arate means fighting with empty hands (Kara meaning empty, and te meaning hand) and includes kicking, hitting and blocking techniques without using a weapon [4]. Dachi is a different form of standing in karate, which is responsible for creating power, flexibility, movement, as well as the performing the techniques correctly in different positions [1]. Zenkutsu-Dachi is a form of standing with one leg forward putting more weight on the front leg and the rear leg backward and flat with heel on the ground. The front and rear legs have a 30-degree outward rotation, and the transverse distance of the legs is equal to the width of the shoulders [3]. 
This movement is performed in a few seconds. This speed includes parameters such as reaction time, selection of appropriate response, start of the movements or performing the techniques [1]. Lotfian et al. [3] and Khanzadeh et al. [7] have conducted studies on the Zenkutsu-Dachi techniq most important Dachi is Zenkutsu-Dachi. The knee and ankle joints work together in a forward movement as a chain of motion. The motion axis of these joints is the frontal axis and their motion plane is the sagittal plane. The pattern of Zenkutsu-Dachi movement is bringing the back foot forward which shows the hip joint flexion. This pattern is similar to walking or running. Methods

In this study, 12 male karate athletes (height= 175±5 cm; weight=75±5 kg, age=25±5 years, history=8±2 years), who had at least 5 years of membership in the national team and had no injuries and or any specific disease in the lower extremity, were participated. A 3-D motion analyzer with 6 synchronized infrared cameras and a video recording speed of 200 frames per second, and cortex 2.5.0 software were used to analyze the recordings. Athletes performed the warm-up session (8) and then performed the Zenkutsu-Dachi movement in 6 positions, all of which were compared to their normal position. The three patterns (1=standard width and length, 2= slightly wider but standard length, 3= more leg forward, standard width) were implemented in two modes: bent rear knee and straight rear knee. In the testing process, each subject had 3 attempts, and the selection criterion was the maximum linear velocity of the ankle marker along the x-axis. The analysis was performed on the right foot, which was the superior foot, and the cameras were arranged in a semicircular arc at the right side of the subject. We used 5 markers that had the property of reflecting light placed in the areas of anterior superior iliac spine, great trochanter, lateral femoral condyle, external ankle, and big toe. The study parameters were maximum angular velocities of the hip, knee and ankle joints and linear velocity of the ankle. After confirmation of the normality of data distribution by Shapiro-Wilk test, repeated measures ANOVA and Bonferroni post hoc test in SPSS V.25 were used to test the research hypotheses  at a significance level of P<0.05.

According to the results of repeated measures ANOVA (P= 0.004 and F = 5.204), there was a significant difference between Zenkutsu-Dachi movement patterns only in the hip joint. Using the Bonferroni post hoc test, the differences in the maximum angular velocity of the hip joint between different Zenkutsu-Dachi movement patterns were also reported. The difference was significant between patterns 3 and 4 (mean difference=69.72, and p=0.006) and between patterns 4 and 5 (mean difference=-41.54, p=0.03). Table 1 shows that pattern No. 3 had the highest angular velocity in the hip joint, while pattern No. 4 had the lowest angular velocity.


 

Dachi is the most important technique in karate [1]. The most important Dachi is Zenkutsu-Dachi. The knee and ankle joints work together in a forward movement as a chain of motion. The motion axis of these joints is the frontal axis and their motion plane is the sagittal plane. The pattern of Zenkutsu-Dachi movement is bringing the back foot forward which shows the hip joint flexion. This pattern is similar to walking or running. The main flexor muscle of the foot is iliopsoas muscle [9], and plays a role in swinging the foot forward when walking or running [10]. Therefore, considering the similarity of the movement pattern in this technique with the that of walking and running, it can be said that the hip joint and psoas muscles are the main and most important factors for performing the forward movement of Zenkutsu-Dachi. Hence, the performance of this technique can be improved if positive changes be made in the position and range of motion of the hip joint and iliopsoas muscles. In the third movement pattern with more leg forward, more stretching was created in the iliopsoas muscle which increased the elastic energy and produced more kinetic energy when released. This technique is in a closed chain, where the moving head of the iliopsoas muscle attaches to the femur near the hip joint support and the lower limb and creates a lever. Therefore, with less force, more displacement in the range of motion of the hip joint occurs, which shows the importance of this joints and the iliopsoas muscle. Bending the knee shortens the torque arm, which increases the angular velocity of the hip joint and the speed of the foot swing while performing this technique.

All ethical principles were considered in this article.

This research did not receive any specific grant from funding agencies in the public, commercial, or non-profit sectors

Conceptualization, methodology and supervision, review and editing: All authors; Review and writing the original draft and sources: Ali Amiri Khorasani.

The authors declared no conflict of interest.
 

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