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Talyene G.C. Corrêa, Stephanie V.S. Donato, Kauê C.A. Lima, Ronaldo V. Pereira, Mehmet Uygur and Paulo Barbosa de Freitas

The ability to produce muscle force rapidly (i.e., neuromuscular quickness) is an important feature of the human motor repertoire. Self-initiated rapid movements are clearly necessary in some sports actions and, occasionally, in daily activities (e.g., catching a fly, deviating from a moving object

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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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Paavo V. Komi

To understand cross-country (X-C) siding it is important to record and identity forces of skis and poles separately and together. They both contribute to the forward progression, but their functional significance may be more complex than that of the ground reaction forces in running and walking. This report presents two methods to record forces on skis and poles during normal X-C skiing. A long force-platform system with four rows of 6-m long plates is placed under the snow track for recording of Fz and Fy forces of each ski and pole separately. This system is suitable especially for the study of diagonal technique under more strict experimental conditions. The second system consists of small lightweight Fz and Fy component force plates which are installed under the boot and binding. These plates can be easily changed from one ski to another, and telemetric recording allows free skiing over long distances and with different skiing techniques, including skating. The presentation emphasizes the integrated use of either system together with simultaneous cinematographic and electromyographic recordings.

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Marco J. Konings, Jordan Parkinson, Inge Zijdewind and Florentina J. Hettinga

and by relating these to neuromuscular adjustments in the knee extensors and perceived exertion. We hypothesized that the presence of a virtual opponent would invite a change in pacing and evoke an improvement in performance, leading to a greater decline in voluntary muscle force after a 4-km TT than

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Jefferson W. Streepey, M. Melissa Gross, Bernard J. Martin, Sundravalli Sudarsan and Catherine M. Schiller

The relationship between playing surface and muscle fatigue was examined in 22 male subjects performing a simulated basketball task on a conventional wood floor and less stiff composite floor. Force and electromyographic activity (EMG) were measured during maximum and submaximum (10% of maximum) voluntary contractions of knee extensor and ankle plantarflexor muscles before and after completion of the simulated basketball task. Jump height was evaluated during the task, and perceived fatigue was assessed at the end of the task. Although not all subjects jumped significantly higher on the composite floor compared to the wood floor. competitive basketball players showed a significant improvement in jump height (3.4 cm. 6%) when jumping on the composite floor. Perceived fatigue was significantly lower for the composite floor (21.7%) than the wood floor (30.2%). The objective measures indicated the occurrence of fatigue; however, force and EMG magnitudes obtained during maximum exertions were not sensitive lo floor types. Post-task increase in EMG magnitude indicated a significant fatigue effect for the soleus muscle on the wood floor only. These findings suggest that the composite floor may benefit human performance without increasing fatigue during basketball-related activities.

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Robert W. Meyers, Jon L. Oliver, Michael G. Hughes, Rhodri S. Lloyd and John B. Cronin

Purpose:

The aim of this study was to examine the influence of age and maturation upon magnitude of asymmetry in the force, stiffness and the spatiotemporal determinants of maximal sprint speed in a large cohort of boys.

Methods:

344 boys between the ages of 11 and 16 years completed an anthropometric assessment and a 35 m sprint test, during which sprint performance was recorded via a ground-level optical measurement system. Maximal sprint velocity, as well as asymmetry in spatiotemporal variables, modeled force and stiffness data were established for each participant. For analysis, participants were grouped into chronological age, maturation and percentile groups.

Results:

The range of mean asymmetry across age groups and variables was 2.3–12.6%. The magnitude of asymmetry in all the sprint variables was not significantly different across age and maturation groups (p > .05), except relative leg stiffness (p < .05). No strong relationships between asymmetry in sprint variables and maximal sprint velocity were evident (rs < .39).

Conclusion:

These results provide a novel benchmark for the expected magnitude of asymmetry in a large cohort of uninjured boys during maximal sprint performance. Asymmetry in sprint performance is largely unaffected by age or maturation and no strong relationships exist between the magnitude of asymmetry and maximal sprint velocity.

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Lars Janshen, Klaus Mattes and Günter Tidow

In sweep-oar rowers, asymmetrical force production of the legs is a known phenomenon. The purpose of this study was to investigate the muscular activity of the legs that may cause this asymmetry even when oarsmen perform a symmetrical endurance task. Seven male young elite oarsmen performed an all-out 2000-m test on a rowing ergometer. During stroke kinematics, myoelectric activity of six muscles of each leg and pressure distribution under both feet were measured. Data were collected over two 30-s time windows starting 1 and 5 min after the test started. No significant differences were observed between legs and time windows for the range of motion of the hip, knee, and ankle joint as well as for the onset/offset timing of muscles. However, in the drive phase, the knee and hip muscles of the leg on the oar side (inside leg) showed 20–45% (both p < .05) higher activation intensities compared with the leg opposite the oar (outside leg). Corresponding to this, 56–91% (both p < .05) higher mean pressure values under the ball of the inside foot compared with the outside foot indicated an asymmetrical force production of the legs even under kinematically symmetrical working conditions.

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Travis J. Peterson, Rand R. Wilcox and Jill L. McNitt-Gray

Our aim was to determine how skilled players regulate linear and angular impulse while maintaining balance during the golf swing. Eleven highly-skilled golf players performed swings with a 6-iron and driver. Components contributing to linear and angular impulse generated by the rear and target legs (resultant horizontal reaction force [RFh], RFh-angle, and moment arm) were quantified and compared across the group and within a player (α = .05). Net angular impulse generated by both the rear and target legs was greater for the driver than the 6-iron. Mechanisms used to regulate angular impulse generation between clubs varied across players and required coordination between the legs. Increases in net angular impulse with a driver involved increases in target leg RFh. Rear leg RFh-angle was maintained between clubs whereas target leg RFh became more aligned with the target line. Net linear impulse perpendicular to the target line remained near zero, preserving balance, while net linear impulse along the target line decreased in magnitude. These results indicate that the net angular impulse was regulated between clubs by coordinating force generation of the rear and target legs while sustaining balance throughout the task.

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Tobias Kalenscher, Karl-Theodor Kalveram and Jürgen Konczak

This study investigated force adaptation in humans during goal-directed flexion forearm motion. The ability of the motor system to adapt to changes in internal or external forces is essential for the successful control of voluntary movement. In a first experiment, we examined how under- or overdamping differentially affected the length of the adaptation and the arm kinematics between force transitions. We found that transitions diverging from a null-force produced larger transition effects than transitions converging to a null force condition, indicating that re-adaptation was less error-prone. Whether the subjects had previously experienced underdamping or the null-force had no significant impact on the spatial trajectory after switching to overdamping. That is, prior force experience had no differential effect on the spatial transition kinematics. However, the transitions underdamping-to-overdamping and underdamping-to–null force did produce differently strong transition effects. These results indicate that exposure to the new force rather than previous force-field experience is responsible for transition- and after-effects. In a second experiment, we investigated whether learning was law-like—that is, whether it generalized to unvisited workspace. Subjects were tested in new, unvisited workspaces in the null-force condition after sufficient training in either force condition. The occurrence of transferred after-effects indicated that adaptation to both positive and negative damping was mediated by rule-based rather than exclusive associative processes.

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Alexander W. Hooke, Sohit Karol, Jaebum Park, Yoon Hyuk Kim and Jae Kun Shim

The purpose of this study was to investigate central nervous system (CNS) strategies for controlling multifinger forces during a circle-drawing task. Subjects drew 30 concentric, discontinuous clockwise and counter clockwise circles, at self and experimenter-set paces. The three-dimensional trajectory of the pen’s center of mass and the three-dimensional forces and moments of force at each contact between the hand and the pen were recorded. Uncontrolled Manifold Analysis was used to quantify the synergies between pen-hand contact forces in radial, tangential and vertical directions. Results showed that synergies in the radial and tangential components were significantly stronger than in the vertical component. Synergies in the clockwise direction were significantly stronger than the counterclockwise direction in the radial and vertical components. Pace was found to be insignificant under any condition.