many countries are becoming increasingly aware of various injuries of the elderly whose 
 proportion of entire population is rapidly increasing worldwide . in particular , falls are 
 caused by weakened lower limb muscle strength and reduced balance ability , and are the most 
 frequently experienced accident by the elderly . in addition , falls ranked the second and 
 third for the elderly injuries , unlike for younger people1 , 2 . therefore , many 
 researchers have been interested in ways of reducing falls by the elderly fall . previous 
 studies have reported that continuous exercise can improve the lower limb muscular strength 
 and balance of the elderly reducing their chances of fall3,4,5 . the exercises researchers have studied can be largely divided into 
 land exercises such as walking , tai chi , and lower limb exercise , and aquatic exercises in 
 which these exercises are performed in water with support from buoyancy . land exercises may 
 have better effects because buoyancy counteracting gravity is absent , but they are reported 
 to be more likely to cause injuries to the elderly who have weak physical strength6 , 7 . although there is risk of injuries depending on the training method , it has been proven and 
 reported by many researchers that continuous exercise by the elderly can reduce their risk 
 of falls and improve their health . the major external fall risk factors for the elderly include the environment when walking , 
 loss of balance , and obstacles on the ground . among them obstacles on the ground therefore , to better understand the mechanisms of falls by the 
 elderly , many researchers have reproduced the characteristics of common obstacles such as 
 door sills , bathroom thresholds , stairs , pathways , and parking bumps for research into falls 
 by the elderly . chen et al.9 set the 
 heights of obstacles to 2.5  cm , 5.2  cm and 15.2  cm , which are common heights of bathroom 
 thresholds , road bumps , and toys , in their research , while austin et al.10 set them at 31  mm and 126  mm , which are 
 common heights of doorsills , curbs , or parking bumps , and the median height of the two , 
 76  mm . other researchers have used obstacle heights proportional to subjects leg lengths to 
 reduce effects related to subjects height11,12,13,14,15,16,17 . the obstacles that can cause falls by the elderly in day - to - day life have a common 
 characteristic : the elderly inevitably have to cross them . it would be ideal if the elderly 
 could avoid such situations but this is not a feasible solution . therefore , to measure the 
 risk of falls by the elderly , due to obstacle - crossing , it seems more practical to evaluate 
 how the elderly overcome obstacles instead of indirectly assessing improvement of muscular 
 strength due to training . although many training studies have been conducted on reducing 
 falls by the elderly , from the perspective of the elderly who are supposed to accept and use 
 such information , additional information such as maintenance of training effect ( detraining 
 effect ) is necessary . in other words , although the fact that continuous exercise reduces the 
 risk of fall is very important information for the elderly , the detraining effect in terms 
 of how long the effect of such exercise lasts is more important to them for preventing 
 falls . however , little research has been performed on the detraining effect despite its 
 importance . in general , the detraining effect usually defined simply such as the reduction 
 of muscle strength after suspension of exercise . this type of information does not seem to 
 be clear enough for the elderly to understand how much they are exposed to the risk of fall . 
 therefore , clearly understanding the detraining effect is , along with continuous training , 
 very important information for the elderly to prevent falls . most of previous research on detraining effects has so far used indirect methods , and has 
 concluded that muscular strength is reduced somewhat after the suspension of training18,19,20 . these indirect methods do not provide 
 clear and direct information for the elderly regarding the use of these findings . in other 
 words , it seems insufficient to use indirect methods , such as simple reduction of muscular 
 strength . rather , we should be expressing what types of movements the elderly should make in 
 the environments where they frequently experience falls . in a previous study that study was 
 limited to gait stability ( i.e. inclination angles ) during obstacle gait and failed to 
 examine how long the training effect lasted . furthermore , our previous study did not reveal 
 the relationship between obstacle heights and the swing foot which approaches the obstacle . therefore , the purpose of this was to provide useful information for fall prevention for the 
 elderly by investigating how safely the elderly cross an obstacle after 8 weeks water 
 exercise , and how much of the training effect remained 8 weeks after finishing the 
 exercise . the subjects of this study were the same as those who participated in the previous study 
 conducted by the author and colleagues21 . after termination of the aquatic training , the purpose of the study regarding the detraining 
 effect was explained to the research subjects . the subjects did not perform further exercise 
 for 8 weeks after termination of the training , and they were asked to contact the author if 
 they participated in any exercise other than usual . none of the research subjects 
 participated in any continuous exercise other than natural exercise in daily life , and this 
 fact was reconfirmed to the author before starting final test . this study was approved by 
 the institutional review board of korea national sport university and prior to their 
