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PubMed1996

Diet-induced changes in serum cholesterol concentrations do not alter tryptophan hydroxylation rate or serotonin concentrations in gerbil brain.

The relationship between serum cholesterol concentrations and serotonin synthesis rate in brain was examined in Mongolian gerbils chronically fed diets containing 20% fat (safflower oil, beef tallow or butterfat) with or without added cholesterol (0.5%, dry weight). After 22 days on these diets, circulating cholesterol concentrations ranged between approximately 1.5 and approximately 20 mumol/ml. Despite this enormous range, in vivo tryptophan hydroxylation rate, and serotonin and 5-hydroxyindoleacetic acid concentrations in cerebral cortex, hypothalamus and brainstem did not differ significantly among the diet groups. Tryptophan concentrations in serum and brain were also unaffected. These results do not support the hypothesis that the link between depression, suicide and violent deaths and below-normal or reduced serum cholesterol concentrations in humans involves an alteration in serotonin synthesis and/or release by brain neurons.

Animals↗

PubMed2006

Effects of simultaneous ozone exposure and nitrogen loads on carbohydrate concentrations, biomass, growth, and nutrient concentrations of young beech trees (Fagus sylvatica).

Beech seedlings were grown under different nitrogen fertilisation regimes (0, 20, 40, and 80 kg Nha(-1)yr(-1)) for three years and were fumigated with either charcoal-filtered (F) or ambient air (O3). Nitrogen fertilisation increased leaf necroses, aphid infestations, and nutrient ratios in the leaves (N:P and N:K), as a result of decreased phosphorus and potassium concentrations. For plant growth, biomass accumulation, and starch concentrations, a positive nitrogen effect was found, but only for fertilisations of up to 40 kg Nha(-1) yr(-1). The highest nitrogen load, however, reduced leaf area, leaf water content, growth, biomass accumulation, and starch concentrations, whereas soluble carbohydrate concentrations were enhanced. The ozone fumigation resulted in reduced leaf area, leaf water content, shoot growth, root biomass accumulation, and decreased starch, phosphorus, and potassium concentrations, increasing the N:P and N:K ratios. A combined effect of the two pollutants was detected for the leaf area and the shoot elongation, where ozone fumigation amplified the nitrogen effects.

Air Pollution↗

PubMed2006

Breath alcohol concentration determined with a new analyzer using free exhalation predicts almost precisely the arterial blood alcohol concentration.

A new breath alcohol (ethanol) analyzer has been developed, which allows free exhalation, standardizes measured exhaled alcohol concentration to fully saturated water vapor at a body temperature of 37 degrees C (43.95 mg/L) and includes a built-in self-calibration system. We evaluated the performance of this instrument by comparing standardized alcohol concentration in freely expired breath (BrAC) with arterial (ABAC) and venous (VBAC) blood alcohol concentrations in fifteen healthy volunteers who drank 0.6 g of alcohol per kg body weight. The precision (coefficient of variation, CV) of the analyzer based on in vivo duplicate measurements in all phases of the alcohol metabolism was 1.7%. The ABAC/BrAC ratio was 2251+/-46 (mean+/-S.D.) in the post-absorptive phase and the mean bias between ABAC and BrAC x 2251 was 0.0035 g/L with 95% limits of agreement of 0.033 and -0.026. The ABAC and BrAC x 2251 were highly correlated (r=0.998, p<0.001) and the regression relationship was ABAC = 0.00045 + 1.0069 x (BrAC x 2251) indicating excellent agreement and no fixed or proportional bias. In the absorption phase, ABAC exceeded BrAC x 2251 by at most 0.04+/-0.03 g/L when tests were made at 10 min post-dosing (p<0.05). The VBAC/BrAC ratio never stabilized and varied continuously between 1834 and 3259. There was a proportional bias between VBAC and BrAC x 2251 (ABAC) in the post-absorptive phase (p<0.001). The pharmacokinetic analysis of the elimination rates of alcohol and times to zero BAC confirmed that BrAC x 2251 and ABAC agreed very well with each other, but not with VBAC (p<0.001). We conclude that this new breath analyzer using free exhalation has a high precision for in vivo testing. The BrAC reflects very accurately ABAC in the post-absorption phase and substantially well in the absorption phase and thereby reflects the concentration of alcohol reaching the brain. Our findings highlight the magnitude of arterio-venous differences in alcohol concentration and support the use of breath alcohol analyzers as a stand-alone test for medical and legal purposes.

Adult↗

PubMed2006

Comment on "Analysis of groundwater contamination using concentration-time series recorded during an integral pumping test: Bias introduced by strong concentration gradients within the plume" by Allelign Zeru and Gerhard Schäfer.

We consider the results of a recent paper in this journal [Zeru, A. and Schäfer, G., 2005. Analysis of groundwater contamination using concentration-time series recorded during an integral pumping test: Bias introduced by strong concentration gradients within the plume. Journal of Contaminant Hydrology 81 (2005) 106-124], which addresses the field-scale characterisation of contaminant plumes in groundwater. There, it is concluded that contaminant concentration gradients can bias Integral Pumping Test (IPT) interpretations considerably, in particular if IPTs are conducted in advective fronts of contaminant plumes. We discuss implications of this setting and also argue that the longitudinal and transverse dispersivities used in the examples of Zeru and Schäfer (2005) of up to 30 m and 3 m, respectively, are generally very high for the here relevant capture zone scale (<20 m). However, regardless of both longitudinal and transverse concentration gradients, we further show through a counter-example that IPT results are unbiased as long as the concentration attenuation along the flow direction is linear over the capture zone extent.

Bias↗

PubMed2002

Study on the concentration effects in size exclusion chromatography VII. A quantitative verification for the model theory of concentration and molecular mass dependences of hydrodynamic volumes for polydisperse polymers.

A model theory of concentration effects for polydisperse polymers was proposed in 1988. It is successful in relating the concentration of the injected solution to the effective hydrodynamic volumes of peak, the retention volumes of peak and the polydispersity index (Dc = (Vhcw)/(Vhcn) of hydro-dynamic volume distribution for polydisperse polymers at a given concentration. The dependence of the concentration of injected polymer solution on the effective hydrodynamic volumes, the retention volumes of peak and the polydispersity index of hydrodynamic volume distribution for narrow disperse and polydisperse polystyrene, poly(dodecyl methacrylate), poly(tridecyl methacrylate) and poly(methyl methacrylate) in tetrahydrofuran solvent were studied. The proposed theory was verified by these experimental data. Results show that the proposed theory can predict the concentration effects in GPC for polydisperse polymers quantitatively and can provide a theoretical foundation for the two methods of calibrating the universal calibration curves with polydisperse polymers and of determining the second virial coefficients (A2) of polymers. It is found that the determined values of A2 for narrow disperse and polydisperse polymers by the proposed method are in agreement with those obtained by the LALLS method, and the two universal calibration curves with narrow disperse and polydisperse polymers are in excellent agreement.

Calibration↗

PubMed2003

High plasma homocysteine concentrations are associated with plasma concentrations of thrombomodulin in patients with type 2 diabetes and link diabetic nephropathy to macroangiopathy.

In type 2 diabetic patients with or without nephropathy, we examined relationships between plasma concentrations of total homocysteine (tHcy) and clinical macroangiopathy, as well as endothelial dysfunction indicated by plasma thrombomodulin (TM) concentrations. We studied 103 type 2 diabetic patients including 26 with macroangiopathy (12 patients with coronary artery disease [CAD], 10 with stroke, and 4 with peripheral vascular disease [PVD]). Plasma tHcy was measured by high-performance liquid chromatography. Plasma TM was determined by enzyme immunoassay. As an index of glomerular filtration rate, creatinine clearance (Ccr) also was determined in a 24-hour urine collection. Considering all diabetic patients, plasma tHcy concentrations were significantly higher in those with macroangiopathy than in those without (10.4 +/- 3.7 v 8.5 +/- 2.8 micromol/L, P=.0077). By univariate and multivariate analyses, plasma tHcy was correlated inversely with Ccr. Plasma tHcy concentrations were significantly higher in the patients with overt albuminuria than in those with normoalbuminuria or microalbuminuria. After exclusion of patients with renal insufficiency (Ccr<60 mL/min), differences in plasma tHcy concentrations between patients with and without macroangiopathy were abolished. By multivariate analysis, total cholesterol, urinary albumin, Ccr, C-peptide, and tHcy retained significant influence on the plasma TM. Even in patients with normal renal function (Ccr > or = 80 mL/min), plasma tHcy was correlated positively with plasma TM. In conclusions, diabetic nephropathy is a main determinant of plasma tHcy elevation in type 2 diabetic patients. Since plasma TM is independently associated with plasma tHcy, in diabetic patients with overt nephropathy, elevation of tHcy reflecting reduced clearance is a likely cause of endothelial dysfunction, resulting in the atherosclerosis underlying development of cardiovascular disease.

Aged↗

PubMed2000

Sexual maturational changes circulatory inhibin concentration in relation to FSH concentration and testicular size in Suffolk and DLS rams.

Developmental patterns in immunoactive inhibin and FSH concentrations in peripheral blood were determined for Suffolk and DLS (Dorset x Leicester x Suffolk) rams born in January Blood samples were taken every 3 to 4 wk when testes were developing during puberty (5 to 44 wk of age) and redeveloping in early adulthood (17 to 23 months of age). Suffolk lambs had a greater average daily gain (195 vs. 143 g/day, P<0.01), and they developed larger testes (P<0.01) than DLS lambs. Inhibin and FSH concentrations peaked at about the same pubertal (8 wk) and early adult (19 or 20 months) ages in both breeds. Elevations in FSH were greater (P< 0.05) in Suffolk than DLS rams at each stage of development. The pubertal inhibin peak was nearly 70% larger (P<0.01) in DLS than Suffolk rams, and the early adult peak was comparable in rams of both breeds, but much smaller (P<0.01) than the pubertal peak. Nonetheless, inhibin was positively correlated (r=0.48 to 0.57) with FSH in both breeds during each developmental stage. Inhibin and testicular size were negatively correlated in Suffolk (r=-0.74) and DLS (r=-0.86) rams during puberty, and positively correlated in DLS rams (r=0.46) in early adulthood. We conclude that 1) inhibin concentrations are higher in juvenile rams at the time Sertoli cell numbers are being established than in adult rams during testicular recrudescence and 2) rises in FSH concentration participate in regulating corresponding rises in inhibin concentration in both stages of testicular development.

Age Factors↗

PubMed1997

Low concentrations of caffeine raise intracellular calcium concentration only in the presence of extracellular calcium in cultured molluscan neurons.

1. The effects of low concentrations of caffeine (100 and 300 microM) on the intracellular calcium concentration [Ca2+]i in four cultured, identified neurons of the pond snail Lymnaea stagnalis (L) were investigated. 2. Intracellular CA2+ levels in these neurons were measured with the cell-permeable Ca2+ indicator Fura-2/AM, both in the presence and absence of extracellular Ca2 (o-Ca2+/EGTA). 3. In the presence of Ca2+ in the external medium, caffeine was found to induce a substantial elevation in the free [Ca2+]i in all cell types. 4. In some cases, the rise in [Ca2+]i was found to be both time- and concentration-dependent. 5. Low doses of caffeine did not produce any appreciable rise in [Ca2+]i in the absence of Ca2+ in the external medium, but calcium was still available from stores, as clinical concentrations of halothane rose [Ca2+]i in the absence of extracellular calcium. 6. These results indicate that the actions of caffeine, when applied at low concentrations, are dependent on extracellular calcium.

Animals↗

PubMed2001

Neurotransmitter concentrations and binding at dopamine receptors in rats after maternal exposure to 3,4,3',4'-tetrachlorobiphenyl: the role of reduced thyroid hormone concentrations.

Polychlorinated biphenyls (PCBs) are environmental contaminants, which accumulate in the food chain and are transferred to the offspring during prenatal development through the placenta and postnatally via breast milk. It is reported that PCBs exert effects on thyroid hormone levels and brain neurotransmitter levels. Both actions may alter neuronal development. The aim of the present study was to investigate, if PCB-induced effects on concentrations of catecholamines and serotonin can be attributed to PCB-induced reductions in thyroid hormone concentrations. In addition, binding to dopamine D(1) and D(2) receptors was examined. Time-mated Wistar rats were treated prenatally with 1 mg 3,4,3',4'-tetrachlorobiphenyl (PCB 77)/kg bodyweight or the vehicle. A third group serving as the positive control received perinatally 5 mg propylthiouracil (PTU)/l drinking water. There were no overt toxic signs in dams or offspring. Thyroid hormone measurements demonstrated effects in dams and offspring up to postnatal day 40. In particular, total T(4) in serum and in the thyroid were decreased in PCB- and PTU-treated dams and offspring. Only PTU exposed rats exhibited significantly increased concentrations of TSH in the serum and pituitary. Measurement of neurotransmitters revealed changes in the PCB-exposed offspring at PND 40, while PTU-treatment was without effect. Dopamine and DOPAC were increased in the medial prefrontal cortex. In adulthood, there were no PCB-related effects on thyroid hormones and neurotransmitters. Binding studies of dopamine D1 and D2 receptors demonstrated that PCB and PTU had no influence on receptor concentration and affinity. Comparison of PCB 77 exposed offspring to PTU exposed offspring demonstrated differential effects on TSH and neurotransmitter levels, the latter result indicating that not all PCB-induced effects on the nervous system can be ascribed to decreases in thyroid hormone concentrations.

Journal Article↗

PubMed2002

Steady-state concentration distribution of artificial receptor and target analyte in plasticized PVC membrane between solutions differing in target analyte concentration.

A barbiturate receptor has proven effective in improving selectivity in solid-phase microextraction of barbiturates when doped into plasticized poly(vinyl chloride) (PVC). It would be beneficial to have selective extractions for any given organic species; however, the receptors do not exist. They will be found by screening of libraries of potential receptors; thus, a screening method is needed. It is important to screen the receptors in the medium in which they will work: plasticized PVC. We hypothesize that we can make receptors move in solution in response to the presence of a solute to which they bind. This work examines whether we can establish a sufficient free energy gradient for a good receptor to move to a predetermined place in space. A difference in the barbiturate solute (substrate or guest) concentration in solutions bathing the two sides of a plasticized PVC membrane containing the barbiturate receptor (or host) creates a spatial concentration gradient of the substrate in the membrane. This causes the receptor's chemical potential to vary across the membrane. Upon binding to the analyte, the receptor undergoes a local activity drop, which decreases its free energy. This process produces a flux of receptor to accumulate at place where there is a high substrate concentration. A concentration gradient of substrate can be maintained across the membrane at steady state. In membranes for which the formation of the complex is favored, the receptor responds to the gradient of substrate. In membranes for which binding is not favored, a gradient of substrate is completely ignored by the receptor. Thus, the receptor does respond to the gradient but only if the concentration gradient of guest corresponds to a chemical potential gradient.

Barbiturates↗

PubMed2001

Areas with high concentrations of selenium in the soil and forage produce beef with enhanced concentrations of selenium.

Beef provides a significant portion of human dietary selenium (Se), and it is possible that modest portions of beef produced in areas with high-Se soil and forage could provide the entire Recommended Dietary Allowance (RDA) for Se. The present study has addressed the environmental conditions that resulted in the production of high-Se beef. One hundred and thirty-eight cull cows were obtained from 21 ranches in five distinct geographic regions that, on the basis of soil parent material, reports of Se deficiency, and previous soil and forage Se surveys, were likely to have high or low Se concentrations in the soil. Grass and soil samples were taken from ranch sites, and hair, whole blood, skeletal muscle, diaphragm muscle, and liver samples were obtained from the animals. Hair and whole blood samples were taken 1 day prior to shipping. Selenium concentrations of all samples were determined by hydride generation atomic absorption spectroscopy. Geographic origin affected Se content of all samples (p < 0.05). Selenium concentrations in soil (r = 0.53; p < 0.01) and grass (r = 0.63; p < 0.01) were correlated to Se content of skeletal muscle. Selenium concentrations in whole blood, diaphragm, hair, and liver also were significantly correlated to Se content of skeletal muscle (p < 0.01). Cows that received Se in mineral supplements did not have significantly higher concentrations of Se in sampled tissues (p > 0.05). Results of this study suggest that the greatest source of variation in Se content of bovine skeletal muscle was the geographic region from which the beef originated and not production or management practices. Results also demonstrated that a 100 g serving of high-Se beef could provide 100% of the RDA for Se.

Animal Feed↗

PubMed2000

Association of fasting breath nitrous oxide concentration with gastric juice nitrate and nitrite concentrations and Helicobacter pylori infection.

Fasting breath nitrous oxide (N2O) concentration was determined in relation to pH, nitrate (NO3-) and nitrite (NO2-) concentrations in gastric juice, and Helicobacter pylori infection in 86 successive patients. N2O was measured with an infrared-photoacoustic analyzer. NO3- and NO2- were measured using the Griess reaction. Fasting breath N2O concentration in controls (87 +/- 21 ppb) was not significantly different from that in patients with gastric ulcer or other gastric lesions. Breath N2O was significantly correlated with gastric NO3- (P < 0.01) and was higher in patients with elevated gastric NO2- (246 +/- 87 ppb) than in patients without NO2- (75 +/- 13 ppb). Breath N2O did not differ significantly between subjects who were positive or negative for H. pylori. In conclusion, fasting breath N2O concentration is in some manner related to intragastric NO3- and NO2- concentrations. The possible use of measuring breath N2O as predictors of cancer needs further research.

Adult↗

PubMed1999

Effects of low-fat stanol ester enriched margarines on concentrations of serum carotenoids in subjects with elevated serum cholesterol concentrations.

OBJECTIVE: To investigate the effects of low-fat stanol ester margarines on concentrations of serum carotenoids. DESIGN: A randomized parallel double-blind study design consisting of a 4-week run-in (high-fat diet) and an 8-week experimental (low-fat, low-cholesterol diet) period. During the experimental diet period subjects consumed low-fat wood stanol ester (WSEM), vegetable oil stanol ester (VOSEM) or control (no stanol esters) margarine daily. The daily mean total stanol intake was 2.31 and 2.16 g in the WSEM and VOSEM groups, respectively. SETTING: Outpatient clinical trial with free-living subjects. SUBJECTS: Altogether, 60 hypercholesterolaemic subjects were selected for the study out of 91 originally screened. The study was completed by 55 subjects. MAIN OUTCOMES MEASURES: Serum alpha- and beta-carotene and lycopene determined by the HPLC. RESULTS: Serum alpha-carotene concentration did not change significantly in either of the experimental groups, whereas beta-carotene concentration decreased significantly in the WSEM and VOSEM groups (P<0.01), and the change differed significantly (P<0.05 and P <0.01, respectively) from that of the control group. Decrease in alpha+beta-carotene concentration was significantly greater (P <0.05) in both experimental groups than in the control group. However, the change in alpha-, beta- or alpha+beta-carotene/total cholesterol ratio did not differ significantly among the groups. No significant changes were found in serum lycopene or lycopene/total cholesterol ratio in both experimental groups. CONCLUSIONS: Low-fat stanol ester margarines appeared to have little effect on serum concentrations of alpha-, beta- or alpha + beta-carotene, or lycopene. SPONSORSHIP: Grant to the University of Kuopio by Raisio Benecol Ltd, Raisio, Finland.

Adult↗

PubMed2004

Concentrations of polychlorinated dibenzo-p-dioxins, dibenzofurans, non-ortho polychlorinated biphenyls, and mono-ortho polychlorinated biphenyls in Japanese flounder, with reference to the relationship between body length and concentration.

The concentrations of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), non-ortho polychlorinated biphenyls (non-ortho PCBs), and mono-ortho polychlorinated biphenyls (mono-ortho PCBs) in Japanese flounder (Paralichthys olivaceus, body length 10.4-36.6 cm) collected from Sendai Bay, Japan, were determined using high-resolution gas chromatography-mass spectrometry. The relationship between the concentrations of these compounds (dioxins) and the body length of the Japanese flounder was examined. The total PCDD and total PCDF concentrations did not correlate with body length (both r(2) < 0.1, both p > 0.05), whereas the total non-ortho PCB and total mono-ortho PCB (coplanar polychlorinated biphenyls, Co-PCBs) concentrations were significantly correlated (r(2)= 0.8, p < 0.05 and r(2)= 0.63, p < 0.05, respectively). The bioaccumulation properties of PCDD/Fs in Japanese flounder differed from those of Co-PCBs. Toxicity equivalency quotient (TEQ) values derived from the Co-PCBs made up 46.3%-63.7% of the total TEQ value for all the dioxins. Although the concentrations of non-ortho PCBs were lower than those of mono-ortho PCBs, the TEQ value for non-ortho PCBs was higher than that for mono-ortho PCBs. The TEQ value for non-ortho PCBs increased more with increasing body length than did the values for PCDDs, PCDFs, and mono-ortho PCBs. These results show that from the standpoint of risk management, non-ortho Co-PCBs are the most important of the dioxins in Japanese flounder.

Animals↗

PubMed2003

Application of artificial neural network modelling to identify severely ill patients whose aminoglycoside concentrations are likely to fall below therapeutic concentrations.

OBJECTIVE: Identification of ICU patients whose concentrations are likely to fall below therapeutic concentrations using artificial neural network (ANN) modelling and individual patient physiologic data. METHOD: Data on indicators of disease severity and some physiologic data were collected from 89 ICU patients who received arbekacin (ABK) and 61 who received amikacin (AMK). Three-layer ANN modelling and multivariate logistic regression analysis were used to predict the plasma concentrations of the aminoglycosides (ABK and AMK) in the severely ill patients. RESULTS: Predictive performance analysis showed that the sensitivity and specificity of ANN modelling was superior to multivariate logistic regression analysis. For accurate modelling, a predictable range should be inferred from the data structure before the analysis. Restriction of the predictable region, based on the data structure, increased predictive performance. CONCLUSION: ANN analysis was superior to multivariate logistic regression analysis in predicting which patients would have plasma concentrations lower than the minimum therapeutic concentration. To improve predictive performance, the predictable range should be inferred from the data structure before prediction. When applying ANN modelling in clinical settings, the predictive performance and predictable region should be investigated in detail to avoid the risk of harm to severely ill patients.

Amikacin↗

PubMed1999

Effect of factor VIII concentrate on leucocyte cytokine production: characterization of TGF-beta as an immunomodulatory component in plasma-derived factor VIII concentrate.

Clinical and subclinical immunological abnormalities have been reported in HIV-seronegative haemophiliacs. The mechanisms by which these abnormalities arise remain unclear. As cytokines are important biological response modifiers, the effect of a FVIII concentrate on production of a range of cytokines, by a variety of cells, was investigated. A whole blood technique was used and the in vitro modulation of cytokine synthesis by an intermediate-purity plasma-derived factor VIII (pdFVIII) concentrate was analysed using multiparameter flow cytometry. In cell cultures exposed to pdFVIII, T cells showed reduced production of TNF-alpha, IL-2 and IFN-gamma; monocytes showed reduced production of TNF-alpha, IL-1alpha, IL-1beta, IL-6, IL-8 and IL-12 but an increase in IL-10 synthesis; IFN-gamma synthesis by NK cells was reduced. All changes in cytokine synthesis and the reduction in cell surface expression of CD69, a signal transduction molecule contributing to both cytokine and cytokine receptor synthesis, were in a dose-dependent manner in cultures exposed to FVIII concentrate. These changes were characteristic of TGF-beta. Addition of anti-TGF-beta to FVIII reduced these changes in T-cell cytokine production, suggesting TGF-beta may be an important immunomodulatory agent in the pdFVIII concentrate. The Th2 cytokine bias shown in the presence of pdFVIII concentrate, in vitro, may explain the increase in rates of certain types of infections reported in these patients, which require Th1 cytokine production for an effective response.

Antigens, CD↗

PubMedDate not supplied

Granulocyte concentrates. Glucose concentrations and glucose utilization during storage at 22 degrees C.

Neutrophil metabolism is dependent on the available stores of either exogenous or endogenous glucose. We studied 38 granulocyte concentrates collected by four different centrifugal cytapheresis systems: Haemonetics model 30, IBM 2997, Fenwal CS-3000, and Fenwal Celltrifuge II. Extracellular glucose concentrations were measured immediately following collection and after 24 hours of storage. The Fenwal CS-3000 produced the highest concentrations of platelets and leukocytes, and the units had the lowest initial glucose levels and pH. After 24 hours of storage, there was a mean glucose of 1.7 mg per dl in the Fenwal CS-3000 granulocyte concentrates and 9 of 12 units had no detectable glucose. In contrast, concentrates collected from other systems had sufficient glucose available to support neutrophil metabolism for a longer period.

Blood Glucose↗

PubMed2003

Maximal voluntary eccentric, isometric and concentric torque recovery following a concentric isokinetic exercise.

To examine neuromuscular fatigue and recovery following an isokinetic fatiguing exercise, nine active females performed a fatiguing exercise comprising of ten sets of ten maximal concentric knee extensions. Before (pre-test), five minutes (post-test), 24 h and 48 h after the fatiguing exercise, maximal voluntary eccentric (-1.05 rad x s(-1); -2.09 rad x s(-1)), isometric (0 rad x s(-1)) and concentric (1.05 rad x s(-1); 2.09 rad x s(-1)) torque were measured. In order to distinguish central from peripheral factors involved in torque decrement, activation level (twitch interpolation technique) and twitch contractile properties were recorded. During the course of the fatiguing exercise, concentric torque was significantly lower during the 3rd set than pre-test (-5.6 +/- 12.3 %) and further decreased to the 10th (-10.3 +/- 9.5 %). Eccentric and isometric torques were significantly lower during post-test than pre-test (-16.8 +/- 8.8 % at -2.09 rad x s(-1), -15.1 +/- 7.4 % at -1.05 rad x s(-1), and -10.4 +/- 5.9 % at 0 rad x s(-1); p < 0.05), while concentric torque was not significantly modified. Voluntary activation, peak twitch torque, twitch maximal rates of force development and relaxation were also significantly declined (p < 0.05) at post-test. Twenty-four hours later, all the measured parameters were close to their pre-fatigue values. The present results reveal that the best way to test concentric-induced alteration of neuromuscular function was to use stressful testing conditions, such as eccentric contractions.

Adult↗