aging affects all species , particularly in terms of the quality and activities of life . isaac et al . reported that the loss of muscle strength and power 
 that are related to human aging are partially caused by a change in the skeletal muscle 
 structure and a volume reduction in skeletal muscle2,3,4,5 . clearly , aging decreases 
 the cross sectional area of the skeletal muscles and the volume of the contractile tissue on 
 the cross sectional area . such changes alter muscle function , such as the characteristics of 
 motor unit firing , the aerobic capacity of the skeletal muscles , decreasing the function and 
 productivity of power6 . for example , aging leads to broad and quantitative changes in 
 both white and gray matter . a decrease in nervous system function commonly leads to a change in the contractile ability 
 of the skeletal muscles ; however , eccentric contraction is less affected than concentric 
 contraction8 , 9 . voluntary eccentric contraction and concentric contraction show a 
 unique activation pattern in the brain10 . because of the differences in the muscular actions of these 2 contraction types , various 
 exercise programs for patients have used in clinical care . however , exercise programs that successfully improved the functional 
 ability and muscle strength of elderly patients using resistance training12 . moreover , muscle adaptation through 
 eccentric contraction training can be beneficial for preventing damage due to intense 
 exercise13 and the functional loss of 
 skeletal muscles due to aging14 . various tools have been used to investigate the effect of resistance training on the 
 nervous system and the regulatory mechanisms of contraction types . in particular , the 
 cortical potential related to movement measuring activity of neurons in the cerebral cortex 
 has been used as electrophysiological evidence for distinguishing hypofunction of the 
 nervous system15 , 16 . a movement - related cortical potential ( mrcp ) using 
 electroencephalography ( eeg ) describes the brain potential from an eeg that is related to 
 voluntary movement17 . a mrcp can record 
 the activity of the cerebral cortex that is related to active movement and voluntary 
 impulse18 . notably , the techniques for 
 measuring a mrcp are cost - effective in the clinic19 . thus , here we investigated the activity of the cerebral cortex 
 after resistance training based on 2 contractile types in the elderly . we also evaluated the 
 clinical neuropsychological basis of 2 contractile types and the usefulness of an mrcp from 
 an eeg . this study received the approval of the bioethics committee of the sehan university center 
 ( irb ) ( approval number : 2015 - 11 ) . the study subjects were 11 females and 11 males aged 
 between 65 and 70  years with a right - side predominance ( table 1table 1.general subject characteristicsexperimental group i ( n=11)experimental group ii ( n=11)age ( years)67.1  1.868.2  1.4height ( cm)162.8  5.3159.0  4.9weight ( kg)63.5  8.161.1  8.0gender ( m / f)6/55/6mean  sd , shapiro - wilk . the subjects consistently had no training for muscle strength for a year and had 
 not consistently taken medicine . the subjects were randomly assigned to either a group 
 performing an eccentric contraction ( n=11 ) or a group performing a concentric contraction 
 ( n=11 ) . experimental group i performed the eccentric contraction exercise and experimental 
 group ii performed the concentric contraction exercise . the subjects understood the purpose 
 of this study and voluntarily agreed to participate , as documented with the written informed 
 consent of each subject . experimental group ii : concentric contraction exercise group we measured activities of the rectus femoris , vastus medialis , and vastus lateralis in the 
 non - dominant lower extremity by using a surface emg , and measured brain activity by using an 
 eeg before conducting an intervention . the intervention was performed 40 minutes per 
 session , once a day , 3 times a week for 4 weeks . goleta , ca , usa ) and eeg100c ( biopac system inc . ) to measure mrcp based on voluntary 
 contraction of knee extensor muscles on the non - dominant side . the sampling rate for signal 
 collection was set to 200  hz , and the frequency band filter was set at 1 to 35  hz . the 
 acqknowledge 3.8 software program ( biopac system inc . ) was used to analyze the pp ( positive 
 potential ) of the mrcp in the collected signal . the one - rep - max ( 1rm ) for the concentric contraction training group was measured based on 
 the maximum weight that the subjects could maintain from flexing their knee at a 90-degree 
 angle to extending their knee at a 180-degree angle for 5 seconds . the 1rm for the eccentric 
 contraction training group was measured based on the maximum weight that the subjects could 
 maintain from extending their knee at a 180-degree angle to flexing their knee at a 
 90-degree angle for 5 seconds . the measurement was performed in triplicate , and sufficient 
 resting time was provided to prevent muscle fatigue in the subjects . the mp 150 system 
 ( biopac system inc . ) was used as a surface emg , the sampling rate for signal collection was 
 200  hz , and the frequency band filter was set to 1 to 35  hz . the acqknowledge 4.2.2 software 
 program ( biopac system inc . ) was used to analyze the collected signal . the rectus femoris is 
 located at the center of the anterior surface of the thigh , and approximately half the 
 distance between the knee and iliac spine . the 2 active electrodes were placed 2  cm apart 
 and parallel to the muscle fiber . the electrodes for the vastus medialis oblique were placed 
 with 2  cm spacing and at an oblique angle ( 55 degrees ) , 2  cm medially from the superior rim 
 of the patella . the vastus lateralis activity was measured using 2 active electrodes that 
 were placed 2  cm apart and were approximately 3 to 5  cm above the patella at an oblique 
 angle just from lateral to mid line . during extension of the knee standing posture as a standards action was set in an emg signal , and the root mean square 
 ( rms ) was measured for 10 seconds . the rms was collected during the maximal voluntary 
 isometric contraction of the knee extensor in a sitting posture using the manual muscle test 
 as suggested by kendall20 and are 
 expressed as percentages . all of the measurements were performed in triplicate and the mean value was 
 used . each measurement was taken repeatedly after a sufficient interval of resting time to 
 prevent muscle fatigue . measuring the posture of a cerebral cortex neuron was similar to measuring the posture of 
 the 1rm . signals of the brain waves that were collected sequentially and repeated 30 times 
 with a 30% 1rm weight . an assistant aided the subjects in performing either a concentric 
 contraction or an eccentric contraction . next , among signals of collected emgs , we selected 
 and averaged the brain wave signal at 2 seconds before initiating an emg signal starting 
 action and the signal a second after initiating an emg signal starting action . the mp 150 
 system ( biopac , usa ) and eeg100c ( biopac , usa ) were used , and the sampling rate for signal 
 collection was set to 200  hz with a frequency band filter of 1 to 35  hz . active electrodes 
 were placed in cz , c3 , c4 , and fz based on the international 1020 system , and cz was placed 
 at the central part of the scalp of motor area . an electrode for c3 and c4 was placed on the 
 left and right scalp of the m1 area . the ground electrode and reference electrode ( i.e. , a1 and a2 , 
 respectively ) were placed in the mastoid process . the acqknowledge 4.2.2 software program 
 ( biopac system inc . ) was used to analyze the negative potential ( np ) of the mrcp in the 
 collected signals , and brain map-3d software ( laxtha , korea ) was used to analyze the brain 
 mapping of brain wave before and after conducting the intervention . amplitudes of these values were expressed in 
 colors and overlapped with the standardized three - dimensional scalp image . weight for 
 training was set to 70% of the 1rm to determine the exercise weight of the subjects based on 
 the measured 1rm . the eccentric contraction group maintained a full extension of the knee 
 extensor muscles of the non - dominant side for a second on the nk table and then flexed their 
 knee for 5 seconds , adjusting to the metronome . when the subject in the eccentric 
 contraction group returned to the starting position , an assistant instructed them to flex 
 their knee joints passively . the concentric contraction group flexed their knee extensor 
 muscle of the non - dominant knee joint at a 90-degree angle for a second on the nk table and 
 then fully extended their knee for 5 seconds , adjusting to metronome . when the subject in 
 this group returned to the starting position , an assistant instructed them to extend their 
 knee joints passively . the intervention was performed 10 times per set for 3 sets , three 
 times a week for 4 weeks . two weeks later , 1rm was re - measured and training began again for 
 2 weeks , increasing the weight for training to 70% of the increased weight . the subjects 
 rested for 5 minutes after each set to prevent muscle fatigue , and another exercise training 
 was performed 48 hours after the session . spss version 18.0 was used to analyze data , and shapiro - wilk test was used to analyze data 
 normality distribution . an ancova was used to analyze differences between the experimental 
 groups at a significance level of 0.05 . 1 ) the data followed a normal distribution indicating that there were no distinct 
 characteristics between the groups ( table 
 1 ) . 2 ) there was a statistically meaningful difference between the c4 area and cz area 
 ( p<0.05 ) ( table 2table 2.comparison of the difference in the cerebral cortex area between groupsgroupprepostfzexperimental group i1.4  0.41.6  0.4experimental group ii1.3  0.61.4  0.6c3experimental group i2.0  0.92.2  0.7experimental group ii1.6  0.81.7  0.6czexperimental group i1.9  0.82.4  0.7*experimental group ii1.4 0.51.6  0.6c4experimental group i1.5  0.81.9  0.4*experimental group ii1.0  0.31.1  0.3*p<0.05 . mean  sd , ancova .. experimental group i : eccentric 
 contraction exercise group . fz : prefrontal area , c3 : primary motor area ( left ) , cz : supplementary motor 
 area , c4 : primary motor area ( right ) ) . * p<0.05 . mean  sd , ancova .. experimental group i : eccentric 
 contraction exercise group . fz : prefrontal area , c3 : primary motor area ( left ) , cz : supplementary motor 
 area , c4 : primary motor area ( right ) 3 ) there was a statistically meaningful difference for the activity of the rectus femoris 
 ( p<0.05 ) ( table 3table 3.comparison of the muscle activity between groupsitemsgroupspre - testpost - testrectus femoris ( % ) experi - group i104.8  13.2127.7  13.6*experi - group ii106.8  18.2114.1  15.7vastus medialis obliqus ( % ) experi - group i98.8  14.8107.3  16.3experi - group ii95.7  15.3103.2  13.8vastus lateralis ( % ) experi - group i100.6  13.8109.2  14.2experi - group ii99.9  14.8105.4  15.2*p<0.05 . the sensorimotor area of the cerebral cortex is consistently changing by experience21 , and reversibility of cortex related - aging 
 that is associated with a decrease in physical ability is related to broad neurochemical and 
 neurophysiological changes22 . pellicciari 
 et al.23 reported that normal aging is 
 associated with hypoexcitability of inhibitor circuits that exist in the cerebral cortex and 
 the loss of synapse connection . lee et al.24 reported that morphological changes in the peripheral nervous 
 system , namely , abnormal myelination or loss of axons , results in functional changes , 
 including the loss of sensory receptors and a decrease of innervated tissues . however , 
 despite such changes , progressive resistance exercise can drive changes in musculoskeletal 
 system and accompanying changes in the nervous system in older adults25 . smith et al.26 emphasized that the improvement of competence after training both 
 hands for a short period of time appeared to decrease reaction times , namely because of a 
 decrease in the latency of the bereitschaftspotential ( bp ) and amplitude , these results 
 indicate that the activity of neurons in the cerebral cortex increase after training . we 
 note that active and voluntary movements are needed to generate effective cortical 
 activation . yang et al.27 investigated 
 differences in the activities of spinal neurons based on muscle contraction types and 
 cerebral cortical neuron potential , and reported that the peak values in cz , c3 and fz 
 during eccentric contraction are higher than those during concentric contraction . falvo et 
 al.28 insisted that mrcp after 
 intervention , but not before , has an earlier onset ( by as much as 28% ) in 11 normal subjects 
 who had been trained with resistance exercise of the knee extensor muscles for 3 weeks . that is , c4 and cz in the motor area had a 
 higher positive potential ( pp ) mean value after performing an eccentric contraction 
 exercise . eccentric resistance training resulted in higher activities in the primary motor 
 area , and thus contributes to an increase in the excitability of the cerebral cortex . these 
 results suggest that sensory feedback occurs more during an eccentric contraction compared 
 to a concentric contraction as a result of having plans in the cerebral cortex about 
 additional movements or have to deal with problems specific to eccentric contraction16 . generally , increasing voluntary muscle 
 strength occurs through 2 main mechanisms , neural adaptation and myohypertrophia , and 
 increasing muscle strength requires changes to the nervous system at the beginning of a 
 training program.29 many advanced 
 meta - analysis that gault and willems performed showed that eccentric contraction training , 
 but not concentric contraction training , could improve muscle strength in both the young and 
 old when performing reinforcement training of a single joint through concentric , eccentric , 
 and isokinetic contraction30 . in 
 particular , gault and willems suggest that knee extensor muscles are an important factor in 
 the elderly . roige et al.31 suggested 
 that the average conservation rate of an eccentric contraction is 21.6% , and ranges from 2% 
 to 48% , based on their comparison of studies of concentric contraction and eccentric 
 contraction in the elderly . these studies support the clinical significance of low intensity 
 eccentric contraction exercise in the elderly , indicating that it could be useful for early 
 and rehabilitative resistance training . lastayo et al.32 suggest that the neural adaptation of eccentric resistance exercise 
 at a high intensity is beneficial for muscle strengthening or injury prevention in athletes , 
 and that this approach has many advantages for the rehabilitation of the elderly . our 
 results support the research of others , showing that an increase in the muscle activity of 
 the rectus femoris after eccentric contraction training . the muscle activities of the vastus 
 medilis and vastus lateralis increased in both eccentric and concentric training groups , 
 with no meaningful difference between them . the most significant effect of exercise occurred 
 in the rectus femoris because it takes a neutral posture in the ankle joint and a training 
 posture in the hip joint , and thus has the greatest load . in summary , our results demonstrate that a mrcp based on an eeg has the advantage in 
 rehabilitative research of being both non - invasive and cost - effective . we found that 
 eccentric contraction was associated with overall higher neural activity , and there was a 
 statically meaningful difference for the activity in c4 , cz , and the primary motor area . similar to previous studies , we found more complex and higher activity in cerebral cortex 
 after eccentric contraction training . we found that eccentric contraction in older adults is 
 a more effective exercise through stimulation of the nervous system and musculoskeletal 
 system , supporting the use of eccentric contraction training for preventing falls and 
 rehabilitation exercise training in the elderly . however , we did not control for the daily 
 life activities of all of the subjects . moreover , the results of our study need to be 
 verified using a longer experimental period . furthermore , prospective studies are needed to 
 clarify the mechanism of eccentric contraction exercise , which will be useful for research 
 related to aging and neural plasticity .
[ purpose ] here we investigated the activity of the cerebral cortex after resistance 
 training in the elderly . 
 we evaluated the clinical neuropsychological basis of 2 
 contractile types , and determined the usefulness of a movement - related cortical potential 
 ( mrcp ) from an electroencephalography ( eeg ) . 
 [ subjects and methods ] the subjects were 11 
 females and 11 males aged between 65 and 70  years . 
 the subjects were randomly assigned 
 into a group that performed an eccentric contraction exercise ( experimental group i , n=11 ) 
 and a group that performed a concentric contraction exercise ( experimental group ii , 
 n=11 ) . 
 we measured activities of the rectus femoris , vastus medialis , and vastus lateralis 
 in the non - dominant lower extremity by using surface electromyography ( emg ) , and measured 
 brain activity using eeg before conducting an intervention . 
 an intervention was conducted 
 40 minutes per session , once a day , 3 times a week for 4 weeks . 
 [ results ] after the 
 intervention , activity in c4 , the cz area and rectus femoris were significantly different . 
 [ conclusion ] our results demonstrate that mrcp from an eeg has the advantage of being 
 non - invasive and cost - effective . 
 nonetheless , prospective studies are needed to reveal the 
 specific mechanism underlying eccentric contraction exercise , which can provide baseline 
 data for research related to aging and neural plasticity .