cardiac hypertrophy is a phenomenon with a genetic or environmental cause ; however , it is 
 not been yet completely understood .
one of the most reasonable pieces of evidence is high 
 blood pressure due to a narrowing heart valve .
a long - term exercise requires the heart to utilize and 
 oxidize adequate amounts of fatty acids to function appropriately .
the oxidation of 
 fatty acids in the mitochondria is the main process for providing adenosine triphosphate 
 ( atp ) for the heart , particularly during periods of fasting and prolonged exercise , even 
 though the heart can utilize carbohydrates as energy substrates1 .
long - chain fatty acids are the primary fuel source for the 
 heart when the heart is in its normal resting condition .
in other words , long - chain acids 
 are the most important energy source , providing over 90% of cardiac energy2 . for this rich source of potential energy to 
 be used during exercise and fasting conditions
, adipose tissue triglycerides must first be 
 hydrolyzed , and the resultant fatty acids must then be exported from adipose tissue and 
 delivered to the tissue where they are oxidized3 .
thus , endurance types of exercise induce a physiological change in 
 the heart to adapt to the increased mechanical load4 . participating in exercise training induces cardiac hypertrophy5 , although it has not been identified . 

therefore , the purpose of this study was to investigate whether an endurance exercise 
 program for eight weeks would have an impact on the ratio of heart weight to body weight in 
 mice compared with the sedentary mice .
all experiments were approved by the institutional animal care and use committee of the 
 university of arkansas .
fifteen - week - old wild - type male 129 svj / c57bl6 mice ( n=12 ) were used 
 for this study .
the mice were divided into two experimental groups ( exercise , n=6 ; control , 
 n=6 ) .
they were housed five animals per cage with a light - dark cycle of twelve hours and had 
 access to laboratory rodent chow ad libitum .
the exercised group ran on a motor - driven 
 treadmill five days per week for 40 minutes at a speed of 24 mmin for 8 weeks 
 including a 5-minute warm - up and cool down , respectively , at 10 m / min .
the sedentary 
 experimental group was left sedentary for the experiment . before the training section , all 
 animals were allowed a minimum 1-week familiarization of 15 minutes of exercise at 1015 
 m / min based on the animal status . during the final week of this study ,
when a mouse was unable to 
 keep up with the treadmill , the exercise session was terminated . at the end of the 
 experimentation period ,
both groups of mice were anesthetized with sodium pentobarbital ( 40  mg / kg , ip ) . 

when anesthesia was confirmed , the hearts were rapidly removed from the animals and rinsed 
 in ice - cold buffer containing 225  mm mannitol , 75  mm sucrose , 10  mm mops , 10  mm tris hcl and 
 1  mm egta at ph 7.2 ( buffer i ) .
the heart was minced on ice and placed back into a test tube to be 
 weighed .
all mice were weighed once a week to monitor for excessive increases or decreases 
 in weight .
post - training 
 weight was also taken on the day of final data collection .
an independent t - test was used to 
 compare the exercise and control groups .
table 1table 1 . body weight , heart weight , ratio of heart weight to body weight , and run time 
 after the endurance exercise trainingvariablestrained ( n=6)untrained ( n=6)body weight ( g)25.92.229.31.6*heart weight ( mg)140816029*ratio of heart weight ( mg ) to body weight ( g)5.4015.461run time ( min)40.19.433.57.3*values are meansse .
* significantly different ( p<0.05 ) from the trained mice displays the results of the t - test for heart weight to body weight ratio .
the 
 untrained mice had a significantly greater heart weight to body weight ratio compared with 
 the wild - type mice .
there was also a significant difference in body weight between the two 
 groups ( p<0.05 ) .
the ratio of heart weight to body weight was lower in the untrained 
 mice , but no significance was observed .
cardiac hypertrophy is a thickening of the heart muscle ( myocardium ) that results in a 
 decrease in the size of the chamber of the heart , including the left and right ventricles . 
 in other words ,
a 
 common cause of cardiac hypertrophy is high blood pressure and heart valve stenosis . even 
 though there are many exercise benefits such as improving cardiac function and development 
 of the skeletal system , exercise training induces changes in the cardiovascular system 
 including oxygen delivery capacity and blood flow to the body6 .
the present study found that 8 weeks of exercise training could not 
 induce significant cardiac hypertrophy in mice compared with sedentary mice .
in other words , 
 the results indicated that cardiac hypertrophy was less severe in the trained mice compared 
 with the untrained mice .
this finding indicates that exercise training for the mice did not 
 provoke a change in cardiac function .
this result is consistent with research conducted on 
 the effects of treadmill running on cardiovascular phenotypes in transgenic mice7 .
endurance training has been proposed to 
 have beneficial effects on oxidative phosphorylation through increased mitochondrial 
 biogenesis8 . in this study ,
the trained 
 mice ran more than the untrained mice during a single bout of treadmill running , although 
 the difference in the ratio of heart weight to body weight was not significant . advantages 
 and disadvantages of different types of exercise training are controversial . based on the 
 results of this study , the intensity and frequency of the exercise program were not enough 
 to increase the ratio of heart weight to body weight .
one limitation of this study was that 
 due to physical and psychological stress from forced treadmill running , it may have been 
 difficult to motivate the mice to keep running for the scheduled time .
however , this stress 
 may induce a change in the endocrine system in animals .
an interesting finding in this study is that the sedentary 
 mice showed a greater heart weight due to high body weight compared with the trained mice . 

this physiological advantage could not alter the untrained mice , decreasing run time . 
 according to a study conducted by maron and pelliccia9 , an increase in left ventricular mass
the present study used endurance exercise training as an independent 
 variable , but it is necessary for future researchers to use other factors influencing 
 endurance exercise training - induced cardiac hypertrophy including age , sex , and exercise 
 type and intensity . also , there are many different ways to measure cardiac hypertrophy .
we 
 used the ratio of heart weight to body weight , which is the most common index of cardiac 
 hypertrophy .
   [ purpose ] the purpose of this study was to investigate the effects of eight weeks of an 
 endurance exercise training program on cardiac hypertrophy in mice . 
 [ subjects ] male 129 
 svj / c57bl6 mice ( n=12 ) were used . 
 the exercised mice ran on a motor - driven treadmill five 
 days per week for 40 minutes at a speed of 24 m / min for eight weeks . 
 all mice were weighed 
 once a week to monitor excessive increases or decreases in weight . 
 peak weight was 
 determined as the highest weekly recorded weight . 
 post - training weight was also taken on 
 the day of final data collection . 
 following body weight measurement , the heart was excised 
 from the body and weighed . 
 the ratio of heart weight to body weight was calculated as an 
 indicator of cardiac hypertrophy in the current study . 
 using an independent t test , the 
 ratio of heart weight to body weight was compared between the exercised mice and the 
 sedentary mice . 
 [ results ] the results show that the untrained mice had a significantly 
 greater heart weight to body weight ratio compared with the wild - type mice . 
 there was also 
 a significant difference in body weight between the exercised and sedentary groups . 
 the 
 ratio of heart weight to body weight was lower in the untrained mice , but no significance 
 was observed . 
 [ conclusion ] running on the motor- driven treadmill five days per week for 
 40 minutes at a speed of 24 m / min for eight weeks did not increase in the ratio of heart 
 weight to body weight in mice compared with the sedentary . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION