Effects of biomechanical and task constraints on the organization of movement in precision aiming

Nine participants performed a reciprocal precision aiming task under different experimental conditions. Due to the anisotropy of the work space, varying the direction of motion (from 0 degrees to 315 degrees in steps of 45 degrees ) allowed exploration of the effects of biomechanical constraints that were found to affect the duration of movement but not the shape of the kinematic pattern. Varying the size of the targets to be attained (W: 2.5, 1.25, and 0.625 cm, for a constant intertarget distance of 10 cm) and the nature (linear or non-linear) of the mapping between effector space (motion of a handheld stylus on a graphics tablet) and task space (motion of a pointer between targets on a computer screen) also led to changes in movement duration. However, the latter type of constraint gave rise to systematic changes in the pattern of movement, with progressively more difficult tasks being characterized by progressively less harmonic motion patterns. We conclude that in contrast to (biomechanical) constraints at the level of the effector, (informational) constraints at the level of the task affect the processes underlying movement organization. For the range of values studied, the effects of these two types of constraint can be considered to be independent.     

The influence of a chiropractic manipulation on lumbar kinematics and electromyography during simple and complex tasks: a case study

OBJECTIVE: To investigate whether a more sophisticated and detailed analysis of both simple and complex tasks may yield more information regarding the short-term influence of an adjustment on spine biomechanics. METHODS: The study used a single-subject, before-after design. Three-dimensional spine kinematics and trunk muscle electromyography were assessed during a variety of tasks performed by a professional golfer exhibiting non-specific, chronic, low back pain. The patient received a right-to-left and left-to-right spinous pull adjustment. RESULTS: After the adjustment, changes were seen in all 3 axes of motion during a golf swing, with concomitant muscle responses. In addition, changes in the off axes of motion were seen during simple movement tasks. CONCLUSIONS: A more detailed spine kinematic analysis, specifically analysis of motion in the nonprincipled axes, yielded more information regarding the short-term influence of an adjustment on lumbar spine motion and muscle function.     

Head stabilization during various locomotor tasks in humans

Summary This experiment, which extends a previous investigation (Pozzo et al. 1990), was undertaken to examine how head position is controlled during natural locomotor tasks in both normal subjects (N) and patients with bilateral vestibular deficits (V). 10 normals and 7 patients were asked to perform 4 locomotor tasks: free walking (W), walking in place (WIP), running in place (R) and hopping (H). Head and body movements were recorded with a video system which allowed a computed 3 dimensional reconstruction of selected points in the sagittal plane. In order to determine the respective contribution of visual and vestibular cues in the control of head angular position, the 2 groups of subjects were tested in the light and in darkness. In darkness, the amplitude and velocity of head rotation decreased for N subjects; these parameters increased for V subjects, especially during R and H. In darkness, compared to the light condition, the mean position of a line placed on the Frankfort plane (about 20–30° below the horizontal semi-circular canal plane) was tilted downward in all conditions of movement, except during H, for N subjects. In contrast, this flexion of the head was not systematic in V subjects: the Frankfort plane could be located above or below earth horizontal. In V subjects, head rotation was not found to be compensatory for head translation and the power spectrum analysis shows that head angular displacements in the sagittal plane contain mainly low frequencies (about 0.3–0.8 Hz). The respective contribution of visual and vestibular cues in the control of the orientation and the stabilization of the head in space is discussed.     

Kinematic analysis of upper limb during walking in diplegic children with Cerebral Palsy

Movements of the lower limbs during walking have been widely investigated in literature, while quantification of arm movement during gait is scanty. The aim of the present study was to assess quantitatively the upper limb motion during gait in children with Cerebral Palsy (CP). Sixteen children with diplegic CP were evaluated using a full-body marker set, which allows assessing both the lower and upper limb kinematics. Our results demonstrated that movement of the arms was characterized by an abducted shoulder and a more flexed elbow position at the initial contact of the gait cycle with a quite physiological range of motion if compared to controls. These data showed that gait of children with diplegic CP is generally characterized by abnormal upper limb position which could be considered a strategy to keep balance and posture control during walking.     

Females with knee osteoarthritis use a detrimental knee loading strategy when squatting

BackgroundThe purpose of this study was to identify sex differences in lower limb kinematics, kinetics, and muscle activation patterns between individuals with osteoarthritis and healthy controls during a two-legged squat.MethodThirty OA (15 females) and 30 healthy (15 females) participants performed three 2-legged squats. Sagittal and frontal plane hip, knee, and ankle kinematics and kinetics were calculated. Two-way ANOVAs (Sex X OA Status) were used to characterize differences in squatting strategies between sexes and between those with and without knee OA.ResultsA greater decrease in sagittal hip, knee, and ankle range of motion and knee joint power was observed in the OA participants compared to the healthy controls. Females with OA had significantly reduced hip and knee adduction angles compared to the healthy females and males with OA. Females also had decreased hip power, hip flexion, and hip adduction moments and knee adduction moments compared to their male counterparts, with the greatest deficits observed in the females with OA. Females with OA also had the highest magnitude of muscle activation for the quadriceps, hamstrings, and gastrocnemius throughout the squat, while males with OA showed increased activation of the vastus lateralis and medial gastrocnemius compared to the healthy males.ConclusionsOA significantly altered biomechanics and neuromuscular control during the squat, with males employing a hip-dominant strategy, allowing them to achieve a greater lower limb range of motion.     

The kinematics of motor imagery: comparing the dynamics of real and virtual movements

Motor imagery (MI) is a key tool for studying the cognitive functions of movement. These studies assume that movements and their MI (virtual movements) involve the same cognitive functions. The real-virtual isochrony and isometry of movements of different complexity and accuracy, and the kinematics of real and virtual movements (real-virtual spatial homology and partial isometry) were studied to test this hypothesis. Isochrony was high in complex attention-demanding tasks but not in simple or inaccurate tasks, with isometry and spatial homology also being different for different motor patterns. These data suggest that movements and their MI do not always involve the same cognitive functions, and are particularly different in simple motor tasks requiring low attention levels.     

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.