior-posterior tilt, and intra-extra rotation, respectively, while 2.38° ± 1.63°, 2.47° ± 1.77°, and 4.92° ± 3.14° for the infraspinal sensor. The same behavior was confirmed in shrug movements, where 4.35° ± 3.24°, 4.63° ± 3.09°, and 5.34° ± 6.67° are mean and standard deviations of the supraspinal sensor RMSE for up-down rotation, anterior-posterior tilt, and intra-extra rotation, respectively, while 2.76° ± 1.87°, 2.83° ± 2.53°, and 4.68° ± 5.22° for the infraspinal sensor. This method of quantitative assessment of scapular motion is shown to have good accuracy and low error between the sensor measurements and actual bone movement in multiple planes of scapular motion, both over the entire range of motion and in its individual segment intervals. The decreased amount of error with the infraspinal sensor placement suggests that placement is ideal for clinical quantitative assessment of scapular motion.

Functional morphology of the hindlimb of fossilized pygmy hippopotamus from Ayia Napa (Cyprus).

We studied the functional morphology of the postcranial skeleton of the endemic hippopotamus Phanourios minor, derived from the Upper Pleistocene site of Ayia Napa. The deposit, which consists of a hard limestone substrate on which the species moved, has yielded a great abundance of hippopotamus material, making the Ayia Napa locality one of the most important paleontological sites in Cyprus. The immigration of the large-sized mainland Hippopotamus to Cyprus led to the emergence of a new insular species with its main characteristic being the extremely reduced body size. In this study, all the hindlimb elements of the Cypriot hippo are described in detail and compared with those of the modern species, with the extant Hippopotamus amphibius being considered similar to the possible ancestor of P. minor. In some cases, the morphological comparison is reinforced using bones of other extinct insular and mainland hippos. Additionally, we provided a functional analysis of the hindlimb joints, suggesting specific locomotor habits for the species. The anatomical examination reveals that the elements in P. minor are robust with marked muscular insertion areas resembling those found in Hippopotamus. However, there are also similarities with Choeropsis liberiensis in certain morphofunctional traits. P. minor adapted to slow but powerful locomotion with remarkable stabilization, particularly in the zeugopodium and the autopodium. The knee was less mobile in the craniocaudal direction compared with that in recent hippos, while the abduction-adduction movements of the thigh were advanced. The pes presented good mobility in the sagittal plane and limitation in transversal movements. Thus, P. minor displayed modifications to its limbs, influenced by the mountainous island environment and the body size reduction, resulting in specialized locomotion, which was different from that of extant hippopotamuses.

Differences in the Glenohumeral Joint before and after Unilateral Breast Cancer Surgery: Motion Capture Analysis.

After mastectomy, women might lose mobility and develop kinematic changes in the shoulder. The objective of this research was to compare the kinematics of the glenohumeral joint in women, before and after unilateral breast cancer surgery. This was a longitudinal study with a pre- and post-evaluation design; in total, 15 Mexican women who had a mastectomy for breast cancer and who received a physical therapy program after surgery were evaluated. Flexion–extension and abduction–adduction movements of the glenohumeral joint were evaluated (15 days before and 60 days after mastectomy). For the kinematic analysis of the glenohumeral joint, an optoelectronic motion capture system was used to monitor 41 reflective markers located in anatomical landmarks. There was no significant difference in the range of motion of the glenohumeral joint when comparing pre- and post-mastectomy, flexion–extension (p = 0.138), and abduction–adduction (p = 0.058). Furthermore, patients who received chemotherapy (53%) before mastectomy were more affected (lower range of motion) than those who did not receive it. There were no significant differences in the kinematics of the glenohumeral joint after mastectomy in this group of patients who received a physical therapy program after surgery. Moreover, patients who received chemotherapy treatment before breast cancer surgery tended to have a lower range of motion than those who did not receive it. Therefore, it is necessary for the physical rehabilitation team to attend to these patients even before the mastectomy.

