gait analysis provides us with important information on the 
 functional capacity of patients when making disability assessments , and in intervention and 
 treatment planning2 , 3 .
the gait speed substantially influences the gait pattern , and 
 kinematic and kinetic characteristics4 , 5 . when quantifying human gait by kinematic and kinetic characteristics ,
subjects are 
 typically asked to walk at what is called their normal gait speed6 , 7 . in general , normal 
 gait speeds have been shown to range from 1.05 to 1.43 m / s in healthy adults8 , 9 . 

these subject - specific speeds of healthy subjects have been used to produce normative gait 
 data that can be used as a reference when abnormal and/or pathological gait is assessed .
a 
 possible limitation of this procedure is that slower gait speeds may be associated with 
 decreased joint movements and joint kinetics . at faster gait speeds ,
clinical evidence 
 suggests that increased joint power is responsible for certain types of overuse injuries of 
 the musculoskeletal system10 , 11 .
thus , it is generally accepted that normal gait 
 parameters follow a consistent pattern of change in response to changes in gait speed .
many previous studies have investigated the relationship between kinematics of the lower 
 limbs and gait speed7 , 12 , 13 .
in addition , gait speed 
 has been shown to have a significant effect on gait kinematics and clinicians can provide 
 normative kinematic data as goals for patients who walk slowly at their normal gait speed . 

recent research has proposed the use of self - selected gait speeds to specify walking speed , 
 because it offers the advantages of allowing comparisons between speeds , while concurrently 
 allowing the subjects to act as their own control to normalize gait parameters10 , 11 .
thus , self - selected gait speeds are recognized as valid and 
 sensitive measures of gait performance , and identifying kinematic profiles that relate to 
 gait speed could provide guidance for intervention strategies aimed at improving normal 
 gait .
recent studies have addressed gait movement patterns using three - dimensional ( 3d ) 
 motion analysis systems , but these have been limited to the sagittal plane and have 
 neglected the frontal and transverse planes7 , 14 .
both the frontal and transverse planes 
 are important because gait performance occurs in three - dimensional space .
therefore , we 
 investigated the individual kinematic gait profiles of normal subjects in all three planes 
 and identified frontal and transverse profiles in addition to the sagittal profile at 
 self - selected gait speeds .
forty healthy subjects who had no previous history of neurological , musculo - skeletal or 
 other medical conditions that could have affected gait were recruited .
all the subjects 
 understood the purpose of this study and gave their written and informed consent prior to 
 their participation .
the study protocol was approved by the local institutional review board 
 and complied with the ethical principles of the declaration of helsinki .
the subjects were first asked to walk along a 10  m walkway at a comfortable pace .
the 
 procedure was repeated at two different gait speeds , performed in a random order , to give 
 three sequences of data for each subject .
the three gait speeds were as follows and were 
 always performed at a self - selected speed : slow speed ( ss ) : a gait somewhat slower than 
 normal walking speed ; normal speed ( ns ) : a gait at a normal , comfortable speed ; fast speed 
 ( fs ) : a gait somewhat faster than normal walking speed13 . the experimental order of the self - selected gait speeds . a twelve - camera video - based motion analysis system ( vicon , uk )
sixteen reflecting markers were placed on specific anatomical landmarks on the hip 
 ( asiss and psiss ) as well as on each mid - thigh ( the lower lateral 1/3 of the thigh ) , knee 
 ( lateral epicondyle ) , mid - tibia ( lower 1/3 of the shank and lateral malleolus ) , and foot 
 ( second metatarsal head and heel ) for capturing joint motion .
the marker protocol was based 
 on the plug - in - gait marker set .
usa ) were placed at the centre of the 10  m walkway to 
 measure the gait cycle .
data collected from the force plates were digitized at 500  hz and 
 low - pass filtered at 1,000  hz .
the system was capable of measuring separate repeated steps 
 over successive strides for extended trials .
only trials that included three consecutive 
 clean force platform data and complete data were considered .
demographic data such as age , 
 height and weight were analyzed by one - way anova .
the values of the different gait speeds 
 were compared using one - way anova and least - squares difference as a post hoc test . 

the subjects had an average age of 23.163.76  years , an average body mass of 65.886.97  kg , 
 and an average height of 171.043.52  cm .
the flexion peak and external rotation peak of the knee joint significantly increased with 
 increase of gait speed ( p<0.05 ) .
the results of the lsd posthoc test show that the 
 flexion peak of the knee joint was significantly different between ss and ns ( p<0.05 ) 
 ( table 1table 1.comparison of kinematic from gait speed on lower extremity joint ( )jointplaneanglessnsfship jointsagittalflexion peak26.36.0528.65.2030.37.40extension peak10.35.6712.95.8213.86.04frontalabduction peak2.785.094.154.054.624.20adduction peak5.698.028.623.217.668.56transexternal rotation peak21.912.216.012.416.314.3internal rotation peak1.079.538.2011.39.4111.9knee jointsagittalflexion peak44.36.6154.36.8353.36.03extension peak1.495.221.904.562.265.79frontalabduction peak11.416.915.810.711.14.16adduction peak0.057.802.354.451.088.80transexternal rotation peak5.514.017.705.748.074.31internal rotation peak3.3912.13.588.587.708.73ankle jointsagittaldorsiflexion peak11.85.2112.73.2610.38.87plantarflexion peak7.857.8212.99.1116.16.83frontalabduction peak4.534.334.952.774.902.98adduction peak0.423.530.901.991.362.37transexternal rotation peak4.4011.74.5912.43.659.84internal rotation peak23.910.225.610.225.210.9significant difference between the ss and fs groups ( p<0.05 ) . 

the external rotation peak of the knee joint was significantly different 
 between ss and ns , ss and fs ( p<0.05 ) ( table 
 1 ) .
plantarflexion peaks of the ankle joint significantly increased with increase 
 of gait speed ( p<0.05 ) .
the results of the lsd posthoc test show that plantarflexion of 
 the ankle joint was significantly different between ss and ns , and ss and fs ( p<0.05 ) 
 ( table 1 ) .
in the current study , we found that between the pre - swing and the mid - swing the flexion 
 peak and the external rotation peak of the knee joint and the plantarflexion peak of the 
 ankle joint significantly increased with the increase of the gait speed .
these results imply 
 that there is a need for greater power generation at higher gait speeds for propelling the 
 body forward , and it is accompanied by coupling motion of the external rotation of the knee 
 joint .
gait speed has an important influence on the kinematic parameters of the lower extremity 
 joints .
in particular , the kinematic parameters of the knee and ankle joints have a positive 
 relationship with gait speed13 , 15 , 16 . in this study , 

the knee flexion peak during pre - swing and mid - swing significantly increased with the 
 increase of gait speed .
the knee flexion angle in the gait cycle has a significant positive 
 correlation with the gait speed , according to previous studies13 , 16 , indicating 
 that the angle of the knee flexion increases with increase of gait speed .
it is possible 
 that this is due to the need for greater shock absorption at higher speeds .
in addition , our 
 findings show that the external rotation peak of the knee joint significantly increased with 
 increase of gait speed .
previous studies have reported that one joint segment of the lower 
 extremities affects the others during the gait .
therefore , we think that gait speed is affected by coupling motion 
 of the lower extremity .
the plantarflexion peak of the ankle joint significantly increased with increase 
 of gait speed .
this result is in agreement with other studies that have suggested that 
 plantarflexion of the ankle joint is closely related to gait speed .
in addition , the ankle 
 joint plays an important role in changing gait speed , and it has been suggested that 
 plantarflexion is a strong predictor of step length and gait speed18,19,20 . in conclusion , we examined the changes in the lower extremity joints at different gait 
 speeds using a 3-dimensional motion analysis system .
our results suggest that coupling 
 motion of the knee joint and plantarflexion of the ankle joint significantly increase with 
 increase of the gait speed .
these results provide important insights into the gait 
 mechanisms underlying speed regulation in walking and provide a foundation on which to 
 investigate the influence of walking speed on various measures of interest in pathological 
 populations . in this study ,
we restricted recruitment to males of standard height and weight 
 to negate the effects of external factor . therefore , further studies involving a larger 
 population are suggested .
 [ purpose ] the purpose of this study was to investigate the changes in hip , knee and ankle 
 kinematic variables of the lower extremities at different gait speeds . 
 [ subjects and 
 methods ] forty healthy subjects who had no previous history of neurological , 
 musculo - skeletal or other medical conditions that could affect gait were recruited . 
 the 
 subjects were asked to walk 10  m down a walkway at three different gait speeds : normal 
 gait speed , and self - selected fast , and slow speeds . 
 the experimental order was randomly 
 chosen across these gaits . 
 the hip , knee and ankle kinematic data were evaluated using a 
 vicon 3d motion analysis system and force plates . [ results ] the flexion peak and external 
 rotation peak of the knee joint 
 significantly increased with the increase of gait speed . 
 
 the plantarflexion peaks of the ankle joint significantly increased with increase of gait 
 speed . 
 however , none of the kinematic data of the hip joint were significantly dependent 
 on increase of gait speed . 
 [ conclusion ] the relationship of the knee and ankle joint can 
 be described as coupling motion which is dependent on gait speed . 
 our present findings 
 suggest that coupling motion of the knee joint and plantarflexion of the ankle joint 
 significantly increase with increase of gait speed . 
 these results will provide important 
 insight into gait mechanisms for the evaluation of pathological populations . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION