recently , a large number of cardiovascular risk factors have been detected , but the role of new risk factors added to traditional ones in predicting or preventing cardiovascular diseases and mortality is still unknown .
homocysteine and lipoprotein a are two new risk factors of heart diseases and may cause plaque formation on vessel walls . however , the pathogenic role of these risk factors in the developing cardiovascular disease is still debating .
homocysteine is a nonessential sulfur containing amino acid mediating metabolic path of nonessential methionine amino acid .
it is well documented that in humans and animals an encoding in homocysteine metabolism gene enzyme results in increased homocysteine and causes several metabolic disorders such as atherosclerosis , clotting in vessels and endothelial malfunctions .
epidemiological studies have proved the positive relationship between homocysteine concentration and risk of cardiovascular disease .
randeva et al . examined the effect of a 6 month exercise program on homocysteine levels .
duncan et al . examined the effect of severity and frequency of exercise sessions per week on homocysteine levels in middle age and observed a small increase in homocysteine levels .
it exacerbates atherosclerosis and its structure is similar to low density lipoprotein ( ldl ) , but with a glycoprotein called apoprotein an attached to it and its concentration being genetically determined .
research findings indicate that increased lipoprotein a < 30 mg / d lit increases cardiovascular diseases risk 3 - 10 times depending on the existence of other factors .
there are two mechanisms , which may explain the relationship between lipoprotein a and cardiovascular disease .
first , it is argued that lipoprotein a , like ldl , plays a role in initiating the progression of atheromatous plaque as a particle .
second , it is suggested that this particle competes with the plasminogen particles in preventing thrombolytic process .
zafari examined the effects of regular exercise on lipoprotein a levels in middle age men and observed that lipoprotein a levels in active and sedentary individuals are less than coronary artery disease patients .
almeida et al . studied the effects of 12 week of aerobic and strength training on rats and found no significant differences in lipoprotein a levels .
surveyed the effect of 8 week walking on lipoprotein a levels in women and observed no significant difference .
physical fitness reduces cardiovascular risk up to 50% in middle aged and is accompanied by preventing the developments of triglyceride ( tg ) , cholesterol and ldl risk factors and increasing high density lipoprotein ( hdl ) levels . from general health point of view , aerobic training is one the most effective ways to reduce the risk of cardiovascular diseases .
aerobic training is a key factor either alone or in combination with appropriate lifestyle in improving blood lipid profile .
aerobic training is recommended for improving lipid and lipoprotein levels as a low cost way for middle age .
researches have reported significant improvements in lipid profile and lipoprotein levels as a result of aerobic training positive . however , several paradoxes have been reported .
indicated the effect of 16 week of progressive aerobic training with moderate intensity on lipid profile in middle aged men .
as research shows , significant improvements will be observed in tg , cholesterol , ldl and hdl levels after aerobic training .
akcakoyun investigated the changes in lipid profile after moderate intensity training programs in middle aged men .
the results showed that levels of serum tg decreased , and hdl increased in the experimental group after the training program . in a study banitalebi
et al . investigated the effects of 12 week of progressive aerobic exercise on blood lipids and lipoproteins in 23 - 49 years old men .
no significant changes in levels of tg , cholesterol , ldl and hdl after 12 week were observed between the two groups .
long term studies show that physical inactivity in middle aged increases the risk of cardiovascular diseases up to 50% , in this study , we examined the effect of 12 week of aerobic training on homocysteine , lipoprotein a , and lipid profile levels in sedentary middle age men .
regarding controversies in previous studies findings and limitation of study about the influence of aerobic training on homocysteine and other lipoproteins this study seem necessary .
objectives , procedure , as well as possible risks of training programs were described to the subjects and their written consents were obtained .
subjects were selected according to their age , > 30 body mass index , physical health , not attending in regular exercises since 6 month before the study , normal lipid profile status and lack of a specific diet , medication , and smoking . the primary criterion for evaluating subjects health was to check the physical examination done by a physician and review the health questionnaire .
none of the subjects were affected to chronic autoimmune , systemic , cardiovascular , hepatic or other diseases , which can continuously change the lipid status .
also at the preliminary session the participants were asked not to change their diet and lifestyle during the 12 week .
qualified individuals were randomly assigned into two aerobic ( n = 12 ) and control ( n = 12 ) groups .
participant characteristics of the aerobic training and control group the subjects performed training sessions using a treadmill 3 times a week ( on nonconsecutive days ) and 20 min / session ( 60% of maximum heart rate ) to 60 min ( 75% of maximum heart rate ) .
subjects height and weight were recorded using a medical scale with stadiometer ( seca : 220 , germany ) .
body compositions were measured using a body composition analyzer ( inbody 3.0 , south korea ) .
blood samples were collected after 12 h fasting at pretest and 48 h after the last training session at posttest . after collecting blood samples at each step ,
axis homocysteine eia reagent kit ( axis - shield co. , dundee , uk ) .
kit ( made in england ) was used to measure homocysteine levels and drg elisa total human lipoprotein ( a ) ( drg international inc .
pars azmoon kit ( pars azmoon co. , tehran , iran ) and enzymatic method were used for the measurement of plasma levels of tg , total cholesterol and hdl ; and ldl was calculated by friedwald equation ( ldl = tc  ( hdl + tg/5 ) in terms of milligrams per deciliter .
statistical analysis was performed using spss for windows software , version 18 ( spss inc .
paired t - test was used for within group comparison and independent t - test was used for between groups comparison .
the subjects performed training sessions using a treadmill 3 times a week ( on nonconsecutive days ) and 20 min / session ( 60% of maximum heart rate ) to 60 min ( 75% of maximum heart rate ) .
subjects height and weight were recorded using a medical scale with stadiometer ( seca : 220 , germany ) .
body compositions were measured using a body composition analyzer ( inbody 3.0 , south korea ) .
blood samples were collected after 12 h fasting at pretest and 48 h after the last training session at posttest . after collecting blood samples at each step ,
axis homocysteine eia reagent kit ( axis - shield co. , dundee , uk ) .
kit ( made in england ) was used to measure homocysteine levels and drg elisa total human lipoprotein ( a ) ( drg international inc .
pars azmoon kit ( pars azmoon co. , tehran , iran ) and enzymatic method were used for the measurement of plasma levels of tg , total cholesterol and hdl ; and ldl was calculated by friedwald equation ( ldl = tc  ( hdl + tg/5 ) in terms of milligrams per deciliter .
statistical analysis was performed using spss for windows software , version 18 ( spss inc . ,
paired t - test was used for within group comparison and independent t - test was used for between groups comparison .
research findings indicate that there were statistically significant differences in the levels of homocysteine , lipoprotein a , tg , cholesterol , ldl and hdl in posttest compared to pretest ( p = 0.002 , 0.003 , 0.008 , 0.024 , 0.019 , and 0.017 , respectively ) .
table 3 shows the comparison of the variables between the aerobic training and control groups following 12 week .
the table 's results show significant differences between the values of homocysteine , lipoprotein a , tg , cholesterol , ldl and hdl between the two groups ( p = 0.005 , 0.001 , 0.006 , 0.015 , 0.022 and 0.004 , respectively ) .
the results of paired t test in aerobic training and control group before and after the intervention comparison of changes in measured variables following 12-week in two groups
this study was designed to investigate the effect of 12 week of aerobic training on homocysteine , lipoprotein a and lipid profile levels of sedentary middle age men .
the findings revealed that there was a significant decrease in homocysteine levels at posttest compared to pretest , and following 12 week of aerobic training significant differences between aerobic and control groups .
. one of the mechanisms associated with homocysteine function in cardiovascular diseases is due to a decrease in hdl levels .
homocysteine decreases hdl concentration in plasma by inhibiting hepatic synthesis of apoprotein a existing in hdl .
decreased hdl concentration and increased homocysteine levels may increase the risk of cardiovascular diseases . decreased homocysteine due to participating in regular training probably increase available apoprotein a existing in hdl .
three major factors influencing homocysteine levels except for regular training are mode , intensity and duration of the exercises .
the reason for inconsistency might be different mode , intensity and duration of the training programs in mentioned studies .
the findings revealed that there were significant decreases in lipoprotein a levels at posttest compared to pretest , and following 12 week of aerobic training significant differences were observed between aerobic and control groups .
these results were consistent with zafari but did not match almeida et al . and firozeh et al .
recent data from cross sectional studies have shown that regular training with moderate intensity is effective in reducing the concentration of lipoprotein a , but intense training does not induce this effect .
transient increase of lipoprotein a levels immediately after severe or prolonged exercise is because of the role of lipoprotein a in repairing tissues , which have been damaged due to free radicals and severe and prolonged training .
one reason for the reduction in lipoprotein a is an anti oxidant effect of aerobic training , because free radicals oxygen increase expression of inflammatory mediators and attaching molecules .