Three-dimensional kinematic analysis of upper limb movements between individuals with and without subacromial shoulder pain exploring the statistical parametric mapping

Subacromial shoulder pain (SSP) accounts for 44–65% of all cases of shoulder pain. Kinematic alterations in the upper limbs have been observed in individuals with SSP, although there is no consensus on such alterations in the literature. Therefore, the present study aimed to compare the three-dimensional kinematics of the scapula, trunk, and arm during shoulder flexion-extension and abduction-adduction movements in individuals with SSP and a control group using statistical parametric mapping (SPM). We evaluated 117 participants [61 with SSP and 56 in the control group (CG)]. The three-dimensional kinematic analysis was performed starting from arm extension/adduction (0%), moving to flexion/abduction, and ending returning to extension/adduction, respectively (100%) in both groups. SSP group flexed more their trunk (0–100%, p < 0.001) and rotated scapula internally (0–20%, p < 0.001 and 75–100%, p < 0.001); rotated upwards (17–32%, p < 0.005 and 58–87%, p < 0.003) and posteriorly tilted (28–79%,p < 0.001 and 81–95%,p < 0.006) less than CG group during arm abduction-adduction. Through arm flexion-extension, the SSP group flexed (38–82% p < 0.009) less their trunk, rotated upwards (5–10% p = 0.021) less their scapula, and posteriorly tilted scapula (0–100% p < 0.001) more than CG. Combining conventional variables used to describe motion in individuals with SSP, such as minimum and maximum values, range of motion, and results provided by SPM can furnish a detailed description of the compensations and limitations of the patient, enabling a better understanding of the function of the scapular girdle as well as improvements in the evaluation process and clinical decision making.

Wearable Wrist Movement Monitoring Using Dual Surface-Treated Plastic Optical Fibers

Regarding high-sensitivity human wrist joint motion monitoring in exercise rehabilitation; we develop a pair of novel wearable and sensitivity-enhanced plastic optical fiber (POF) strain sensors consisting of an etched grating fiber and a side-polished fiber stitched into a polyamide wrist brace. The two flexible and surface-treated fibers are; respectively; featured with an etched periodic gratings with a pitch of 6 mm and a depth of 0.5 mm and a D-shaped side-polished zone of ~300 µm depth and ~30 mm length; which, correspondingly, show the sensitivities of around 0.0176/° and 0.0167/° in a normalized bending angle by far larger than a conventional commercial POF, because it achieves a more sensitive strain-induced evanescent field interaction with the side-machined fibers. Moreover, in terms of the sensor response to bending deformation in the range of −40°~+40°, the former exhibits a better sensitivity in lower angle change, while the latter is superior as the bending angle increases; thereby arranging the two modified POFs separately at the side and back of the human wrist, in order to decouple the wrist joint behaviors induced by typical flexion-extension or abduction-adduction movements. Then, the circular and pentagonal wrist motion trajectory patterns are investigated, to demonstrate the maximum average single-axis motion error of 2.94° via the transformation of spatial angle to plane coordinate for the fabricated couple of POF sensors, which is lower than a recognized standard of 5°, thus suggesting the great potential in wearable exercise rehabilitation of human joints in the field of medical treatment and healing.

Neurophysiological markers discriminate different forms of motor imagery during action observation

The dual-action simulation hypothesis proposes that both an observed and an imagined action can be represented simultaneously in the observer's brain. These two sensorimotor streams would either merge or compete depending on their relative suitability for action planning. To test this hypothesis, three forms of combined action observation and motor imagery (AO + MI) instructions were used in this repeated-measures experiment. Participants observed index finger abduction-adduction movements while imagining the same action (congruent AO + MI), little finger abduction-adduction (coordinative AO + MI), or a static hand (conflicting AO + MI). Single-pulse transcranial magnetic stimulation was applied to the left primary motor cortex. The amplitude of motor evoked potential responses were recorded from both the first dorsal interosseous (FDI) and abductor digiti minimi (ADM) muscles of the right-hand while eye movements were tracked. When controlling for the influence of relevant eye movements, corticospinal excitability was facilitated relative to control conditions in the concurrently observed and imagined muscles for both congruent and coordinative AO + MI conditions. Eye-movement metrics and social validation data from post–experiment interviews provided insight into the attentional and cognitive mechanisms underlying these effects. The findings provide empirical support for the dual-action simulation hypothesis, indicating for the first time that it is possible to co-represent observed and imagined actions simultaneously.

REHABILITATIVE STRATEGIES OF MULTIPLE LOWER LIMBS TRAINING MODELS

According to the combination of lower limbs rehabilitative robot (LLRR), the effect of multi-point and single point driving form on muscle force and joint torque is explored, and the rehabilitation effect of the training mode of the active–passive rehabilitation training is studied. The musculoskeletal model of lower limbs is established based on the physiological structure of human lower limbs. And considering the position of the attachment points of each muscle, the mechanical properties of muscles and applied moment of joints can be obtained under different rehabilitative training strategies by inverse dynamic analysis. The rehabilitation training strategies of flexion–extension and abduction and adduction movements are put forward according to the movement of lower limbs. And using the wire-driven rehabilitation robot as the driving device of the rehabilitation training, the robot is used to simulate the motor function of patients’ lower limbs by modifying the parameters of muscle which can affect the resistance moment of joint motion, then the effects of driving form and the active–passive training mode are analyzed. The results show that single point driving form is better than multi-point on muscle strength and joint strength training; the rehabilitation training strategies of flexion–extension and abduction–adduction movements show different superiority.

