Significant Loss Of Strength Research Articles

사진분석법을 이용한 고온에 노출된 고로슬래그 콘크리트의 색상변화도 평가

When reinforced concrete is subjected to high temperatures in a fire, there is a deterioration in its properties. It is very important to know loss in compressive strength, loss of elastic modulus, cracking and spalling of the concrete. To determine whether a structure can be repaired rather than demolished after a fire, an assessment of structural integrity must be made. To assess the remaining bearing capacity of the structural elements after fire, information of the temperatures reached inside the elements is necessary. On heating, a change in color from normal to a pink/red is often observed and this is useful since it coincides with the onset of significant loss of concrete strength. The purpose of this study is to quantify changes in color for blast-furnace slag concrete using photo image analysis and to identify the relationship between color change and increasing temperatures. For this purpose, we manufactured concrete samples with varying water-to-binder ratios and heated them to target temperatures of 100, 200, 300, 400, 500, 600, and <TEX>$700^{\circ}C$</TEX> in an electric oven, whereupon their color changes in photos of the specimen were measured using photoshop program. The result of this study shows that color changes in a concrete exposed to high temperature have a consistent relationship with several variables according to RGB, HSB, and Lab color coordinates. Therefore, it is possible to estimate how much temperature the specimen was exposed considering these results of color change.

A new method to prepare rubber toughened epoxy with high modulus and high impact strength

Although epoxy resins can be substantially toughened by addition of a reactive liquid rubber, the improvement in toughness is inevitably accompanied by a significant loss in elastic modulus and yield strength. This paper presents a novel route for preparing the liquid rubber/epoxy composites with high yield strength, Young׳s modulus and impact strength. By this new method, the epoxy composites with different grades of carboxyl terminated butadiene acrylonitrile copolymer (CTBN) and cured by different curing agents were prepared, and their mechanical properties were characterized. It is found that no matter what grades of CTBN, also regardless of curing agents, the composites prepared by the new method always exhibit much higher impact strength, yield strength and Young׳s modulus than the corresponding traditional composites, proving the new method to be somewhat universal. Especially, some CTBN/epoxy composites exhibit even higher yield strength and Young׳s modulus than that of pure epoxy.

Liquefaction Hazard Assessment Using SPT and VS for Two Cities in India

The seismic behavior of a saturated soil depends on the potential for significant strains or strength loss that can contribute to ground deformations or instability during an earthquake. Historic large earthquakes throughout the world explain that the liquefaction related ground failure commonly causes extensive structural and lifeline damage in urban areas. Detailed assessment of liquefaction hazard is important for evaluating and reducing the risk through appropriate mitigation techniques. Soil liquefaction generally occurs in areas underlain by low density, saturated granular sediments. The liquefaction susceptibility can be mapped using specific, well established geologic and geotechnical criteria. Damages caused by liquefaction of saturated soil revealed that after liquefaction the ground failed, sand boiling occurred and the structure subsided unevenly causing tilting, cracking or even collapse. After the devastating 2001 Gujarat earthquake, the Government of India has paid serious attention to carry out the detailed site characterization and ground response studies which are very crucial in seismic microzonation and it is also accepted as a guiding tool in land use planning and safe construction practices to avoid the loss from the future earthquakes. Very preliminary process of reducing the effects of earthquake is by assessing the hazard itself. As part of the national level microzonation program, Department of Science and Technology, Govt. of India has initiated microzonation of 63 cities in India. In this research paper two urban centers Delhi and Vijayawada city which falls in seismic zones IV and III respectively are considered for liquefaction hazard assessment. Since these two cities are falling in the areas with high and moderate seismic probability, there is a great need for the assessment of liquefaction potential. An attempt has been made estimate the liquefaction hazard for these two cities considered using the measured shear wave velocities and SPT borehole data. From the detailed liquefaction assessment, it is observed that the possibility is severe in the north and north eastern side of Delhi and is very less in the western side of the city. In the south and central part of the area where shear wave velocities of the soil strata is ≥180 m/s the possibility of liquefaction is unlikely and in Vijayawada city, the occurrence of liquefaction is likely at several locations especially in Patamata, Autonagar and Kanuru.

Functional outcome after successful internal fixation versus salvage arthroplasty of patients with a femoral neck fracture.