the reason for this difference is probably related to differences in the subjects of this study as well as the intensity and duration of training sessions . furthermore , in mentioned studies due to low exercise capacity of subjects , training intensity was lower than this study .
the findings revealed that there were significant decrease in tg levels at posttest compared to pretest , and following 12 week of aerobic training between aerobic and control groups .
these results were consistent with martin et al . and akcakoyun but did not match banitalebi et al .
aerobic training reduces the risk of cardiovascular diseases , and based on research evidence ; sedentary individuals are exposed to these risk factors .
one mechanism related to reducing the risks of cardiovascular diseases could be due to reducing tg levels .
lipoprotein lipase is an enzyme catalyzing tg and causing the release of free fatty acids from tg in order to provide energy during aerobic training .
thus , a high correlation exists between lipoprotein lipase enzyme activity and blood tg removal .
probably , aerobic training increases the activity of lipoprotein lipase enzyme and the enzyme activity lead to reducing the levels of tg at the posttest .
present research findings have indicated that cholesterol levels decreased significantly posttest compared to pretest in an aerobic group , and also significant differences were observed after 12 week of aerobic training between the control and aerobic groups .
these results were consistent with szymanska et al . but did not match banitalebi et al .
one of the first and the most obvious changes observed during aerobic training is reduced plasma insulin . therefore , probably one of the factors that may influence plasma cholesterol is plasma insulin levels . and
it can be stated that reduction in plasma insulin leads to activation of lipolysis from fat tissue and increasing the concentration of free fatty acids in plasma . and
both hormones lead to increased activity of ketogenesis which then changes the cholesterol precursor buildup .
research findings showed that there were statistically significant decreases in an aerobic group in ldl levels at posttest compared to pretest , and following 12 week of aerobic training significant differences were observed between aerobic and control groups .
these results were consistent with monda et al . but did not match banitalebi et al . from physiological and molecular mechanisms involved in the reduction of ldl levels , it can be stated that exercising leads to increased lipoprotein lipase activity . because of the effect of this enzyme increase on cholesterol rich lipoprotein catabolism , the amount of ldl reduces due to physical activity . since the increase in serum lipid is of cardiovascular diseases risk factors , it can be acknowledged that increased aerobic training reduces some of risk factors such as ldl levels .
research findings showed a significant increase in hdl levels in posttest compared to pretest in an aerobic group , and following 12 week of aerobic training significant differences were observed between aerobic and control groups .
hence , one of the reasons for an increase in hdl levels can be its increased production by the liver and alterations in several enzymes such as increased activity of lipoprotein lipase , lecithin cholesterol acyl transferees activity , and decreased activity of hepatic lipase .
the results showed that 3 sessions / week of aerobic training induce a positive influence on homocysteine , lipoprotein a and lipid profile levels in sedentary middle aged men .
 background : the purpose of this study was to investigate the effect of 12-week of aerobic training on homocysteine , lipoprotein a and lipid profile levels in sedentary middle - age men.methods:this was a quasi - experimental study . 
 subjects of the study were 24 men ( age 40 - 60 ) who participated is the study voluntarily and were randomly assigned in aerobic ( n = 12 ) and control ( n = 12 ) groups . 
 the subjects participated in progressive aerobic training on treadmill 3 times a week ( 20 min / session ( 60% maximum heart rate ) to 60 min ( 75% maximum heart rate ) . 
 homocysteine , lipoprotein a , triglyceride ( tg ) , cholesterol , low - density lipoprotein ( ldl ) and high - density lipoprotein ( hdl ) were measured before and after 12-week . 
 data were analyzed using paired t - test and independent t - test statistical methods.results:research findings showed a significant decrease in homocysteine ( p = 0.002 ) , lipoprotein a ( p = 0.003 ) , tg ( p = 0.008 ) , cholesterol ( p = 0.024 ) and ldl ( p = 0.019 ) , significant increase in hdl ( p = 0.017 ) in posttest compared to pretest . 
 furthermore , research findings showed that homocysteine ( p = 0.005 ) , lipoprotein a ( p = 0.001 ) , tg ( p = 0.006 ) , cholesterol ( p = 0.015 ) , ldl ( p = 0.022 ) , and hdl ( p = 0.004 ) levels between the two groups.conclusions:these findings reveal the 3 sessions / week of aerobic training cause reduction of homocysteine , lipoprotein a , and lipid profile levels in sedentary middle - aged men and can be recommended for prevention of cardiovascular disease . 
INTRODUCTION
METHODS
Aerobic training program and measurement of research variables
Statistical analysis
RESULTS
DISCUSSION
CONCLUSIONS