walking disorders , which constitute one of the major problems in hemiplegic patients , are a 
 result of weakness of the affected side of the body1 and the relatively posterior location of the center of gravity , 
 which limits their movements and reduces the risk of falls2 .
treadmill walking is well known as an effective intervention for 
 increasing walking ability , stability of the lower extremity , muscle strength , balance , and 
 re - recognition of motor control required for the walking pattern3 .
underwater therapy helps improve physical functioning for a 
 better quality of life by utilizing the properties of water .
hydrostatic pressure , buoyancy , 
 friction , and viscous resistance are important water properties , and underwater resistance , 
 in particular , is 12 times greater than overground resistance .
exercising in water helps achieve an acquired symmetrical gait and 
 limits unnecessary movement , thereby affecting not only energy efficiency but also muscle 
 strength and endurance5 .
recently , a few 
 studies investigated the effects of treadmill exercise in restricted water depth on 
 improvement of muscle strength and gait velocity .
moreover , previous studies have proved 
 that underwater treadmill walking training ( utwt ) is beneficial for weight bearing in the 
 stance phase , which improves both gait and postural control in patients with hemiplegia6 .
several studies have been conducted on the 
 effects of utwt on balance and gait . however
, a quantitative evaluation of isokinetic muscle 
 strength in hemiplegic patients has not been studied sufficiently .
therefore , the purpose of 
 this study was to compare the effects of utwt and those of overground treadmill walking 
 training ( otwt ) on peak knee flexion and extension torques .
thirty - two subjects with hemiplegia 
 of 1  year onset participated in the study . the subjects were allocated randomly to an 
 experimental group ( eg ) ( n=16 ) and a control group ( cg ) 
 ( n=16 ) .
the general characteristics of the subjects are shown in table 1table 1.general characteristics of the subjects ( n=32)eg ( n=16)cg ( n=16)age ( years)50.9 ( 9.9)49.3 ( 10.7)weight ( kg)62.5 ( 11.0)63.5 ( 9.1)height ( cm)165.4 ( 6.9)166.9 ( 5.2)gender ( male / female)11/510/6affected side ( right / left)7/95/11lesion ( infarction / hemorrhage)10/69/7period since the onset of stroke ( months)7.9 ( 2.5)8.0 ( 2.4)values are presented as mean ( standard deviation ) ; eg : experimental group ( underwater 
 treadmill walking training ) ; cg : control group ( overground treadmill walking 
 training ) .
values are presented as mean ( standard deviation ) ; eg : experimental group ( underwater 
 treadmill walking training ) ; cg : control group ( overground treadmill walking 
 training ) there were no significant differences in homogeneity of the subjects in general 
 characteristics .
the inclusion criteria were as follows : mini - mental state examination - korea 
 score > 24 points ; able to walk independently for 20 minutes ; and no history of orthopedic 
 or neurologic problems other than a stroke .
all subjects provided written informed consent 
 for participation in the study prior to its initiation .
the patients participated in the training for 30 
 minutes / session , 3 sessions / week , for 6 weeks , from november 3 to december 12 , 2014 .
warm - up 
 exercises were performed for 5 minutes to induce muscle relaxation , and these were followed 
 by utwt for 20 minutes , and cool - down exercises and stretching for the final 5 minutes to 
 reduce muscle fatigue .
hydro physio ( syspal limited , england ) , an underwater treadmill , was 
 used at a velocity that was 36% of the overground gait speed at the start , and the velocity 
 was gradually increased by 0.1 m / s until the subjects were walking as fast as possible7 .
the subjects wore aqua shoes for safety . 
 water temperature and depth were 34  c and up to the xiphoid process , respectively6 .
rtm 500 ( biodex , usa ) , an overground 
 treadmill , was used following the same procedure as the utwt .
the isokinetic dynamometer 
 ( biodex , usa ) was used to assess knee extension peak torque ( kept ) and knee flexion peak 
 torque ( kfpt ) .
the subjects were instructed to stand holding a chair , with the thigh and 
 ankle on the test side fixed by a stabilization strap .
the maximum torque was assessed 3 
 times at 60 and 120/sec and the highest torque among these was selected .
this test tool has high test - retest reliability ( r=0.81 ) and 
 validity ( r=0.99)8 .
all data were analyzed 
 using spss version 12 ( statistical package for the social science ) .
the 
 pearson  and independent t - tests were used for homogeneity of subject 
 characteristics . the paired t - test and independent t - test
were used to compare pre- and 
 post - test values in each group and the differences between both groups , respectively
there were significant differences post - intervention in the kept and kfpt at 
 the angular velocity of 60/sec in both the eg and cg .