O210 Abnormal movements mimicking tremor in amyotrophic hands in adults

Adult patients presenting with slowly progressive hand weakness and wasting (HWW) without signs of upper motor neuron involvement and unconvincing cervical MRI signs of disk protrusion are a diagnostic challenge. Clinical and electrophysiological follow-up is needed to reach the most probable diagnosis. Objective We describe 4 adult patients who presented with HWW and involuntary tremor-like movements of the thumb. Methods We performed electrodiagnostic testing (EDX) two times, between 3 and 6 months and 12 and 24 months, after onset of symptoms. Cranial and cervical magnetic ressonance and laboratory workout were performed in all patients. Results Hyposthesia in the ulnar territory was the most common complaint that did not change between consultations. Muscle strength was decreased in fingers abduction-adduction movements. Thumb tremor was present and correlated with fasciculations in thenar and interossei muscles. The compound muscle and sensory nerve action potentials were reduced in median and ulnar nerves. We observed denervation signs in thenar and hypothenar muscles but not in biceps. The EDX signs did not change in the second examination. Conclusion Fasciculations in wasted hand muscles may induce involuntary movements mimicking tremor. Stabilization of symptoms and neurophysiological data favor spinal cord focal lesions over motor neuron disease.

Kinematic predictors of wrist shot success in floorball/unihockey from two different feet positions

ABSTRACTThe objective of this study was to identify biomechanical predictors for accuracy and speed of the wrist shot in floorball, comparing two different starting feet positions.Ten floorball players performed 2 series of 10 stationary wrist shots, in 2 different positions (feet at a right angle to the end of the stick, oriented towards a target and feet parallel to the end of the stick and to the target). A 12-camera motion capture system, tracking reflective markers on key landmarks, was used to record participant and stick kinematics. Accuracy of the shot was quantified by distance of impact from target centre. Player gaze was approximated from head position.Shot accuracy was significantly better (P = 0.007) when feet were at right angle (0.22 [0.14] m) than when they were parallel (0.27 [0.20] m). Ball speed was no significantly different (P = 0.485) between the right angle position (23.50 [17.52] m · s−1) and the parallel position (23.50 [17.95] m · s−1). Between self-selected position and imposed position, there was no significant difference. Players looking at the target during shooting had greater accuracy. Regression models suggested that ball speed was mainly influenced, in both positions, by the flexion of the supporting leg (ankle, knee and hip), by the rotation of the hip and of the trunk, especially for the spine angles, and by the rotation and abduction–adduction movements of the wrist of the hand on the top of the stick. The comparison between players showed important differences in these technical skills.

Design and development of a parallel robot based on an XY table for ankle rehabilitation

The continuous passive motion (CPM) machines are used in the rehabilitation of members that have been injured to recover their range of motion and prevent stiffness. Nowadays, some CPM machines for knee, ankle, arm and elbow are available commercially. In this paper, a novel design of a parallel robot based on an XY table for ankle rehabilitation, that provides dorsiflexion-plantarflexion and abduction-adduction movements, is presented. Some results are presented in order to show the performance of the parallel robot for ankle rehabilitation. Proportional-derivative (PD), proportional-integral-derivative (PID) and generalised proportional integral (GPI) controllers for trajectory tracking are implemented in the virtual and physical prototype.

Ambulatory assessment of shoulder abduction strength curve using a single wearable inertial sensor.

The aim of the present article was to assess the reliability of strength curves as determined from tridimensional linear accelerations and angular velocities measured by a single inertial measurement unit (IMU) fixed on the upper arm during a shoulder abduction movement performed holding a 1 kg dumbbell in the hand. Within-subject repeatability of the task was assessed on 45 subjects performing four trials consisting of one maximal shoulder abduction-adduction movement. Intraclass correlation coefficient (ICC) was computed on the average movement angular velocity (VEL) and range of movement (ROM) across the four trials. Within-subject repeatability of torque curves was assessed in terms of waveform similarities by computing the coefficient of multiple determination (CMD). Accuracy of the estimated ROM was assessed using an isokinetic dynamometer. High ICC values of ROM (0.955) and VEL (0.970) indicated a high within-subject repeatability of the task. A high waveform similarity of torque curves was also found between trials (CMD = 0.867). Accuracy with respect to isokinetic dynamometer in estimating ROM was always <1 degree (p = 0.37). This study showed the effectiveness of using a single wearable IMU for the assessment of strength curve during isoinertial movements in a way that complies with the needs of clinicians in an ambulatory setting.

