Reduced Movement Speed Research Articles

Non-back-drivable clutch based self-locking mechanism of prosthetic joint to improve manipulation stability.

During activities of daily living (ADLs), the wrist is mainly engaged in positioning and directing the hand. Researches have demonstrated that restoring wrist mobility can significantly enhance the manipulation ability, reduce body distortion caused by motion compensation, and improve the quality of life for amputees. However, most daily activities, particularly the delicate ones, place high demands on the ability of wrist to maintain a certain rotation angle, also known as non-back-drivable ability, which poses a challenge to the design of prosthetic wrists. To address this issue, various solutions have been proposed, including motor holding brakes, high reduction ratio reducers, and worm gears. However, the motor holding brake only functions after a power outage and cannot continuously prevent torque from the load end. The latter two solutions may alter the transmission ratio, resulting in reduced movement speed and transmission efficiency. Therefore, how to design a miniaturized non-back-drivable mechanism without changing the transmission ratio so that the forearm rotational freedom can be locked at any position for any duration is a problem to be solved in the research of prosthetic wrist designs. This paper presents a line-contact based non-back-drivable clutch (NBDC) that does not cause changes in the transmission ratio, ensuring the motion performance of the prosthetic limb. At the same time, it does not introduce additional friction in the forward transmission process, guaranteeing the overall efficiency. Most importantly, it only allows the torque transmitting from the motor to the load, prevents the load reversely from driving back even in a power failure condition, significantly improving the stability, safety, and comfort. Detailed kinematic and static analyses of the working process has been conducted, and transient dynamics simulation has been performed to verify its effectiveness. Through experiments, it is demonstrated that the self-locking torque of the output end could reach approximately 600Nmm, and the unlocking torque of the input end is about 80Nmm, which can be effectively integrated in prosthetic wrist rotation joints, contributing to the performance, safety and energy saving of prosthetic joint systems.

Digital health metrics reveal upper limb impairment profiles in ARSACS

ObjectiveAdults with autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) often present with reduced upper limb coordination affecting their independence in daily life. Previous studies in ARSACS identified reduced performance in clinical assessments requiring fine and gross dexterity as well as prehension. However, the kinematic and kinetic aspects underlying reduced upper limb coordination in ARSACS have not been systematically investigated yet. In this work, we aimed to provide a detailed characterization of alterations in upper limb movement patterns and hand grip forces in 57 participants with ARSACS. MethodsWe relied on a goal-directed technology-aided assessment task, which provides eight previously validated digital health metrics describing movement efficiency, smoothness, speed, and grip force control. ResultsFirst, we observed that 98.3% of the participants were impaired in at least one of the metrics, that all metrics are significantly impaired on a population level, and that grip force control during precise manipulations is most commonly and strongly impaired. Second, we identified high inter-participant variability in the kinematic and kinetic impairment profiles, thereby capturing different clinical profiles subjectively observed in this population. Lastly, abnormal goal-directed task performance in ARSACS could be best explained by reduced movement speed, efficiency, and especially force control during precise manipulations, while abnormal movement smoothness did not have a significant effect. InterpretationThis work helped to refine the clinical profile of ARSACS and highlights the need for characterizing individual kinematic and kinetic impairment profiles in clinical trials in ARSACS.

Effect of a Training Protocol on Movement Function in Men with Cerebrovascular Accident