there were significant differences post - intervention in the 
 kept at the angular velocity of 120 /sec in both the eg and cg .
there was a significant difference 
 post - intervention in the kfpt at the angular velocity of 120/sec in the eg ( table 2table 2.comparison of the peak knee extension and flexion torques at each angular 
 velocity ( n = 32)eg ( n=16)cg ( n=16)60/secextensionpre - test49.4 ( 21.4)47.2 ( 16.9)post - test73.9 ( 21.6)57.7 ( 16.6)flexionpre - test42.6 ( 21.5)38.1 ( 14.1)post - test52.8 ( 17.4)45.9 ( 13.5)120/secextensionpre - test31.0 ( 14.6)30.8 ( 9.8)post - test50.3 ( 20.8)39.0 ( 10.0)flexionpre - test24.8 ( 11.6)26.5 ( 13.6)post - test33.3 ( 10.0)30.4 ( 13.7)values are presented as mean ( standard deviation ) ; * p<0.05 ; * * p<0.01 ; eg : 
 experimental group ; cg : control group ; unit : nm ; , in group ; , 
 between groups ) .
values are presented as mean ( standard deviation ) ; * p<0.05 ; * * p<0.01 ; eg : 
 experimental group ; cg : control group ; unit : nm ; , in group ; , 
 between groups
the knee joint plays an important role during participation in exercises and activities of 
 daily living
. the peak torque can be useful data in assessing a subject s exercise 
 ability9 . in this study
, there was no 
 significant difference in the kfpt at the angular velocity of 120/sec in the cg .
however , 
 there was a significant difference in the kept at the angular velocity of 120/sec in the 
 cg . in addition , there were significant differences in the kfpt and kept at the angular 
 velocity of 60/sec in both the eg and cg . in previous studies ,
otwt for 12 weeks improved 
 overall lower extremity strength in hemiplegic patients10 , and treadmill walking training applied in 10 hemiplegic patients 
 for 12 weeks positively affected the isokinetic muscle strength in the paralyzed knee 
 joint11 . therefore , utwt is beneficial 
 for improving both muscle strength and recovery from paralysis .
there were significant 
 differences in the kept and kfpt at all angular velocities after the utwt .
in previous 
 studies , utwt has been shown to improve lower extremity muscle strength , which improved 
 walking velocity , cadence6 , and muscle 
 endurance4 in the elderly . moreover
, 
 there was no significant difference in the kfpt at all angular velocities in both groups , 
 but the eg group showed significant improvement in the kept compared to the cg .
a previous 
 study reported that utwt applied in 10 elderly people influenced activation of gluteus 
 maximus , tensor fascia latae , and biceps femoris in the stance phase12 and improved hip flexor strength , as a result of which , 
 there was improvement in gait velocity and stride7 .
however , the reason for a significant difference in the kept but 
 not in the kfpt was that underwater exercise influences muscle strength more than overground 
 exercise owing to water resistance , which was proved in the previous study . according to 
 han s study , knee extension during the swing phase in utwt
in addition , previous studies have reported that muscle 
 contraction in the quadriceps femoris during utwt was higher than that during otwt14 , and the anteroposterior postural 
 perturbation of static postural control in the utwt group showed a considerable difference , 
 decreasing by 41% compared to that before training15 .
the limitations of this study were a small sample size , lack of a 
 follow - up test to determine the carry - over effects , and no constraint of the effects of 
 other joints .
further investigation of the effects of an underwater therapy program in 
 hemiplegic subjects with modifications to address the above - mentioned limitations is 
 needed .
 [ purpose ] this study investigated the effects of underwater treadmill walking training on 
 the peak torque of the knee in hemiplegic patients . [ subjects and methods ] thirty - two 
 subjects , who were randomly allocated to an experimental group ( n=16 ) and 
 a control group ( n=16 ) , performed underwater treadmill walking training 
 and overground treadmill walking training , respectively , for 30 minutes / session , 3 
 sessions / week , for 6 weeks . 
 an isokinetic dynamometer was used to assess the peak torque . 
 
 [ results ] the subjects in the experimental group showed an increase in the peak knee 
 extension torque compared to the control group . 
 [ conclusion ] the results suggested that 
 underwater treadmill walking training has a greater effect on peak knee extension torque 
 at velocities of 60/sec and 120/sec than overground treadmill walking training . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION