# Development and Validation of a System for Game Control Based on a Force Plate
## 5 Results and Discussion  
The goal of this experiment was the validation of the developed prototype of the system for game control based on a force plate. The calibration and work testing experiment on the game control system was conducted with one participant as the player (the article's author) with prior consent. The player stood with both of his feet on the force plate (see Figure 2) and was asked to stand quiet and upright for the next 20 s during the first step of the system calibration procedure. Figure 11 shows the player's CoP measurement in frame {O} during quiet and upright standing. The blue color shows the graph of the player's CoP position during such standing in frame {O}. The red pluses show the average value of the player's CoP (i.e., the \({}^{O}\)**h** position vector calculated based on Equation (9)). The components for the \({}^{O}\)**h** position vector were \(x_{CoP0}=-2.21\) mm and \(y_{CoP0}=-8.73\) mm. Figure 12 shows the ground reaction force measurement in frame {O} during quiet and upright standing. The average value of the ground reaction force on the graph was 871.23 N. According to the relation in Equation (8), the player's mass was \(m_{H}=88.81\) kg. The components of the \({}^{O}\)**h** position vector and the \(m_{H}\) player mass were the results of the first step of the calibration procedure for the game control system. While conducting the second system calibration step, the player was asked to move his body's CoM during a 20 s period so as to reach the maximum CoP deviations along the \(x\) and \(y\) axes. The goal of this step was to find the player's work plane. The searching for the player's work plane is shown in Figure 13. The graph showing the CoP position in the local frame {H} shows the following parameters: \(\max(^{H}x_{CoP})=79.25\) mm, \(\max(-^{H}x_{CoP})=68.57\) mm, \(\max(^{H}y_{CoP})=71.20\) mm, and \(\max(-^{H}y_{CoP})=65.50\) mm. Figure 10: PC application for data acquisition, system calibration, and game control. Figure 11: Measuring the player’s CoP in the frame [O] during quiet and upright standing (first system calibration step). Figure 12: Measuring the ground reaction force during quiet and upright standing (first system calibration step). Figure 13: Searching for the player’s work plane (second step of system calibration). The smallest maximum distances of the player's CoP position from the origin and along the positive and negative \(x\) and \(y\) axes represent the borders of the player's work plane (see Figure 5), which were found during the second calibration step. The graph from Figure 13 shows the following: \(\min(\max(-Hx_{CoP}),\max(Hx_{CoP}))=68.57\) mm and \(\min(\max(-Hy_{CoP}),\max(Hy_{CoP}))=65.50\) mm. Based on the aforementioned smallest maximum distances of the player's CoP position from the origin, the linear transformation factors were calculated based on the relations in Equations (11) and (12). The result of the second system calibration step was presenting the player's CoP position in the local frame {G}, which is also the frame used to control games. In the third step of the system calibration procedure, the player was asked to perform impulse half squats on the force plate for 20 s. Figure 14 shows the player's CoM acceleration measurements along the \(z\) axis during the performance of the impulse half squats. The blue color on the graph represents the player's CoM acceleration along the z axis (\(a_{max}=\bar{z}_{CoM}\)), while the red pluses show the maximum values of the player's CoM acceleration along the \(z\) axis (\(a_{maxx}\)) while performing the impulse half squats. The graph in Figure 14 shows the following values: The lowest local acceleration maximum value was \(\min(a_{maxi})=2.47\) m/s\({}^{2}\), while the global acceleration maximum value was \(\max(a_{maxi})=5.84\) m/s\({}^{2}\). The mean value of all acceleration maximums amaxi was \(4.35\) m/s\({}^{2}\), and the median was \(4.46\) m/s\({}^{2}\).