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Bouwien C. M. Smits-Engelsman, Stephan P. Swinnen and Jacques Duysens

It has been shown that crossing the midline affects the performance of fine motor skills but the underlying mechanisms are not well understood. This issue is particularly important with respect to the development of motor activities such as writing or pointing in children. Forty-eight right-handed children performed goal-directed movements toward targets positioned either at the midline, or in the left (contralateral side), or right (ipsilateral) hemispace. Findings revealed that movements were more accurate in ipsilateral than in contralateral space and their overall accuracy increased by 42% between 6 and 10 years of age. Differences in movement time among hemispaces depended on the joints predominantly involved in producing the movements (wrist versus fingers). Lower accuracy of movements in contralateral workspace is also present when participants do not have to cross the midline but only move within this workspace. In motor proficient children, no developmental trends were found for these hemispace effects.

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Bert Steenbergen

The present reaction on the paper of Smeets and Brenner focuses on two premises of their proposed model The first is that grasping is nothing more than pointing with two fingers. It is argued that this assumption cannot be upheld in light of the differences between both actions with respect to neuromuscular structures, muscular innervation, use of visual feedback, and basic function The second premise of the model is that the velocity profile of the transport component is symmetrical and independent of intrinsic object properties. It is shown that the symmetrical velocity profile represents a boundary condition and is influenced by intrinsic object properties. Given these concerns, it is doubtful that the model in its present form will add much to our understanding of the control of grasping.

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Bouwien C.M. Smits-Engelsman, Gerard P. Van Galen and Jacques Duysens

Ninety-four participants (age 5–93 years) performed isometric force production tasks at five different levels of their maximum voluntary contraction (MVC) with either one or two index fingers. Research questions were whether variability measures in the bimanual task condition were different compared to the unimanual condition and whether this difference showed a developmental trend. Results showed that force regulation was more demanding during bimanual tasks (33% increase in error). During development signal-to-noise ratio (SNR) increased threefold from 5–12 years of age and again 60% from 12 years to adulthood. SNR for the elderly was comparable to values of 9 to 10-year-olds. SNR decreased in the bimanual task, particularly for the older persons. For adults and elderly, optimal SNR levels were observed around 36% of their MVC. In younger children, however, the inverted U-shape in the SNR over the full range of forces was not yet present.

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Ida M. Bosga-Stork, Jurjen Bosga and Ruud G.J. Meulenbroek

The development of the ability to adapt one’s motor performance to the constraints of a movement task was examined in a longitudinal study involving 7 to-9-year-old children who were asked to perform a preparatory handwriting task. The capacity for sensorimotor synchronization was captured by the standard deviation of the relative phase between pacing signals and writing movements and the capacity to adjust wrist-finger coordination while performing repetitive movements was analyzed by autocorrelations of the vertical pen-tip displacements. While the capacity for synchronization improved with age, the autocorrelations were positive at short time lags only and hardly changed with age. A measure of “the long-term memory” of time series (Hurst exponent) confirmed that the findings were systematic rather than noise. Collectively, the results indicate that flexible movement strategies emerge early on in the first 3 years of formal handwriting education. Implications for educational and clinical practice are considered.

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Blanka Hejduková, Nasser Hosseini, Bo Johnels, Pall E. Ingvarsson, Goran Steg and Torsten Olsson

During transport of an object using the precision grip with thumb and index finger, a modulation of the grip force is needed in response to the forces evoked by the movement. We measured the grip force (GF) and the load force (LF) in 10 healthy participants moving a 640-g object forward and upward. The task was repeated with various speeds. There were considerable changes with speed of the LF trajectory but not of the GF trajectory. A loss of synergy between GF and LF appeared in fast lifts. This is in contrast to the close coupling between load force and grip force repeatedly demonstrated during simple lifts. We suggest that (a) speed should be considered as an input parameter for movement planning, and (b) regulation of GF and of LF are independent under certain conditions. We discuss whether the grip-load force synergy should be considered a special case rather than a more general principle.

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Marco Rathschlag and Daniel Memmert

The present study examined the relationship between self-generated emotions and physical performance. All participants took part in five emotion induction conditions (happiness, anger, anxiety, sadness, and an emotion-neutral state) and we investigated their influence on the force of the finger musculature (Experiment 1), the jump height of a counter-movement jump (Experiment 2), and the velocity of a thrown ball (Experiment 3). All experiments showed that participants could produce significantly better physical performances when recalling anger or happiness emotions in contrast to the emotion-neutral state. Experiments 1 and 2 also revealed that physical performance in the anger and the happiness conditions was significantly enhanced compared with the anxiety and the sadness conditions. Results are discussed in relation to the Lazarus (1991a, 2000a) cognitive-motivational-relational (CMR) theory framework.

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Joseph P. Stitt and Karl M. Newell

This paper presents the stochastic modeling of isometric force variability in the steady-state time series recorded from the index finger of young adults in the act of attempting to hold different levels of constant force. The isometric force time series were examined by assuming that the stochastic (random) models were linear. System identification techniques were employed to estimate the parameters of each linear model. Once the models were parameterized, the values of the estimated parameters were compared to determine if a single linear time-invariant model was applicable across the entire isometric force range. Although the overall random models were found to be nonlinear functions of the target force level, within a fixed target level, linear modeling provided adequate estimates of the underlying processes thus enabling the use of well-known linear system identification algorithms.

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Claudia Voelcker-Rehage and Ben Godde

We examined the effect of high frequency tactile stimulation (tHFS) on tactile and motor performance as well as tactile-motor interactions. Seventeen right-handed participants (66–78 years) underwent a pretest (tactile frequency and spatial discrimination task, manual dexterity test, and precision grip task) with their left hand, received 30 min of tHFS on the tips of their left index finger and thumb, and performed a posttest (control group: no stimulation). Results indicated an improvement in frequency and spatial discrimination in the experimental but not the control group. In the precision grip task, however, training effects as found for the control group seem to be blocked in the experimental group. For the manual dexterity task no effect was found. Our data indicate that tHFS positively influences tactile performance. Assuming tHFS-induced plastic reorganization in somatosensory cortex our results give further evidence to the notion of an interrelation between sensory and motor performance.

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Werner W.K. Hoeger, David R. Hopkins, Sherman Button and Troy A. Palmer

This study compared the proposed modified sit and reach test (MSR) and the commonly administered sit and reach test (SR) to determine if the MSR can administratively control possible limb-length biases. Subjects (N=258) were administered two trials of each test. The MSR test incorporates a finger-to-box distance (FBD) to account for proportional differences between legs and arms. Individuals with high FBD measurements demonstrated a poorer performance on the SR test. An analysis of the subjects failing to meet the Physical Best standard (25 cm) indicated a higher probability of failure for those with larger FBD scores. The subjects were subsequently separated into three groups: high, medium, and low FBD. There were no significant difference among the groups on MSR performance but a significant difference was found on SR performance. The MSR test appears to eliminate the concern of disproportionate limb-length bias expressed by many practitioners.

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L.R. McNaughton, R.J. Lovell, J. Siegler, A.W. Midgley, L. Moore and D.J. Bentley

Purpose:

The purpose of this work was to determine the effects of caffeine on high intensity time trial (TT) cycling performance in well-trained subjects.

Subjects:

Six male cyclists with the following physical characteristics (mean ± SD) age 30.7 ± 12, height 179.3 ± 7.5 cm, mass 70.0 ± 7.5 kg, VO2max 65.0 ± 6.3 mL·kg−1·min−1 undertook three 1-h TT performances, control (C), placebo (P) and caffeine (CAF), on a Velotron cycle ergometer conducted in a double-blind, random fashion. Subjects rested for 60 min and were then given CAF or P in a dose of 6 mg·kg−1 body mass and then commenced exercise after another 60 min of rest. Before ingestion, 60 min postingestion, and at the end of the TT, finger-prick blood samples were analyzed for lactate.

Results:

The cyclists rode significantly further in the CAF trial (28.0 ± 1.3 km) than they did in the C (26.3 ± 1.5 km, P < .01) or P (26.4 ± 1.5 km, P < .02) trials. No differences were seen in heart rate data throughout the TT (P > .05). Blood lactate levels were significantly higher at the end of the trials than either at rest or postingestion (P < .0001), but there were no differences between the three trial groups.

Conclusion:

On the basis of the data, we concluded that performance was improved with the use of a caffeine supplement.