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M.J.M. Volman and Reint H. Geuze

The stability of single and bimanual (i.e., in-phase and antiphase) rhythmic finger movements was studied in 24 children with a developmental coordination disorder (DCD) and 24 matched controls from a dynamic pattern perspective. Stability was assessed by applying perturbations and measuring the time the system needed to return to its initial stability (i.e., the relaxation time). In addition, fluctuations of the patterns were measured. For antiphase coordination patterns, the frequency at which loss of stability occurred was also determined. Children with DCD displayed less stable single and bimanual rhythmic coordination patterns than control children. Further, within the DCD group, 9 children were identified as having particularly poor bimanual coordination stability. Individual differences suggested that variability of individual limb oscillations might have contributed to this poorer interlimb coordination stability. Findings were discussed in relation to a previous study on DCD in which the Wing-Kristofferson timekeeper model was applied.

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S. Morrison, Murray G. Tucker and Rod S. Barrett

This study examined changes in movement variability, coupling, and muscle activity across three different bilateral finger movements (e.g., postural, isometric, and isotonic). It was predicted that movements characterized by increased interlimb coupling would be associated with increased levels of muscle activity and reduced movement variability. The results demonstrated task-specific differences in interlimb relations with coupling being lowest during postural tasks and highest under isotonic conditions. However, a similar pattern was not observed for muscle activity and movement variability. Of the three tasks, postural tremor movements were more variable and had lower levels of muscle activity. Alternatively, increased muscle activity and more regular movement dynamics were seen under isometric conditions. Overall, it would appear that differences in bilateral coupling across tasks are not reflective of a single driving mechanism but rather reflect differential contribution from intrinsic neuromuscular and mechanical sources.

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Beatriz H. Thames and Stacey L. Gorniak

have indicated that persons with type II diabetes also exhibit subtle motor function changes of the fingers. 14 – 16 Patients with type II diabetes are known to be susceptible to skin changes including tactile impairment, vascular compromise, and dry skin. Recent data also indicates that tactile

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Dennis A. Nowak, Joachim Hermsdörfer and Helge Topka

Amyotrophic lateral sclerosis is a degenerative motor neuron disorder with progressive and exclusive loss of motor neurons in the spinal cord, brainstem, and motor cortex. Five patients with amyotrophic lateral sclerosis, and 5 age-matched, healthy control subjects performed vertical point-to-point arm movements with an instrumented hand-held object. In between the movements, the object was held stationary. Compared with healthy controls, all patients generated greater grip forces during the phase of stationary holding of the object and greater ratios between grip and load force maximums during the arm movements. We conclude that in amyotrophic lateral sclerosis, the ability to scale the grip force magnitude efficiently according to the actual loading requirements is impaired. When performing upward movements, controls increased grip force in parallel with load force right from the movement onset; during downward movements, controls anticipated an early decrease of load force by constant or decreasing grip forces. In contrast, 3 of 5 patients showed an early increase of grip force during both upward and downward movements, indicating that in amyotrophic lateral sclerosis, the differential regulation of the grip force output according to the direction-dependent load force profile may be impaired. In motor neuron disease, the inaccurate grip force scaling and the impaired temporal coupling between grip and load force profiles may either directly result from deficient motor execution or be secondary to accompanying symptoms, such as dyscoordination of hand and finger muscles due to spasticity.

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Nobuyuki Inui and Yumi Katsura

We conducted an experiment to examine age-related differences in the control of force and timing in a finger-tapping sequence with an attenuated-force tap. Participants between 7 and 20 years old tapped on a load cell with feedback on practice trials. They were required to recall the force pattern (300 g, 300 g, 300 g, 100 g) and the intertap interval (400 ms) without feedback on test trials. Analysis indicated that the last attenuated tap affected the first three taps of the tapping sequence in adults and adolescents but not in children. Adults and adolescents appeared to respond with four taps as a chunk, resulting in a contextual effect on the timing of force control, but younger children had difficulty with such chunking. Further, adults and adolescents were able to more accurately produce individual force magnitudes to match target magnitudes than younger children. For the ratio of force in serial positions 1:4, 2:4, and 3:4, consequently, 7- to 8-year-old children had lower ratios than the other age groups. Although there was no difference among age groups for timing control of peak force to press duration as a control strategy of force, 7- to 8-year-old children spent more time to produce force than the other age groups. Peak force with a decreased force was more variable in the attenuated force serial position (4) than in the other serial positions in all five age groups. Peak force variability was particularly robust in younger children. These findings suggest that younger children have difficulty with both temporal and spatial (i.e., magnitude) components of force control.

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Veena Iyengar, Marcio J. Santos and Alexander S. Aruin

We investigated whether slower velocity of arm movement affects grip-force generation in conditions with the finger touch provided to the wrist of the target arm. Nine subjects performed the task of lifting and transporting an object at slow, intermediate, and fast velocities with a light finger touch from the contralateral arm and without it. There was an effect of velocity of arm movement on grip-force generation in both conditions. However, when the no touch and touch trials performed with similar velocity were matched, the effect of touch on grip-force reduction was statistically significant (p < .001). The observed decrease in grip force could not be explained by slower movement execution in the touch conditions and underlines the importance of using a contralateral touch in the performance of activities of daily living. It also points to a possibility of the development of therapeutic advances for the enhancement of grip-force control in patients with neurological impairments.

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Nobuyuki Inui

An experiment was conducted to examine contextual effects of the magnitude of changes in force on force control in a finger-tapping sequence with an accentuated- (accentuated-force condition) or attenuated-force tap (attenuated-force condition). Participants were trained to produce a finger-tapping sequence with an intertap interval of 500 ms and four force patterns. During practice, visual force feedback pertaining to the two target forces in the tapping sequences was provided. After practice, the participants reproduced the learned tapping sequences in the absence of feedback. A main result was that the last accentuated-force tap affected the first three taps of the tapping sequence. For the accentuated-force conditions, the larger the difference between the first three target forces and the last target force, the larger the first three forces. This indicates the contextual effect of serial position for force control. This effect was not observed, however, under the attenuated-force conditions.

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Nobuyuki Inui and Takuya Ichihara

To examine the relation between timing and force control during finger tapping sequences by both pianists and nonpianists, participants lapped a force plate connected to strain gauges. A series of finger tapping tasks consisted of 16 combinations of pace (intertap interval: 180. 200, 400. or 800 ms) and peak force (50, 100. 200. or 400 g). Analysis showed that, although movement timing was independent of force control under low or medium pace conditions, there were strong interactions between the 2 parameters under high pace conditions. The results indicate that participants adapted the movement by switching from separately controlling these parameters in the slow and moderate movement to coupling them in the fast movement. While variations in intertap interval affected force production by nonpianists. they had little effect for pianists. The ratios of time-to-peak force to press duration increased linearly in pianists but varied irregularly in nonpianists, as the required force decreased. Thus, pianists regulate peak force by timing control of peak force to press duration, suggesting that training affects the relationship between the 2 parameters.

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Waneen W. Spirduso, Britta G. Schoenfelder-Zohdi, Jonghwan Choi and Susan M. Jay

This study investigated age-related differences in tapping speed with respect to warm-up and fatigue effects and also with respect to task complexity. An additional purpose was to determine the site of age-related slowing in stationary tapping. Adult females from three different age groups were asked to tap as fast as possible for 25 s with a specified digit combination by depressing microswitches on one or two metal boxes that were mounted on a data acquisition board. All groups showed a warm-up period during the first block, reached their peak tapping speed during the second block, and then gradually fatigued, as indicated by a decreasing number of taps. These findings suggest that to assess true tapping speed, a trial should not last more than 15 s, or the results may be confounded by fatigue effects. It was found that tapping with the thumb and index finger simultaneously is more difficult than tapping with one or both index fingers, regardless of age.

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Jon Almquist