nonalcoholic fatty liver disease ( nafld ) is the terminology used for a wide spectrum of disorders ranging from simple steatosis to progressive nonalcoholic steatohepatitis ( nash ) , hepatic fibrosis and cirrhosis and its diagnosis in clinics is based on ultrasonography ( 1 , 2 ) . although , the actual prevalence of nafld remains unknown ( 3 ) , the prevalence of nafld ranges from about 20% - 35% in the western population and about 19% - 32% in asian population ( 4 ) , with the prevalence being higher ( 70% - 90% ) in obese individuals ( 5 ) . one study reported that the prevalence of nash in iranian males is twice than females ( 6 ) . nonalcoholic fatty liver disease is characterized by elevated liver enzymes including alanine amino transferase ( alt ) and aspartate amino transferase ( ast ) and also , build - up of fat within liver cells ( 7 ) . obesity , sedentary lifestyle and insulin resistance are well - established risk factors for nafld ; however , the pathogenesis of nafld is incompletely understood and factors that determine disease severity remain unclear ( 8) . although , the severity of fatty liver was positively related to anthropometric measurements including body mass index ( bmi ) , waist and hip circumference , subcutaneous adipose tissue thickness and hypertriglyceridaemia ( 3 , 9 ) currently , there is no specific drug therapy approved for the treatment of nafld and management focus on treatment of the  metabolic syndrome  rather than nafld as an individual entity ( 10 ) . lifestyle change and physical activities are currently the main recommendation for people with nafld . lifestyle interventions in the form of calorie restriction and increasing the physical activity level with an aim to reduce weight remain the cornerstone of treatment for patients with nafld ( 11 ) . exercise training ( et ) is a major component of treatment for nafld ( 8) as recommended by the american gastroenterological association ( 12 ) . however , the role of et in the treatment of this condition has not been thoroughly investigated and only few studies have investigated the effect of et on nafld , usually in combination with diet and weight loss ( 4 , 13 - 18 ) . exercise training has been shown to reduce the risk of insulin resistance , aminotransferase levels , dyslipidemia , and impaired fasting glucose and can be beneficial for glucose - lipid metabolism ( 8 , 19 ) . aerobic and resistance exercise can be therapeutic in reducing liver fat deposition by increasing energy expenditure , improvement in skeletal lipid oxidation , reduction in total and abdominal adiposity , reduction in subcutaneous fat and free fatty acid flux to liver ( 4 , 14 , 19 - 21 ) . overall , there is very limited data on the effectiveness of aerobic and resistance exercise on hepatic function in nafld . ( 17 ) demonstrated a significant reduction in aminotransferase levels and liver fat in patients with nash who adhered to an aerobic exercise program . the results of one study demonstrated that , short - term exercise can target hepatic lipid composition , which may reduce the risk of nafld progression ( 16 ) . ( 15 ) present that the long - term exercise therapy along with aerobic and resistance therapy was significantly effective in improving noninvasive biomarkers of nafld . in another study , damor et al . ( 4 ) present that moderate intensity progress resistance training is associated with significant improvement in hepatic fat , subcutaneous fat and insulin sensitivity in patients with nafld . ( 14 ) evaluated the effects of aerobic exercise on liver enzymes and hepatic fat in subjects with nafld . they reported that after eight weeks , aminotransferase levels and hepatic fat were significantly reduced in the aerobic group . so far , to the best of our knowledge , there are no data on the effect of aerobic and resistance exercise on liver aminotransferase levels and hepatic fat among the iranian men with nafld ; therefore , this study was undertaken . the present study was conducted to examine the effect of aerobic and resistance exercise training on liver enzymes and hepatic fat in men with nafld in iran . in this randomized clinical trial study , subjects were randomly selected from the liver clinic in the department of gastroenterology / hepatology at baqiyatallah hospital in tehran city , iran . sample size estimation was performed through single proportion formula with 95% confidence interval and the calculated sample size was 30 . inclusion criteria including men with hepatic steatosis , which was confirmed by ultrasonography with acceptable sensitivity and specificity and was based on a hepatic triglyceride content greater than 5% ( 22 ) . exclusion