fall - related injuries are high in the developed countries , and in the us .
they are recorded 
 as the second largest source of unintentional fatal injuries and the main source of non 
 fatal injuries1,2,3 . in 2005 ,
the national 
 center of injury prevention and control ( ncipc ) of korea reported elderly females to be more 
 likely than men to have injuries due to falling . in 2005
, kannus4 found that over 80% of elderly patients were admitted to 
 hospital due to falls , and roach5 report 
 that over 50% of these patients died within 1  year after they were hospitalized .
it is well 
 known that besides the acute injuries sustained , the long - term effects of hospitalization 
 are more serious as they can prevent the recovery of a patient 's muscle strength , reducing 
 their ability to be self sufficient .
there are many factors that can cause falls by older adults : joint instability and muscle 
 imbalance6,7,8,9 , reduction in joint range of motion , reduction in the ability to 
 ambulate proficiently10 , and deficiencies 
 in lower body strength11,12,13,14 .
a decreased ability to ambulate proficiently arises from 
 a loss of muscle mass and strength which is attributable to aging2 , 15 .
other factors 
 that can also cause serious falls are medicinal side effects , and chronic diseases 
 associated with aging , e.g. arthritis .
ultimately , preventing falls is better than cure , and kavanagh16 and many researchers have concluded older adults should 
 participate in exercise programs to prevent falls and maintain self - sufficiency , which is 
 linked to a high quality life . berg and his colleagues17 state that older adults should participate in regular exercise to 
 prevent falls .
it is recommended that a fall prevention exercise program should strengthen 
 the lower body18 , rectify muscle 
 imbalances16 , incorporate balance 
 exercises19 and increase 
 flexibility20 .
wolf21 implemented tai chi as a falling 
 prevention exercise program and reported that after 15 weeks of tai chi , the frequency of 
 falls was reduced by 47.5% .
dayhoff22 
 implemented an elastic band exercise for 14 weeks and reported an increase in the subjects ' 
 preferred gait speed .
skeleton23 had 
 participants perform resistance training for 10 weeks and reported that subjects ' muscle 
 strength and gait speed both increased . however , since older adults are susceptible to 
 arthritis , lower range of motion and chronic diseases exercise training programs should be 
 carefully developed so as not to exacerbate any pre - existing problems .
aqua aerobic exercise has been shown by many studies to be highly effective at reducing 
 pain for patients with arthritis and disabled populations24 , as well as improving flexibility , strength , and balance 
 disorders25 and has a significant 
 positive psychological effect26 .
kim27 reported that aqua therapy increases 
 cardiovascular endurance , flexibility , muscle strength , muscle balance and reduces the 
 percentage of body fat .
* indicates a 
 significant interaction between time and group , p<0.05 . * * indicates a significant difference between before and after , p<0.05 .
subjects ' bone density 
 was measured by whole body dual energy x - ray absoptiometry ( dexa ; ma ) .
twenty of the 
 subjects had a score below 1 , and they were excluded from this study due to the high impact 
 nature of the forced perturbation .
twenty subjects commenced the aqua aerobic therapy 
 training , and they were divided randomly into two groups of 10 . during the 12 weeks of aqua 
 therapy exercise 5 subjects dropped out leaving only 7 in the control group and 8 in the 
 experimental group ( table 1 ) .
as in rikli and jones study19 , subjects ' 
 flexibility , agility , balance and muscle strength were measured and recorded ( table 4 ) .
subjects ' muscle strength was measured by 
 a cybex ( 770 , new york ) .
both knee flexion and extension were measured at two speeds ; 60/s 
 and 180/s .
muscle power was defined as the peak torque generated at a constant velocity of 
 180/s .
similarly muscle strength was defined as the peak torque generated at a constant 
 velocity of 60/s .
each trial lasted 5 seconds and was repeated three times with three 
 minutes of rest between each trial , as recommended by rikli and jones19 .
the peak torque was recorded for knee flexion strength 
 and knee extension power , was testing was performed one week before the gait experiment .
therefore this current study investigated the effects that an aqua exercise therapy has on 
 the physiological and biomechanical factors of gait .
a secondary aim was to examine if 
 improvements in gait variables would improve older adults ' responses in a perturbed gait 
 condition . during gait observations , kinematics at 60  hz
were recorded by 8 oqus 500 cameras 
 ( qualisys , sweden ) , and kinetics on by 2 amti force platforms ( amti , usa ) were recorded at 
 1200  hz by qualisys track manager ( qtm , qualisys sweden ) . after explanation of the testing 
 procedures and obtaining subjects ' informed consent , the experiment began .
subjects strapped 
 into an overhead harness for safety . for the dynamic trials the participants walked at a 
 self - selected pace three times down a walkway .
the participants were then escorted out of 
 the room while the walkway was raised and the perturbation device was set up .
next , the 
 participants were instructed to walk along the walkway and then step down .
the participants 
 were informed that this step - down procedure would have to be done three times .
after each 
 trial the participants were escorted back outside the laboratory and the perturbation device 
 was reset . during these final 3 trials the perturbation platform would open up randomly and 

perturbation data was 
 collected once for each participant as they became apprehensive of walking on the walkway 
 after the perturbation .
the aqua therapy exercise program was carried out three times per week for one hour in each 
 session ( table 2 ) .
there were three main parts 
 to the exercise session : including warm up , aqua aerobics , and cool down .
the indoor pool 
 was 25  m long , 4  m wide and 1.3  m deep , and had a water temperature of 281c and a room 
 temperature of 26c .
after the participants began to feel 
 warmer a slow aqua aerobics pace was set which was then increased steadily .
the aqua therapy 
 consisted of aquatic adaption time , breathing techniques , floating and posturing .
equipment 
 were introduced to maintain the participants ' enjoyment , and as each piece of equipment 
 could be used to train difference aspects of fitness , they were used for overall variation 
 and stimulus of different muscles .
the cool down gave the participants time to do stretching 
 and have some free time .
the intensity of the aqua therapy was set according to the ratings 
 of the borg perceived exertion ( rpe ) scale set at an intensity level of 711 for the first 3 
 weeks then the intensity was increased to 1213 .
after labeling of the data and interpolation in qtm , the data were exported to a c3d file , 
 and modeling and manipulation were performed with visual3d ( c - motion , usa ) . a 2  2 ( group  
 time ) anova with repeated measures
were performed to compare the data between the two groups 
 according to the measurement time .
independent 
 t tests were used to verify that there were no significant differences between the control 
 and experimental group at the initial stage of the study .
further , significant differences 
 were investigated using the paired t - test to investigate the differences between pre and 
 post treatment .
participants ' weight , muscle mass , fat mass and mineral mass for both the control and 
 experiment groups before and after the aqua aerobic therapy were measured using an inbody 
 720 .
there was no significant interaction between groups and time for the muscle mass and 
 the mineral mass , but there were significant reductions in weight ( p<0.05 ) and body fat 
 mass ( p<0.05 ) ( table 3 ) . *
* indicates a 
 significant interaction between time and group , p<0.05 . there were no significant differences between before and after the intervention in muscle 
 strength and power , but there were significant interaction effects ( p<0.05 ) . for 
 flexibility and agility , there were significant interactions .
there were significant increases in muscle 
 strength , power , flexibility , agility and balance of the participants in the aqua therapy 
 group , whereas the control group demonstrated either reductions or no change ( table 4 ) . *
* indicates a 
 significant interaction between time and group , p<0.05 . to investigate how participants recovered after the perturbation various gait - related 
 variables were measured and calculated .
there were no significant differences between the 
 experiment and control groups before and after the intervention in support time , step length 
 and jerk cost .
there were statistical differences and interactions in stride and step times 
 between the groups .
these results demonstrate that the experiment group participants reduced 
 their stride time , which shows that they recovered more quickly after the perturbation 
 ( table 5 ) .
the kinetic variables calculated were the maximum moments of the ankles , knees and hips , 
 and the propulsion force of the perturbed foot after landing .
there were both significant 
 main effects ( p<0.05 ) and interaction effects ( p<0.01 ) of the maximum ankle moment . 

similarly for the maximum knee moment there were both significant main ( p<0.05 ) and 
 interaction ( p<0.05 ) effects .
there were no significant effects found for the maximum hip 
 moment and the propulsion impulse . to summarize the kinetic data ,
the participants in the 
 experiment group were able to develop more ankle and knee moment to prevent their body 
 falling and recover .
the hip moments did not seem to affect the recovery of the participants 
 ( table 6 ) .
the increasing risk of falls increases with aging , and the aims of this study were to 
 investigate whether aqua exercise therapy can help the elderly by preventing falls and 
 improving their gait patterns after a perturbation .
it was our hypothesis that aqua exercise 
 training would increase the elderly participants ' physical strength , flexibility , and 
 balance which would in turn help improve a subjects ' ability to react to a perturbation .
our 
 results are similar to those of previous studies which have reported that 12 weeks aqua 
 therapy exercise improves lower body strength , power , flexibility , agility and balance16 , 19 , 20 .
also , due to the training effect the 
 weight and body fat mass was reduced , whereas no significant changes were seen in these 
 variables in the control group .
kinematics and kinetics were recorded and compared to evaluate subjects ' reaction to 
 perturbation .
our data show that the older adults of the experiment group managed the 
 perturbation more efficiently and had a more stable gait pattern .
oddsson and his 
 colleagues29 demonstrated that recovery 
 after a perturbation takes about 3 or 4 steps depending on limb strength and age .
the 
 present study found no significant differences in the support time , step time , step length 
 and jerk cost after the perturbation .
however , recovery started at the second step , shown by 
 the significant difference in stride times between before and after the perturbation .
the 
 maximum joint moment of the landing leg show that subjects due to an increase in strength 
 were able to create more ankle and knee moment which helped their quick recovery of balance 
 after the perturbation .
one of the main limitations of this study was the danger associated with perturbed gait , 
 especially with older adult subjects .
subjects with a high bone density were selected due to 
 the risks of perturbed gait , and they might not have been representative of the general 
 older adult female population , as it has been shown that exercising has a positive effect on 
 the bone density of older adults aged in their sixties to eighties30 . to conclude , aqua exercise therapy may be used as a method of training for older female 
 adults to prevent falls .
we recommend further study of older adults ' reaction to a 
 perturbation , includingthe measurement of emg as well as more detailed kinematic and kinetic 
 data analysis of the first few steps after the perturbation .
   [ purpose ] the purpose of the present study was to examine the effects of an aqua aerobic 
 therapy exercise for older adults on biomechanical and physiological factors affecting 
 gait . 
 [ subjects ] a total of 15 subjects participated in this study and they were randomly 
 divided into the experimental and the control group . [ methods ] physiological variables , 
 leg strength , power and flexibility , and biomechanical variables , both kinematic and 
 kinetic , were measured before and after the aqua aerobic therapy exercise . 
 each subject 
 was instructed to walk along an elevated walkway and during the trials a trapdoor opened 
 at random to create a 10  cm falling perturbation . 
 full body motion and kinetics was 
 gathered during the gait . 
 [ results ] there were significant reductions in body weight , and 
 body fat mass , and stride time after the perturbation . 
 significant increases in leg 
 strength corresponded to the maximum joint moment of the landing leg showing that the 
 subjects ' ability for recovery of balance after the perturbation improved . 
 [ conclusion ] as 
 the results showed significant improvements in gait pattern and recovery time after 
 perturbed gait , we conclude that aqua aerobic therapy is an effective exercise method for 
 training older adults to reduce their risk of falling . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION