1.    Introduction
Running is a fast form of movement of the human body on the ground, which is characterized by alternating movement of the human body. Therefore, running, in its various forms, is a basic skill for performing a variety of sports activities (1). Knowledge of the biomechanical performance of lower limb muscle groups and joints across a wide range of running speeds is important in improving the existing understanding of high performance in the athlete as well as in helping to identify factors that may be associated with injury (3). Many lower limb muscles and joints that play an important role during running have specific actions that are not limited to one anatomical level (3). Consequently, running is controlled by coordinated muscle and joint activity at all three anatomical levels, suggesting that any research on the biomechanics of running should ideally be approached from a three-dimensional perspective (3). Therefore, the aim of this study is to investigate the effect of speed on the parameters obtained from kinematic analysis in the lower limb during the stance phase of running at different speeds (2.5, 3.5 and 4.5 m/s) in all three movement planes. It was assumed that running speed has a significant effect on the peak values of movements in all three sagittal, frontal, and transverse planes in the hip, knee, and ankle, and considering these limitations, more research is needed to create a more complete analysis of the effects. Increasing the running speed on the lower limb joint kinematics is required.
2.    Methods
The current research was semi-experimental. Through available sampling, 28 subjects voluntarily participated in the current research. The inclusion criteria of the subjects included elite runners who had a minimum average speed of 1 km/5 min during 10 km races for more than 20 km per week and were completely familiar with running on a treadmill.  The criteria for leaving the subjects was any injury or neurological and muscular disorders that would endanger the health of the person and the process of conducting this research.  The study was conducted in the Biomechanics and Movement Control Laboratory of the Federal University and was approved by the ethics committee of this university with the code of ethics (CAAE:53063315.7.000.5594).  Written and informed consent was obtained from the participants before conducting the study.  Subjects ran on the equipped treadmill at three speeds (2/5, 3/5, 4/5) while the kinematic data were collected through a 3D system in the stance phase of running by recording 12 cameras with resolution 4, Cortex 0.6 and 4 software.  Motion analysis was collected.
 The normality and homogeneity of variance of the hypotheses of the dependent variables were tested using Bartlett and Lunn tests.  A repeated measurement test was performed to measure the angles of the dominant hip, knee and ankle joints in the stance phase of running in three planes.  Statistical calculations were also done in SPSS software.  A significant level was considered for all statistical analyzes (P<0.05).
3.    Results
The results of descriptive statistics and demographic parameters including height, weight and age of subjects are shown in Table 1.  The results of descriptive statistics and inferential statistics are presented in Table 2.
In descriptive statistics, the mean and standard deviation of hip, knee, and ankle joint angles in three planes of motion, in three speeds, and in inferential statistics, according to the results of the follow-up test, in the angles of the lower limb joints during running in the stance phase in motion planes.  Sagittal, frontal and transverse were discussed, which include the following.  There was a significant difference in the maximum changes of the hip joint angles in the frontal plane (x) in all three speeds, in the transverse plane (Y) in 3.5 and 4.5 speeds, and in the sagittal plane in all three speeds.  There was a significant difference in the maximum changes of the knee joint angles only in the frontal plane at the 4.5 speed with the other two speeds.  There was no significant difference in the maximum changes of ankle joint angles in any of the planes and speeds.  There was a significant difference in the minimum changes of the hip joint in the frontal plane at each speed, in the transverse plane at 3.5 speeds, and in the sagittal plane at all three speeds.  There was no significant difference in the minimum changes of the knee joint in the frontal plane in any of the planes and speeds.  There was a significant difference in the minimal changes of the ankle joint in the frontal plane at all three speeds, the transverse plane at 2.5 speeds with the other two speeds, and the sagittal plane at all three speeds (P<0.05).

Table 2: Comparison of the angles and range of motion of the lower limb joints in the stance phase.
  

4.    Conclusion
The aim of this study was to increase the speed of running on the three-dimensional kinematics of the lower limb joint angles in the stance phase. In this study, the maximum, minimum and range of motion parameters of the lower limb joints were examined in three planes by two participants at speeds of 2.5, 3.5, and 4.5 m/s.
 The findings of this research showed that changes in running speed had an effect on some three-dimensional kinematic parameters of the lower limb joints in the stance phase. These results showed that any change in the angles of the joints of the lower limbs can help to optimize a person's performance or cause risk factors of injury in daily activities such as walking, running and other activities. It is suggested that this factor should be taken into consideration in the design of training programs in order to improve the performance and execution of skills, as well as the analysis of movement related to running speed, and it can also play a very important role as a way to prevent these risk factors.
There is a lot of evidence that running has many health benefits, but finally knowing the kinematic parameters and mechanical properties of lower limb joints can be essential in maintaining and optimizing performance during running.

Ethical Considerations
Compliance with ethical guidelines
All ethical principles were considered in this article. The participants were informed about the purpose of the research and its implementation stages; they were also assured about the confidentiality of their information; Moreover, they were allowed to leave the study when-ever they wish, and if desired, the results of the research would be available to them.
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.