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Effects garlic on aerobic performance

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Abstract

The effects of the administration of a single dose of garlic on the aerobic performance of college endurance athletes were investigated in this study. Ten trained male athletes participated voluntarily in this study. A 900-mg dose of dried garlic powder or placebo was administered randomly in a double-blind cross-over fashion. Five hours after ingestion of the tablets, the subjects underwent an incremental treadmill running test according to the Bruce protocol until subjective exhaustion. During the test, blood pressure and heart rate were monitored at 3 rain intervals. After a one-week wash out period, the subjects were crossed over and the procedures were repeated for the other substance. A paired t test was used for statistical analyses. There was a significant increase in maximum oxygen consumption (VO2max) and endurance performance time 5 h after garlic administration as compared to the placebo (p<0.05). The administration of single dose of garlic was thus shown to increase VO2max and endurance performance time of college endurance athletes during a treadmill running test according to the Bruce protocol.

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... The average relative VO 2 max was 59.8 ml • kg −1 • min −1 and 61.4 ml • kg −1 • min −1 for the placebo and garlic trials, respectively. Ince & colleagues [41] administered a single dose of garlic to ten college-aged endurance athletes and observed a significant increase in VO 2 max (57.3 ml • kg −1 • min −1 for the garlic trial and 55.6 ml • kg −1 • min −1 for the placebo trial) five hours after garlic ingestion. It was speculated that the observed differences between the garlic and placebo trials were due to improvements in the fluidity of the blood whereby whole-blood viscosity was decreased due to garlic-induced reductions in fibrinogen concentration. ...
... It was speculated that the observed differences between the garlic and placebo trials were due to improvements in the fluidity of the blood whereby whole-blood viscosity was decreased due to garlic-induced reductions in fibrinogen concentration. However, fibrinogen was not measured by Ince & colleagues [41] or in the current study so this possibility cannot be proven. Interestingly, Morihara & coworkers [20] also examined the impact of aged garlic extract (AGE) on succinate dehydrogenase (SDH) activity. ...
... The present study found a 1.6 ml • kg −1 • min −1 increase in VO 2 max without a corresponding improvement in treadmill time. Conversely, Ince & colleagues [41] observed a 2 ml • kg −1 • min −1 increase in VO 2 max as well as a 53.6 s increase in treadmill time. Both studies used groups of healthy trained college aged males. ...
... The average relative VO 2 max was 59.8 ml • kg −1 • min −1 and 61.4 ml • kg −1 • min −1 for the placebo and garlic trials, respectively. Ince & colleagues [41] administered a single dose of garlic to ten college-aged endurance athletes and observed a significant increase in VO 2 max (57.3 ml • kg −1 • min −1 for the garlic trial and 55.6 ml • kg −1 • min −1 for the placebo trial) five hours after garlic ingestion. It was speculated that the observed differences between the garlic and placebo trials were due to improvements in the fluidity of the blood whereby whole-blood viscosity was decreased due to garlic-induced reductions in fibrinogen concentration. ...
... It was speculated that the observed differences between the garlic and placebo trials were due to improvements in the fluidity of the blood whereby whole-blood viscosity was decreased due to garlic-induced reductions in fibrinogen concentration. However, fibrinogen was not measured by Ince & colleagues [41] or in the current study so this possibility cannot be proven. Interestingly, Morihara & coworkers [20] also examined the impact of aged garlic extract (AGE) on succinate dehydrogenase (SDH) activity. ...
... The present study found a 1.6 ml • kg −1 • min −1 increase in VO 2 max without a corresponding improvement in treadmill time. Conversely, Ince & colleagues [41] observed a 2 ml • kg −1 • min −1 increase in VO 2 max as well as a 53.6 s increase in treadmill time. Both studies used groups of healthy trained college aged males. ...
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Background The purpose of this project was to examine the effects of acute garlic supplementation on fibrinolysis and vasoreactivity both at rest and following maximal exercise. Methods Eighteen healthy trained males (20.9 ± 2.2 years, 178 ± 7.7 cm, 75.5 ± 9.6 kg, VO2max = 59.8 ± 6.7 ml • kg−1 • min−1) performed a graded treadmill test to volitional exhaustion. Blood samples were taken at rest, within two minutes post-exercise, and one hour post-exercise. Eleven of the subjects also had a brachial vasoreactivity test performed immediately after the blood sample to assess flow-mediated dilation (FMD) of the brachial artery. Participants were randomly assigned to ingest either 900 mg of powdered garlic or a placebo three hours before the exercise session. The supplement was distributed in a double-blind, crossover fashion. Participants repeated the protocol with the other treatment after a 14-day washout period. Paired t-tests were used to compare VO2max between the two trials. A two-factor (treatment and time) repeated measures analysis of variance (ANOVA) was used to assess changes in FMD, tPA activity, tPA antigen, and PAI-1 activity. A priori statistical significance was set at P <0.05. Results VO2max was greater for the garlic treatment trial vs. placebo (Placebo = 59.8 ± 6.7 ml • kg−1 • min−1; Garlic = 61.4 ± 6.6 ml • kg−1 • min−1). There was no main effect for treatment and no treatment x time interaction for FMD or any fibrinolytic variables examined. Conclusion Acute garlic supplementation does not alter vasoreactivity, fibrinolytic potential or the fibrinolytic response to exercise in young healthy trained males. Acute garlic supplementation does, however, cause a small but statistically significant increase in VO2max. It remains unclear if this increase in VO2max is of functional importance.
... Several proposed mechanisms may determine the effect of garlic on obesity including decrease in fatty acid synthesis [21,22], decrease in intestinal triglyceride absorption [23], increase in the oxygen consumption [24], inhibiting human preadipocyte differentiation and lipid accumulation [25], increase in apoptosis in 3T3-L1 adipocytes [26]. Meanwhile, studies on anti-obesity properties of garlic are controversial and inconsistent. ...
... Moreover, a study in 2013 showed that garlic tends to decrease intestinal triglyceride absorption resulting in an increased triglyceride level in stool [51]. Another mechanism by which garlic seems to have a role in controlling body fat may be due to its thermogenic properties and its related derivatives which increase the oxygen consumption [24]. 1,2-vinyldithiin (a garlic-derived organosulfur) suppresses gene expression of peroxisome proliferator-activated receptor gamma in differentiated preadipocyte which leads to inhibiting differentiation of human preadipocyte [25]. ...
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Obesity is related to increase in the incidence of morbidity and mortality. Studies have suggested anti-obesity properties of garlic; however, results are inconsistent. This systematic review and meta-analysis is done to summarize the data obtained from available randomized clinical trials on the effect of garlic supplementation on body weight, Body Mass Index (BMI), and Waist Circumference (WC). The online databases of Scopus, PubMed, Google Scholar and Cochrane library were searched until March 2018 for related publications using relevant keywords. Effect sizes of eligible studies were pooled using random-effects models. Cochran’s Q-test and I2 index were used for assessing heterogeneity. To assess the publication bias, funnel plot and Egger’s tests were used. We found 1241 records in our initial search, of which 13 randomized clinical trials (RCTs) with 15 treatment arms were included. Pooled analysis showed that garlic administration might significantly decrease WC (Weighed Mean Difference (WMD): -1.10 cm, 95% CI: -2.13, -0.07, P= 0.03, I2= 0 %). However, garlic intervention had no significant effect on body weight (WMD): -0.17 kg, 95% CI: : -0.75 to 0.39, P= 0.54 , I2= 0%) and BMI (WMD: -0.17 kg/m2, 95% CI: -0.52, 0.16, P= 0.30, I2= 44.5 %) as compared to controls. From Subgroup analysis, it was ascertained that the effect of garlic supplementation on BMI was significant in trials with duration <12 weeks (WMD: -0.58 kg/m2, 95% CI: -1.08, -0.08, I2=19.8%, P= 0.02). The current meta-analysis results suggest that garlic supplementation seems to reduce waist circumference unlike body weight and BMI.
