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Marcus Börjesson, Carolina Lundqvist, Henrik Gustafsson and Paul Davis

example, an upset stomach, feelings of physical weakness, and muscle stiffness or tension (e.g.,  Grossbard, Smith, Smoll, & Cumming, 2009 ). Physiological indices of increased arousal include elevated heart rate, secretion of stress-hormones, muscle tension, and heightened blood-pressure ( Noteboom

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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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Paul W.M. Marshall, Ric Lovell and Jason C. Siegler

Purpose:

Passive muscle tension is increased after damaging eccentric exercise. Hamstring-strain injury is associated with damaging eccentric muscle actions, but no research has examined changes in hamstring passive muscle tension throughout a simulated sport activity. The authors measured hamstring passive tension throughout a 90-min simulated soccer match (SAFT90), including the warm-up period and every 15 min throughout the 90-min simulation.

Methods:

Passive hamstring tension of 15 amateur male soccer players was measured using the instrumented straight-leg-raise test. Absolute torque (Nm) and slope (Nm/°) of the recorded torque-angular position curve were used for data analysis, in addition to total leg range of motion (ROM). Players performed a 15-min prematch warm-up, then performed the SAFT90 including a 15-min halftime rest period.

Results:

Reductions in passive stiffness of 20–50° of passive hip flexion of 22.1−29.2% (P < .05) were observed after the warm-up period. During the SAFT90, passive tension increased in the latter 20% of the range of motion of 10.1−10.9% (P < .05) concomitant to a 4.5% increase in total hamstring ROM (P = .0009).

Conclusions:

The findings of this study imply that hamstring passive tension is reduced after an active warm-up that includes dynamic stretching but does not increase in a pattern suggestive of eccentric induced muscle damage during soccer-specific intermittent exercise. Hamstring ROM and passive tension increases are best explained by improved stretch tolerance.

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Gerald L. Gottlieb

The lambda version of the equilibrium-point (EP) hypothesis as developed by Feldman and colleagues has been widely used and cited with insufficient critical understanding. This article offers a small antidote to that lack. First, the hypothesis implicitly, unrealistically assumes identical transformations of lambda into muscle tension for antagonist muscles. Without that assumption, its definitions of command variables R, C, and lambda are incompatible and an EP is not defined exclusively by R nor is it unaffected by C. Second, the model assumes unrealistic and unphysiological parameters for the damping properties of the muscles and reflexes. Finally, the theory lacks rules for two of its three command variables. A theory of movement should offer insight into why we make movements the way we do and why we activate muscles in particular patterns. The EP hypothesis offers no unique ideas that are helpful in addressing either of these questions.

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Shinya Ogaya, Hisashi Naito, Akira Iwata, Yumi Higuchi, Satoshi Fuchioka and Masao Tanaka

Toe-out angle alternation is a potential tactic for decreasing the knee adduction moment during walking. Published reports have not examined the medial knee contact force during the toe-out gait, although it is a factor affecting knee articular cartilage damage. This study investigated the effects of increased toe-out angle on the medial knee contact force, using musculoskeletal simulation analysis. For normal and toe-out gaits in 18 healthy subjects, the muscle tension forces were simulated based on the joint moments and ground reaction forces with optimization process. The medial knee contact force during stance phase was determined using the sum of the muscle force and joint reaction force components. The first and second peaks of the medial knee contact force were compared between the gaits. The toe-out gait showed a significant decrease in the medial knee contact force at the second peak, compared with the normal gait. In contrast, the medial knee contact forces at the first peak were not significantly different between the gaits. These results suggest that the toe-out gait is beneficial for decreasing the second peak of the medial knee contact force.

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James M. Robbins and Paul Joseph

The types and frequency of sensations experienced by runners when required to miss a run or series of runs was studied. Most of 345 runners of various weekly mileage levels reported some kind of distress; irritability, restlessness, frustration, guilt, and depression were reported most often. Sleeping problems, digestive difficulties, and muscle tension and soreness were reported less frequently. Three causes of exercise withdrawal were proposed: (a) a misinterpretation of the return of dysphoria that had been temporarily masked by the effects of running; (b) an inability to cope with stress in periods when the coping mechanism of running is temporarily unavailable; and (c) the loss of regular, predictable reinforcement of feelings of self-fulfillment gained through success or achievement in previously unimagined and unattainable ways. Results, based on cross-sectional data, were consistent with these hypotheses but do not rule out alternative explanations. The reciprocal nature of number of miles run in an average week and exercise deprivation sensations was also studied. Results indicated that runners tended to run longer in order to avoid the negative sensations that would come from not running, but that an escalation in mileage did not necessarily result in more frequent experiences of distress when not able to run.

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Matthew T.G. Pain and John H. Challis

The aims of this study were to quantify intrasegmental motion using an array of 28 surface-mounted markers to examine frequency and amplitude measurements of the intrasegmental motion to calculate forces and energy transfer; and to show that the underlying muscles are a major contributor to the skin marker motion. One participant performed 27 trials under three conditions in which his forearm was struck against a solid object fixed to a force plate while the locations of the markers were recorded at 240 Hz. For impacts with equal peak forces, the muscle tension significantly affected the amount of intrasegmental motion. Tensing the arm reduced the intrasegmental motion by 50%. The quadrilateral sectors defined by the markers changed in area by 11% with approximately equal motion in the vertical and horizontal direction. The maximum linear marker motion was 1.7 cm. The intrasegmental motion had distinct frequency components around 14 and 20 Hz. Soft tissue deformation could account for 70% of the energy lost from the forearm during these impacts. The study has demonstrated the important role that intrasegment soft tissue motion can have on the kinetics of an impact.

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Alon Eliakim, Ita Litmanovitz and Dan Nemet

in the immediate postnatal period and include passive range-of-motion exercise with gentle compression at the end of the flexion/extension range, lasting 5–15 minutes per day for 4–8 weeks. This exercise regimen may cause an increase in joint pressure and muscle tension leading to increased

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Mary Hellen Morcelli, Dain Patrick LaRoche, Luciano Fernandes Crozara, Nise Ribeiro Marques, Camilla Zamfolini Hallal, Mauro Gonçalves and Marcelo Tavella Navega

associated with maximal muscle strength. 16 , 30 Taken together, these data suggest that a poor ability to rapidly activate and develop muscle tension at the onset of contraction is related to slow gait speed in older women. Resistance exercises targeting rapid force development may, therefore, be

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James Hackney, Jade McFarland, David Smith and Clinton Wallis

stiffness at similar forces result in greater joint compliance. This may reflect the effect of fatigue on lower body muscle tension (this possibility is addressed as a limitation), or motor learning or adaptation to the task of absorbing landing force. The finding that variability in initial jump height, as