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Strength Loss (strength + loss)

Distribution by Scientific Domains

Polymers and Materials Science	33%

Selected Abstracts

Influence of concurrent exercise or nutrition countermeasures on thigh and calf muscle size and function during 60 days of bed rest in women

ACTA PHYSIOLOGICA, Issue 2 2007
T. A. Trappe
Abstract Aim:, The goal of this investigation was to test specific exercise and nutrition countermeasures to lower limb skeletal muscle volume and strength losses during 60 days of simulated weightlessness (6° head-down-tilt bed rest). Methods:, Twenty-four women underwent bed rest only (BR, n = 8), bed rest and a concurrent exercise training countermeasure (thigh and calf resistance training and aerobic treadmill training; BRE, n = 8), or bed rest and a nutrition countermeasure (a leucine-enriched high protein diet; BRN, n = 8). Results:, Thigh (quadriceps femoris) muscle volume was decreased (P < 0.05) in BR (,21 ± 1%) and BRN (,24 ± 2%), with BRN losing more (P < 0.05) than BR. BRE maintained (P > 0.05) thigh muscle volume. Calf (triceps surae) muscle volume was decreased (P < 0.05) to a similar extent (P > 0.05) in BR (,29 ± 1%) and BRN (,28 ± 1%), and this decrease was attenuated (P < 0.05) in BRE (,8 ± 2%). BR and BRN experienced large (P < 0.05) and similar (P > 0.05) decreases in isometric and dynamic (concentric force, eccentric force, power and work) muscle strength for supine squat (,19 to ,33%) and calf press (,26 to ,46%). BRE maintained (P > 0.05) or increased (P < 0.05) all measures of muscle strength. Conclusion:, The nutrition countermeasure was not effective in offsetting lower limb muscle volume or strength loss, and actually promoted thigh muscle volume loss. The concurrent aerobic and resistance exercise protocol was effective at preventing thigh muscle volume loss, and thigh and calf muscle strength loss. While the exercise protocol offset ,75% of the calf muscle volume loss, modification of this regimen is needed. [source]

Residual compressive behavior of alkali-activated concrete exposed to elevated temperatures

FIRE AND MATERIALS, Issue 1 2009
Maurice Guerrieri
Abstract This paper reports the effect of elevated temperature exposures, up to 1200°C , on the residual compressive strengths of alkali-activated slag concrete (AASC) activated by sodium silicate and hydrated lime; such temperatures can occur in a fire. The strength performance of AASC in the temperature range of 400,800°C was similar to ordinary Portland cement concrete and blended slag cement concrete, despite the finding that the AASC did not contain Ca(OH)2 , which contributes to the strength deterioration at elevated temperatures for Ordinary Portland Cement and blended slag cement concretes. Dilatometry studies showed that the alkali-activated slag (AAS) paste had significantly higher thermal shrinkage than the other pastes while the basalt aggregate gradually expanded. This led to a higher thermal incompatibility between the AAS paste and aggregate compared with the other concretes. This is likely to be the governing factor behind the strength loss of AASC at elevated temperatures. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Combined Effect of Salt Water and High-Temperature Exposure on the Strength Retention of NextelÔ720 Fibers and NextelÔ720-Aluminosilicate Composites

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2006
Triplicane A. Parthasarathy
The relative contribution of fiber strength loss to reported degradation in the mechanical behavior of NextelÔ720-aluminosilicate composites after exposure to salt fog (ASTM B117) was explored. Single filament tension tests were performed on NextelÔ720 (3M, Inc., Minneapolis, MN) fibers after immersion in NaCl solutions followed by high-temperature exposure in air. The results were compared with the behavior of control specimens which received high-temperature exposure but were not immersed in NaCl solution. There was no degradation in fiber strengths for NaCl solutions below 1 wt%. However, significant degradation was observed at 5 wt% NaCl upon exposure to temperatures between 900° and 1150°C, while no degradation was observed upon an exposure to 1200°C. The relative contribution of fiber strength loss to composite degradation was estimated as nearly 50%, indicating that both fibers and matrix/interface degrade from exposure to salt water. X-ray diffraction and transmission electron microscopy of the exposed fibers and composites were conducted to help rationalize the observations. Microstructure of degraded fibers showed presence of Na at grain boundaries near the surface, without any evidence of a crystalline phase, indicating weakening from segregation or formation of an amorphous phase. The degraded composites showed that matrix and fiber/matrix interfaces had Na rich regions/phases. [source]

Influence of concurrent exercise or nutrition countermeasures on thigh and calf muscle size and function during 60 days of bed rest in women

Damage evolution in low velocity impacted unreinforced vinyl ester 411-350 and 411-C50 resin systems

POLYMER COMPOSITES, Issue 6 2000
M. Motuku Assistant Professor
Damage evolution in plaques made of vinyl ester resin systems was investigated as a function of specimen thickness, impact energy level and matrix material. Dow DERAKANE vinyl ester 411-350 and 411-C50 resin systems, which have low viscosity and are ideally suited for low-cost liquid processing techniques like vacuum assisted resin transfer molding (VARTM), were considered for the low velocity instrumented impact testing. Characterization of damage evolution was undertaken using optical microscopy and analysis of impact load histories recorded during the impact event. Radial cracking, perforations at the point of impact (in the form of a truncated cone), and damage resulting from the support constraints were identified as the dominant failure characteristics in both resin systems. Radial cracking, which originated from the bottom surface, was operative in all failed specimens and was attributed to the catastrophic failure due to extensive flexural tensile strength losses. For specimens that could deflect significantly, radial cracking and support-constraint-induced damage were the operative failure mechanisms. Radial cracking and through-thickness shearing led to failure in stiffer plaques. The DERAKANE 411-350-vinyl ester resin system was found more damage resistant than the 411-C50 system. [source]