: Cerebrovascular accident (CVA) refers to any kind of damage caused by direct or indirect damage to the brain and its related elements. It is estimated that about 60% of brain injury victims have a permanent disorder. The consequences of CVA include reduced movement speed, weakness, functional impairment, reduced power, and balance. The purpose of this study was to investigate the effect of a 12-week selected training protocol on motor function following brain injury. In a semi-experimental study, 30 male subjects with a mean and standard deviation of 52.2 ± 5.4 years, weight 173.2 ± 4.2 kg, and height of 78.8 ± 5.3 cm were selected purposefully and accessible with inclusion and exclusion criteria. The participants were randomly divided into experimental (n = 15) and control groups (n = 15). In order to evaluate the physical-motor performance, 10-meter walking tests, get up and go tests, and climbing stairs tests were used. The training program lasted for 12 weeks, three sessions per week, and each session for 30 - 60 minutes. Data were analyzed by independent t-test and dependent t-test using SPSS-21 software at P ≤ 0.05 level. Based on dependent t-test and covariance test, there were significant differences in all three components of motor function (10 m walk time tests, get up and go test, and stair climbing test), there was a significant increase after training in men with CVA (P = 0.00). From the findings of this study, it can be concluded that the special exercises of the present study have a positive effect on motor function parameters of male patients with CVA, so it can be recommended as one of the most important rehabilitation strategies for these patients.

Differences in multi-segmental spine kinematics between patients with different stages of axial spondyloarthritis and healthy controls

BackgroundThe effects of inflammation and ankylosis on spinal kinematics of patients with axial spondyloarthritis (axSpA) are poorly understood. Furthermore, existence of (mal)adaptive movement profiles within axSpA, and differences between movement profiles in sensation of pain or fear of movement has never been investigated. ObjectivesTo investigate differences in range of motion in six spinal regions and the hips between inflammatory and ankylosed patients with axSpA, and to increase insight in different movement profiles of patients with axSpA and their association with pain and fear. DesignObservational, cross-sectional. MethodsThree-dimensional motion analysis was performed in 20 patients with axSpA and 23 healthy controls during range of motion tasks in all three planes. We compared patients with inflammatory (n = 8) and ankylosed (n = 12) axSpA, and controls. Patients were also classified into Flexion or Lordotic profile. Questionnaires regarding pain and fear of movement were conducted.Results/findings: Both inflammatory and ankylosed axSpA patients have limited spinal ROM and reduced movement speed compared to healthy controls. Patients with a Lordotic profile showed significantly less ROM in lumbar regions and experienced more pain during forward bending than patients with a Flexion profile. ConclusionsBoth inflammation and ankylosis contribute to spinal mobility impairment, and axSpA patients with a lordotic profile experienced more pain. This profile may be a maladaptive movement strategy to prevent further pain increase. Suggesting that pain and fear of movement, might be better variables to specify patients’ spinal mobility limitations for individual physical therapy and rehabilitation patient profiling.

Understanding the limits to the hydraulic leg mechanism: the effects of speed and size on limb kinematics in vagrant arachnids.

Among invertebrates, spiders (order Araneae) may be unique in their relationship between speed and mass as they use a combination of direct muscular contractions to flex their appendages, and internally controlled hydraulic pressure to extend them. To explore this, we measured maximal running speeds in 128 individual lycosids and sparassids, which varied in mass between 0.0054 and 3.01g. We show maximum speed scaled with M0.353, while mean running speed scaled much lower as M0.197. We show no strong limitation of the hydraulic mechanism, with leg extension speed being equal to or greater than leg flexion speed. The reduction in leg flexion speed, only apparent in the distal most joint of the limb, might be a result of the requirement for flexor muscles to act against the hydraulic system. We explored the role of the limbs and found an alternating pattern of joint use among limbs, which may represent a strategy to avoid interference with adjacent limbs during running. Furthermore, we observed a reduced movement speed (increased leg dragging) in the rearward facing fourth limb with size. This may be linked to the increased size of the abdomen in larger spiders and may suggest a speed limitation in larger individuals.

