Author(s): CAPRIOLI, L., BONAIUTO, V., CAMPOLI, F., EDRISS, S., ROMAGNOLI, C., SALVI, V., PADUA, E., ANNINO, G., Institution: TOR VERGATA UNIVERSITY OF ROME, Country: ITALY, Abstract-ID: 1615

INTRODUCTION:
Assessing the distance to the ball in the tennis forehand is critical. Proper distance maximizes ball contact in the ideal area of the racquet, known as the "sweet spot" allowing more control over the direction and power of the shot. In fact, if the impact occurs too close to the body the extension of the arm is limited, and as well as in the case of excessive distance reduced power and accuracy of the shot. Keeping the right distance from the ball also can help reduce the risk of injury, as it allows you to execute the shot with proper technique and without excessive stress on joints, muscles, and ligaments. The help a non-invasive assessment system can provide a technician is even more apparent in amateur tennis, where players still unaware of the act need continuous feedback.
METHODS:
The analysis was conducted on 3 amateur tennis players (32.7 ± 6.8 years, 175.3 ± 8.2 cm) with an average of 4 years of playing experience. The subjects wore a sensorized chest strap with an inertial unit Movella DOT acquired at 120Hz. A Tennis Tutor Plus ball-launching machine, positioned on the opposite baseline at 1.60m from the mid-point, was set to two settings for two practice sets. For the first set, subjects received 10 balls each, at speed 4 with no effect, and easy to handle. In the second instead, 10 balls at speed 6 with top-spin. Two action cameras 240 Hz captured 20 forehands of each player from side and rear perspectives both aligned about 6m from the point of impact and placed on a stand at 1.10m above the ground. Video analysis was conducted using the BIOMOVIE ERGO software to identify the anteroposterior and lateral distance of the ball at the point of impact from the longitudinal axis coincident with the first toe of the nondominant foot. Jasp 0.18.1 was used for data analysis. Pearsons correlation between ball distance and trunk inclination during the impact phase (coinciding with the point of maximum angular velocity of trunk rotation) was investigated for each player and the group.
RESULTS:
A highly significant strong Pearsons correlation was found in all the subjects. In player 1 the correlation between Euler Y angle, (i.e., flexion-extension angle) and lateral distance of the ball was 0.7 p<0.001, in player 2 of 0.8 p<0.001, and in player 3 of 0.7 p<0.001. A more moderate partial correlation of 0.4 p<0.001 was found in the analysis of the 60 forehand shots of the whole group, due to the variability of distance to the ball in players with different body stature and joint levers.
CONCLUSION:
This preliminary study found a strong correlation between the torso tilt detected by the IMU system and the lateral distance to the ball at the impact point. This bodes well for how a sensorized chest strap can aid the technician in assessing the individual optimal distance to the ball in the forehand of amateur tennis players. Subsequent studies are needed to develop the full potential of the system, broaden the sampling of the investigation, and examine all game fundamentals.