Combined action observation and imagery facilitates corticospinal excitability.

Observation and imagery of movement both activate similar brain regions to those involved in movement execution. As such, both are recommended as techniques for aiding the recovery of motor function following stroke. Traditionally, action observation and movement imagery (MI) have been considered as independent intervention techniques. Researchers have however begun to consider the possibility of combining the two techniques into a single intervention strategy. This study investigated the effect of combined action observation and MI on corticospinal excitability, in comparison to either observation or imagery alone. Single-pulse transcranial magnetic stimulation (TMS) was delivered to the hand representation of the left motor cortex during combined action observation and MI, passive observation (PO), or MI of right index finger abduction-adduction movements or control conditions. Motor evoked potentials (MEPs) were recorded from the first dorsal interosseous (FDI) and abductor digiti minimi (ADM) muscles of the right hand. The combined action observation and MI condition produced MEPs of larger amplitude than were obtained during PO and control conditions. This effect was only present in the FDI muscle, indicating the facilitation of corticospinal excitability during the combined condition was specific to the muscles involved in the observed/imagined task. These findings have implications for stroke rehabilitation, where combined action observation and MI interventions may prove to be more effective than observation or imagery alone.

Assessment of hand kinematics using inertial and magnetic sensors.

BackgroundAssessment of hand kinematics is important when evaluating hand functioning. Major drawbacks of current sensing glove systems are lack of rotational observability in particular directions, labour intensive calibration methods which are sensitive to wear and lack of an absolute hand orientation estimate.MethodsWe propose an ambulatory system using inertial sensors that can be placed on the hand, fingers and thumb. It allows a full 3D reconstruction of all finger and thumb joints as well as the absolute orientation of the hand. The system was experimentally evaluated for the static accuracy, dynamic range and repeatability.ResultsThe RMS position norm difference of the fingertip compared to an optical system was 5±0.5 mm (mean ± standard deviation) for flexion-extension and 12.4±3.0 mm for combined flexion-extension abduction-adduction movements of the index finger. The difference between index and thumb tips during a pinching movement was 6.5±2.1 mm. The dynamic range of the sensing system and filter was adequate to reconstruct full 80 degrees movements of the index finger performed at 116 times per minute, which was limited by the range of the gyroscope. Finally, the reliability study showed a mean range difference over five subjects of 1.1±0.4 degrees for a flat hand test and 1.8±0.6 degrees for a plastic mold clenching test, which is smaller than other reported data gloves.ConclusionCompared to existing data gloves, this research showed that inertial and magnetic sensors are of interest for ambulatory analysis of the human hand and finger kinematics in terms of static accuracy, dynamic range and repeatability. It allows for estimation of multi-degree of freedom joint movements using low-cost sensors.

Feasibility of computer-assisted surgery for trapeziometacarpal prosthesis: a preliminary experimental study

The main complication of trapeziometacarpal replacement is trapezial cup loosening due to an imperfect positioning of the trapezial component. This problem is quite similar to those related to other arthroplasties. Hip surgery was progressed toward computer-assisted surgery (CAS) for the improvement of acetabular cup positioning. In this study, we propose an analysis of the feasibility of CAS in trapeziometacarpal replacement. We implanted the hand of a cadaver with a trapeziometacarpal prosthesis (Elektra, by SBI). The surgical procedure and the analysis of motion with CAS were carried out in 6 steps: incision, bone morphing preparation and initialisation, trapezial and metacarpal recordings, first kinematic analysis, prosthesis insertion, and second kinematic analysis. The evaluation of the results was carried out as the comparison of the 2 curves sequences before and after prosthesis insertion. We did not notice any dislocation of the prosthesis. The comparison of 2 curves showed differences regarding motion. For instance, as for abduction-adduction movements, before prosthesis insertion, an opposed-phase automatic rotation was clearly observed whereas after prosthesis insertion, no rotation was observed. CAS makes it possible to analyze the trapeziometacarpal joint motion in terms of biomechanics rather than in terms of anatomy. Such progress should result in measurement standardization that in turn should improve the positioning of prostheses and perhaps the lengthening of their life expectancy by decreasing the rates of prosthesis loosening.