Non epileptogenic Rasmussen`s encephalitis: a case report

Rasmussen's encephalitis (RE) is a very rare chronic inflammatory unilateral encephalopathy with still unknown etiology. It predominantly affects children under the age of 10, but can also affect adolescents and adults. Current evidence on possible etiologies are divided in two main theories. The first one is based on brain inflammation caused by a reaction to a foreign antigen. The second one is based on an autoimmune disease that is limited to a single hemisphere of the brain. The common presentation is intractable and frequent focal motor seizures, often associated with progressive neurological decline, and progressive unilateral focal cortical atrophy. Progression of the inflammatory process in MRI is considered a good biomarker in RE. Objectives: Report a rare case of a female infant presenting atypical manifestations of uncommon symptoms without seizures caused by Rasmussen's encephalitis. Case Report: A ten-year-old right-handed female presented to the emergency department with sudden onset of abnormal involuntary movements of the right upper and lower limbs, face paresia of the same side and loss of attention without loss of consciousness. The involuntary contractions were brief, random, irregular, and worsened with activity, along with a positive milkmaid grip sign. She also displayed reduced movement speed and hyperactive biceps, triceps, patellar and ankle jerk reflexes. Associated with the motor abnormalities, the girl presented with a recent but progressive decrease in cognitive functions, which caused a decline in school performance and impaired reasoning, and affective blunting. She had no sign of previous neuropsychomotor development abnormality. She was taken to a quaternary hospital where a MRI and a CT of the brain were performed. MRI showed atrophy of the left cerebral hemisphere, predominantly in the operculum and head of the caudate nucleus, hypersignal in the insular cortex and adjacent white matter. CT presented with hypoattenuation of the left frontal lobe and parieto-occipital white matter associated with atrophy of the head of the caudate nucleus of the same side and enlargement of the adjacent fissures and sulcus. A subsequent PET-CT showed a left cerebral hemisphere hypometabolism, predominantly in the basal ganglia, temporal, frontal and insular lobes. Functional evaluation detected diffuse unilateral disorganization of brain electric activity, but no epileptic paroxysmal discharges were found on the electroencephalogram. After hospitalization, human immunoglobulin at the dose 2g/kg/day was used for five days. The girl remained stable, with no complications. After sixteen days, she was discharged with a rehabilitation program and follow-up care.

Electronic measures of movement impairment, repositioning, and posture in people with and without neck pain\u2014a systematic review

BackgroundNeck pain is a major public health problem. Our objective was to describe differences in measures of movement and posture between people with and without neck pain.MethodsPubMed and Embase were searched before 15 February 2019 for studies comparing people with neck pain with controls using electronic measurements of neck movement and/or posture. Data were extracted on participants, device, test methods, active range of motion (RoM) and quality of motion, joint positioning sense, and posture. Study quality was assessed using the quality assessment of studies of diagnostic accuracy included in systematic reviews (QUADAS) and Guidelines for Reporting Reliability and Agreement Studies (GRRAS) guidelines.ResultsThirty-six studies were included: 24 studies included measurement of active RoM, 15 quality of motion, 12 joint positioning sense, and 5 cervical spine posture. Measurements and test methods were heterogeneous. The reporting of study populations and methods were poor, whereas devices and statistics were well described. All studies on RoM showed reduced active RoM in people with neck pain when compared with controls, 5 of 10 studies reported reduced movement speed for people with neck pain, and 5 of 9 studies reported significantly greater joint positioning error for people with neck pain compared with controls. Due to heterogeneous test parameters and methods, no conclusion regarding differences in conjunct motion, tracking a motion pattern, and measures of posture could be drawn.ConclusionsPeople with neck pain appear to have reduced active RoM, movement speed, and head repositioning accuracy when compared with controls. However, quality of reviewed studies was low and better descriptions of participants and methods are required before firm conclusions can be drawn.

Behavioral response of a generalist predator to chemotactile cues of two taxonomically distinct prey species

Chemotactile cues unintentionally left by animals can play a major role in predator–prey interactions. Specialized predators can use them to find their prey, while prey individuals can assess predation risk. However, little is known to date about the importance of chemotactile cues for generalist predators such as ants. Here, we investigated the response of a generalized predatory ant, Formica polyctena, to cues of two taxonomically distinct prey: a spider (Pisaura mirabilis) and a cricket (Nemobius sylvestris). In analogy, we studied whether crickets and spiders showed antipredator behavior in response to ant cues. When confronted with cues of the two prey species, Formica polyctena workers showed increased residence time and reduced movement speed, which suggests success-motivated searching behavior and thus increased foraging effort. The ants’ response did not differ between cues of the two prey species, coinciding with similar aggression and consumption rates of dead prey. However, the cuticular hydrocarbons, which likely resemble part of the potential cues, differed strongly between the species, with only few methyl-branched alkanes in common. This suggests that ants respond to multiple compounds left by other organisms with prey-search behavior. The two prey species, in turn, showed no detectable antipredator behavior in response to ant cues. Our study shows that ants can detect and respond to chemotactile cues of taxonomically and ecologically distinct prey species, probably to raise their foraging success. Using such chemotactile cues for prey detection may drastically increase their foraging efficiency and thus contribute to the high ecological success of ants.

Power training induced change in bradykinesia and muscle power in Parkinson's disease

Power-based resistance training (PWT), using low load and high velocity, can improve physical function and quality of life in older persons. Patients with Parkinson's disease (PD), exhibiting muscular weakness and reduced movement speed, have been shown to be benefit from resistance training; however, little is known about the advantages of PWT for PD. PurposeTo evaluate the effects of PWT on bradykinesia and muscular performance in older patients with PD. MethodsTwenty-six patients with mild to moderate PD were randomly assigned to a PWT or control group (CON). The PWT program was three months, incorporating two sessions/wk of high-speed resistance training combined balance and agility drills. Outcome measures included: upper and lower limb bradykinesia scores, one repetition maximums (1RM) and peak powers on biceps curl, chest press, leg press, hip abduction and seated calf, and quality of life (PDQ-39). ResultsThe PWT group produced significant improvement in both upper and lower limbs bradykinesia scores, 1RM and muscle peak power (p < .05), which surpassed the CON group except for power during the seated calf exercise. No significant correlations between changes in clinical measure of bradykinesia and muscle peak power were observed after training. Significant improvements were seen in the PDQ-39 overall score, subsections for mobility, activities of daily living and social support for the PWT group. ConclusionThe 3-month PWT program significantly reduced bradykinesia and increased muscle strength and power in older patients with PD. Power training is an effective training modality to improve physical function and quality of life for PD.

Commentary: Cerebellar direct current stimulation enhances on-line motor skill acquisition through an effect on accuracy.

