# Foot Insole Pressure Distribution during the Golf Swing in Professionals and Amateur Players
## 2 Methods
### Data Collection  
The plantar pressures of each foot were recorded by means of two instrumented insoles (F-Scan; Tekscan model 3000 E) with a total of 900 pressure sensors working at 100 Hz [23]. To avoid any interference of the instrument with the player performance, the insoles were used under the original insoles of the golf shoe owned by each subject. Each insole is connected to the portable transmitter unit (Versatek VW-1) via a thin cable. The transmitter unit sends the information to the computer using a wireless protocol. In addition to the pressure sensor data, video images were recorded using a Sony A7 III video camera with a 20 mm fixed focal length lens working at 50 Hz and connected to the F-Scan system via HDMI port. Images and pressures data streams were synchronized internally by the system, and the key instants of the swing (stand (ST), middle backswing (MB), top of the backswing (TB), ball impact (IM), and early finish (EF)) were manually labeled. Figure 1 shows a graphical example of these five key instants. Simultaneously, we tracked the ball flight and the clubface movement via a launch monitor (Foresight model CG2 + HMMT), which consists of 4 stereoscopic high-speed cameras and detects small flat reflective markers (5 mm diameter) adhered to the ball and the club face. The launch monitor provides real time information to the players about their swing, including performance metrics such as the launch distance, the club speed, the ball speed, and the ball spin.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **Handicap** & **Height (m)** & **Age (Years)** & **Weight (kg)** & **Driver (Mph)** & **5-Iron (Mph)** \\ \hline Pro (15) & 0 & \(1.76\pm 0.05\) & \(39\pm 12.32\) & \(81\pm 12.65\) & \(108.72\pm 5.33\) & \(92.81\pm 4.18\) \\ Medium (15) & \(9\pm 4.82\) & \(1.79\pm 0.07\) & \(48\pm 14.71\) & \(78.2\pm 13.11\) & \(103.44\pm 7.17\) & \(89.83\pm 6.47\) \\ High (25) & \(22.5\pm 6.66\) & \(1.78\pm 0.05\) & \(36.5\pm 12.65\) & \(77.95\pm 10.17\) & \(98.89\pm 9.61\) & \(85.85\pm 8.12\) \\ \hline \hline \end{tabular}
\end{table}
Table 1: Descriptive statistics of the sample (mean and standard deviation) for the three player groups considered: Pro, Medium, and High handicap. Driver (Mph) and 5-iron (Mph) refers to the club speed during the impact expressed in miles per hour.  
Figure 1: Key instants of the swing: Stand (ST), then the club start its movement; Middle Backswing (MB), when the club shaft is parallel to the ground; Top of backswing (TB), when the descent begins; Ball Impact (IM), when the club contacts the ball; Early finish (EF), when the salt surpasses the vertical axis to the ground.  
Each participant hit balls with the two clubs, until he made five good shots with each of the 5-iron and Driver club. After each shot, the player (under the supervision of a professional player) decides whether the shot was good enough or not using the information recorded by the launch monitor: ball release velocity, maximum flight, and distance of the trajectory. These five good shots for each club were chosen for the later analysis. Figure 2 shows an example of the recording environment.