criteria were identified as genetic , metabolic or endocrine diseases ( 15 ) , alcohol consumption  30 g / day ( 13 ) , heart and pulmonary disease , patients with chronic hepatitis b and c , autoimmune hepatitis , drug abuse , and patients with diabetic mellitus and fasting hyperglycemia . the study protocol was approved by the human research ethics committees of the baqiyatallah university of medical sciences ( january 5 , 2014 with code no : 34 ) . an informed consent was obtained from all patients , including agreement of the patients to participate as volunteers . the patients were then divided into three equal groups , aerobic , resistance and control groups ( n = 10 in each group ) . during the 8 week intervention period , an aerobic training ( at ) program including a 45 minute session three times a week ( 135 min / week ) under the supervision of an exercise physiologist and sport medicine . aerobic exercise consists of three phases : warm - up , training and cool down . at the beginning of exercise session , subjects had a ten minute warm - up . the warm - up protocol was consisted of stretching movements and slowly running on treadmill . then , the warm - up phase was followed by the training phase . at baseline , the training phase commenced with two 15 minute running on treadmill at 60% of their maximal heart rate ( mhr ) in the first week and increased to two 15 minute running on treadmill at 75% mhr per week by the final week of training ( 23 ) . to assure that the desired heart rate ( exercise intensity ) was achieved and maintained for 30 minute , during the aerobic sessions , each participant underwent heart - rate monitoring with polar ( model : ft1 ) heart rate monitor ( 24 ) . maximum heart rate was calculated using the formula ( 25 ) : resistance training was performed during 8-weeks with thrice weekly sessions on nonconsecutive days . the program consisted of seven exercises : triceps press , biceps curl , calf raise , leg press , leg extension , lat pull down and sit - ups ( 21 ) . each session lasted approximately 45 minute and consisted of a 5 minute warm - up with stretching followed by resistance exercise done as a circuit , ending with 5 minute cool down . the 1 repetition maximum ( 1rm ) was measured at baseline and following the intervention ( 26 ) . initially , participants did two circuits using 50% of their 1rm and repeated them 10 times for the first and second weeks , progressing to two circuits , using 60% of their 1rm and repeated 10 times for the third and fourth weeks . in fifth and sixth weeks , participants did three circuits using 60% of their 1rm and repeated 10 times . in the last two weeks , patients did three circuits using 70% of their 1rm and repeated 10 times ( 27 ) . a 90-second rest was allowed between sets of exercises . at three preliminary sessions then , anthropometric components and body composition elements of any patient were determined in the start and the end of the study . waist circumference and hip circumference were measured to the nearest 0.5 cm with a nonelastic tape measure . to calculate the subcutaneous fat , the pectoral , abdominal and thigh skin fold were measured using the slim guide skin fold caliper ( model : ac-6575 ) on the dominant side of the body ( 28 ) . also , fat mass of whole body , bmi and weight of any patient were determined using the body composition analyzer ( model : tanita , bc-418 ) . subjects did not perform any exercise 48 hour before testing and were on 12 hours fasting prior to testing . blood samples were taken from the antecubital vein and collected in heparinized tubes and analyzed for liver enzymes ( alt and ast ) or frozen and stored at -70c for subsequent analysis of plasma glucose and insulin . the alt and ast enzymes levels were measured by biosystem kits ( biosystem s.a . , sonography was used to measure liver fat and performed by one radiologist in all subjects with the same equipment at baqiyatallah hospital . fatty liver was diagnosed via abdominal ultrasonography ( us ) using standardized criteria ( 30 ) . grade 0 ( no steatosis ) , grade one ( mild ) slightly increased echogenicity , grade two ( moderate ) moderately increased echogenicity and grade three ( severe ) markedly increased echogenicity ( 31 ) . following the 8-week exercise training intervention , subjects repeated the same tests in the same manner and order . to prevent the acute effects of exercise training altering posttraining test results , moreover , the fasting insulin level was measured using a chemiluminescent immunoassay ( liaison insulin assay , diasorin , saluggia , italy ) , and samples were analyzed on the liaison analyzer ( diasorin ) . the homeostasis model