numerous studies have investigated aging 
 effects on human movement patterns , especially on walking2,3,4 . the elderly tend to use a slower gait and shorter step length 
 during gait1 , 2 . the changes in joint angles mainly involve lower peak plantar 
 flexion2 , 4 , ankle range of motion ( rom)5 , and peak hip extension3 , 
 4 . however , in other studies no 
 age - related kinematic changes were found4 , 6 , 7 . thus , it remains controversial whether joint kinematics during gait are age - related . furthermore , previous studies have mostly focused on the sagittal plane motion , but no study 
 has reported the frontal and transverse plane motions , particularly those of the knee 
 joint . due to the differences in lifestyle , in most asian countries the elderly usually perform 
 activities that involve high flexion angles ( > 120 ) , for instance , squatting8 . the joint patterns during high flexion 
 activities might be related to patterns during gait . to our knowledge , no study has yet 
 assessed the correlation of joint kinematics between walking and squatting . therefore , the 
 objective of this study was to investigate the correlations of different age - groups , thereby 
 providing data for age - associated kinematics changes , and contributing to our understanding 
 of joint biomechanics . a sample of 16 healthy young subjects ( 8 females and 8 males ) and 8 healthy elderly 
 subjects ( 5 males and 3 females ) were recruited for this study . all subjects had a 
 traditional lifestyle involving squatting or other high flexion activities on a daily basis . none of the subjects had a history of injury or pain in the lower limbs , or 
 balance problems . this study was approved by the ethics committee of china university of 
 mining and technology , and all participants signed a consent form before participating . the optotrak certus 3020 dynamic tracking system ( northern digital 
 inc . , canada ) was employed to capture the kinematic data at a frequency of 100  hz . the subjects performed the 
 squatting exercise from an initial upright position with their feet shoulder width apart . the subjects were instructed to deeply lower their body , hold the position for 3  s and then 
 ascend back to the upright position , without moving their feet . for each subject , six 
 successful trials were recorded for each activity . local coordinate systems were defined for each lower 
 limb segment through bony landmarks8 . 
 then , 3d knee joint angles were calculated based on the coordinate systems . to generate 
 ensemble graphs , the data of one movement cycle were normalized to 100% . the average 
 measures of each subject were obtained from the six trials , and then these individual means 
 were averaged across the group of subjects . additionally , the relationships of 3d knee roms between walking and squatting 
 were evaluated by testing the correlation using a linear regression model . a comparison of 3d knee joint angles between the young and elderly subjects is presented in 
 table 2table 2 . mean ( sd ) three - dimensional knee angles during walking and squatting of the 
 young and elderly subjectsangles ( degree)walkingsquattingyoungelderlyyoungelderlymax . internal rotation4.83.95.87.37.64.7 * 21.712.8 * * significant age - related difference ( p<0.05 ) ( unit :  ) . during walking , no significant difference was demonstrated between the young 
 and the elderly group ( p>0.05 ) , although the elderly displayed increased minimum knee 
 flexion and decreased maximum knee flexion compared to the young subjects . conversely , there 
 were significant age - associated differences during squatting : the elderly demonstrated 
 higher maximal adduction , maximal internal rotation and external rotation than the young 
 subjects ( p<0.05 ) . correlation of knee rom between walking and squatting for the young and elderly 
 subjectsmotion planesyoungelderlysagittal0.700.23frontal0.520.0004transverse0.450.05 shows the correlation of knee rom between walking and squatting within each 
 group . positive correlations were detected for the young subjects in all three planes 
 ( r=0.70 , 0.52 , and 0.45 , respectively ) . interestingly , it was observed that 
 the knee rom during walking was not strongly correlated to that during squatting in the 
 elderly group ( r=0.23 , 0.0004 , and 0.05 , respectively ) . * significant age - related difference ( p<0.05 ) ( unit :  ) the objective of the present study was to investigate the correlation of knee kinematics 
 between walking and squatting for both the young and the elderly . to the best of our 
 knowledge , this is the first attempt to investigate the relationship of 3d knee kinematics 
 between walking and squatting . the findings would not only enable therapists and clinicians 
 to develop diagnostic measures and rehabilitation programs for the elderly individuals , but 
 also guide the design of prosthetics and rehabilitation protocols for asian populations . the results of the present study demonstrated that the elderly displayed increased knee 
 flexion at mid - stance and decreased knee flexion during the swing phase ; however , the 
 differences were not significant between the age groups . this result is consistent with 
 those of previous studies1 , 2 , 6 . in the 
 non - sagittal planes , the differences between the young and the elderly subjects were not 
 significant either ( p>0.05 ) . conversely , significant differences were observed in the 
 frontal and transverse plane motions during squatting . compared to the young subjects , the 
 elderly demonstrated much higher peak adduction angle and peak rotation angle . although the 
 knee motions in the sagittal plane were almost identical in the two age groups , the 
 age - related differences in non - sagittal plane motions may indicate subtle alterations in the 
 sensory and nervous systems , or physiological changes in the elderly . besides , due to much 
 higher adduction and rotation of the knee , mechanical changes would accelerate degeneration 
 of articular cartilage ; thus , it might be injurious for the elderly to perform the squatting 
 exercise . the most interesting finding of this study was that positive correlations of knee rom 
 between walking and squatting were demonstrated by the young subjects , but not by the 
 elderly subjects . this could be attributed to decreased muscle strength2 , 4 and joint 
 laxity1 in the elderly . during walking , the demands on muscle activities and joint rom were relatively small , so the elderly were 
 able to exhibit a normal gait similar to the young . however , with increasing demands , the 
 limited joint laxity of the elderly would interfere with joint rom , while the young would 
 still be able to control their performances . as a consequence , the joint rom during 
 squatting would be less related to that during walking in the elderly group . on the other 
 hand , the secondary movements of the knee are mostly constrained by the periarticular 
 connective tissue ( e.g. ligaments , joint capsule and tendon etc . ) . it has been reported that 
 the mechanical properties of these tissues appear to change with advanced age1 . besides , degeneration of articular cartilage might also 
 influence joint rom during deep squatting9 . irrespective of the mechanisms behind them , the results of this study 
 suggest that the elderly should avoid performing high flexion activities .
[ purpose ] the purpose of this study was to study the correlation of knee range of motion 
 between walking and squatting for young and elderly populations . 
 [ subjects ] sixteen young 
 and eight elderly healthy subjects were recruited for this study . 
 [ methods ] 
 three - dimensional joint motions of each subject were captured while they performed walking 
 and squatting exercises . 
 [ results ] significant differences in the non - sagittal plane knee 
 motions ( peak adduction , and peak external and internal rotation ) were revealed between 
 the young and the elderly during squatting . 
 correlations of three - dimensional knee range 
 of motion between walking and squatting were positive and high in all three planes for the 
 young subjects ( r2=0.70 , 0.52 , and 0.45 , respectively ) , but not for the elderly 
 subjects ( r2=0.23 , 0.0004 , and 0.05 , respectively ) . 
 [ conclusion ] we suggest 
 that changes in secondary knee kinematics and poor correlations between walking and 
 squatting for the elderly may result from degeneration of the sensory and neuromuscular 
 systems 
 . it could be injurious for the elderly to perform high flexion activities .