... Therefore, having a good regime A and proper use of appropriate supplements have an important role in the performance of athletes [1]. Numerous studies have shown that medicinal plants such as garlic, ginger, fenugreek, pomegranate extract, etc., by preventing platelet aggregation and activating fibrinolytic factors, increase blood fluidity and thus increase blood flow to muscles and increases a person's ability to perform sports activities [2]. A group of antioxidants that are often good candidates for antioxidant therapy because of their potential role in health are flavonoids. ...
Article
Objective: Due to the uncertainty of the impact of thyme plant on endurance sport performance, despite its high antioxidant property, this study aims to assess the effect of aerobic exercise combined with thyme extract supplementation on the PGC-1α gene expression in male rats. Methods: This experimental study was conducted on 40 adult male Wistar rats randomly classified into five groups of 8 including control, sham, aerobic exercise, thyme extract (400 mg per kg per day), and aerobic exercise + thyme extract. The rats began their exercise on a treadmill for 10 minutes a day with a speed of 10 m/min and a slope of 10%. Speed and duration of exercise gradually increased over the next two weeks until they reached 27 m/min and one hour per day, respectively. The real-time Polymerase Chain Reaction (PCR) method was used to investigate the PGC-1α gene expression extracted from the soleus muscle of rats. Results: There was a significant difference in PGC-1α gene expression after intervention between the combined group and control and sham groups (Mean=1.01±0.0306; F=4.238, P=0.05). However, the PGC-1α gene expression rate in aerobic exercise group and supplementation group was no significantly different compared to control and sham groups (Mean=1.01±0.0306; F=0.00001, P=0.005). Conclusion: It seems that thyme extract supplementation along with aerobic exercise increases the PGC-1α gene expression.
... The antiobesity effect of garlic may be explained by its thermogenic properties, and this is confirmed by Ince et al. (2000), who found that garlic and its derivatives increased oxygen consumption. SAMC can lower serum levels of free fatty acid, which can cause initial pathological changes during NAFLD and significantly decrease lipid accumulation in hepatocytes (Xiao et al., 2013). ...
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Purpose This paper aims to determine the effect of black garlic (BG) on visceral fat, oxidative stress and insulin resistance (IR) compared with metformin and vitamin E in nonalcoholic fatty liver disease (NAFLD) rats. Design/methodology/approach A randomized post-test only design with control group was used in this study. Rats were given high-fat fructose diet enriched with 1.25% cholesterol and 0.5% cholic acid for eight weeks to induce NALFD condition. The administration of BG dose of 450 mg/200 gBW, 900 mg/200 gBW and 1350 mg/200 gBW with a comparative control of 45 mg/200 gBW of metformin and vitamin E of 9 IU/200 gBW were given for four weeks via oral gavage to reduce visceral fat, oxidative stress and improve IR. Statistical analyses were performed to examine differences between groups with one-way analysis of variance and nonparametrics test. Findings Rats given with three different doses of BG for four weeks did not reduce body weight from 244 ± 4.4 to 284 ± 4.6 g, 242 ± 2.5 to 272 ± 3.1 g and 240 ± 2.4 to 270 ± 3.6 g, respectively, but significantly reduced visceral fat ( p = 0.001) on BG groups with 3.7 ± 1.3, 2.7 ± 0.7 and 1.8 ± 0.6 g, respectively. BG improved oxidative stress ( p = 0.001) with malondialdehyde level 5.1 ± 0.2, 3.0 ± 0.06 and 2.3 ± 0.06 ng/mL, respectively, but did not better than vitamin E group 1 ± 0.03 ng/mL. Significant ( p = 0.001) improvement on insulin resistance with homeostatic model assessment IR in BG groups were 5.3 ± 0.1, 4.4 ± 0.1 and 4 ± 0.1, respectively, but not as good as metformin group 3.7 ± 0.1. Research limitations/implications Based on the experiment, there are several limitations including small sample size, performed on animal models in a relatively short time, did not examine organosulfurs compound (OSC) content of BG specifically and OSC affects metabolism in NAFLD remains unclear and will require further investigation. Practical implications BG is a functional food made from heated fresh garlic owing to the Maillard reaction and the organosulfur compounds as antioxidants. The higher the dose of BG, the greater the improvement in visceral fat, oxidative stress and IR in model NAFLD rats. Social implications NAFLD is a liver disorder caused by excessive fat and energy intake, the treatment strategies among others through diet modification. Originality/value In model NAFLD rats, BG administration improved NALFD markers but did not better rather than the metformin and vitamin E result.
... Such modifications are also mostly environmentally friendly. Increasing plant-based foods also boosts vasodilatory, antioxidant, and anti-inflammatory properties of the diet, which can lead to improved blood flow, reduced oxidative stress and inflammation, and thus, enhanced endurance performance, reduced muscle damage, and speedier recovery [124][125][126]. ...
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Purpose of review: Sustainable production and healthy consumption have been the topic of recent publications. Due to the high environmental impact of the current food system, significant changes in how food is produced, distributed, and consumed are needed in all sectors and groups. While most research in sustainable diets has focused on the general population, limited work has involved athletes. The purpose of this review is to summarize the current knowledge on food and sustainability in athletes. Recent findings: Meeting but not exceeding protein requirements through flexitarian and plant-based approaches, reducing packaged foods and food waste, and prioritizing seasonal produce were identified as possible mitigation options in athletes. There is urgency for more research on plant-centric, whole food-based strategies for post-exercise skeletal muscle and training adaptation, the effect of sustainable diets on health and performance, and behaviors to reduce packaging and food waste in athletes.
... 31 Possible mechanisms of garlic affecting obesity are reduction of intestinal absorption of triglycerides, inhibition of PPAR gamma gene expression, and consequently suppression of human preadipocyte differentiation and lipid accumulation in differentiated preadipocyte, as well as the thermogenic effects of garlic. 16,32,33 Very few clinical trials, however, have examined the effect of garlic powder supplementation on body composition. In a 15week study by Soleimani et al., 19 garlic powder supplementation improved obesity indices such as weight and fat mass in patients with NAFLD; nonetheless, no significant weight loss was observed in our study. ...
Article
Background Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease worldwide. Insulin resistance, oxidative stress, and obesity are major contributors to NAFLD pathogenesis. The effects of garlic powder supplementation on these risk factors in patients with NAFLD was investigated. Methods In this 12-wk, randomized controlled clinical trial, ninety patients with NAFLD were randomly assigned to two groups. The treatment group received four tablets of garlic (each coated tablet contained 400 mg garlic powder) daily and the control group received four tablets of placebo (each coated tablet contained 400 mg starch). Results A significant decrease was seen in the treatment group compared to the control group in waist circumference (P = 0.001), body fat percent (P < 0.001), serum concentration of fasting blood sugar (P = 0.01), insulin (P < 0.001), homeostatic model assessment for insulin resistance (P < 0.001), and malondialdehyde (P < 0.001), as well as significant increase in skeletal muscle mass (P = 0.002), serum concentration of superoxide dismutase (P < 0.001), and total antioxidant capacity (P < 0.001). Conclusion Garlic powder supplementation improved risk factors of NAFLD. Further studies are needed to determine the effects of garlic on hepatic features in patients with NAFLD. The study protocol was registered at Iranian clinical trials website under code IRCT20170206032417N4.
