Author(s): HAUTIER, C., LE SOLLIEC, T., ZHANG, Q., GASSIER, R., GILBERT, B., TRAMA, R., Institution: UNIVERSITÉ CLAUDE BERNARD LYON 1, Country: FRANCE, Abstract-ID: 1730

INTRODUCTION:
By adapting the characteristics of sports equipment to childrens physical development, sports movements can be performed more successfully and with more desirable movement patterns (1). This also allows mechanical constraints to be adapted to the childs physical abilities. That way, the International Tennis Federation has proposed the "Play and Stay" method to make tennis more accessible to all children. However, studies have yet to look at the influence of these adaptations on the muscular and vibratory stresses experienced by young tennis players. This study aimed to evaluate the vibrations and muscle activation patterns in children aged 5 to 13 performing a flat forehand following the ITF recommendations.
METHODS:
Sixty junior tennis players were separated into four groups of fifteen players (Yellow, Green, Orange, and Red). Two triaxial accelerometers were taped to the back of the participants dominant hand and the rackets throat to capture the vibration signal. Also, eight surface electromyographic (EMG) sensors were fixed on arm muscles, including the Pectoralis Major, Upper Trapezius, Deltoideus Anterior, Deltoideus Medius, Biceps Brachii, Triceps brachii, Flexor Carpi, and Extensor Carpi. After a standardized warm-up, players were instructed to perform maximal isometric voluntary contractions for each muscle group, followed by fifteen maximal forehands flat. Statistical nonparametric Mapping (SnPM) analysis was used to perform statistical inferences on the EMG and vibration parameters obtained from the continuous wavelet transform.
RESULTS:
No significant differences were found for EMG activation patterns. The total magnitude of vibration increased significantly from the red to the yellow category for the racket (from 1051.7 ± 362.2 to 2691.2 ± 783.8 UA, p < 0.05) and hand (from 526.8 ± 241.9 to 1334.4 ± 530.2 UA, p < 0.05). The median frequency of the hand increased between the red and yellow categories (from 158.7 ± 15.0 to 168.3 ± 15.6 Hz, p < 0.05), whereas it followed the opposite trend for the racket (from 206.2 ± 36.0 to 190.4 ± 26.6 Hz, p < 0.05). The damping time for racket vibrations did not differ between the four categories but was significantly higher in the orange group for hand vibrations.
CONCLUSION:
Analysis of the various EMG parameters shows that the Play and Stay method enables children to produce an adapted activation pattern that suggests a progression in performance without any drastic change in technique during growth. The vibrations show that the vibratory stress tends to increase in proportion to the speed of the ball but that the damping time is relatively stable during growth.
REFERENCE
1) Buszard & al., 2020