assessment of insulin resistance ( homa - ir ) , a measure of insulin resistance , was determined according to the following equation ( 33 ) : the control group had no exercise training program during the 8-week period of the study . when significance occurred , a tukey s honestly significant difference ( hsd ) post - hoc test was used to determine the source of the difference . in this randomized clinical trial study , subjects were randomly selected from the liver clinic in the department of gastroenterology / hepatology at baqiyatallah hospital in tehran city , iran . sample size estimation was performed through single proportion formula with 95% confidence interval and the calculated sample size was 30 . inclusion criteria including men with hepatic steatosis , which was confirmed by ultrasonography with acceptable sensitivity and specificity and was based on a hepatic triglyceride content greater than 5% ( 22 ) . exclusion criteria were identified as genetic , metabolic or endocrine diseases ( 15 ) , alcohol consumption  30 g / day ( 13 ) , heart and pulmonary disease , patients with chronic hepatitis b and c , autoimmune hepatitis , drug abuse , and patients with diabetic mellitus and fasting hyperglycemia . the study protocol was approved by the human research ethics committees of the baqiyatallah university of medical sciences ( january 5 , 2014 with code no : 34 ) . an informed consent was obtained from all patients , including agreement of the patients to participate as volunteers . the patients were then divided into three equal groups , aerobic , resistance and control groups ( n = 10 in each group ) . during the 8 week intervention period , an aerobic training ( at ) program including a 45 minute session three times a week ( 135 min / week ) under the supervision of an exercise physiologist and sport medicine . aerobic exercise consists of three phases : warm - up , training and cool down . at the beginning of exercise session , subjects had a ten minute warm - up . the warm - up protocol was consisted of stretching movements and slowly running on treadmill . then , the warm - up phase was followed by the training phase . at baseline , the training phase commenced with two 15 minute running on treadmill at 60% of their maximal heart rate ( mhr ) in the first week and increased to two 15 minute running on treadmill at 75% mhr per week by the final week of training ( 23 ) . to assure that the desired heart rate ( exercise intensity ) was achieved and maintained for 30 minute , during the aerobic sessions , each participant underwent heart - rate monitoring with polar ( model : ft1 ) heart rate monitor ( 24 ) . resistance training was performed during 8-weeks with thrice weekly sessions on nonconsecutive days . the program consisted of seven exercises : triceps press , biceps curl , calf raise , leg press , leg extension , lat pull down and sit - ups ( 21 ) . each session lasted approximately 45 minute and consisted of a 5 minute warm - up with stretching followed by resistance exercise done as a circuit , ending with 5 minute cool down . the 1 repetition maximum ( 1rm ) was measured at baseline and following the intervention ( 26 ) . initially , participants did two circuits using 50% of their 1rm and repeated them 10 times for the first and second weeks , progressing to two circuits , using 60% of their 1rm and repeated 10 times for the third and fourth weeks . in fifth and sixth weeks , participants did three circuits using 60% of their 1rm and repeated 10 times . in the last two weeks , patients did three circuits using 70% of their 1rm and repeated 10 times ( 27 ) . a 90-second rest was allowed between sets of exercises . at three preliminary sessions , subjects came to the laboratory to familiarize with the training equipment and procedure . then , anthropometric components and body composition elements of any patient were determined in the start and the end of the study . waist circumference and hip circumference were measured to the nearest 0.5 cm with a nonelastic tape measure . to calculate the subcutaneous fat , the pectoral , abdominal and thigh skin fold were measured using the slim guide skin fold caliper ( model : ac-6575 ) on the dominant side of the body ( 28 ) . also , fat mass of whole body , bmi and weight of any patient were determined using the body composition analyzer ( model : tanita , bc-418 ) . subjects did not perform any exercise 48 hour before testing and were on 12 hours fasting prior to testing . blood samples were taken from the antecubital vein and collected in heparinized tubes and analyzed for liver enzymes ( alt and ast ) or frozen and stored at -70c for subsequent analysis of plasma glucose and insulin . the alt and ast enzymes levels were measured by biosystem kits ( biosystem s.a . , barcelona , spain ) and through the spectrophotometry method ( 29 ) . sonography was used to measure liver fat and performed by one radiologist in all subjects with the same equipment at baqiyatallah hospital . fatty liver was diagnosed via abdominal ultrasonography ( us ) using standardized criteria ( 30 ) . grade 0 ( no steatosis ) , grade one ( mild ) slightly increased echogenicity , grade two ( moderate ) moderately increased echogenicity and grade three ( severe ) markedly increased echogenicity ( 31 ) . following the 8-week exercise training intervention , subjects repeated the same tests in the same manner and order . to prevent the acute effects of exercise training altering posttraining test results , barcelona , spain ) , which is an enzyme colorometric test without deproteinization . moreover , the fasting insulin level was measured using a chemiluminescent immunoassay ( liaison insulin assay , diasorin , saluggia , italy ) , and samples were analyzed on the liaison analyzer ( diasorin ) . the homeostasis model assessment of insulin resistance ( homa - ir ) , a measure of insulin resistance , was determined according to the following equation ( 33 ) : the control group had no exercise training program during the 8-week period of the study . when significance occurred , a tukey s honestly significant difference ( hsd ) post - hoc test was used to determine the source of the difference . an informed consent was obtained from 30 patients and they were enrolled in the study . table 1 shows anthropometric and body composition data of subjects with nafld before and after interventions . however , weight ( kg ) and bmi ( kg / m ) were improved significantly only in the resistance exercise group . repeated measure anova analyses showed a significant difference regarding mean alt , ast changes between the groups ( table 2 ) . post - hoc analyses showed significant differences in alt , ast and hepatic fat between the control and aerobic groups , and the control and resistance groups ( table 3 ) . basal fatty liver that was diagnosed by sonography , after intervention , was significantly decreased in the aerobic and resistance exercise groups . however , in the control group , the liver fat content was slightly increased after 8weeks ( figure 1 ) . moreover , after training intervention , the aerobic group only presented significantly lower values of homa - ir compared to the control group ( figure 2 ) . abbreviations :  ,  is differences between post and baseline ( mean of changes ) ; alt , alanine transaminase ; alp , alkaline phosphatase ; ast , aspartate transaminase . for some time we have been interested in how much exercise training , what types ( modes ) of exercise and what exercise intensity are most beneficial for peoples with nafld . although , it is a fact that not any one amount or type of exercise is likely to be best for patients with nafld ( 34 ) . in this study , we compare the effects of aerobic and resistance exercise on hepatic fat and liver enzymes in peoples with nafld . because , it is important for the clinician to understand whether resistance or aerobic training is superior in inducing changes in hepatic fat liver enzymes and body composition in individuals with nafld . an 8-week aerobic and resistance exercise program brought about a significantly reduction in liver fat and improving in fasting insulin resistance ( homa ) . this was accompanied by a significantly increase in insulin sensitivity , and decreased alt and ast levels after aerobic exercise in the absence of any change in body weight . although in the resistance group , these changes were associated with a significant reduction in body weight and bmi . our findings are consistent with previous studies that observed a decrease in hepatic fat following aerobic exercise in people with nafld . ( 14 ) demonstrated that hepatic fat and the serum ast and alt levels were reduced after 8 weeks aerobic exercise . ( 35 ) demonstrated that a 12-week aerobic exercise program without weight loss or change in bmi , results in reduced visceral and hepatic fat content , and decreased insulin resistance in obese adolescents . chen et al . ( 36 ) in their study showed that insulin resistance and hepatic fat were significantly decreased after a 10-week aerobic exercise . haus et al . ( 16 ) reported aerobic exercise can target hepatic fat , which may reduce the risk of nafld progression . they have suggested that the improvement in hepatic lipid composition may be driven by adiponectin , fat oxidation and increase on insulin sensitivity . ( 21 ) expressed that the mechanisms