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Josje van Houwelingen, Sander Schreven, Jeroen B.J. Smeets, Herman J.H. Clercx and Peter J. Beek

In this paper, a literature review is presented regarding the hydrodynamic effects of different hand and arm movements during swimming with the aim to identify lacunae in current methods and knowledge, and to distil practical guidelines for coaches and swimmers seeking to increase swimming speed. Experimental and numerical studies are discussed, examining the effects of hand orientation, thumb position, finger spread, sculling movements, and hand accelerations during swimming, as well as unsteady properties of vortices due to changes in hand orientation. Collectively, the findings indicate that swimming speed may be increased by avoiding excessive sculling movements and by spreading the fingers slightly. In addition, it appears that accelerating the hands rather than moving them at constant speed may be beneficial, and that (in front crawl swimming) the thumb should be abducted during entry, catch, and upsweep, and adducted during the pull phase. Further experimental and numerical research is required to confirm these suggestions and to elucidate their hydrodynamic underpinnings and identify optimal propulsion techniques. To this end, it is necessary that the dynamical motion and resulting unsteady effects are accounted for, and that flow visualization techniques, force measurements, and simulations are combined in studying those effects.

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Jérémy Rossi, Benjamin Goislard De Monsabert, Eric Berton and Laurent Vigouroux

The objectives of this study were to investigate the effect of handle shape on the grip force distribution in the hand and on the muscle forces during maximal power grip tasks. Eleven subjects maximally grasped 3 handles with different external shapes (circular, elliptic, and double-frustum). A handle dynamometer, equipped with both a force sensor and a pressure map, was used to record the forces exerted at the hand/handle interface. The finger and wrist joint postures were also computed from synchronized kinematic measurement. These processed data were then used as input of a biomechanical hand model to estimate muscle forces. The results showed that handle shape influences the maximal grip force, the grip force distribution, and the finger joint postures. Particularly, we observed that the elliptical shape resulted in a 6.6% lower maximal grip force compared with the circular and double-frustum handle. Concomitantly, the estimated muscle forces also varied significantly according to the handle shape, with up to 48% differences for the flexor digitorum superficialis muscle for example. Interestingly, different muscle coordination strategies were observed depending on the handle shape, therefore suggesting a potential influence of these geometrical characteristics on pathological risks such as tendonitis.

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Tarkeshwar Singh, Vladimir M. Zatsiorsky and Mark L. Latash

The effects of muscle fatigue on the stability of precision grasps are not well known. The purpose of the current study was to investigate the effects of exercise-induced fatigue of a digit on prehension synergies in a static precision grasp. One group of participants performed the fatiguing exercise using the thumb (group-thumb) and the second group performed the exercise using the index finger (group-index). Grasp force and load-resisting force-stabilizing synergies were weaker during fatigue for group-thumb and showed no significant change for group-index. These results indicate that fatiguing the thumb compromises the stability of the precision grasp more than when the index finger is fatigued. Our results support the idea of hierarchical organization of prehension control. We proffer an explanation of our results based on two control constructs: a) Principle of superposition. This principle states that prehension can be viewed as a superposition of two independent processes controlling the slip and the tilt of the object respectively; and b) The referent configuration hypothesis. According to this hypothesis, the neural control of actions is associated with defining a set of referent values for task-related coordinates (given an external force field) defined as the referent configuration.

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Jacob J. Sosnoff, Sae Young Jae, Kevin Heffernan and Bo Fernhall

The purpose of the current investigation was to examine the relation between cardioballistic impulse and the fluctuations in continuous isometric force production. Subjects produced isometric force via index finger flexion to constant force targets (0.5, 1 and 2 N) with and without visual feedback while beat to beat blood pressure of their middle finger was recorded. Force fluctuations were quantified using distributional statistics. The association between blood pressure oscillations and fluctuations in force output were quantified with coherence analysis. Overall, it was found that force variability (i.e., SD) increased with force level and removal of visual feedback. Coherence values between blood pressure oscillations and force fluctuations were significant and the greatest in the 8–12 Hz bandwidth. There was no effect of force magnitude on the coupling strength between blood pressure oscillations and force production. This coupling was greater in the visual condition. These data suggest that peripheral alterations in blood pressure are related to fluctuations in isometric force production independent of force level and that this interaction is influenced by visual feedback.

