Biomechanical Kinetic Chain Analysis of Service Motion for Speed Ball Prediction Through SBM-03 App Development

Background. The kinetic chain of the serve stroke is a coordinated activation of body segments (legs, torso, shoulders, arms, and hands) that begins with the ground reaction force against the legs on the ground and ends with racket acceleration through the ball. The objective of this study is to place the end segment, hand, and racket in an optimal position at an optimal speed to "make the ball travel" as best as possible. The efficient use of the kinetic chain segment creates a much greater racket velocity than its parts. On the contrary, a broken kinetic chain makes the ball speed less optimal and can even lead to injury. However, the reality is that the kinetic chain movement and ball speed rate cannot be seen simply using the observation method. Thus, a specific technology is needed to diagnose it. Objectives. This study aimed to develop a digitalized system of software to help measure the ball speed rate based on the kinetic chain of the serve stroke. Materials and methods. The research method employed in this study was research and development (R&D).  The data were collected by recording videos of 10 professional athletes’ serve strokes. These videos were then analyzed using software to check their movement angles. Results. The findings showed that the average angles were as follows: elbow = 120.490, shoulder = 166.010, hip = 165.330, knee = 165.880, ankle = 173.790, and ball speed = 24.33 m/s. Conclusions. Some conclusions were drawn from this study. First, the more significant portion of the kinetic energy of force produced in a serve was developed on the legs and body torso. Every segment generated force and acted as a stabilizer structure for the next segment’s activity. Fifty-one percent of kinetic energy and 54 up to 60 percent of the total force were produced this way. Second, the kinetic chain was oriented towards changing the linear or straight-line momentum into an angular or rotational momentum around the stable pillar leg. Third, each segment had tilting or stabilization and acceleration phases. Fourth, a big and fast movement was needed in the joints, especially the shoulders. Finally, the broken segment or kinetic chain reduced the ultimate force or energy available to travel the ball and put enormous pressure on the surrounding segments. A decrease in kinetic energy by 10 percent from the hip or body to the shoulder while doing the serve required an increase in the shoulder’s rotation by 14 percent or an increase in the shoulder’s mass by 22 percent to create the same kinetic energy on the hands and racket. There were some reasons for the broken kinetic chain, but the most general ones included muscle weakness, inflexibility, joint injury, and poor stroke mechanics.