underlying the change in hepatic fat following exercise training are likely to reflect changes in insulin sensitivity , circulatory lipids and energy balance . our findings would support other reports that exercise training increases body glucose disposal at least partly due to increases expression of glut4 in skeletal muscles , insulin receptor and glycogen storage ( 37 ) . also , moderate to vigorous exercise training increases fatty acid oxidation from adipose , intramyocellular , and possibly hepatic sources ( 38 ) . ( 21 ) reported that an 8-week resistance exercise program improves nafld ( reduction in liver lipid and homa - ir ) independent of any change in body weight . in this study , we found significant reductions in alt and ast levels , independent of weight loss , after 8weeks of aerobic exercise in men with nafld . although in resistance training , reduction in alt and ast were dependent to weight loss and decrease in bmi . similar findings have been reported previously about the relation between aerobic exercise training with alt and ast ( 17 ) and also physical activity and alt in nafld ( 32 ) . although limited number of studies have explored the role of aerobic and resistance exercises on alt and ast levels in patients with nafld . de piano et al . ( 15 ) compared the effectiveness of resistance and aerobic ( at + rt ) with aerobic exercise in obese adolescents with nafld . in those who underwent resistance and aerobic exercise , presented lower alt after intervention compared with aerobic training . ( 19 ) also , reported that moderate intensity aerobic exercise helps in normalizing alt levels in patients with nafld . comparisons between aerobic and resistance training groups in the current study suggest that resistance training decreases both body weight and bmi significantly more than aerobic training . the lack of body mass loss observed with aerobic training in this study supports the findings of others and is likely driven by an increase in lean body mass ( 39 - 41 ) . finally , this study demonstrated that 8 weeks of exercise training favorably decreases abdominal obesity ( as measured by waist circumference ) , body fat and fat mass and greatly improves hip circumference and abdominal subcutaneous fat in aerobic and resistance groups . surprisingly , however , other markers of adiposity , such as pectoral and thigh subcutaneous fat were unaltered at the end of the study . in one study , bell et al . reported that an 8-week combined aerobic and resistance exercise program without weight loss resulted in decreased insulin resistance and reduced waist circumference in sedentary obese individuals ( 42 ) . also , with regard to body composition , gutin and owens observed that a 12-week aerobic exercise program attenuated growth - related increase in abdominal subcutaneous fat and visceral fat accumulation compared to the control group ( 43 ) . in another study , gutin et al . ( 44 ) demonstrated that an 8-month program of physical activity combined with lifestyle education decreased abdominal subcutaneous fat and visceral fat content . our results indicate that aerobic exercise without weight loss results in decreased abdominal subcutaneous fat and visceral fat content but not pectoral and thigh subcutaneous fat . we postulate that this is due to the fact that abdominal subcutaneous and visceral fat is more metabolically active ( 35 , 45 ) . first , the small size of patients can be considered as a limitation of study . undoubtedly , study of broader spectrum of nafld patients is necessary to increase the external validity of our findings . second , in the present study , nafld was not diagnosed based on histology ; so , the fat content was not measured bybiopsy . third , an important limitation of this study is that hepatic fat measures obtained from us , similar to other reports ( 46 , 47 ) , while highly correlated to liver fat measures from magnetic resonance spectroscopy ( mrs ) and liver biopsy studies ( 48 , 49 ) are not direct measures of liver fat . however , the changes in hepatic fat are very similar to the patterns of change across the two exercise groups in alt , ast , waist and hip circumference , abdominal subcutaneous fat and homa - ir . in conclusion , the results of this randomized controlled trial demonstrate that 8 weeks of aerobic training and resistance training are equally effective in reducing hepatic fat content and liver enzymes levels ( alt and ast ) in patients with nafld . interestingly , in the aerobic group , these changes are independent of weight loss and decrease of bmi . our data indicate that exercise training ( aerobic and resistance ) can provide benefit for the management of nafld .