In the past decade, human cortical activity has been shown to be modulated by applying direct low electrical current. The current flowing through the skull and brain between two surface electrodes increases excitability of the cortical tissue under the anode and decreases it under the cathode. This transcranial direct current stimulation (tDCS) improves motor adaptation to environmental change (Galea et al., 2011; Hardwick and Celnik, 2014; Parikh and Cole, 2015) as well as skilled motor learning (Reis et al., 2009; Prichard et al., 2014; Cantarero et al., 2015). The cortical sites that have been shown to impact motor control under tDCS stimulation are the primary motor area (M1; Nitsche et al., 2003) and the cerebellum (Galea et al., 2011). A recent study investigated the effects of cerebellar tDCS (ctDCS) on motor skill learning (Cantarero et al., 2015). Participants attempted to quickly and accurately navigate a cursor on a screen by modulating the isometric key pinch force. To perform the sequential visual isometric pinch task (Reis et al., 2009; Cantarero et al., 2015), the brain has to integrate three types of information: visual feedback, force feedback (proprioception), and motor command. Therefore, improving sensory-motor integration would improve performance in this task. Recently, the cerebellum has shown multimodal arrangements, providing an anatomical basis for this sensory-motor integration. Proville et al. (2014) demonstrated that sensory and motor information from the cerebral cortex converges on single cells in the cerebellum. Proprioceptive information from the spinocerebellar tract and motor information from the cerebral cortex also converge on single cells in the cerebellum (Huang et al., 2013; Requarth et al., 2014). Therefore, cerebellar stimulation can potentially improve sensory-motor integration. Results of Cantarero et al. (2015) showed that anodal ctDCS improved motor accuracy relative to anodal tDCS and sham groups. The improved accuracy was not associated with reduced movement speed (Cantarero et al., 2015, Figure 3C). This change in the speed-accuracy tradeoff demonstrated an improvement in motor skill. Although not reported in the text, Figure 3A in Cantarero et al. (2015) clearly showed that the effect of ctDCS on accuracy was not gradual but immediate (Day 1, Block 2), consistent with the immediate enhancement of conditioned eyeblink responses reported during anodal ctDCS (Zuchowski et al., 2014). After this immediate shift, accuracy remained stable across training days and did not show a typical learning curve. The effect of ctDCS on motor accuracy is unlikely related to the visual system which can hardly be improved. This effect may rather result from improved proprioception. Specifically, in the sequential visual isometric pinch task, improving proprioception would improve the ability to accurately match visual and muscle-force information. Based on studies testing cerebellar patients (e.g., Bhanpuri et al., 2013), it has been suggested that the integration of peripheral proprioceptive information and central motor information in the cerebellum (Huang et al., 2013; Requarth et al., 2014) produces refined proprioception (Boisgontier and Swinnen, 2014). Therefore, if ctDCS improves proprioception this is likely through an improvement of this integration. Sensory-motor integration is performed on three types of information: Space, quantity, and time (Walsh, 2003). Proprioception refers to space (e.g., position of the segments) and quantity (e.g., intensity of the muscle contraction). Wessel et al. (2015) showed that anodal ctDCS does not significantly improve online motor skill learning in a synchronization tapping task, suggesting that anodal ctDCS does not impact the temporal component of sensory-motor integration. M1 tDCS also immediately improves performance in a motor skill task, as demonstrated by Prichard et al. (2014), and visible in Reis et al. (2009). Nevertheless, the immediate effects for ctDCS and M1 tDCS may have different grounds. As described above, immediate ctDCS effects may result from an improved proprioception. Immediate M1 tDCS effects could instead be due to refined spatiotemporal patterns of neuronal activity in M1, which have been associated with improved motor control (Peters et al., 2014). Furthermore, Parikh and Cole (2015) showed that applying M1 tDCS during practice of the Grooved pegboard test improved performance on a grip-lift task, thereby suggesting that this tDCS-induced refinement of neuronal activity in M1 could be transferred between tasks. In conclusion, Cantarero et al. (2015) study showed an immediate ctDCS effect on movement accuracy. Here I propose that this effect is mediated by improved sensory-motor integration in the cerebellum resulting in refined proprioception. This immediate effect has also been reported in motor skill learning studies using M1 tDCS, although the underlying mechanism here may instead be related to the refinement of the spatiotemporal patterns of neuronal activity in M1.

Power Training Effects on Motor Function and Neuromuscular Performance in Older Adults with Parkinson’s Disease

