Throwing accuracy in the vertical direction during prism adaptation: not simply timing of ball release.
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In a previous study, others have hypothesized that the variance in vertical errors that occurs while throwing at visual targets is caused by changes in any of three throw parameters: hand location in space, hand translational velocity, and hand orientation. From an analysis of skilled throwers, those authors concluded that vertical error is best correlated with variance in hand orientation, which in turn is related to the timing of ball release. We used a vertical prism adaptation paradigm to investigate which of these throwing parameters subjects use when adapting to external perturbation. Our subjects showed no correlation between hand position or hand translational velocity and ball impact height in normal, over-practiced throwing. However, video-based motion analysis showed that modifications both of position and speed of the hand play an important role when subjects are forced to compensate for a vertically shifting prism perturbation during a dart-like throw (these factors contribute approximately 30% of the adaptation). We concluded that, during adaptation, more degrees of freedom and more sources of potential error are modified to achieve the gaze-throw recalibration required to hit the target than are employed in this type of throw during normal conditions. (+info)
Survey of joint mobility and in vivo skin elasticity in London schoolchildren.
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A survey of joint mobility was conducted in 295 healthy children between the ages of 5 and 10 years who attended a London primary school. Estimates of the commonly used measurements, that is passive dorsiflexion of the wirsts and ankles, passive hypertension of the elbows and knee, were too insensitive to detect any age effect. However, a method of estimating extensibility of the 5th metacarpophalangeal joint in response to a standard load detected a highly significant inverse correlation between joint mobility and age in the samples significant inverse correlation between joint mobility and age in the samples tested ( r = -0.586; P less than 0.0001). There was no apparement sex difference. Skinfold thickness using the Harpenden caliper over the 3rd metacarpal bone and the in vivo skin elasticity measured using a suction cup device performed on a sample of 78 of the children revealed no influence of either age or sex on these parameters. This is in sharp contradistinction to the effect of both age and sex in these two parameters in adults... (+info)
Biometric study of the relationships between palmar neurovascular structures, the flexor retinaculum and the distal wrist crease.
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During surgical exposure of the carpal tunnel it is possible to injure the neurovascular structures closely related to the flexor retinaculum, such as the superficial palmar arch and the communicating branch between the ulnar and median nerves. Because of the importance of these structures and with the purpose of increasing knowledge of anatomical details concerning to their location, a biometric study was performed on the retinaculum and the communicating branch, and between the communicating branch and the distal wrist crease, as well as between the retinaculum and the superficial palmar arch. We dissected 56 hands from 28 Brazilian formalin-preserved cadavers of both sexes (24 male) at the Federal University of Sao Paulo-Escola Paulista de Medicina, Brazil. The communicating branch was observed in 96.4% of cases and the superficial palmar arch in 78.6%. The communicating branch was found between the common palmar digital nerve of the 4th interosseous space (from the ulnar nerve) to the homonymous nerve of the 3rd interosseous space (from the median nerve). In males, the distance between the distal wrist crease and the site where the communicating branch originates from the ulnar component had an average of 33.9 +/- 5.5 mm on the right side and 30.2 +/- 8.2 mm on the left. The distance between the distal wrist crease and the junction of the communicating branch with the common palmar digital nerve of the 3rd interosseous space was 43.6 +/- 6.9 mm on the right and 40.2 +/- 6.2 mm on the left side. Conversely, in 14.8% of cases (1 female), the communicating branch was observed to emerge from the common palmar digital nerve of the 3rd interosseous space. The distance between the retinaculum and the superficial palmar arch in the axial line of the 4th metacarpal bone was on average 7.3 +/- 4.3 mm on the right and 8.3 +/- 3.5 mm on the left side. At the same level, the distance between the retinaculum and the communicating branch was 6.2 +/- 3.7 mm on the right side and 5.1 +/- 2.8 mm on the left. These results can be used as a reference during surgical procedures in the palmar region. (+info)
Vitamin D status after resection of ileum in childhood.
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Serum 25-hydroxycholecaliciferol levels and x-rays of the wrist were normal in children who had had extensive resections of ileum and no supplementary vitamin D for considerable periods. These results suggest that normal vitamin D status occurs in the absence of the ileum and that supplementary vitamin D is unnecessary. (+info)
Changes in intracortical excitability induced by stimulation of wrist afferents in man.
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1. Inhibitory and facilitatory neuronal circuits may be explored in the human motor cortex by double pulse transcranial magnetic stimulation (TMS). At short interstimulus intervals (2-5 ms), conditioned motor-evoked potentials (MEPs) are reduced (intracortical inhibition, ICI), whereas they are facilitated at longer interstimulus intervals (8-25 ms; intracortical facilitation, ICF). The aim of this study was to investigate the effects of homonymous and antagonist nerve stimulation on the intracortical inhibition and facilitation in the cortical areas that control the wrist extensor and flexor radialis muscles. 2. Sixteen subjects were asked to contract either their wrist extensor or flexor muscles. The MEP evoked by a test TMS (at 1.2 x MEP threshold) and recorded in the target muscle was then conditioned by subthreshold TMS (at 0.8 x MEP threshold) 2 and 14 ms before the test TMS. The median and radial nerves were stimulated at 0.8 x motor threshold (MT). 3. In both flexor and extensor muscles, antagonist nerve stimulation 40 ms before the test TMS decreased ICI and increased ICF. In contrast, homonymous nerve stimulation had no effect on ICI and ICF. 4. The intensity of the antagonist nerve stimulation required to alter ICI and ICF was as low as 0.6 x MT, which suggests that thick diameter afferents may be involved. The nerve stimulation had to be applied 35-45 ms prior to the test TMS to alter significantly the intracortical excitability. 5. Cutaneous afferents were probably not responsible for the alterations of intracortical excitability, since cutaneous stimulation had no effect on either ICI or ICF at the investigated intervals. 6. The present data suggest that antagonist muscular afferent inputs may evoke reciprocal facilitation or disinhibition at the cortical level. This pattern of antagonist sensory afferent effects may be of significance for control of the wrist extensor and flexor muscles when used as synergists during manipulatory finger movements and gripping tasks. (+info)
Human motor control consequences of thixotropic changes in muscular short-range stiffness.
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1. The primary aim of the present study was to explore whether in healthy subjects the muscle contractions required for unrestrained voluntary wrist dorsiflexions are adjusted in strength to thixotropy-dependent variations in the short-range stiffness encountered in measurements of passive torque resistance to imposed wrist dorsiflexions. 2. After a period of rest, only the first movement in a series of passive wrist dorsiflexions of moderate amplitude exhibited clear signs of short-range stiffness in the torque response. During analogous types of voluntary movements, the extensor EMG during the first movement after rest showed a steep initial rise of activity, which apparently served to compensate for the short-range stiffness. 3. The passive torque resistance to minute repetitive wrist dorsiflexions (within the range of short-range stiffness) was markedly reduced after various types of mechanical agitation. During analogous low-amplitude voluntary wrist dorsiflexions the extensor EMG signals were weaker after than before agitation. 4. Mechanical agitation also led to enhancement of passive dorsiflexion movements induced by weak constant torque pulses. In an analogous way, the movement-generating capacity of weak voluntary extensor activations (as determined by EMG recordings) was greatly enhanced by mechanical agitation. 5. The signals from a force transducer probe pressed against the wrist flexor tendons--during passive wrist dorsiflexions--revealed short-range stiffness responses which highly resembled those observed in the torque measurements, suggesting that the latter to a large extent emanated from the stretched, relaxed flexor muscles. During repetitive stereotyped voluntary wrist dorsiflexions, a close correspondence was observed between the degree of short-range stiffness as sensed by the wrist flexor tension transducer and the strength of the initial extensor activation required for movement generation. 6. The results provide evidence that the central nervous system in its control of voluntary movements takes account of and compensates for the history-dependent degree of inherent short-range stiffness of the muscles antagonistic to the prime movers. (+info)
Associations between hand-wrist musculoskeletal and sensorineural complaints and biomechanical and vibration work constraints.
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A 3-year prospective epidemiological study was conducted to investigate the relationship between musculoskeletal complaints (MS) and sensorineural complaints (SN) of the workers in the hand-wrist region. A group of 69 workers (G1) using vibrating tools in eight different working situations was compared to a group of 62 workers (G2) performing heavy work without vibration and 46 workers (G3) performing light work without vibration. Biomechanical constraints (force, postures, repetitiveness and movement velocities) were analysed for each working situation and the vibration exposure at the eight workplaces with the 69 workers. MS and SN data were collected using the nordic questionnaire, modified to collect information about the frequency intensity and duration of complaints. The prevalence of complaints at the start of the study was significantly greater for G1 (72.5%) than for G2 (56.5%), itself greater than for G3 (30.4%). The prevalence of SN was about 40% for G1 and 2.5 times smaller in the two other groups. During the two years follow-up, new cases of 'serious' MS and SN developed. The annual incidence was respectively 8.3 and 5.4% on average. The incidence of MS was slightly but not statistically significantly greater for G1, while the incidence of SN was statistically higher (P<0.01) for G1 (10.9%) than for the two other groups (4.1 and 2.1%). Forces and angular repetitiveness were the only biomechanical factors significantly greater for G1. The vibration exposure duration of the G1 workers varied, in average, from 10 to 70% of the work time and the weighted personal exposure amplitude (A(EPw)) varied from 0.5 to 25.4 ms(-2). The probabilities of complaints at the beginning of the study (cross-sectional study) were estimated using multiple logistic regression models. The prevalence odds ratio (POR) for MS was equal to 4 for G1 compared to G2 and equal to 9 compared to G3. Force and vibration exposure were the main constraint parameters associated with this likelihood. As far as the SN are concerned, G2 and G3 were not statistically different, but the POR for the G1 workers was 4.5 compared to both groups. The most significant constraint factor was the weighted personal exposure acceleration. The same procedure was used to estimate the likelihood of development of 'serious' complaints (longitudinal study). The three groups did not appear significantly different concerning the 'serious' MS, while the incidence odds ratio (IOR) of 'serious' SN was very high (28.5) and significantly greater for G1 than for the two other groups. The likelihood of development of 'serious' SN increased with A(EPw). According to this prediction model, the risk of 'serious' SN would be about 6% at the proposed European 'action' value (2.5 ms(-2)) and about 10% at the 'limit' value (5 ms(-2)). (+info)
Increased synchronization of cortical oscillatory activities between human supplementary motor and primary sensorimotor areas during voluntary movements.
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In human, both primary and nonprimary motor areas are involved in the control of voluntary movements. However, the dynamics of functional coupling among different motor areas has not been fully clarified yet. Because it has been proposed that the functional coupling among cortical areas might be achieved by the synchronization of oscillatory activity, we investigated the electrocorticographic coherence between the supplementary motor and primary sensorimotor areas (SMA and S1-M1) by means of event-related partial coherence analysis in 11 intractable epilepsy patients. We found premovement increase of coherence between the SMA proper and S1-M1 at the frequency of 0-33 Hz and between the pre-SMA and S1-M1 at 0-18 Hz. Coherence between the SMA proper and M1 started to increase 0.9 sec before the movement onset and peaked 0.3 sec after the movement. There was no systematic difference within the SMA (SMA proper vs pre-SMA) or within the S1-M1, in terms of the time course as well as the peak value of coherence. The phase spectra revealed near-zero phase difference in 57% (20 of 35) of region pairs analyzed, and the remaining pairs showed inconsistent results. This increase of synchronization between multiple motor areas in the preparation and execution of voluntary movements may reflect the multiregional functional interactions in human motor behavior. (+info)