Monday, January 25, 2010

New evidence mechanical factors

New evidence identifies mechanical factors that limit human running speeds


Jamaican sprinter Usain Bolt's record-setting performances have unleashed a wave of interest in the ultimate limits to human running speed. A new study published in the Journal of Applied Physiology offers intriguing insights into the biology and perhaps even the future of human running speed.
The newly published evidence identifies the critical variable imposing the biological limit to running speed, and offers an enticing view of how the biological limits might be pushed back beyond the nearly 28 miles per hour speeds achieved by Bolt to speeds of perhaps 35 or even 40 miles per hour.
The new paper, "The biological limits to running speed are imposed from the ground up," was authored by Peter Weyand of Southern Methodist University; Rosalind Sandell and Danille Prime, both formerly of Rice University; and Matthew Bundle of the University of Wyoming.
"The prevailing view that speed is limited by the force with which the limbs can strike the running surface is an eminently reasonable one," said Weyand, associate professor of applied physiology and biomechanics at SMU in Dallas.
"If one considers that elite sprinters can apply peak forces of 800 to 1,000 pounds with a single limb during each sprinting step, it's easy to believe that runners are probably operating at or near the force limits of their muscles and limbs," he said. "However, our new data clearly show that this is not the case. Despite how large the running forces can be, we found that the limbs are capable of applying much greater ground forces than those present during top-speed forward running."
In contrast to a force limit, what the researchers found was that the critical biological limit is imposed by time -- specifically, the very brief periods of time available to apply force to the ground while sprinting. In elite sprinters, foot-ground contact times are less than one-tenth of one second, and peak ground forces occur within less than one-twentieth of one second of the first instant of foot-ground contact.
The researchers took advantage of several experimental tools to arrive at the new conclusions. They used a high-speed treadmill capable of attaining speeds greater than 40 miles per hour and of acquiring precise measurements of the forces applied to the surface with each footfall. They also had subjects' perform at high speeds in different gaits. In addition to completing traditional top-speed forward running tests, subjects hopped on one leg and ran backward to their fastest possible speeds on the treadmill.

The unconventional tests were strategically selected to test the prevailing beliefs about mechanical factors that limit human running speeds -- specifically, the idea that the speed limit is imposed by how forcefully a runner's limbs can strike the ground.
However, the researchers found that the ground forces applied while hopping on one leg at top speed exceeded those applied during top-speed forward running by 30 percent or more, and that the forces generated by the active muscles within the limb were roughly 1.5 to 2 times greater in the one-legged hopping gait.
The time limit conclusion was supported by the agreement of the minimum foot-ground contact times observed during top-speed backward and forward running. Although top backward vs. forward speeds were substantially slower, as expected, the minimum periods of foot-ground contact at top backward and forward speeds were essentially identical.
According to Matthew Bundle, an assistant professor of biomechanics at the University of Wyoming, "The very close agreement in the briefest periods of foot-ground contact at top speed in these two very different gaits points to a biological limit on how quickly the active muscle fibers can generate the forces necessary to get the runner back up off the ground during each step."
The researchers said the new work shows that running speed limits are set by the contractile speed limits of the muscle fibers themselves, with fiber contractile speeds setting the limit on how quickly the runner's limb can apply force to the running surface.
"Our simple projections indicate that muscle contractile speeds that would allow for maximal or near-maximal forces would permit running speeds of 35 to 40 miles per hour and conceivably faster," Bundle said.

Sunday, January 17, 2010

Mechanical Engineers Are More Focused on Sustainable Design

The first annual sustainable design-trend watch survey jointly commissioned by the American Society Mechanical Engineers and autodesk  found that two-thirds of respondents have worked on designing sustainable products.
The survey of ASME members is the first research conducted to understand the factors and impacts of sustainable design on mechanical engineers and their manufacturing businesses in industries including automotive and transportation, industrial machinery, consumer products and energy. Sustainable engineering refers to the design and manufacture of a volume of goods and services while using Earth’s resources more efficiently and producing less waste.
A key trend highlighted by the survey is that more than half of the practicing engineers responding reported they expect to increase their use of sustainable design practices in the next year. Primary design concerns focused on using less energy, reducing emissions and complying with environmental and regulatory standards. Additionally, a separate survey of ASME student members found that half of the respondents have encountered sustainable design practices in their studies and are extremely interested in green and sustainable information and causes.
“Engineers have to understand the impact of their decisions on built and natural systems,” says ASME Executive Director Thomas G. Loughlin. “They must be skillful at collaborating closely with colleagues in an increasingly interdisciplinary work environment to meet efficiency and resources goals impacting our only Earth.”
The results of the survey confirm that designing with sustainability in mind is now a primary aim of mechanical engineers, says Robert “Buzz” Kross, senior vice president, manufacturing industry goup at Autodesk.

Mechanical Engineering Priorities Trending Toward Renewable Materials
 

Along with creating designs that use less energy, reduce emissions and comply with regulatory standards, respondents also indicated that design priorities include using renewable, recyclable and recycled materials, reducing material waste in manufacturing and improving manufacturing processes to use fewer resources.
However, cost is a major consideration when deciding to factor sustainability into developing a new product, according to the survey. One-third of the professional engineer respondents indicated that they would consider sustainable technologies for new products only if they are cost-competitive.
 
Survey Methodology and Demographics
 
The online survey of 50,000 ASME professionals and 18,000 ASME student members was conducted over a two-week period in December. The questionnaire covered 16 questions and generated nearly 3,500 respondents in the U.S. Approximately 60% of the practicing engineers responding to the survey have careers spanning more than 20 years, with more than 25% focusing on the design and development of products, systems or equipment. Nearly 20% of the respondents work in the energy and power industry, and more than 10%, respectively, work in professional services and in manufacturing fields.

Thursday, January 14, 2010

Mechanical ventilation.

Basic concepts in mechanical ventilation.

Mechanical ventilatory support is a major component of the clinical management of critically ill patients admitted into intensive care. Closely linked with the developments within critical care medicine, the use of ventilatory support has been increasing since the polio epidemics in the 1950s (Lassen 1953). Initially used to provide controlled mandatory ventilation, today with advances in technology, most mechanical ventilators are triggered by the patient, increasing the awareness of the complexity of patient/ventilator interaction (Tobin 1994). Though ventilator appearance and design may have changed quite significantly and the variety of options for support extensive, the basic concepts of mechanical ventilatory support of the critically ill patient remains unchanged. This paper aims to outline these concepts so as to gain a better understanding of mechanical ventilatory support.

Tuesday, January 5, 2010

Muscular Tension and Body Posture in Relation to Voice Handicap and Voice Quality in Teachers with Persistent Voice Complaints


 
The aim of this study was to investigate the relationship between extrinsic laryngeal muscular hypertonicity and deviant body posture on the one hand and voice handicap and voice quality on the other hand in teachers with persistent voice complaints and a history of voice-related absenteeism. The study group consisted of 25 female teachers. A voice therapist assessed extrinsic laryngeal muscular tension and a physical therapist assessed body posture. The assessed parameters were clustered in categories. The parameters in the different categories represent the same function. Further a tension/posture index was created, which is the summation of the different parameters. The different parameters and the index were related to the Voice Handicap Index (VHI) and the Dysphonia Severity Index (DSI). The scores of the VHI and the individual parameters differ significantly except for the posterior weight bearing and tension of the sternocleidomastoid muscle. There was also a significant difference between the individual parameters and the DSI, except for tension of the cricothyroid muscle and posterior weight bearing. The score of the tension/posture index correlates significantly with both the VHI and the DSI. In a linear regression analysis, the combination of hypertonicity of the sternocleidomastoid, the geniohyoid muscles and posterior weight bearing is the most important predictor for a high voice handicap. The combination of hypertonicity of the geniohyoid muscle, posterior weight bearing, high position of the hyoid bone, hypertonicity of the cricothyroid muscle and anteroposition of the head is the most important predictor for a low DSI score. The results of this study show the higher the score of the index, the higher the score of the voice handicap and the worse the voice quality is. Moreover, the results are indicative for the importance of assessment of muscular tension and body posture in the diagnosis of voice disorders.

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