Effect and Durability of Eight-Week of Core Stability Training on Body Balance and Force of Direct Foot Kick in Young Men Jeet Kune Do (Wushu) Players With Somatotype Emphasis

* Corresponding Author: Majid Soltani Shirazi, PhD. Address: Department of Sport Biomechanics, Faculty of Physical Education and Sport Science, Central Tehran Branch, Islamic Azad University, Tehran, Iran. Tel: +98 (912) 8231889 E-mail: mssh.phd@gmail.com 1. Department of Sport Biomechanics, Faculty of Physical Education and Sport Science, Central Tehran Branch, Islamic Azad University, Tehran, Iran. 2. Department of Sport Biomechanics and Injury, Faculty of Physical Education and Sport Sciences, Kharazmi University, Tehran, Iran. 3. Department of Sport Biomechanics, Kinesiology Research Center, Kharazmi University, Tehran, Iran. *Majid Soltani Shirazi1 , Heydar Sadeghi2,3


Introduction
irect kick impact is one of the most practical techniques in gaining points in Jeet Kune Do sport, which depends on two factors: "impact strength" and "maintaining D balance during and after the technique." Athlete readiness, which depends on the type and methods of the protocol for more effective execution of the impact during the fight ("impact strength" and "balance"), has become one of the main concerns of coaches and athletes.
Accurate knowledge of the amount and role of influential factors in creating and maintaining balance and performing appropriate exercise to make the impact more efficient. Also, recognizing each of the factors involved is a determining factor for athletes' performance in this sport. This study aimed to investigate the effect and durability of eight weeks of core stability exercise on body balance and direct kick impact in young male elite Jeet Kune Do (Wushu) practitioners.
Given the existing knowledge, regardless of the type of test used for the assessment and regardless of the kind of exercise program used, it is claimed that in general, continuous exercise improves balance in individuals. For example, in research on the sport of Wushu, the kinematics of traditional Wushu to improve the balance of the body to the extent that it provides a theoretical basis for exercise physiology and practice has been evaluated as positive [1].
In the study of postural balance control in elite and beginner Tai Chi Chuan athletes, it was discovered that the number of balance changes in elite tai chi practitioners compared to beginners in the same field in performing complicated and balanced Tai Chi movements [2]. An examination of the type of exercise used suggests that core stability exercise improves balance in athletes and nonathletes. Particularly in the field of Wushu, research has revealed that compared with core stability exercise, Tai Chi Chuan had a positive effect on neuromuscular function in the lower extremity in the elderly while reducing their nonspecific chronic low back pain [6].
In other martial arts, the effect of four weeks of traditional martial arts training on balance was significant compared to modern martial arts training [7]. Limited studies have been conducted on the effect of core stability and martial arts exercises on the impact force. The impact of core stability exercises on the distal limb's function during Muay Thai ballistic shock maneuvers was investigated in a study. It was discov-ered that static and dynamic activities for the core stability zone could increase the impact's speed and force [8].
The effect of core stability zone strength exercise on karate spinning wheel kick and physical variables of "balance", "power", and "reaction speed" were also evaluated as positive for young women [9]. Electromyographic examination of pelvis, lumbar and pelvic floor muscles were considered higher in taekwondo practitioners in a high-round kick than in the middle-round kick [10].

Methods
A total of 24 Jeet Kune Do practitioners with Mean±SD age of 26.95±0.47 (years) and body mass of 70.33±7.83 (kg) were randomly divided into "experimental" and "control" groups. In addition to regular exercise, the experimental group performed core stability exercises for eight weeks. "Static balance" (standing stork test), "dynamic balance" (Tandem test), and "direct kick impact" of both groups in the three stages of "pre-test", "after eight weeks of core stability exercise" and "after four weeks without exercise" (persistence test) was measured.

Results
The repeated measures ANOVA and Bonferroni post hoc tests were used to compare the experimental and control groups. The results confirmed that core stability exercise was effective and stable on static and dynamic balance ( Figure 1). However, despite the significant effect of applying for the core stability exercise program on the direct kick impact force, no significant persistence was observed ( Figure 2). Figure 1. The core stability exercise on static and dynamic balance A: Mean static balance; and B: Bynamic balance scores for control and experimental groups in three stages of testing; * Indicates a significant difference compared to the previous stage of measurement for a group; † Indicates a significant difference between the two groups in that stage of measurement.

Discussion and Conclusion
In martial arts, especially Jeet Kune Do (Wushu), the efficiency of performing basic techniques such as direct kick impact requires a high speed of the lower limbs along with dynamic control of body stability throughout the movement [7,13]. Maintaining balance when performing effects, or in other words, the high ability of elite people to control the backward and posterior transmission of the Center of Pressure (COP) after hitting the punching bag, is significant. This indicates these individuals' ability to control body position more effectively throughout the impact movement [7,13]. It should be noted that the center of the body's stability as a set of lumbar-pelvic and thigh is located where the center of gravity of the body is located. The body movements begin from there [13,25]. The core stability zone is considered a box that plays an essential role during the motor kinetic chain, especially for circulatory activities in the stability of the trunk, pelvis, and the transfer of force from the lower limb to the pelvis and vertebrae [13]. It acts as a linker during various movements [25].
It seems that core stability exercise by strengthening the muscles of the central region of the body and improving the function of the musculoskeletal system modulates the displacement of the center of gravity outside the base of support and reduces its fluctuations and thus Improves the balance function with durability and increases the force of direct kick impact. Therefore, along with specialized training programs in this sport, to improve static and dynamic balance and increase the force of direct kick impact, the core stability exercises can be used.

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 whenever they wish, and if desired, the results of the research would be available to them.

Funding
This study was extract from MA. thesis of first author at the Department of Sport Biomechanics, Faculty of Physical Education and Sport Science, Islamic Azad University, Central Tehran Branch, Tehran.

Authors' contributions
All authors contributed equally in preparing all parts of the research.

Conflicts of interest
All rights of this research reserved exclusively to the corresponding author, the supervisor and Islamic Azad University.