muscle fatigue in human performance is defined as any exercise - induced decrease in maximal 
 voluntary force or power produced by a muscle or muscle group1 .
nevertheless , the beneficial 
 effects of training could be obtained by exercising at higher intensity and adapting this 
 exercise stimulus .
thus , physical adaptation to fatigue is important to the enhancement of 
 aerobic capacity .
after their first session of moderate - intensity exercise , individuals often experience 
 muscle soreness because they do not have sufficient time to adapt to various factors such as 
 increased mitochondrial activity leading to malondialdehyde ( mda ) production from lipid 
 peroxidation of the plasma membrane3 , 4 .
this phenomenon can cause muscle damage , 
 leakage of creatine kinase ( ck)4 , 5 into the circulation , and inflammation6 , 7 .
exhaustive and/or unfamiliar exercises ( particularly those involving high - intensity muscle 
 contractions ) are known to induce temporary muscle damage .
this damage consists of a series 
 of events : damage to the sarcolemma and the muscle cell membrane ; and the release of 
 biochemical markers of muscle damage , including lactate dehydrogenase ( ldh ) , ck , and 
 myoglobin ( mb)8 , 9 .
ck and ldh are the metabolites produced within the human body during exercise , and an 
 increase in exercise intensity and duration is known to result in a substantial 
 corresponding increase in cardiac and skeletal muscle activity .
the serum ck level is the 
 most important indicator of muscle tissue damage10 , while the ldh level is a specific indicator of fatigue11 , 12 .
in addition , the level of hs - crp , an acute inflammatory marker , 
 increases rapidly after exercise13 . in 
 physical tissue damage and other inflammatory conditions , hs - crp is the main acute - phase 
 protein and a very sensitive and objective indicator14 .
the purpose of this study was to investigate differences in the concentrations of ck , ldh , 
 and hs - crp in male sprague - dawley rats during one bout of prolonged ( 3-h ) treadmill exercise 
 following different training / non - training regimens .
forty male sprague - dawley rats ( age 6 weeks ; weighing 150180  g each ) were used in this 
 study .
all animals were housed ( three rats per cage ) at 23  2  c and 50  5% humidity with 
 a 12-hour light / dark cycle .
the rats were given a 7-day period for adapting to the 
 environment before the experiment .
the rats were randomly divided into the following four groups ( n=10 
 each ) : control , high - intensity exercise , moderate - intensity exercise , and non - exercise .
this 
 study was approved by the institution of animal care and use committee of daegu university , 
 and the experimental procedure complied with the management guidelines for experimental 
 animals .
the exercise intensity levels used in this study were set on the basis of the results of a 
 study by shepherd and gollnick ( 1976 ) in which the maximal oxygen uptakes of white 
 sprague - dawley rats were measured using a metabolic rate - measuring instrument and a 
 treadmill . as a result , the levels were set at 15 m / min , i.e. , approximately 65% of the 
 maximal oxygen uptake ; and 28 m / min , based on the reference data that defined the relevant 
 velocity as being approximately 82% of the maximal oxygen uptake15 .
this study s aerobic exercise groups first performed a 
 preliminary aerobic adjustment exercise for 20  min daily for 4 days and then performed their 
 main treadmill training for 35  min / day , 6 days per week ( except sunday ) for 4 weeks .
the 
 high- and moderate - intensity exercise groups maintained intensity levels of 28 m / min and 15 
 m / min , respectively .
after the training , the high- and moderate - intensity exercise groups 
 and the non - exercise group simultaneously performed one bout of prolonged treadmill exercise 
 at 15 m / min for 3  h. following this bout of prolonged treadmill exercise , the animals were 
 weighed ; they were anesthetized using ether as an inhalation anesthetic ; the abdominal 
 cavity was dissected immediately , and 10  ml of blood was collected from the main artery 
 using a syringe .
the collected blood was put into an eppendorf tube and centrifuged at 
 18,000  rpm at 4  c for 18  min .