To determine patient independency, health-related and disease-specific quality of life (QOL), gait pattern, and muscle strength in patients after salvage arthroplasty for failed internal fixation of a femoral neck fracture. Secondary cohort study to a randomized controlled trial. Multicenter trial in the Netherlands, including 14 academic and nonacademic hospitals. Patients after salvage arthroplasty for failed internal fixation of a femoral neck fracture were studied. A comparison was made with patients who healed uneventfully after internal fixation. None (observatory study). Patient characteristics, SF-12, and Western Ontario McMaster osteoarthritis index scores were collected. Gait parameters were measured using plantar pressure measurement. Maximum isometric forces of the hip muscles were measured using a handheld dynamometer. Differences between the fractured and contralateral leg were calculated. Groups were compared using univariate analysis. Of 248 internal fixation patients (median age, 72 years), salvage arthroplasty was performed in 68 patients (27%). Salvage arthroplasty patients had a significantly lower Western Ontario McMaster osteoarthritis index score (median, 73 vs. 90; P = 0.016) than patients who healed uneventfully after internal fixation. Health-related QOL (SF-12) and patient independency did not differ significantly between the groups. Gait analysis showed a significantly impaired progression of the center of pressure in the salvage surgery patients (median ratio, -8.9 vs. 0.4, P = 0.013) and a significant greater loss of abduction strength (median, -25.4 vs. -20.4 N, P = 0.025). Despite a similar level of dependency and QOL, salvage arthroplasty patients have inferior functional outcome than patients who heal after internal fixation of a femoral neck fracture. Therapeutic level III.

Enhancement of Steel/Carbon Fibre-Reinforced Polymer Adhesively-Bonded Joints at Elevated Temperatures through Curing

Although carbon fibre-reinforced polymer (CFRP) a promising approach to the strengthening of existing steel structures, such an adhesively-bonded system exhibits a significant loss of stiffness and strength in an elevated temperature range. Curing at elevated temperature is examined in this paper, in order to enhance the mechanical performance in the elevated temperature range. Two types of epoxies — with and without carbon nanotube (CNT) modification - were used to prepare steel/CFRP adhesively-bonded joints and both were cured at room temperature (20 °C) and at an elevated temperature (80 °C), and then tested in tension at temperatures from 20 to 80 °C. Remarkable enhancement of stiffness and strength was found for the joints, with or without CNT modification, cured at the elevated temperature, compared to corresponding joints cured at room temperature. The partial safety factors used for laminates by hand lay-up were further evaluated for designing such joints under elevated temperatures.

Enhancement of steel/carbon fibre-reinforced polymer adhesively-bonded joints at elevated temperatures through curing

Although carbon fibre-reinforced polymer (CFRP) a promising approach to the strengthening of existing steel structures, such an adhesively-bonded system exhibits a significant loss of stiffness and strength in an elevated temperature range. Curing at elevated temperature is examined in this paper, in order to enhance the mechanical performance in the elevated temperature range. Two types of epoxies - with and without carbon nanotube (CNT) modification - were used to prepare steel/CFRP adhesively-bonded joints and both were cured at room temperature (20 degreesC) and at an elevated temperature (80 degreesC), and then tested in tension at temperatures from 20 to 80 degreesC. Remarkable enhancement of stiffness and strength was found for the joints, with or without CNT modification, cured at the elevated temperature, compared to corresponding joints cured at room temperature. The partial safety factors used for laminates by hand lay-up were further evaluated for designing such joints under elevated temperatures.

Human Brain Biochemistry

The human brain that serves as a center of the nervous system is structurally unique. It is extraordinarily complex and highly specialized in its distinct heterogeneous anatomical regions as its function remains a great challenge. The neuron is the functional unit that depends on special anatomical and chemical connections with other units of the system. The essential biochemical connections of the nerve cell have special morphological features: synaptic contact that is mediated by chemical molecules ensures sequential propagation of neurotransmission of electrical pulses through units of the system. The chemical energy expended in maintaining the distribution gradients of cations across cellular membranes, and the chemical neurotransmission causes an alteration in cation distribution. The energy utilization mechanisms that underlie cations re-distribution are not peculiar to the nervous system, but they are of particular importance to neural function because the mechanisms of chemical transmission are peculiar to the nervous system. Human nerve cells have the ability to generate electrical impulses that can travel through the body without a significant loss of impulse strength. Such unique features are based on semi-permeable excitable membranes that alter permeation to small chemical molecules and to cations. The biochemical function of the brain is demonstrated in the efficient production of energy required to accomplish the processes mentioned above, and it is essentially ATP that is stored and produced from glucose oxidation to carbon dioxide and water. The brain has virtually no reserves of chemical energy (glucose 1-2 µmoles/g and ATP 3 µmoles/g) to function for minutes only, considering that this organ is 2% of total adult weight that consumes 20% of the whole body glucose through a constant blood supply. Yet, the various factors that regulate glucose uptake and its utilization in the central nervous system are not well understood. This review is an attempt to update the rapidly expanding information on human brain neurotransmission biochemistry, though the adaptive processes of learning; cognitive performance and memory in the brain have subtle relationships.

Durability under thermal loads of polyvinyl alcohol fibers

In the present paper, the thermal durability of polyvinyl alcohol fibers (PVA) was studied after fiber samples had been subjected to temperatures ranging from 90°C to 250°C. Residual mechanical properties, such as tensile strength, elastic modulus and elongation at break, and physical properties, such as density were determined. Weibull statistics were used to quantify the degree of variability in fiber strength, at the different temperature. In addition, thermal analysis of PVA fibers were carried out employing thermogravimetry and differential scanning calorimetry up to the temperature of 800°C. SEM analysis of heated and unheated samples had been carried out in order to allow the identification of the changes in the microstructure of the fibers. The degradation process of PVA fibers manifests itself in a significant loss of mass, stiffness and strength of the fibers, which is progressive with increasing temperature. Thermal analysis has shown that the melting point of PVA fibers begins at approximately 200°C and thermal degradation initiates at about 239ºC. However, progressive loss in tensile strength and elastic modulus was observed starting at a temperature as low as 90°C, due to glass transition temperature of PVA fibers at approximately 66°C. At 220°C, the elastic modulus and strength were reduced at about 45% and 52%, respectively, when compared with respective values of unheated samples. With regards to Weibull modulus, the statistical parameter did not exhibit significant influence on temperature for samples heated up to 145°C, which ranged from 23.4 to 28.8. However, samples heated to 220°C showed a sudden reduction in Weibull modulus to 8.6, indicating that a significant change occurred in the populations of fracture inducing flaws at this temperature level, which clearly affect the tensile strength and Weibull modulus.

Inelastic deformation and failure of partially strengthened profiled blast walls

Blast walls that separate the potentially hazardous regions of the topside on an offshore platform were designed to resist lower loads than those envisaged today thus it is desirable to upgrade their blast resistance in a cost-effective and non-intrusive manner. One proposal is to retrofit the existing blast walls partially with centrally located composite patches. This study presents an assessment tool, which provides understanding of the effect of a composite patch on the blast resistance of blast walls. Numerical simulations of a proposed retrofitted wall are performed to gain insight into the failure progression of the wall ab initio. Damage in the composite patch was considered, and the numerical simulations showed that fiber fracture did not occur thus there was no significant loss of in-plane stiffness and strength. Based on these observations, the rapid assessment tool, analytically formulated to incorporate the effect of the composite patch which strengthens the wall and moves the plastic hinge locations away from the wall centre to the composite-steel edge, is deemed a suitable tool. The assessment tool and the numerical simulations are partially validated by the experimental results. The tool runs quickly and provides reasonable accurate predictions for the deformation response of the walls.

Compressive properties of nanoparticle modified epoxy resin at different strain rates

Epoxy resins often exhibit high strength yet are often brittle, especially at high strain rates. Block copolymer modified epoxy resins have generated significant interest since it was demonstrated that the combination could lead to nanostructured thermosets through the self-assembly of the block copolymer. Such nanostructured epoxies exhibit increased ductility without the significant loss in yield strength exhibited by traditional rubber-modified epoxies. In this study, the effect of different nanoscale additives on the compressive yield strength of a model epoxy resin has been studied. In the first case, a block copolymer styrene-b-butadiene-b-polymethylmethacrylate (SBM) was added to the model epoxy resin. In the second case, carbon nanotubes (CNTs) were added. In the final case, both additives were mixed simultaneously with the epoxy resin. The compressive mechanical behavior of these materials has been investigated over a wide range of strain rates (0.001–3500s−1). The yield behavior was found to fit the cooperative yield model proposed by Fotheringham and Cherry.

Evidence for reduced neuromuscular function in men with a history of androgen deprivation therapy for prostate cancer

Indices of body composition and muscular strength were compared between men with prostate cancer (PCa) treated with androgen deprivation therapy (ADT) and asymptomatic matched men. Nine subjects aged 63-83years with PCa who received ADT (PCa+ADT; duration 6-180months) and 11 asymptomatic aged-matched eugonadal men (HM) aged 59-80years were assessed for prostate-specific antigen (PSA) and total testosterone (TT). Total body non-osseous lean mass (TBLM) and right thigh non-osseous fat-free mass (RTLM) were assessed using dual-energy X-ray absorptiometry. Peak torque of the right knee extensors at 0°s(-1) (ISO) and 60°s(-1) (CON), maximal handgrip strength of the dominant hand (MHS) and whole-body strength (WBS) were assessed. ISO and CON per unit mass of RTLM and MHS and WBS per unit mass of TBLM were calculated. Age, height, mass, body mass index and prostate-specific antigen were comparable between groups (P>0·05), while TT was lower in PCa+ADT (P<0·01). RTLM was similar between groups (P≥0·075). Absolute ISO and CON were lower for PCa+ADT (P<0·01) as were CON per unit of RTLM and ISO per unit of RTLM (P<0·05). Absolute MHS, WBS and MHS per unit of TBLM and WBS per unit of TBLM were lower for PCa+ADT (P<0·01; P<0·05). Men with PCa who receive ADT experience significant losses in whole-body muscular strength compared with asymptomatic age-matched men, which may impair functional capacity. These losses in muscular strength appear to involve neuromuscular mechanisms that are yet to be identified.

Durability of Underwater-Made Butt Steel Adhesive Joints under Laboratory Conditions: Theoretical Model

Epoxide resins are widely employed as adhesives and are being increasingly used in engineering industries. However, adhesively bonded components may suffer significant loss in strength when exposed to environmental attack. The most severe threat is water, and adhesive joint strength decay can be accelerated if externally applied stresses are present. In this work an attempt has been made to develop a model to predict the theoretical durability of butt mild steel joints made underwater. The model was based on experimentally obtained data using double-torsion underwater-made joints and ambient air-made double-torsion and butt joints. All joints were subjected to similar conditions, i.e., static stresses in the presence of water. The first step in developing a test method and model for predicting the environmental fracture data of butt joints made underwater has been proposed that was independent of the detailed butt joint geometry. The model appeared to be successful and accounted for the phenomenon of crack tip blunting that occurs in the adhesives. This is the first time such a model is reported in the literature that may be useful when all variables are included.

Ultra-High-Strength Concrete-Filled FRP Tubes: Compression Tests on Square and Rectangular Columns

This paper presents the partial results of an experimental program undertaken to investigate the behavior of square and rectangular ultra-high-strength concrete (UHSC)-filled fiber reinforced polymer (FRP) tubes (UHSCFFTs) under axial compression. The effects of the amount of confinement, cross-sectional aspect ratio and corner radius were investigated experimentally through the tests of 24 concrete-filled FRP tubes (CFFTs) that were manufactured using unidirectional carbon fiber sheets and UHSC with 108 MPa average compressive strength. Test results indicate that sufficiently confined square and rectangular UHSCFFTs can exhibit highly ductile behavior. The results also indicate that HSCFFTs having tubes of low confinement effectiveness may experience a significant strength loss at the point of transition on their stress-strain curves. Examination of the test results have led to a number of important observations on the influence of corner radius and sectional aspect ratio, which are presented and discussed in the paper.

Type VI collagen turnover‐related peptides—novel serological biomarkers of muscle mass and anabolic response to loading in young men

BackgroundImmobilization-induced loss of muscle mass is a complex phenomenon with several parallels to sarcopenic and cachectic muscle loss. Muscle is a large organ with a protein turnover that is orders of magnitude larger than most other tissues. Thus, we hypothesize that muscle loss and regain is reflected by peptide biomarkers derived from type VI collagen processing released in the circulation.MethodsIn order to test this hypothesis, we set out to develop an ELISA assay against an type VI collagen N-terminal globular domain epitope (IC6) and measured the levels of IC6 and an MMP-generated degradation fragment of collagen 6, (C6M) in a human immobilization–remobilization study setup with young (n = 11) and old (n = 9) men. They were subjected to 2 weeks of unilateral lower limb immobilization followed by 4 weeks of remobilization including thrice weekly resistance training, using the contralateral leg as internal controls. Subjects were sampled for strength, quadriceps muscle volume and blood at baseline (PRE), post-immobilization (2W), and post-remobilization (4W). Blood were subsequently analyzed for levels of the C6M and IC6 biomarkers. We subsequently tested if there was any correlation between C6M, IC6, or the C6M/IC6 ratio and muscle mass or strength at baseline. We also tested whether there was any relation between these biomarkers and changes in muscle mass or strength with immobilization or remobilization.ResultsThe model produced significant loss of muscle mass and strength in the immobilized leg. This loss was bigger in young subjects than in elderly, but whereas the young recovered almost fully, the elderly had limited regrowth of muscle. We found a significant correlation between IC6 and muscle mass at baseline in young subjects (R2 = 0.6563, p = 0.0045), but none in the elderly. We also found a significant correlation between C6M measured at the 4W time point and the change in muscle mass during remobilization, again only manifesting in the young men(R2 = 0.6523, p = 0.0085). This discrepancy between the young and the elderly may be caused in part by much smaller changes in muscle mass in the elderly and partly by the relative small sample size.ConclusionWhile we cannot rule out the possibility that these biomarkers in part stem from other tissues, our results strongly indicate that these markers represent novel biomarkers of muscle mass or change in muscle mass in young men.Electronic supplementary materialThe online version of this article (doi:10.1007/s13539-013-0114-x) contains supplementary material.

OBSERVATIONS OF PEAK STRENGTH BEHAVIOR IN CSA CEMENT MORTARS

The purpose of this study was to assess the mechanical property performance behavior of calcium sulfoaluminate (CSA) cement mortar when cured at ambient laboratory temperature of ~23°C (73°F) and constant 50% relative humidity for an extended period of time. Four CSA cement mortars were tested. Three CSA cement mortars contained equivalent mass amounts of calcium sulfate; whereas, the fourth mortar contained double the amount of calcium sulfate. The three CSA cement mortars containing constant mass amounts of calcium sulfate differed as the specific type of calcium sulfate varied across the three formulations—one mortar containing solely anhydrite, one mortar contained half anhydrite and half gypsum while the other mortar solely contained gypsum. The fourth mortar contained double the amount of calcium sulfate when compared with the others while having a 1/1 blend of anhydrite and gypsum. Specific mortars were either tested for direct tensile strength according to ASTM C307 or for compressive strength according to ASTM C109. All tested mortars displayed statistically significant strength loss trends versus time when cured at constant 50% relative humidity. Cement paste samples were analyzed with TGA/SDT and XRD in an effort to identify microstructure changes corresponding to observed strength loss. Cement paste analysis suggests strength loss within the tested CSA cement mortars occurred as a result of ettringite decomposition.

Evaluation of Sulfate Resistance of Portland Cement Mortars Containing Low-Carbon Rice Husk Ash

In this study, a low-carbon rice husk ash (RHA) was used as a supplementary cementing material in cement mortars to evaluate its sulfate resistance in sodium and magnesium sulfate solutions. The sulfate resistance of these mixtures in terms of expansion and loss of compressive strength was determined using the standard test method.. The water to cementitious material (w/cm) ratio and RHA dosage in the mortars was varied from 0.40 to 0.57 and 0 to 15% (by mass), respectively. The results from this investigation suggest that all mortars with a w/cm ratio of 0.40 showed little deterioration, indicating their high sulfate resistance. For mortars with a w/cm ratio of 0.48 and 0.57, the control mortars showed more deterioration than those with RHA. For mortars at any given w/cm ratio, the sulfate resistance decreased with an increase in the RHA dosage. Though both sodium and magnesium sulfates caused significant deterioration in the specimens, the former caused increased expansions in the test specimens while the latter caused significant loss in compressive strength. The sulfate resistance of RHA mortars was comparable with that of silica fume mortars.

The function and muscle strength recovery of shoulder after humeral diaphysis fracture following plating and intramedullary nailing

To evaluate the shoulder function and shoulder girdle muscle strength of humeral diaphysis fractures postoperatively following intramedullary nailing (IMN) and open reduction internal fixation (ORIF). Fifty cases of humeral diaphysis fractures were randomly allocated into two groups. Antegrade IMN and ORIF were, respectively, performed in group I and II. Union status, functional scoring, range of motion, muscle strength of shoulder girdle including external/internal rotation and abduction/adduction strength were recorded at 18 months after surgery. Statistical package for social sciences 13.0 was used for analysis. Group I had lower functional score than group II (P < 0.05). Both groups had approximately 50 % of muscle strength loss on injured side. In group II, the internal rotation strength loss was significantly greater compared to group I (P < 0.01). The total side to side (internal plus external) range of rotation (ROR) lack and external ROR lack of involved shoulder was significantly greater in group I (P = 0.005 and 0.049). The range of abduction lack was also significantly greater in group I. Both surgically treated groups had significant loss of muscle strength of shoulder girdle when measured at 18 months postoperatively. There was greater loss of rotation strength in ORIF group than the IMN group. However, IMN had lower functional scores and a decreased range of motion postoperatively. The assumption that rotator cuff damage caused by nailing leads to weaker abduction strength than plating was not supported.

Behavior of square and rectangular ultra high-strength concrete-filled FRP tubes under axial compression

This paper presents results of an experimental program undertaken to investigate the behavior of square and rectangular ultra high-strength concrete (UHSC)-filled fiber reinforced polymer (FRP) tubes (UHSCFFTs) under axial compression. The effects of the amount of confinement, cross-sectional aspect ratio and corner radius were investigated experimentally through the tests of 24 concrete-filled FRP tubes (CFFTs) that were manufactured using unidirectional carbon fiber sheets and UHSC with 108MPa average compressive strength. As the first experimental investigation on the axial compressive behavior of square and rectangular UHSCFFTs, the results of the study reported in this paper allows a number of significant conclusions to be drawn. Of primary importance, test results indicate that sufficiently confined square and rectangular UHSCFFTs can exhibit highly ductile behavior. The results also indicate that confinement effectiveness of FRP tubes increases with an increase in corner radius and as sectional aspect ratio approaches unity. It is found that UHSCFFTs having tubes of low confinement effectiveness may experience significant strength loss along the initial portions of the second branches on their stress–strain curves. Furthermore, it is observed that the behavior of UHSCFFTs at this region differs from their normal-strength concrete counterparts and is more sensitive to the effectiveness of confining tube. The second half of the paper presents the performance assessment of the existing FRP-confined concrete models in predicting the ultimate conditions of the HSC and UHSCFFTs. The results of this assessment demonstrate that the existing models provide unconservative estimates for specimens with higher concrete strengths. To address this, a new model that was developed on the basis of a comprehensive experimental test database and is applicable to both NSC and HSC of strengths up to 120MPa is proposed. The model comparisons demonstrate that the proposed model provides significantly improved predictions of the ultimate conditions of FRP-confined HSC compared to the existing models.

Grip strength dynamometry: Reliability and validity for adults with upper limb burns

Upper limb (UL) burns can result in significant loss of strength and physical function. The aim of this study was to establish the reliability and validity of grip strength dynamometry (GSD) for measuring burn-affected UL strength over time. A retrospective sample of adult participants (n=89) with UL burns was obtained from Royal Perth Hospital. Data were compiled from assessments conducted at discharge, one, three, six and 12 months afer burn. Within-session reliability and validity was examined through multivariable analyses. GSD demonstrated within-session reliability for all investigated timepoints (ICC's≥0.87, p<0.0005.) Criterion validity was confirmed with GSD and QuickDASH being significantly associated in both right (b=0.17, p=0.002) and left (b=0.14, p=0.002) hands. Construct validity was demonstrated through significant association of GSD values with location of burn (p<0.35); time after burn (p<0.012); surgical intervention (p=0.003) and burn size (p<0.05). This study demonstrates that grip strength dynamometry is a reliable and valid outcome measure for measuring burn-affected UL strength from one month to one year after burn.

The Role of Neural Tension in Stretch-Induced Strength Loss

The purpose of this study was to determine if neural tension during passive stretching affected subsequent strength loss. Eleven healthy subjects (10 men, 1 woman; age 34 ± 12 years) performed maximal isometric hamstring contractions at 100°, 80°, 60°, and 40° knee flexion before and after five 1-minute hamstring stretches performed in either a spinal neutral position or a neural tension position. One leg was stretched in the neutral position and the other in the neural tension position. Hamstring electromyography (EMG) activity was recorded during all contractions and stretches. Passive resistance to stretch was reduced by 11% after stretching (p < 0.01; no difference between neutral or neural tension stretches p = 0.41). Stretch-induced strength loss was apparent after neural tension stretches (12%, p < 0.01) but not after neutral stretches (5%, p = 0.09). There was a rightward shift in the angle-torque curve after neutral stretches (strength loss on ascending limb, strength gain on descending limb, p < 0.01). This effect was not apparent after neural tension stretches (p = 0.43). Stretching did not affect EMG activity during isometric contractions (<2% decline p = 0.58; no difference between neutral and neural tension, p = 0.86). Hamstring stretching with the spine in a neutral position did not result in a significant strength loss but shifted the length-tension relationship such that strength was decreased at short muscle lengths and increased at long muscle lengths. Hamstring stretching with increased neural tension resulted in strength loss with no associated shift in the length-tension relationship.