Parkinson’s disease (PD) compromises strength, power and motor function in older adults. The loss of mobility due to PD can be characterized by rigidity, bradykinesia, and gait disturbances; while reduced movement speed in PD is characterized by motor programming and execution deficits characterized by freezing and movement initiation problems. Physical exercise can reduce these neuromuscular performance and motor deficits; however, the benefits of high-speed resistance training, i.e., power training (PT), an intervention shown to increase power and physical performance in older persons, has yet to be examined in PD patients. PURPOSE: To quantify the effects of PT on UPDRS motor scores, muscular strength and power in PD patients. METHODS: Fourteen patients (9M/5F; H&Y stage: I-III; age: 71.6 ± 6.6 y; weight: 77.8 ± 18.8 kg; height: 1.73 ± .12 m; PD duration: 6.9 ± 4.4 y) enrolled in the program. The Unified Parkinson’s Disease Rating Scale (UPDRS) motor score, 1 repetition maximum (1RM) as a measure of strength and peak power (PP) were tested before and after 3 months of PT. 1RM and PP were tested on 5 pneumatic machines (biceps curl, chest press, leg press, hip abduction and seated calf). PT used 8 wks of high-speed resistance training (twice/week) at established optimal power loads on 11 pneumatic machines (biceps curl, triceps push-down, chest press, seated row, lat pull-down, shoulder press, leg press, leg curl, hip abduction, hip adduction, seated calf) with two 2-wk transitional periods featuring balance and agility training on weeks 5 and 10. Loading was adjusted weekly based on the power plateaus. Subjects had no change in medication or activity levels across the 3-month training period. RESULTS: Significant improvement in UPDRS motor score was seen after training (Meandiff±SE= 11.0±1.1; p<.001). Significant increases (p<.05) in 1RM (kg) and peak power (W) were detected in biceps curl (Meandiff±SE: 1RM=2.31±0.35 kg; PP =14.62±5.70 W), hip abduction (10.66±2.33 kg; 26.38±9.18 W), chest press (3.36±0.61 kg; 45.19±14.23 W), leg press (14.38±3.55 kg; 207.18±39.47 W) and seated calf (31.79±4.79 kg; 51.50±20.65 W). CONCLUSION: A 3-month power training program can improve neuromuscular function and motor performance in older adults with PD and should be considered an important intervention for these patients.

Instrumental Assessment of Bradykinesia: A Comparison Between Motor Tasks.

Bradykinesia, a common symptom in psychiatry, is characterized by reduced movement speed and amplitude. Monitoring for bradykinesia is important, as it has been associated with reductions in quality of life and medication compliance. Subtle forms of bradykinesia have been associated with treatment response in antipsychotic-naïve first episode patients. Therefore, accurate and reliable assessment is of clinical importance. Several mechanical and electronic instruments have been developed for this purpose. However, their content validity is limited. This study investigated which tasks, or combinations thereof, are most suitable for assessing bradykinesia instrumentally. Eleven motor tasks were assessed using inertial sensors. Their capability of distinguishing bradykinetic patients with schizophrenia ( n = 6) from healthy controls ( n = 5) was investigated. Seven tasks significantly discriminated patients from controls. The combination of tasks considered most feasible for the instrumental assessment of bradykinesia was the gait, pronation/supination, leg agility and flexion/extension of elbow tasks (effect size = 2.9).

Manual movement coordination adapted to spinal cord injury and low back pain

Spinal cord injury (SCI) and low back pain (LBP) significantly limit personal and occupational activities. Since upper body movements are crucial to extend hand reach envelopes and maintain postural balance, coordinated control of torso and hand movements is essential. In this study, adapted patterns of coordination were investigated in SCI, LBP and control participants performing seated manual material handling tasks, in which a load was transferred with both hands from a home location to one of 4 targets in the mid-sagittal plane.Torso peak velocities are larger and delayed for the SCI when compared to the control group, while hand peak velocities are comparable. However, hand peak velocities are smaller in the LBP than control group. Hand movements generally precede torso movements for all groups, but more prominently for the SCI than the other groups. Furthermore, for SCIs torso movements were suppressed until the hands were aligned with target elevation.These results indicate that SCI individuals have developed a unique coordination pattern to compensate for their limited balance control, although this strategy may reduce their effective workspace and overload the upper extremities. In contrast, LBPs seem to have reduced movement speed while their coordination patterns are generally similar to those in the control group. Relevance to industryThis study analyzed movements of persons with spinal cord injury or low back pain in manual material handling tasks. Assessing their adapted movement strategies would help to improve workspace design to accommodate workers with limited capacities and to provide quantifiable evidence and guidelines on the effectiveness of occupational rehabilitation programs.

Effect of light quality on movement of Pterostichus melanarius (Coleoptera: Carabidae)

Abstract Behaviour of nocturnal insects is routinely observed under red light, but it is unclear how the behaviour under red light compares to behaviour in complete darkness, or under a source of white light. Here, we measure movement behaviour of the nocturnal carabid beetle Pterostichus melanarius Illiger (Coleoptera: Carabidae) using camera recording under a near‐infrared (nir), red or white radiation source. Red light significantly reduced movement speed in females similar to the effect of white light and different from nir. Also movement activity and pause length were affected by radiation source, with a significant difference between nir and white light, and with intermediate values in red light. The results presented here indicate that P. melanarius has different movement behaviour under the three radiation sources and suggest that nir rather than red radiation is most appropriate for measuring behaviour in total darkness. However, in the field total darkness is rare both because of natural light sources such as the moon and stars but increasingly also because of ecological light pollution, and therefore red light may still be of use for observing ecologically and practically relevant natural night‐time behaviour.

A study of arm movements in Huntington's disease under visually controlled and blindfolded conditions.

The so-called bradykinesia of Huntington's disease (HD) seems not due to reduced movement speed alone but may also be task-dependent. We therefore investigated the influence of visual control on the ability of HD patients to perform a motor task. Ten HD patients, never treated with neuroleptic drugs and with mild functional impairment in activities of daily living, performed the task blindfolded and not blindfolded, as did 10 age- and education-matched healthy controls. The task was to use the dominant hand to trace out the contours of a 20 x 20 cm square in a clockwise direction, pausing at each corner. The square was marked on the table at which the subject sat. Accuracy was stressed rather than speed. A videocamerabased system recorded movement trajectories, from which kinematic and error parameters were derived. Patients and controls moved at comparable speeds but patients took longer to complete the task due to more curvilinear and hence longer trajectories. Patients spent more time in the deceleration phase of the movement, and in the blindfold condition had more variable movements as indicated by greater error variability scores. Correlation analysis showed that kinematic parameters in patients did not correlate with involuntary movement scores. These findings indicate that abnormalities of motor control are present in HD when movement accuracy (and not velocity) is required. HD patients are more dependent on visual control than normal subjects.

Low Elementary Movement Speed Is Associated With Poor Motor Skill in Turner's Syndrome

The article aims to discriminate between 2 features that in principle both may be characteristic of the frequently observed poor motor performance in girls with Turner's syndrome (TS). On the one hand, a reduced movement speed that is independent of variations in spatial accuracy demands and therefore suggests a problem in motor execution. On the other hand, a disproportional slowing down of movement speed under spatial-accuracy demands, indicating a more central problem in motor programming. To assess their motor performance problems, 15 girls with TS (age 9.6-13.0 years) and 14 female controls (age 9.1-13.0 years) were tested using the Movement Assessment Battery for Children (MABC). In additionally, an experimental procedure using a variant of Fitts' graphic aiming task was used to try and disentangle the role of spatial-accuracy demands in different motor task conditions. The results of the MABC reestablish that overall motor performance in girls with TS is poor. The data from the Fitts' task reveal that TS girls move with the same accuracy as their normal peers but show a significantly lower speed independent of task difficulty. We conclude that a problem in motor execution is the main factor determining performance differences between girls with TS and controls.

Leech predation on juvenile freshwater snails: effects of size, species and substrate

The leechGlossiphonia complanata does not appear to have substantial impact on snail populations, but this may be due to most studies focusing on adult snails rather than juvenile snails. In this study I investigated how predation rates ofG. complanata feeding on newly-hatched and juvenile snails was affected by snail species, snail size, snail density and substrate, in a laboratory experiment. Number of snails eaten increased with increasing density resulting in a type II functional response curve. Predation rates were higher when leeches were feeding onLymnaea emarginata than onPhysa gyrina, whereas there was no significant difference in predation rates when they were feeding onL. emarginata andHelisoma anceps. Sandy substrates and greater snail size resulted in decreased predation rates. Sand reduced movement speed ofG. complanata, which probably reduced encounter rates. Thus, there was a comparatively large effect of leech predation on newly-hatched snails, due to a high probability of encounter and high predation rates, but spatial and temporal refuges probably reduce the importance of leech predation as a structuring force in freshwater snail assemblages.