to obtain hypertrophy of skeletal muscle , it is necessary to perform high - intensity 
 training .
however , it is difficult for the elderly to perform high - intensity training when 
 they have decreased in cardiopulmonary function .
therefore , it is necessary to develop an 
 effective low - intensity training program .
eccentric contraction has been shown to produce greater muscle hypertrophy than concentric 
 contraction after training1 , 2 .
in addition to greater hypertrophy , eccentric contraction 
 training tends to exert a lower amount of stress on the cardiovascular system3 .
when eccentric contractions are used , 
 lower - intensity training can be used than when concentric contractions are used to produce 
 muscle hypertrophy .
however , there are no reports on eccentric contraction training based on 
 the lactate threshold in rats . in this study
, we propose a protocol for accurate 
 determination of the lactate threshold using eccentric contraction training in rats . 

downhill 
 running is widely used as a method for eccentric contraction training of skeletal muscle in 
 rats4,5,6 .
therefore , in this experiment , we used 
 downhill running as the eccentric contraction training .
twenty - four female wistar rats ( 1012 weeks of age , 241.8  14.5  g ) were used in this 
 study .
the rats were randomly divided into two groups of twelve rats each : the level running 
 group and the downhill running group .
the rats were 
 housed in a temperature - controlled room at 23  c with a 12-hour light - dark cycle and were 
 given free access to standard rat food and water .
the protocols of this study were approved 
 by the animal experiment committee of the prefectural university of hiroshima ( no . 

the rats were anesthetized with diethyl ether , and a catheter was inserted into the right 
 external jugular vein for blood sampling according to the method reported by hashimoto et 
 al7 .
heparinized saline ( 100 iu / ml ) was 
 infused into the catheter to prevent blood coagulation .
a treadmill made for rats and mice ( exer-3/6 , columbus co. , ltd ) was used . 

the initial speed of the treadmill was 10 m / min , and the treadmill speed was increased every 
 2 minutes by 2 m / min8 .
blood samples 
 ( 5  l ) were taken from the jugular vein catheter at rest and every 2 minutes afterwards for 
 analysis8 .
blood lactate concentrations 
 were measured using a portable lactate analyzer ( lactate pro ; arkray , japan ) .
the blood 
 lactate endurance marker software ( lactate - e)9 determined the 2-line combination that minimizes the total sum of 
 squares for fitting all data . to determine the lactate threshold ,
a graph was made from the 
 results of the blood lactate concentrations at the different running speeds .
results are presented as mean  standard deviation or median ( minimum  maximum ) values . the 
 unpaired t - test or
the mann - whitney u test were used to compare the values of the level 
 running group and downhill running group .
table 1table 1 . blood lactate concentration and running speed during the incremental exercise 
 test ( mean  sd or median [ minimum  maximum])level running group ( n=12)downhill running group ( n=12)lactate at rest ( mmol / l)2.28  0.862.13  0.55lactate at maximal level ( mmol / l)13.6  3.4314.4  2.50running speed at lactate threshold ( m / min)27.9  4.6831.6  5.14*running speed at maximal level ( m / min)38.0 ( 30.042.0)42.0 ( 38.050.0 ) * * p < 0.05 .
significant differences compared with the level running group shows the blood lactate concentration and running speed during the incremental 
 exercise test .
there was no difference between the level running group and the downhill 
 running group with regard to the results of the blood lactate concentration at rest and the 
 maximal blood lactate concentration .
the maximal running speeds were 38.0 ( 30.042.0 ) m / min 
 for the level running group and 42.0 ( 38.050.0 ) m / min for the downhill running group . 

maximal running speeds for downhill running were significantly higher than those for level 
 running ( p<0.05 ) .
the running speeds at the lactate threshold were 27.9  4.68 m / min for 
 the level running group and 31.6  5.14 m / min for the downhill running group . running speeds 
 at the lactate threshold for downhill running were significantly higher those for than level 
 running ( p<0.05 ) .
the current study evaluated the lactate threshold during level and downhill running in 
 rats .
the authors were able to accurately determine the lactate threshold of rats by taking 
 sequential blood samples during incremental exercise tests .
as shown in table 1 , the maximal lactate 
 concentrations and those at rest were not significantly different between downhill running 
 and level running .
however , the maximal running speed and the running speed at the lactate 
 threshold significantly increased during downhill running as compared with level running . 
 these data
may then help show that when the treadmill speed is the same , downhill running 
 can be done at a lower metabolic intensity than when level running is done . in other words , 

downhill running tend to exert a lower amount of stress on the cardiovascular system . 

previous reports10 , 11showed that the maximal oxygen uptake and heart rate decreased more 
 during downhill running as compared with level running and uphill running .
previous 
 reports2 also showed that , as compared 
 with concentric contractions , eccentric contractions are more effective in increasing muscle 
 strength and hypertrophy .
when the exercise intensity is the same , rather than using level 
 running , downhill running may be a good choice for increasing muscle strength and 
 hypertrophy .
however , safety monitoring is important because there is the possibility of falling 
 and injury . in future studies
, we will attempt to do further research on effective training for 
 inducing hypertrophy of skeletal muscle via low - intensity downhill training in rats .
   [ purpose ] the purpose of the present study was to investigate if lactate thresholds in 
 rats could be accurately determined during downhill running in rats . 
 [ subjects ] 
 twenty - four female wistar rats were used in this study . 
 rats were randomly divided into 
 two groups : the level running group and downhill running group . 
 [ methods ] catheters were 
 inserted into the right external jugular veins of the rats . 
 two days after the operation , 
 the rats performed incremental exercise tests . 
 the level running group ran on a treadmill 
 at a 0 incline ; the downhill running group ran on a treadmill at a 16 incline . 
 the 
 lactate threshold was determined using the 2-line combination that minimizes the total sum 
 of squares for fitting all data . 
 [ results ] maximal running speeds and running speeds at 
 the lactate threshold for the downhill running group were significantly higher than those 
 for the level running group . 
 [ conclusion ] in this study , it was possible to accurately 
 determine the lactate threshold during downhill running . 
 these findings suggest that when 
 the treadmill speed is the same , downhill running can be done at lower metabolic intensity 
 than level running . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION