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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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Philip E. Martin and Gary D. Heise

Archery instructors believe that force distribution (FD) between the hand and bow grip can have a considerable effect on arrow flight, but there is no empirical support for this speculation. This study examined FD on the bow grip in experienced archers and explored the possible relationships between FD, performance, and fatigue. FD was quantified for 15 experienced archers (8 highly skilled [HS] and 7 less skilled [LS]) using 15 unobtrusive force sensors as each archer completed 72 shots. Arrow position relative to the target center, estimated net moments and moment arms about vertical and horizontal axes through the grip, and shot-to-shot variability in the estimated moments and moment arms were computed for three blocks of six shots. Results demonstrated that (a) estimated moments and moment arms were not consistently related to observed vertical or horizontal deviations in arrow position, (b) there were no systematic differences in FD between HS and LS archers, (c) fatigue had no quantifiable effect on FD, and (d) HS archers displayed less shot-to-shot variability in vertical FD than LS archers, but similar variability horizontally. Results did not support the above-noted common belief of archery instructors.

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Brian L. Davis, Julie E. Perry, Donald C. Neth and Kevin C. Waters

A device has been designed to simultaneously measure the vertical pressure and the anterior-posterior and medial-lateral distributed shearing forces under the plantar surface of the foot. The device uses strain gauge technology and consists of 16 individual transducers (each with a surface area measuring 2.5 × 2.5 cm) arranged in a 4 × 4 array. The sampling frequency is 37 Hz and data may be collected for 2 s. The device was calibrated under both static and dynamic conditions and revealed excellent linearity (±5%), minimal hysteresis (±7.5%), and very good agreement between applied and measured loads (±5%). Vector addition of the distributed loads gave resultant forces that were qualitatively very similar to those obtained from a standard force plate. Data are presented for measurements from the forefoot of 4 diabetic subjects during the initiation of gait, demonstrating that distributed shear and pressure on the sole of the foot can be measured simultaneously.

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Shiu Hong Wong, Tianjian Ji, Youlian Hong, Siu Lun Fok and Lin Wang

The low impact forces of Tai Chi push-hand exercises may be particularly suited for older people and for those with arthritis; however, the biomechanics of push-hand exercises have not previously been reported. This paper examines the ground reaction forces (GRFs) and plantar force distributions during Tai Chi push-hand exercises in a stationary stance with and without an opponent. Ten male Tai Chi practitioners participated in the study. The GRFs of each foot were measured in three perpendicular directions using two force plates (Kistler). The plantar force distribution of each foot was measured concurrently using an insole sensor system (Novel). The results showed that the average maximum vertical GRF of each foot was not more than 88% ± 6.1% of the body weight and the sum of the vertical forces (103% ± 1.4%) generated by the two feet approximately equals the body weight at any one time. The horizontal GRFs generated by the two feet were in the opposite directions and the measured mean peak values were not more than 12% ± 2.8% and 17% ± 4.3% of the body weight in the medio-lateral and antero-posterior directions respectively. Among the nine plantar areas, the toes sustained the greatest plantar force. This study indicates that push-hand exercises generate lower vertical forces than those induced by walking, bouncing, jumping and Tai Chi gait, and that the greatest plantar force is located in the toe area, which may have an important application in balance training particularly for older adults.

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Gorka Álvarez and Jordi Vinyolas

A pedal is presented that was designed specifically for the evaluation of cycling technique of different cyclists in real conditions. Most of the instrumented force pedals referred to in research literature have been designed for laboratory use, where pedal weight and dimension have not been considered critical characteristics. By means of this new instrumented force pedal, which is externally identical to one of the most popular clipless pedals, cycling forces under real conditions are measured. The interest in this pedal lies in the fact that it can be used in road trials like the sprint or climb, where tridimensional movements must be considered. Some measurements obtained in hill climb cycling, such as maximum normal force and force distribution during crank revolution, are also presented and discussed.

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Mikko Virmavirta, Juha Kivekäs and Paavo Komi

The effect of skis on the force–time characteristics of the simulated ski jumping takeoff was examined in a wind tunnel. Takeoff forces were recorded with a force plate installed under the tunnel floor. Signals from the front and rear parts of the force plate were collected separately to examine the anteroposterior balance of the jumpers during the takeoff. Two ski jumpers performed simulated takeoffs, first without skis in nonwind conditions and in various wind conditions. Thereafter, the same experiments were repeated with skis. The jumpers were able to perform very natural takeoff actions (similar to the actual takeoff) with skis in wind tunnel. According to the subjective feeling of the jumpers, the simulated ski jumping takeoff with skis was even easier to perform than the earlier trials without skis. Skis did not much influence the force levels produced during the takeoff but they still changed the force distribution under the feet. Contribution of the forces produced under the rear part of the feet was emphasized probably because the strong dorsiflexion is needed for lifting the skis to the proper flight position. The results presented in this experiment emphasize that research on ski jumping takeoff can be advanced by using wind tunnels.

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Bastiaan Breine, Philippe Malcolm, Veerle Segers, Joeri Gerlo, Rud Derie, Todd Pataky, Edward C. Frederick and Dirk De Clercq

patterns even more impact intensity will be transmitted under the forefoot part of the shoe than in midfoot contact patterns. Several studies have assessed the influence of foot contact pattern on the shoe-surface pressure and force distribution under the foot. 12 – 14 These studies showed greater

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David Cruz-Díaz, Kyung-Min Kim, Fidel Hita-Contreras, Marco Bergamin, Agustin Aibar-Almazán and Antonio Martínez-Amat

scores. Tai Chi movements promote the proper distribution of the center of mass between both legs during dynamic tasks performed in all directions, with particular attention to postural alignment. These movements may lead to enhancements in postural control, stability strategies, and appropriate force

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Antoine Falisse, Sam Van Rossom, Johannes Gijsbers, Frans Steenbrink, Ben J.H. van Basten, Ilse Jonkers, Antonie J. van den Bogert and Friedl De Groote

activations exceeded 1, suggesting an unrealistic muscle force distribution. It was more optimal to activate the psoas above 1 than to increase the contribution of another muscle (eg, rectus femoris). Muscle activations exceeding 1 were dependent on the static optimization objective function. In more detail

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Ross Armstrong, Christopher Michael Brogden and Matt Greig

. 39 Within female soccer, measurement of force distribution patterns demonstrated higher maximum force under the second metatarsal in players with “ high joint laxity ” (BS ≥4). 40 Both these studies concluded that differences in loading patterns can arise from the presence of “ generalized joint