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Senshi Fukashiro, Dean C. Hay and Akinori Nagano

This paper reviews the research findings regarding the force and length changes of the muscle-tendon complex during dynamic human movements, especially those using ultrasonography and computer simulation. The use of ultrasonography demonstrated that the tendinous structures of the muscle-tendon complex are compliant enough to influence the biomechanical behavior (length change, shortening velocity, and so on) of fascicles substantially. It was discussed that the fascicles are a force generator rather than a work generator; the tendinous structures function not only as an energy re-distributor but also as a power amplifier, and the interaction between fascicles and tendinous structures is essential for generating higher joint power outputs during the late pushoff phase in human vertical jumping. This phenomenon could be explained based on the force-length/velocity relationships of each element (contractile and series elastic elements) in the muscle-tendon complex during movements. Through computer simulation using a Hill-type muscle-tendon complex model, the benefit of making a countermovement was examined in relation to the compliance of the muscle-tendon complex and the length ratio between the contractile and series elastic elements. Also, the integral roles of the series elastic element were simulated in a cyclic human heel-raise exercise. It was suggested that the storage and reutilization of elastic energy by the tendinous structures play an important role in enhancing work output and movement efficiency in many sorts of human movements.

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Diane E. Butterworth, David C. Nieman, Bruce C. Underwood and Kristian D. Lindsied

This study evaluated the relationship between cardiorespiratory fitness, physical activity, and dietary quality in a group of 20- to 40-year-old women (n = 34) who varied widely in levels of physical activity. Nutrient intakes were determined using 10 repeated 24-hr diet records, randomly assigned, over a 10-week period, Physical activity was determined on the same randomly assigned days using the Caltrac Personal Activity Computer. Cardiorespiratory fitness was assessed by two maximal graded treadmill tests with continuous metabolic monitoring at both the beginning and end of the 10-week period. Neither physical activity nor cardiorespiratory fitness was significantly correlated with nutrient density (nutrient/1,000 kcal). Intake of energy (kcal/kg body weight) was higher for the more physically active and fit women, leading to a significant increase in most nutrients consumed per kilogram of body weight.

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Shyh-Chour Huang

This paper presents a description of a general -purpose nonlinear model of the human body. The model is developed to simulate human response to high force and high acceleration as typically experienced in vehicle accidents. The model is composed of connected bodies of segments representing the torso and limbs of the human frame. Nonlinear springs and dampers are used at the connection joints to represent human anatomical characteristics and limits imposed by muscles, ligaments, and soft tissue. The governing dynamical equations are developed using Kane's equations (Kane <&: Levin-son, 1985) and multibody dynamics analysis procedures developed by Huston et al. (1974, 1975, 1978). These equations and procedures form the basis for the algorithms of a computer code. The equations are solved numerically using a fourth-order Runge-Kutta integrator. The results of several accident simulations are also presented.

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Maurice R. Yeadon and David G. Kerwin

At the 1996 Atlanta Olympic Games, 18 single somersaults with one twist in the women’s compulsory floor exercises were recorded using two video cameras. An 11 segment computer simulation model was used to analyze the twisting techniques used. It was found mat counter-rotation techniques accounted for less than one third of the twist for all gymnasts, indicating that the production of twist was mainly a consequence of the angular momentum and a non-zero tilt angle. Contributions to the tilt angle reached at the mid-twist position were used as measures of the twisting potential of various techniques. Contact techniques accounted for 30% of the tilt produced, the remainder being produced using aerial techniques, which primarily comprised a symmetrical lowering of the arms together with minor contributions from asymmetrical arm and hip movements. There was no evidence of a difference in technique between the highest and lowest scoring competitors.

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Eric A. Roy, Linda E. Rohr and Patricia L. Weir

Two experiments are reported that focus on manipulating both the context and the spatial precision of a computer-pointing task. Single goal-directed actions are compared to dual-phase tasks, where participants are required to sequentially attain two goal locations. Results support the idea that for movements in series, movement planning, and online feedback, control can occur simultaneously. Additionally, for single-phase tasks and the final phase of dual-phase tasks, the termination requirement influences the temporal components of the movement. The effects of termination and movement context appear to hold regardless of the spatial precision of the task. This suggests that the effects of spatial precision and movement termination are independent, although both have an impact on the deceleration time for goal-directed movements.

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Veerle Puttemans, Sophie Vangheluwe, Nicole Wenderoth and Stephan P. Swinnen

When performing movements with different spatial trajectories in both upper limbs simultaneously, patterns of interference emerge that can be overcome with practice. Even though studies on the role of augmented feedback in motor learning have been abundant, it still remains to be discovered how overcoming such specific patterns of spatial interference can be optimized by instructional intervention. In the present study, one group acquired a bimanual movement with normal vision, whereas a second group received augmented feedback of the obtained trajectories on a computer screen in real time. Findings revealed that, relative to normal vision, the augmented feedback hampered skill learning and transfer to different environmental conditions. These observations are discussed in view of the benefits and pitfalls of augmented feedback in relation to task context and instructional condition.

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Brian C. Focht, Wendy M. Sanders, Peter H. Brubaker and W. Jack Rejeski

The authors examined the validity of the Computer Science and Application (CSA) activity monitor during a bout of rehabilitative exercise among older adults with chronic disease. In order to determine convergent validity, 50 participants were monitored during a 30-min walk in Study 1. In order to assess concurrent validity, 10 volunteers wore both a CSA accelerometer and a Cosmed K4 b2 portable gas-analysis unit during 30 min of rehabilitative exercise in Study 2. Study 1 results revealed significant (p < .01) positive relationships between mean CSA activity counts and estimated METs (r = .60), pedometer readings (r = .47), 6-min walk (r = .62), and self-efficacy (r = .45). Study 2 results demonstrated a significant (p < .01) positive correlation between CSA activity counts and oxygen uptake (r = .72). The findings suggest that the CSA activity monitor is an effective objective measure of physical activity during a structured, moderate-intensity bout of exercise among older adults with chronic disease.

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Maarten Beek, Carolyn F. Small, Randy E. Ellis, Richard W. Sellens and David R. Pichora

Computer assisted surgical interventions and research in joint kinematics rely heavily on the accurate registration of three-dimensional bone surface models reconstructed from various imaging technologies. Anomalous results were seen in a kinematic study of carpal bones using a principal axes alignment approach for the registration. The study was repeated using an iterative closest point algorithm, which is more accurate, but also more demanding to apply. The principal axes method showed errors between 0.35 mm and 0.49 mm for the scaphoid, and between 0.40 mm and 1.22 mm for the pisiform. The iterative closest point method produced errors of less than 0.4 mm. These results show that while the principal axes method approached the accuracy of the iterative closest point algorithm in asymmetrical bones, there were more pronounced errors in bones with some symmetry. Principal axes registration for carpal bones should be avoided.

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Richard P. Wells, Patrick J. Bishop and Malcolm Stephens

Spinal cord trauma due to head-first collisions is not uncommon in vehicle accidents, shallow water diving, football, or ice hockey. Two approaches to evaluating potential protective devices for ice hockey are described: an evaluative tool based upon an anthropometric test dummy, and a computer simulation of axial head-first collisions. Helmets reduced the peak cervical spine loads during low velocity head-first collisions by up to 8%. It is shown that large thicknesses of appropriate padding are necessary to hold the cervical spine loads to noninjurious levels. A head-first impact of 3.0 m • sec−1 required padding deformations on the order of 94 mm to hold cervical spine loads below 2,000 N.

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Semyon M. Slobounov, Shannon T. Poole, Robert F. Simon, Elena S. Slobounov, Jill A. Bush, Wayne Sebastianelli and William Kraemer

Assessment and enhancement of joint position sense is an inexact science at best. Anew method of evaluating and improving this sense using motion-tracking technology that incorporates computer visualization graphics was examined. Injured and healthy subjects were evaluated for their abilities to determine shoulder joint position, after abduction, in two tasks. The first was active reproduction of a passively placed angle. The second was visual reproduction of such an angle. A training protocol was added to determine the effectiveness of proprioceptive training in conjunction with 3-D visualization techniques. The primary findings were (a) a significant difference (p = .05) in the level of joint position sense in injured vs. healthy subjects; (b) significantly less accurate reproduction of larger shoulder abduction vs. the smaller movement in the active reproduction task; (c) significantly greater ability to accurately reproduce angles actively vs. visually; and (d) that proprioception training using 3-D visualization techniques significantly increased active and visual reproductions of passively placed angles.