Corticomotor excitability and plasticity following complex visuomotor training in young and old adults

Previous studies with transcranial magnetic stimulation (TMS) have shown that advancing age may influence plasticity induction in human motor cortex (M1), but these changes have been assessed with TMS-induced paradigms or simple motor tasks. The aim of this study was to examine changes in corticospinal excitability and intracortical inhibition as markers of corticomotor plasticity following complex motor training in young and old adults. Electromyographic recordings were obtained from the right first dorsal interosseous (FDI) muscle of 16 young (20-35 years) and 16 older (aged 60-75 years) adults before and after motor skill training. Motor training consisted of three 6-minute blocks of a complex visuomotor task that required matching the metacarpophalangeal (MCP) joint angle of the index finger using abduction-adduction movements. Single- and paired-pulse TMS over the left M1 was used to assess changes in right FDI motor-evoked potentials (MEPs) and short-interval intracortical inhibition (SICI) before and after each training block. Visuomotor tracking performance was diminished in old compared with young adults throughout training. However, improvement in tracking error was similar for young and old adults (7-24% increase in each training block). For young and old adults, motor training increased FDI MEP amplitude (≥ 20%) and reduced the magnitude of SICI (≥ 19%) after each visuomotor training block, reflecting use-dependent plasticity. However, no difference in corticomotor plasticity (change in MEP or SICI) was observed between young and old adults. Further studies are needed to identify the experimental or behavioral factors that might contribute to the maintenance of corticomotor plasticity in older adults.

Cortical Excitability in Chronic Stroke and Modulation by Training: A TMS Study

Background. A possible role for GABA in regulating cortical plasticity after stroke has been proposed. Objective. To investigate changes in intracortical inhibitory and facilitatory circuits in the affected hemisphere more than 6 months after stroke, as well as modulation of excitability by a single training session. Methods. A total of 22 patients >6 months after stroke were compared to age- and gender-matched healthy participants. Cortical excitability was assessed by transcranial magnetic stimulation (TMS), including paired-pulse stimulation, before and up to 30 minutes after a single 15-minute session of 1 Hz thumb abduction-adduction movements. Results. At baseline, TMS showed decreased intracortical inhibition in the affected hemisphere of patients (P = .004) compared to healthy participants. After training a short-lasting decline in motor evoked potentials was observed in both patients (P = .002) and healthy participants (P = .06). Moreover, in healthy participants, inhibitory activity decreased up to 30 minutes after training whereas no significant change was seen in the patients. Conclusions. The findings indicate that inhibitory intracortical circuits are less active after stroke, and no change in inhibitory activity is evident after a single training session. This may indicate that intracortical disinhibition is beneficial during recovery and that an impaired capacity for modulation remains in the chronic stage of stroke.

Editorial

Editorial

Diminished task-related adjustments of common inputs to hand muscle motor neurons in older adults

The purpose of this study was to quantify correlated motor unit activity during isometric, shortening and lengthening contractions of a hand muscle in older adults. Thirteen old subjects (69.6+/-5.9 years, six women) lifted and lowered a light load with abduction-adduction movements of the index finger over 10 degrees using 6-s shortening and lengthening contractions of the first dorsal interosseus muscle. The task was repeated 10-20 times while activity in 23 pairs of motor units was recorded with intramuscular electrodes. The data were compared with 23 motor-unit pairs in 15 young (25.9+/-4.6 years, five women) subjects obtained using a similar protocol in a previous study. Correlated motor unit activity was quantified using time-domain (synchronization index; Common Input Strength) and frequency-domain (coherence) analyses for the same motor-unit pairs. For all contractions, there was no difference with age for the strength of motor-unit synchronization, although age-related differences were observed for synchronous peak widths (young, 17.6+/-7.4 ms; old, 13.7+/-4.9 ms) and motor-unit coherence at 6-9 Hz (z score for young, 3.0+/-1.8; old, 2.2+/-1.5). Despite increased synchrony during lengthening contractions and narrower peak widths for shortening contractions in young subjects, there was no difference in the strength of motor unit synchronization (CIS approximately 0.8 imp/s), or the width of the synchronous peak (approximately 14 ms) during the three tasks in old subjects. Furthermore, no significant differences in motor-unit coherence were observed between tasks at any frequency for old adults. These data suggest that the strategy used by the central nervous system to control isometric, shortening, and lengthening contractions varies in young adults, but not old adults. The diminished task-related adjustments of common inputs to motor neurons are a likely consequence of the neural adaptations that occur with advancing age.