the collected sera were stored in a freezer at 70  c prior 
 to analysis .
ck , ldh , and hs - crp were measured using a tsa-200fr neo ( toshiba , japan ) , ck 
 and ldh were measured using an enzyme method , and hs - crp was measured using 
 immunoturbidimetry .
one - way analysis of variance was performed using pasw ( version 18.0 for windows ) to 
 investigate intergroup differences .
the bonferroni post - hoc test was used to perform the 
 post - hoc comparisons .
table 1table 1.results of prolonged intensive exercise in rats accustomed to high- and 
 moderate - intensity trainingcg ( n=10)hg ( n=10)mg ( n=10)ng ( n=10)weight ( g)230220220230ck ( iu / l)97.3  18.5344.6  52.8*430.2  80.2*713.9  123.4*ldh ( iu / l)172.3  33.6282.4  73.7478.2  160.01*661.5  115.2*hs - crp ( mg / dl)0.01  0.000.02  0.00 * 0.02  0.00 * 0.02  0.00**p<0.05 .
cg : control group ; hg : high - intensity group ; mg : moderate - intensity 
 group ; ng : non - exercise group . * significantly different compared with cg ( p<0.05 ) ; significantly different 
 compared with ng ( p<0.05 ) presents the weights of the rats measured for each exercise group after one 
 bout of prolonged treadmill exercise .
ck levels differed significantly among the groups : 
 97.3  18.5 iu / l for the control group , 344.6  52.8 iu / l for the high - intensity exercise 
 group , 430.2  80.2 iu / l for the moderate - intensity group , and 713.9  123.4 iu / l for the 
 non - exercise group ( p<0.05 ) .
the post - hoc analysis showed that the high- and 
 moderate - intensity exercise groups as well as the non - exercise group had significantly 
 higher ck levels than the control group ( p<0.05 ) , while the high- and moderate - intensity 
 exercise groups had significantly lower ck levels than the non - exercise group ( p<0.05 ) 
 ( table 1 ) .
cg : control group ; hg : high - intensity group ; mg : moderate - intensity 
 group ; ng : non - exercise group . * significantly different compared with cg ( p<0.05 ) ; significantly different 
 compared with ng ( p<0.05 ) ldh levels differed significantly among the groups : 172.3  33.6 iu / l for the control 
 group , 282.4  73.7 iu / l for the high - intensity exercise group , 478.2  160.01
iu / l for the 
 moderate - intensity exercise group , and 661.5  115.2 iu / l for the non - exercise group 
 ( p<0.05 ) .
the post - hoc analysis showed that the moderate - intensity exercise group and the 
 non - exercise group had significantly higher ldh levels than the control group ( p<0.05 ) , 
 while the high- and moderate - intensity exercise groups had significantly lower ldh levels 
 than the non - exercise group ( p<0.05 ) ( table 
 1 ) .
following moderate- and high - intensity aerobic exercise , the high - intensity exercise , 
 moderate - intensity exercise , and non - exercise groups showed significantly higher hs - crp 
 levels ( 0.02  0.00  mg / dl ) than the control group ( 0.01  0.00  mg / dl ) ( p<0.05 ; table 1 ) .
following moderate- and high - intensity aerobic exercises , the high- and moderate - intensity 
 exercise groups as well as the non - exercise group showed significantly higher ck levels than 
 the control group , while the high- and moderate - intensity groups showed significantly lower 
 ck levels than the non - exercise group .
it was previously reported that an exercise - induced 
 increase in ck resulted in increased serum ck activity following long - distance running16 , 17 , which reflects the findings of the present study . however , in the 
 present study , following long - distance exercise , the high- and moderate - intensity exercise 
 groups showed significantly lower ck levels than did the non - exercise group .
following moderate- and 
 high - intensity aerobic exercises , the moderate - intensity and non - exercise groups showed 
 significantly higher ldh levels than the control group , while the high- and 
 moderate - intensity groups showed significantly lower ldh levels than the non - exercise group . 

the findings confirm increases in ldh levels after intense exercise in the 
 moderate - intensity exercise group and the non - exercise group in accordance with the 
 literature18 .
however , since the 
 high - intensity exercise group showed no significant increase in ldh level , high - intensity 
 training may inhibit ldh increases associated with skeletal muscle damage induced by intense 
 exercise .
the high- and moderate - intensity exercise groups and the non - exercise group showed 
 significantly higher hs - crp levels than the control group .
several studies have reported 
 that , unlike regular exercise , a single bout of intense exercise increased the hs - crp level 
 and the white blood cell count19 , 20 .
the present study confirms that , compared 
 to the control group , the moderate- and high - intensity exercise groups and the non - exercise 
 group showed significant increases in hs - crp level ; however , no significant differences were 
 found among the three groups , except for the control group . a single bout of exercise causes muscle damage and an inflammatory response , while an 
 increase in exercise intensity or duration may lead to a corresponding higher inflammatory 
 response .
tartibian et al.19 , 20 instructed normal individuals to exercise for 30 minutes 
 at 60% and 75% of the maximal oxygen uptake and reported no differences in muscle damage or 
 the inflammatory response , not only immediately after the exercise but also during the 
 recovery period .
however , gacrial et al.21 reported that when the average duration of exercise was extended 
 from 30 minutes to 87 minutes , despite low exercise intensity , there was a higher 
 inflammatory response . in the present study ,
the most pronounced inflammatory response was 
 noted in the non - exercise group , which did not undergo preliminary training .
this may be 
 because , compared to the other groups , this group found the 3-hour prolonged exercise period 
 comparatively more intense .
wannamethee et al.22 noted that the implementation of regular exercise reduced 
 exercise - induced inflammatory responses ; this was attributed to the adaptive responses to 
 exercise and the anti - inflammatory effects . in the present study ,
the groups that underwent moderate- and high - intensity preliminarily 
 training showed lower muscle damage and inflammatory response levels than the untrained 
 non - exercise group when they performed one bout of intense exercise .
compared to the 
 non - exercise group , the moderate- and high - intensity groups may have decreased their muscle 
 damage indices as their muscles acclimated to the repeated training and recovery 
 process . in conclusion
, the present study found that , compared to the non - exercise group , those rats 
 that underwent preliminary exercise showed less muscle damage and inflammatory responses 
 during prolonged intense exercise ; in particular , the effects were greater after one bout of 
 intense exercise following high- than moderate - intensity training .
 [ purpose ] the purpose of this study was to investigate the effects of exercise on muscle 
 damage indices in male sprague - dawley rats . 
 two groups of rats were trained in either 
 moderate- or high - intensity treadmill running for 4 weeks . 
 subsequently , the 
 concentrations of creatine kinase , lactate dehydrogenase , and high - sensitivity c - reactive 
 protein were examined following a single bout of prolonged ( 3-h ) intensive exercise . 
 [ subjects and methods ] the study included forty 6-week - old male sprague - dawley rats 
 weighing 150180  g each . 
 the aerobic exercise group was divided into high - intensity ( 28 
 m / min ) and moderate - intensity ( 15 m / min ) subgroups . both subgroups were trained for 35  min 
 daily for 6 days per week ( excluding sunday ) over a 4-week period . 
 following training , the 
 high- and moderate - intensity exercise groups and a non - exercise group performed one bout 
 of prolonged ( 3-h ) treadmill exercise for 3 hours at a speed of 15 m / min . 
 [ results ] 
 creatine kinase and lactate dehydrogenase levels differed significantly among the groups . 
 [ conclusion ] the preliminary exercise groups showed lower muscle damage and inflammatory 
 response levels than the non - exercise group after the bout of prolonged intensive 
 exercise . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION