Extended Abstract
1.    Introduction
The biomechanics research has shown that of overweight and obesity lead to changes in body balance and these changes can effect gait and running. Thus checking out gait patterns in overweight people can help prevent the problems these people face in all ages (6-8). In research of lai et all (2008) that was about weight increase and gait in adults, the results showed that obesity is accompanied with low speed gait and increased step width (9) while Nantel et al. in their research on children reported significant differences between over-weight and normal-weight people (10) Their results indicated that there is significant negative solidarity between overweightedness and speed gait, but there is no significant difference in gait speed and lengh in different people with different ages. Thus research is inconsistent in view of the effects of overweightedness. Thus the present study is an attempt to compare the gait kinematics in over-weight and normal-weight people across age groups.
2.    Methods
This was a causal-comparative study in which participants were divided into eight groups (four normal groups and four overweight groups) based on body mass index (BMI). The statistical population of the study consisted of 9-85 year-olds in Mashhad who were selected purposefully based on available sampling from 105 volunteers, from among whom, 40 who had the necessary conditions were selected as the sample. Based on age, they were divided into four groups of 10 children, youth, middle-aged and elderly, including five participants with normal weight and five overweight participants, which included a total of eight groups in four age groups. Sica device was used to measure height and weight and a motion analyzer which analyzed the movements with very high accuracy was also utilized (23). The methodology of the research involved step analyses; thus the place where the step-taking experiment was to be conducted (motion analysis laboratory) was about 35 meters (7*5), and around it, there were eight cameras for motion analysis, markers were installed on the subjects' bodies and the subjects traveled five times in a round-trip distance of six meters from the location of the motion analysis laboratory. QTM software was used to optimize the output information of the device. Kolmogorov–Smirnov test was used for normalization of data distribution, two-way variance analysis and LSD stalking test were run and analyzed using SPSS software version 19 at a level of significance of (p=0.05).
3.    Results
The results of two-way analysis of variance showed a significant difference in step velocity variables [effect of age (0.364) and body postural effect (0.487)}, dual support stage time [age effect (30) 0.4) while the effects of posture (0.092)} and stabilization [age effect (0.094) and body posture effect (0.271)} were not meaningful in different age groups. However, there was a significant difference in step length variables [age effect (0.0001) and body posture effect (0.038)}, step width {age effect (0.01) and body posture effect (0.01) 0.017} and duration of resilience stage [age effect (0.0001) and posture effect (0.731)} between overweight and normal-weight age groups. Now, considering the significance of the effect of age on step length, step width, duration of resilience stage, in order to determine the difference between the age groups, we needed to use LSD tracking test the results of which showed that step length in children is different from that in youth, middle-aged and elderly, and that the step length was also different in young people and the elderly. In the width of the step, there was a difference between children and middle-aged and elderly, and also young people were different from middle-aged. Moreover, in the duration variable, the resilience phase of children was different from young people, middle-aged and elderly. There was also a significant difference in body posture variable during step length and step width; therefore, we used t-test and compared overweight and normal-weight participants in terms of step length and width in each age group, which showed a significant difference in step length variable (p=0.035) in middle-aged and also in step width (p=0.002) in children.
4.    Conclusion
In the step length variable, children were different from the other age groups. As the height of an individual appears to be an effective factor in the variable length of step, which increases with age after childhood, this factor can result in the difference between children's step length and those of other age groups (21). Also, it seems that since the peak of power is in youth and with reaching old age the power decreases, the reason for the difference in step length in the group of youth and the elderly is also strength (26). Also, there was a significant difference between middle-aged and overweight in step length factor, which seems to be due to limb weight and balance index (25, 26). At the width of the step, the results showed a significant difference in the step width of overweight children with middle-aged and elderly, which may be related to the onset of weight gain in childhood. According to developmental studies, most overweight and obese adults have been obese and overweight children which probably indicates the onset of overweightness and obesity to be in the childhood (27). In the present study, there was a significant difference between children  and the youth, middle-aged and elderly during the resilience phase where with increasing age to young hood, the duration of resilience increased, but then during the youth hood, middle-agedness and aging, there were no significant differences between the age groups: therefore, the difference between the group of children and other age groups could be due to the increase in the time of the swinging stage with the increase in step length from childhood to adulthood as with increasing height, step length increases (28) and there is a high correlation between step length and duration of warping stage (29).

Ethical Considerations
Compliance with ethical guidelines
There were no ethical considerations to be considered in this research.
Funding
This research did not receive any grant from funding agencies in the public, commercial, or non-profit sectors.
Authors' contributions
All authors equally contributed to preparing article.
Conflicts of interest
The authors declared no conflict of interest.