Submovements during pointing movements in Parkinson’s disease

Velocity irregularities frequently observed during deceleration of arm movements have usually been interpreted as corrective submovements that improve motion accuracy. This hypothesis is re-examined here in application to movements of Parkinson’s disease (PD) patients in which submovements are specifically frequent. Pointing movements in patients and age-matched controls to large and small targets in three movement modes were studied. The modes were discrete (stop on the target), continuous (reverse on the target), and passing (stop after crossing the target). Two types of submovements were distinguished, gross and fine. In both groups, gross submovements were more frequent during the discrete and passing than continuous mode, specifically for large targets. This suggested that gross submovements were fluctuations accompanying motion termination (stabilization at the target) that was included in discrete and passing but not continuous movements. Gross submovements were specifically frequent in patients, suggesting that PD causes deficiency in smooth motion termination. Although in both groups fine submovements were more frequent for small than large targets, this relation was also observed in passing movements after crossing the target, i.e., when no corrections were needed. This result, together with higher jerk of the entire trajectory found for smaller targets, indicates that fine submovements may also be not corrective adjustments but rather velocity fluctuations emerging due to low speed of movements to small targets. This interpretation is consistent with the recognized inability of PD patients to promptly change generated force as well as to quickly re-plan current motion. The results suggest a need to re-examine the traditional interpretation of submovements in PD and the related theory that the production of iterative submovements is a strategy used by patients to compensate for a decreased initial force pulse.     

The intrinsic value of visual information affects saccade velocities

Let us assume that the purpose of any movement is to position our body in a more advantageous or rewarding state. For example, we might make a saccade to foveate an image because our brain assigns an intrinsic value to the information that it expects to acquire at the endpoint of that saccade. Different images might have different intrinsic values. Optimal control theory predicts that the intrinsic value that the brain assigns to targets of saccades should be reflected in the trajectory of the saccade. That is, in anticipation of foveating a highly valued image, our brain should produce a saccade with a higher velocity and shorter duration. Here, we considered four types of images: faces, objects, inverted faces, and meaningless visual noise. Indeed, we found that reflexive saccades that were made to a laser light in anticipation of viewing an image of a face had the highest velocities and shortest durations. The intrinsic value of visual information appears to have a small but significant influence on the motor commands that guide saccades.     

Masticatory Performance and Chewing Cycle Kinematics—Are They Related?

Objective:To compare chewing cycle kinematics of subjects with better and poorer masticatory performance.Materials and Methods:A cross-sectional study compared masticatory performance, based on the breakdown of the artificial test food Cuttersil®, in 30 subjects with Class I occlusion. Individuals with median particle sizes greater and lesser than the median value for the entire sample were categorized as poorer (15) and better (15) performers, respectively. While chewing Cuttersil, three-dimensional jaw movements of subjects were tracked with an optoelectric computer system. Multilevel linear modeling was used to evaluate differences in estimated cycle shape, cycle duration, and maximum excursions, as well as within-subject variation between the two groups.Results:Poorer performers had a significantly longer opening duration (0.274 ± 0.225 sec vs 0.325 ± 0.270 sec) than better performers. Poorer and better performers also showed significant differences in cycle shape, including a less horizontal path of closure and more posterior jaw movement in the poorer performers. In addition, poorer performers exhibited significantly more cycle-to-cycle (within-subject) variability in chewing cycle duration, excursive movements, and lateral velocity than did better performers.Conclusions:Poorer performers lacked consistency in their chewing cycles, and their cycle shape differs from that of better performers.     

Support for a reduction in the number of trials needed for the star excursion balance test

Robinson RH, Gribble PA. Support for a reduction in the number of trials needed for the Star Excursion Balance Test.

Objective

To determine the number of trials necessary to achieve stability in excursion distance and stance leg angular displacement for the 8 directions of the Star Excursion Balance Test (SEBT).

Design

One-way repeated-measures analysis of variance.

Setting

Athletic training laboratory.

Participants

Twenty participants (10 men, 10 women) without any known musculoskeletal injuries or neurologic deficits that could have negatively affected their dynamic balance volunteered for the study.

Intervention

Participants completed 6 practice and 3 test trials in each of the 8 reach directions of the SEBT.

Main Outcome Measures

Excursion distances of the reaching leg normalized to leg length and angular displacement at the hip and knee of the stance leg in all 3 planes of movement were determined.

Results

There were significant increases in excursion distance, hip flexion, and knee flexion for 7, 4, and 5 of the 8 reach directions, respectively.

Conclusions

For the majority of the reach directions, maximum excursion distances and stance leg angular displacement values achieved stability within the first 4 practice trials, thus justifying a reduction in the recommended number of practice trials from 6 to 4 and supporting the trend toward simplifying SEBT administration.     

Kinematic trajectories while walking within the Lokomat robotic gait-orthosis

Background One of the most popular robot assisted rehabilitation devices used is the Lokomat. Unfortunately, not much is known about the behaviors exhibited by subjects in this device. The goal of this study was to evaluate the kinematic patterns of individuals walking inside the Lokomat compared to those demonstrated on a treadmill.Methods Six healthy subjects walked on a treadmill and inside the Lokomat while the motions of the subject and Lokomat were tracked. Joint angles and linear motion were determined for Lokomat and treadmill walking. We also evaluated the variability of the patterns, and the repeatability of measuring techniques.Findings The overall kinematics in the Lokomat are similar to those on a treadmill, however there was significantly more hip and ankle extension, and greater hip and ankle range of motion in the Lokomat (P < 0.05). Additionally, the linear movement of joints was reduced in the Lokomat. Subjects tested on repeated sessions presented consistent kinematics, demonstrating the ability to consistently setup and test subjects.Interpretation The reduced degrees of freedom in the Lokomat are believed to be the reason for the specific kinematic differences. We found that despite being firmly attached to the device there was still subject movement relative to the Lokomat. This led to variability in the patterns, where subjects altered their gait pattern from step to step. These results are clinically important as a variable step pattern has been shown to be a more effective gait training strategy than one which forces the same kinematic pattern in successive steps.     

Validated robotic laparoscopic surgical training in a virtual-reality environment

Background  A robotic virtual-reality (VR) simulator has been developed to improve robot-assisted training for laparoscopic surgery and to enhance surgical performance in laparoscopic skills. The simulated VR training environment provides an effective approach to evaluate and improve surgical performance. This study presents our findings of the VR training environment for robotic laparoscopy. Methods  Eight volunteers performed two inanimate tasks in both the VR and the actual training environment. The tasks were bimanual carrying (BC) and needle passing (NP). For the BC task, the volunteers simultaneously transferred two plastic pieces in opposite directions five times consecutively. The same volunteers passed a surgical needle through six pairs of holes in the NP task. Both tasks require significant bimanual coordination that mimics actual laparoscopic skills. Data analysis included time to task completion, speed and distance traveled of the instrument tip, as well as range of motion of the subject’s wrist and elbow of the right arm. Electromyography of the right wrist flexor and extensor were also analyzed. Paired t-tests and Pearson’s r were used to explore the differences and correlations between the two environments. Results  There were no significant differences between the actual and the simulated VR environment with respect to the BC task, while there were significant differences in almost all dependent parameters for the NP task. Moderate to high correlations for most dependent parameters were revealed for both tasks. Conclusions  Our data shows that the VR environment adequately simulated the BC task. The significant differences found for the NP task may be attributed to an oversimplification in the VR environment. However, they do point to the need for improvements in the complexity of our VR simulation. Further research work is needed to develop effective and reliable VR environments for robotic laparoscopic training.     

Impact of Morbid Obesity on Chewing Ability

Background  This study compared the chewing parameters in a group of obese adult patients scheduled for gastric bypass surgery with those of a control group. Methods  Chewing parameters were measured in two groups of subjects, one of 44 obese patients scheduled for gastric bypass surgery (body mass index [BMI] = 49.1 ± 7.2) and the other of 30 non-obese control subjects (BMI = 20.9 ± 2.1). In both groups, the subjects’ dental status was characterized by the number of functional dental units. Kinematic parameters, namely chewing time (CT), number of chewing cycles (CC), and chewing frequency (CF), were video recorded during the mastication of five natural standardized foods (banana, apple, sweet jelly, peanut, and carrot). The particle size distribution of the expectorated bolus from carrot and peanuts was characterized by the 50th percentile (D ₅₀). Analysis was carried out to detect any effect of the fixed factors “dental status,” “type of food,” and “subject group” on the variations of the dependent factors CT, CC, CF, and D ₅₀. Results  In obese subjects, CT, CC, and D ₅₀ were variables depending on both dental status and food. For fully dentate subjects, the group of patients with obesity showed higher values for CT and CC and lower values for D ₅₀ for both carrot and peanuts than the control group. Conclusion  The chewing parameters were affected in fully dentate patients with morbid obesity compared with controls, emphasizing the need for a systematic evaluation of both dental status and chewing ability in patients scheduled for bariatric surgery.     

An index for the evaluation of 3D masticatory cycles stability

ObjectivesTo introduce an index (Masticatory Stability Index, MSI) to analyze the stability of chewing cycles in standardized conditions and test it in a group of patients with subclinical mild temporomandibular disorder (TMD).Design23 subjects with mild subacute TMD and 21 healthy subjects were involved; they all responded to a questionnaire about signs and symptoms of TMD (ProTMDmulti) and underwent a myofunctional orofacial evaluation with scores, using the protocol of orofacial myofunctional evaluation with scores (OMES). Their mandibular kinematics was assessed with a 3D motion capture system during deliberate unilateral gum chewing. The MSI was computed synthesizing the information contained in nine kinematics parameters into a single global figure. Patients’ and controls’ MSI were compared considering the preferred and non-preferred chewing side using a 2-way ANOVA (factors: group, side).ResultsTogether with a lower total score of myofunctional orofacial status, the TMD group showed a reduced stability based on MSI (p < 0.05).ConclusionsThe MSI is an efficient method to measure the stability of the masticatory cycles. These preliminary results encourage validating the index on a larger sample. The variability in the motor behavior of chewing can impair the objectivity of its evaluations in several types of patients, including those with TMD. The MSI could be useful to complement clinical assessments, providing data for planning the rehabilitation of masticatory function in these patients.     

Patients with chronic non-specific low back pain have altered movement coordination during functional reaching tasks

BackgroundIdentifying altered motor control patterns during functional movements in patients with chronic non-specific low back pain (LBP) has important clinical implications for reducing the risk of recurrence. While prior research has shown that magnitudes of lumbar and hip motion are not altered in patients with chronic non-specific LBP, it is possible that outcomes which describe coordination could provide greater discriminatory information between pathological and healthy movement.Research questionDetermine the effect of biological sex and chronic non-specific LBP on coordination between hip and lumbar motion during cyclic and discrete reaching.MethodsTwenty participants with chronic non-specific LBP (11 male/9 female, 23.5 ± 4.9 years old) and 21 control participants (12 male/9 female, 22.9 ± 6.1 years old) completed discrete and cyclic reaching tasks to a target in the mid-sagittal plane, while whole-body kinematics were collected using a three-dimensional motion capture system. Movement time, lumbar motion, hip motion, and the ratio between lumbar and hip motion were compared between participants with and without chronic non-specific LBP and between men and women using two-way mixed ANOVAs.ResultsParticipants with chronic non-specific LBP had reduced lumbar-hip ratios relative to control participants during both the cyclic (F = 4.779, p = 0.035, η² = 0.114) and discrete tasks (F = 4.743, p = 0.036, η² = 0.119), however group differences were not observed for hip or lumbar excursion during either task (p > 0.05). Participants with chronic non-specific LBP had slower reaching times relative to controls during the discrete reaching task (F = 4.795, p = 0.035, η² = 0.115). No significant effects of sex, and no interactions between group and sex were observed for any outcome.SignificanceReduced lumbar-hip ratios during reaching likely reflect a compensatory movement strategy that could play an important role in the development and progression of LBP.