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Justin W.L. Keogh, Steve Morrison and Rod Barrett

The current study investigated the effect of 2 different types of unilateral resistance training on the postural tremor output of 19 neurologically healthy men age 70–80 yr. The strength- (n = 7) and coordination-training (n = 7) groups trained twice a week for 6 wk, performing dumbbell biceps curls, wrist flexions, and wrist extensions, while the control group (n = 5) maintained their normal activities. Changes in index-finger tremor (RMS amplitude, peak, and proportional power) and upper limb muscle coactivation were assessed during 4 postural conditions that were performed separately with the trained and untrained limbs. The 2 training groups experienced significantly greater reductions in mean RMS tremor amplitude, peak, and proportional tremor power 8–12 Hz and upper limb muscle coactivation, as well as greater increases in strength, than the control group. These results further demonstrate the benefits of resistance training for improving function in older adults.

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Kathye E. Light and Waneen W. Spirduso

Unlike stimulus–response compatibility, which has been explored for aging effects, the motor behavior issue of response–response (R–R) compatibility has not been addressed in the gerontological literature. R–R compatibility refers to the ease with which two responses can be prepared together either simultaneously or as choice alternatives. In the present study, young, middle-aged, and elderly adult female subjects were tested in a two-choice reaction-time (RT) paradigm involving four types of finger movements paired in every possible choice combination, creating different levels of R–R compatibility. Significant age differences increased as R–R compatibility decreased. The practical significance of this study is to establish R–R compatibility as an important factor influencing task difficulty to which older adults are particularly sensitive and to encourage recognition of this factor when prescribing progressive motor-skill training in elderly clients.

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Michael S. Ferrara and William E. Buckley

The Athletes With Disabilities Injury Registry (ADIR) was designed to collect and analyze injury data from 1990 to 1992. Three hundred nineteen athletes from different disability organizations participated, and 128 reportable injuries were recorded. The injury rate during the study period was 9.45/1,000 athlete-exposures. Overall, 52% of the reported injuries were minor (0–7 days missed), 29% were moderate (8–21 days missed), and 19% were major (22 or more days missed). The shoulder and forearm/wrist accounted for the most days lost, followed by the hand/fingers and the upper arm/elbow. Musculoskeletal injuries accounted for 81 % of the reported injuries, and illness or disability-related problems accounted for 19%. Fifteen percent of the moderate and major injuries were not medically evaluated. This raises questions about access to medical care and the appropriate recognition of an injury. Injury prevention programs should focus on reducing the number of major injuries and educating athletes and coaches about appropriate medical referrals.

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Takashi Kinugasa, Hiroshi Nagasaki, Taketo Furuna and Hajime Itoh

The goal of this study was to identify methods for characterizing high-functioning older adults living in the community. The subjects were 495 older adults from the Longitudinal Interdisciplinary Study on Aging conducted by the Tokyo Metropolitan Institute of Gerontology. Physical performance measures included grip strength, walking at preferred and maximum speeds, one-leg standing with eyes open, and finger tapping rate. Performance scores were created by summing each categorical score. Consistent differences were found among age groups and genders. Scores were lower in subjects who had stroke or diabetes than in those without these conditions. These results suggest that physical performance measures have both discriminant validity and construct validity, which make them useful methods for characterizing high-functioning older persons.

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Weiyun Chen, Inez Rovegno, John Todorovich and Matt Babiarz

The purpose of this study was to describe third grade children’s movement responses to dribbling tasks taught by four accomplished teachers and how children’s dribbling varied with changes in task constraints. Children in four intact classes were videotaped during three dribbling lessons as part of their physical education program. Videotapes were analyzed to provide descriptions of children’s movement responses. Typically, when children dribbled while walking or jogging they controlled the ball, pushed with finger pads, and looked at the ball. When dribbling tasks were more difficult, in general, there was less ball control and more slapping with palms (less mature patterns) while at the same time more instances of children lifting their heads to look up (a more mature pattern). Task constraints had differential impacts on different dribbling elements. One implication is that teachers need to consider this differential impact in designing practice conditions and in selecting assessment tasks.

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Eric G. James

The HKB model and its variants characterize bimanual coordination with fixedpoint dynamics and predict stationarity of the mean and variance of relative phase in stable coordinative states. In the current study, participants performed in-phase and antiphase coordination modes in rhythmic bimanual finger and elbow flexionextension tasks. The results of runs tests revealed that discrete relative phase was nonstationary in 49.25%, 50.25%, and 54% of time-series in the 10, 20, and 30 box runs tests, respectively. In all individual Task conditions >38% of time-series were nonstationary. These findings contradicted model predictions that the mean and variance of relative phase are stationary in bimanual coordination and distinguish the concept of dynamical stability from statistical stationarity. The findings indicated that relative phase was not attracted to a stationary fixed-point and that fluctuations in relative phase are not Gaussian white noise as in existing models of bimanual coordination.