... Compared with omnivores, people following vegan and vegetarian diets have increased antioxidant activity, due to higher intakes of vitamin C, vitamin E, beta-carotene, and other antioxidants [52], as well as to higher antioxidant enzyme production [53]. Researchers have also found potentially beneficial effects of specific antioxidant-rich foods on exercise outcomes, notably beets [54], allium vegetables (e.g., garlic, onions, and leeks) [55], and cherry juice [56]. Antioxidant supplements, such as vitamin E, vitamin C, beta carotene, and glutathione, have been shown to reduce oxidative stress, but some researchers have suggested that they may delay muscle recovery, prevent some of the positive health effects of exercise, and block the improvement of insulin sensitivity associated with exercise [22,57]. ...
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Studies suggest that endurance athletes are at higher-than-average risk for atherosclerosis and myocardial damage. The ability of plant-based regimens to reduce risk and affect performance was reviewed. The effect of plant-based diets on cardiovascular risk factors, particularly plasma lipid concentrations, body weight, and blood pressure, and, as part of a healthful lifestyle, reversing existing atherosclerotic lesions, may provide a substantial measure of cardiovascular protection. In addition, plant-based diets may offer performance advantages. They have consistently been shown to reduce body fat, leading to a leaner body composition. Because plants are typically high in carbohydrate, they foster effective glycogen storage. By reducing blood viscosity and improving arterial flexibility and endothelial function, they may be expected to improve vascular flow and tissue oxygenation. Because many vegetables, fruits, and other plant-based foods are rich in antioxidants, they help reduce oxidative stress. Diets emphasizing plant foods have also been shown to reduce indicators of inflammation. These features of plant-based diets may present safety and performance advantages for endurance athletes. The purpose of this review was to explore the role of nutrition in providing cardioprotection, with a focus on plant-based diets previously shown to provide cardiac benefits.
... These results suggest that garlic treatment can produce a thermogenic effect, which explains the increase in energy expenditure and resistance to weight gain of these mice. It has been reported that garlic increases the expression of UCP1 protein, oxygen consumption, and body temperature (17,18,37). ...
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This study investigated the antiobesity effect of garlic in diet-induced obese mice. Male C57BL/6J mice were fed a high-fat diet (45% fat) for 8 wk to induce obesity. Subsequently, they were fed a high-fat control diet, high-fat diets supplemented with 2%, or 5% garlic (wt:wt) for another 7 wk. Dietary garlic reduced body weight and the mass of various white adipose tissue deposits and also ameliorated the high-fat diet-induced abnormal plasma and liver lipid profiles. Garlic supplementation significantly decreased the mRNA levels of adipogenic genes in white adipose tissues (WAT). However, consumption of garlic increased the expression of mRNA for uncoupling proteins in brown adipose tissue (BAT), liver, WAT, and skeletal muscle. Mice treated with garlic maintained a significantly higher body temperature than untreated mice during a 6-h, 4°C cold challenge and, notably, AMP-activated protein kinase (AMPK) activity was stimulated in BAT, liver, WAT, and skeletal muscle. These results suggest that the antiobesity effects of garlic were at least partially mediated via activation of AMPK, increased thermogenesis, and decreased expression of multiple genes involved in adipogenesis.
Moderate exercise combined with proper nutrition are considered protective factors against cardiovascular disease and musculoskeletal disorders. However, physical activity is known not only to have positive effects. In fact, the achievement of a good performance requires a very high oxygen consumption, which leads to the formation of oxygen free radicals, responsible for premature cell aging and diseases such as heart failure and muscle injury. In this scenario, a primary role is played by antioxidants, in particular by natural antioxidants that can be taken through the diet. Natural antioxidants are molecules capable of counteracting oxygen free radicals without causing cellular cytotoxicity. In recent years, therefore, research has conducted numerous studies on the identification of natural micronutrients, in order to prevent or mitigate oxidative stress induced by physical activity by helping to support conventional drug therapies against heart failure and muscle damage. The aim of this review is to have an overview of how controlled physical activity and a diet rich in antioxidants can represent a "natural cure" to prevent imbalances caused by free oxygen radicals in diseases such as heart failure and muscle damage. In particular, we will focus on sulfur-containing compounds that have the ability to protect the body from oxidative stress. We will mainly focus on six natural antioxidants: glutathione, taurine, lipoic acid, sulforaphane, garlic and methylsulfonylmethane.
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Introduction: The present study aims to investigate the effects of exhaustive running and different doses of short-term garlic supplementation on total antioxidant capacity (TAC) and Malondialdehyde (MDA) in during rest and exercise induced exhaustion in male soccer players. Materials and Methods: Thirty male football players (Average age: 20.8±1.45y; maximum oxygen intake 67.2±5.4 ml/kg/min and body mass index 21.5±1.34 kg/m2) were divided randomly into three homogenous groups, the placebo group and the 2 garlic supplementation groups given two dosages (1200 and 2400 mg/day). The first and second blood samples were taken in the basic state and after the Shuttle Run test and the third and fourth samples were taken after supplementation, in the basic state and after test. The parameters were then analyzed using one-way ANOVA, with a significance level of a=0.05. Results: Exhaustive running significantly decreased TAC and increased MDA level in the blood serum of male football players. On the other hand, garlic supplementation increased TAC (P<0.01) and decreased MDA (P<0.01) in the basic state. Moreover, supplementation hindered significant increase in the level of MDA (P<0.05) in male football players after the test but it failed to stop the decrease in TAC (P<0.05) level. Furthermore, the decrease of TAC level in supplementation group was significantly (P<0.05) less than in the placebo group. Conclusion: Short-term garlic extract supplementation may increase TAC and MDA in male football players in the basic state and hinder the fall in the total antioxidant capacity and oxidative stress after vigorous exercises. On the other hand, neither dosages of 1200 nor 2400 mg/day of garlic extract showed any effects on TAC or MDA in the groups of players investigated.
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Few studies have been conducted to assess adverse events associated with the use of natural products. We thus systematically assessed the evidence relating to the safety of garlic, i.e. adverse events and reports of herb-drug interaction from human studies. Systematic literature searches without language restriction were conducted in 4 electronic databases for data on human use and data also requested from spontaneous adverse event reporting programs including the World Health Organisation. Data from combination products and preparations of individual components of garlic were excluded. Data from clinical studies and spontaneous adverse event reporting schemes indicate that adverse events following garlic supplementation are mild and reversible. The most frequent events were body odour and gastrointestinal upsets. There were isolated case reports of garlic supplements causing increased bleeding during surgery. Few reports on herb-drug reactions were found. Although further rigorous studies are needed to assess the safety of garlic supplementation, the data available seem to indicate that garlic is a safe supplement with the caveat that it should be contraindicated prior to surgery or for patients on blood-thinning agents.
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Exercise changes many body functions including blood rheology. Two aspects are particularly relevant for peripheral vascular disease (PVD): Lack of exercise is a risk factor for PVD, and regular exercise is a therapy for PVD. In order to clarify the role of blood rheology in all this, we have conducted a number of independent trials. Our results show that acute physical stress leads to a marked viscid-alion of blood. A relative lack of exercise is associated with low and being an athlete with high blood fluidity. This does not apply to purely power trained men. Daily exercise improves the initially normal blood rheology of volunteers and normalize the initially abnormal blood rheology of PVD patients. Both cellular and plasmatic components are involved. We conclude that exercise has complex effects on blood rheology which can be used in treating PVD.
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The effect of endurance training on blood viscosity was studied by comparing blood rheological properties in control subjects (untrained) and endurance trained subjects. The effect of running on blood viscosity was studied in the 33 endurance trained subjects before and after a 48-km mountain race (Sandia Wilderness Crossing Research Run). Runners started at an altitude of 1700 m, ran 26 km to 3300 m, then descended 22 km to finish at 1900 m. Venous blood viscosity (eta b) and plasma viscosity (eta p) were measured at 37 degrees C at shear rates of 11.25, 22.5, 45, 90, and 225.s-1, using a cone-plate viscometer. Endurance trained subjects had significantly higher pre-race blood viscosity at 11.25 and 22.5.s-1 than control subjects but similar plasma viscosity and hematocrits. Following the race, there was no significant change in mean hematocrit, but eta b increased significantly at all shear rates except 225.s-1. Plasma viscosity at 225.s-1 increased significantly from 1.44 to 1.53 cP following the run. Since eta b did not increase, an increase in red cell deformability is inferred. The mechanism of the increase in eta b at lower shear rates in runners is due in part to the higher plasma viscosity. An additional mechanism at lower shear rates is in an increase in red cell aggregation. Increased plasma fibrinogen was measured in six of six resting subjects taken from 1600 m to 3300 m and is speculated to be the mechanism of enhanced aggregation and deformability in the runners.
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In a randomized placebo-controlled double-blind cross-over study it could be shown that 5 h after the administration of garlic powder (Kwai, Sapec; total dose of 900 mg garlic powder) a significant increase in capillary skin perfusion by 55% occurs in the healthy volunteers. Placebo did not cause any changes. The difference between the two study phases is also significant. The increased erythrocyte velocity results from vasodilation of precapillary arterioles which increases diameter of erythrocyte column by an average of 8.6%. Simultaneously inflow of interstitial fluidity accompanied by a significant decrease in haematocrit and plasma viscosity occurs (rheoregulation).
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Coagulation and fibrinolysis were evaluated in 29 healthy young male adults before, immediately after and one hr after strenuous exercise on a treadmill. Seven subjects were studied after moderate, prolonged exercise. Fourteen volunteers were tested before and after successful physical conditioning. Measurements included: pulse rate, glass and silicone whole blood clotting times, one stage prothrombin time, Stypven time, 2 stage prothrombin time, prothrombin consumption, partial thromboplastin time, thrombin time, fibrinogen, euglobulin lysis time, antifibrinolysin, hematocrit, and platelet count. Immediately after exercise, a marked increase in fibrinolytic activity and an acceleration of most clotting assays were observed. After physical conditioning there was a decrease in the level of fibrinolytic activity at rest and after exercise, but the reactivity of the fibrinolytic system, i.e., the percent increase in fibrinolytic activity in response to exercise, was unaltered. Following physical conditioning, the clotting times of certain assays were less accelerated.
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The apparent viscosity (n) of blood is determined by plasma viscosity, hematocrit (Hct), cell deformation and cell aggregation. The optimum Hct for oxygen transport varies with shear conditions and shows regional differences. In circulation in vivo, the complex geometry causes inertial, in addition to viscous, losses. Microvessels have low Hct and correspondingly low n. Hydrodynamic interactions between red blood cells (RBCs) and white blood cells (WBCs) may contribute to WBC adhesion to the endothelium. Entry of WBC into diverging branches may cause redistribution of RBCs. There is some understanding of the relation between in vitro and in vivo blood rheology, but further investigations are needed.
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Thirty-one male triathletes performed three experimental trials at one week intervals, with either a semi-solid or liquid carbohydrate feeding, or a liquid placebo. Exercise consisted of three hours of alternately cycling, running, cycling, and running at 75% VO2 max. Venous blood samples were taken before and immediately after the exercise. Viscometry was performed with a Contraves LS-30 viscometer and erythrocyte deformability was measured with the LORCA, a laser diffractometric system. Exercise caused a significant increase in whole blood and plasma viscosity, hematocrit, and osmolality, and a very small, but significant decrease in erythrocyte deformability, irrespective of the feedings consumed. Changes were not related to exercise performance, as defined by the maximal test time, probably due to a large fluid intake. The intake of different amounts of carbohydrate had no influence on the hemorheological parameters, probably since water content was equal among feedings. Erythrocyte deformability changes were small in comparison with the other hemorheological changes and a correlation between erythrocyte deformability and other parameters was absent. This may be due to erythrocyte properties to counterbalance volume shifts to ensure an optimal oxygen delivery in the microcirculation.