 participation , informed consent was received from each subject . the aquatic exercise program used in this study was conducted by a qualified trainer , three 
 times a week , 60 minutes per session for 8 weeks . the exercise was composed of warm - up , 
 cool - down , and main exercise . also , different exercises were applied to the subject 
 according to increase of the period . ( weeks 14)programdurationwarm - upstretching10  minmain exerciseside walking5  minforward waking12  minjogging1  minbackward walking12  mincross stepping5  minforward - backward walking with hip joint rotation5  mincool - downstatic balance exercise5  minstretching5  min and 2table 2 . aquatic exercise program ( weeks 58)programdurationwarm - upstretching & walking10  minmain exerciseside running5  minforward running12  minwalking1  minbackward running12  mincross step running5  minfast forward walking5  mincool - downstatic balance exercise5  minstretching5  min . in order to investigate the training and detraining effect of the 8 weeks of water 
 exercise , the subjects performed three obstacle - crossing walks ( a week before the beginning 
 of water exercise , 1 week after termination of the exercise , and 8 weeks after termination 
 of the exercise ) . before each test , the subjects were explained about the procedure of the 
 test , and during the test they performed enough exercise in order to induce most natural 
 movements . the test procedure and settings of this study were the same as those of the 
 previous study21 . in order to evaluate 
 the detraining effect more accurately , the obstacle heights were set at 30% and 40% of 
 subjects leg lengths , which have been reported as comfortable and more difficult heights to 
 cross16 , 17 . two variables of gait stability and four variables of obstacle - crossing were used to 
 evaluate the risk of fall for the elderly during obstacle - crossing . the gait stability 
 variables used in this study were maximum center of pressure ( maxcop ) and mean center of 
 pressure ( meancop ) . maxcop is the maximum distance from average cop to the cop at any 
 instant during stance phase , and meancop is the mean distance between average cop and cop at 
 each instance during stance phase . in general , change in cop distance during the stance 
 phase the longer and shorter distances of cop suggest 
 that subject is in unstable and stable situation , respectively during stance phases . the 
 variables of obstacle - crossing used in this study were toe clearance ( tc ) , heel clearance 
 ( hc ) , and maximum vertical heel clearance ( mvhc ) . these variables are well known as 
 indicators of obstacle - crossing stability and we follow the definitions of them given by of 
 chen and lu13 . to verify the effect of the training and detraining effects , a repeated one - way anova was 
 performed . in addition , when there was a significant difference among the periods , the 
 bonferroni post - hoc was performed . in this study , the results of obstacle clearance parameters and gait stability parameters among training 
 periods are presented in tables 3 and 4table 3 . cop distances for maxcop and meancop of the training periodsobstacle height(% of leg length)maxcop ( mm)meancop ( mm)30%40%30%40%before - training215.9  27.0**126.7  26.1 * 52.8  4.9**39.3  4.1after - training91.5  17.867.4  5.535.1  5.730.6  2.5de - training97.3  23.5113.5  23.639.6  4.042.9  6.1values are group mean  standard error . * * : a significant difference with before 
 training . * : a significant difference between before and after aquatic training 
 ( p<0.05 ) .. for most of the variables , statistically significant training and detraining 
 effects were found for obstacle heights of 30% leg length ( table 3 and 4 , p<0.05 ) . however , for obstacle heights of 40% 
 leg length , statistically significant training effects were found for most of the variables 
 ( tables 3 and 4 , p<0.05 ) , but only improvement pattern of detraining effects 
 were shown for all the variables ( tables 3 
 and 4 ) . values are group mean  standard error . * * : a significant difference with before 
 training . * : a significant difference between before and after aquatic training 
 ( p<0.05 ) . the main purpose of this study was to examine how safely the elderly cross an obstacle 
 after an 8 weeks of aquatic training , and how much of the training effect remained 8 weeks 
 after finishing the training . for the evaluation , variables that representative of gait 
 stability and obstacle - crossing stability were investigated , and we attempted to verify the 
 detraining effect by using for obstacle heights of 30% leg length , which is comfortable for 
 the elderly to cross , and 40% leg length , which is more difficult to cross . in this study , maxcop and meancop , which were evaluated to investigate the stability of the 
 supporting foot when the elderly subjects crossed obstacles , showed statistically 
 significant training effects at both the obstacle heights of 30% and 40% leg lengths ( table 3 ) . however , at obstacle heights of 30% leg 
 length , which is known as a comfortable obstacle height for the elderly to cross , the 
 training effect was maintained at 8 weeks after ending the exercise , but not at the obstacle 
 heights of 40% leg length . this finding indicates that , although the 8 weeks aquatic 
 exercise helped the elderly to safely cross an obstacle with a height of 30% leg length with 
 the stable support of the supporting foot , it was not effective at maintaining the training 
 effect in crossing obstacles with a height of 40% leg length , a height that requires better 
 balance ability and muscular strength than at the 30% leg length obstacle height . this 
 results seems to be related the intensity or period of the exercise used in this study . 
 therefore , to verify this result , future research will need to investigate exercise over a 
 longer period , such as 16 and 24 weeks , and training intensities , other than the rpe1213 
 used in this study . for the variables of obstacle - crossing , significant training effects were found for all the 
 variables at both obstacle heights , except hc at the obstacle height of 40% leg length 
 ( table 4table 4 . clearance distances of obstacle avoidance parameters of the training periods 
 ( unit : cm)obstacle height(% of leg length)tchcmvhc30%40%30%40%30%40%before - training24.1  1.923.6  1.472.1  3.682.7  4.515.4  1.214.8  2.7after - training31.8 1.831.4  1.888.9  3.987.7  2.119.4  1.518.5  3.7de - training31.8  2.226.6  1.883.4  4.186.5  4.516.7  1.616.2  4.5values are group mean  standard error . * * : a significant difference with before 
 training . * : a significant difference between before and after aquatic training 
 ( p<0.05 ) . , p<0.05 ) . however , in terms of the detraining effect after 8 weeks , only tc 
 at the obstacle height of 30% leg length showed a statistically significant difference 
 ( table 4 , p<0.05 ) . tc and hc are variables 
 representing the safe distances before and after crossing an obstacle , and are reported to 
 be closely related to safe obstacle - crossing9 , 17 . in the case of tc , although the distance 
 after the training increased at both the 30% and 40% leg length obstacle heights ( 30% : 
 24.12  cm < 31.38  cm , 40% : 23.55  cm < 31.40  cm ) , 8 weeks after termination of the 
 training , the effect was maintained the obstacle height of 30% leg length , and the obstacle 
 height of 40% leg length , it decreased to almost the same level as before training ( 31.76  cm 
 and 26.60  cm at obstacle heights of 30% and 40% leg length , respectively ) . values are group mean  standard error . * * : a significant difference with before 
 training . * : a significant difference between before and after aquatic training 
 ( p<0.05 ) . , only one 
 foot is supporting the entire body and the crossing foot is at the highest position above 
 the ground , which requires maximum muscular strength for stability . even though mvhc showed 
 statistically significant increases at both obstacle heights as a result of the 8 weeks 
 aquatic training , it had decreased to almost the same level as before training at 8 weeks 
 after the suspension of training ( 30% : 15.38  cm  19.39  cm  16.72  cm , 40% : 14.79  cm  
 18.52  cm  16.19  cm ) . similar to the results of the gait stability parameters , the reason 
 for this detraining effect seems to be related to either the intensity or period of the 
 exercise used in this study . the findings of this study indicate that 8 weeks of aquatic exercise at the level of rpe 
 1213 may help the elderly safely cross obstacles at the most common height ( 30% leg length ) 
 related to falls for at least 8 weeks after the termination of training . the training 
 effect , however , should not be expected to last for 8 weeks after training at obstacle 
 heights of 40% of their leg length , which is a more difficult height for the elderly to 
 cross . to supplement these findings , further research into the intensity or the duration of 
 exercise needed to maintain the training effect
[ purpose ] this study aimed to provide useful information for fall prevention for the 
 elderly by investigating how safely the elderly cross an obstacle after 8 weeks water 
 exercise , and how much of the training effect remained 8 weeks after finishing the 
 exercise . 
 [ subjects ] eleven elderly participants participated in this study . [ methods ] to 
 identify the training and detraining effect of 8 weeks of water exercise , a 3-d motion 
 analysis with 7 infrared cameras and one force plate , was performed . 
 [ results ] in most of 
 all variables , statistically significant training and detraining effects at obstacle 
 heights of 30% leg length were found . at obstacle heights of 40% leg length , 
 statistically 
 significant training effects were found but only improvement pattern of detraining effects 
 were found for all variables . 
 [ conclusion ] the findings of this study indicate that 8 
 weeks of water exercise at the level of rpe 1213 may help the elderly to safely cross 
 obstacles at the most common height associated with falls ( 30% of leg length ) for at least 
 8 weeks after training termination . 
 the training effect , however , should not be expected 
 to last for 8 weeks after the training at obstacle heights of 40% height of their leg 
 length , which is a more difficult height for the elderly to cross .