COMPARISON OF SHOULDER JOINT MUSCLE ACTIVITIES DURING STANDING AND WHEELCHAIR SITTING TENNIS SERVE MOTION

N. Murata¹, N. Maeda¹, M. Komiya¹, K. Kaneda¹, H. Esaki¹, H. Ishihara¹, D. Hirado¹, Y. Urabe¹

¹Hiroshima University, Department of Sports Rehabilitation, Graduate School of Biomedical and Health Sciences, Hiroshima, Japan

Background: Wheelchair tennis players often experience shoulder joint disorders (Kimura et al., 2011).This may be attributed to excessive upper-limb movement due to restricted lower-limb movement during the serve. The muscle activity of anterior deltoid, serratus anterior, and pectoralis majorare important instanding tennis servemotion (Sleeleyet al., 2008), but their role in wheelchair sitting tennis serve motion is unclear.Comparing muscle activities during standing and wheelchair sitting serve motion will help to examine the differences between the two.

Purpose: This study aimed to compare shoulder joint muscle activities during the tennis serve motion in the standing and wheelchair sitting and to examine the factors that contribute to shoulder joint disorders incurred therein.

Methods: Fifteen healthy men with at least two years of tennis experience participated in this study(mean years of experience; 6.2 ± 2.8 years). Each performed serve motion inthe standing and wheelchair sitting positions.Serve velocity was measured using a Multi Speed Tester II (SSK Inc.). Themuscle activities ofanterior deltoid, serratus anterior, and pectoralis majorwere measuredusing aPersonal-EMG plus (Oisaka Electronic Equipment Co., Ltd.). The maximum voluntary contraction (MVC) was set at 100%. The average %MVC of each muscle was calculated from 1.0 s before to 0.2 s after hitting the ball with the racket (1.2 s in total).
The paired t-test and Wilcoxon signed-rank test were used to compare the two conditions for serving speed and muscle activity, respectively. The significance level was set at 0.05.

Results: Mean serve velocity was significantly lower in the wheelchair sitting (Standing: 101.8 ± 21.4 km/h; Wheelchair sitting: 85.6 ± 13.2 km/h; p<0.05).The average %MVCwere significantly greater in the wheelchair sitting versus standing for the anterior deltoid (by 24.6%; p<0.05), serratus anterior (by 43.7%; p<0.01), and significantly lower for the pectoralis major (by 22.4%; p<0.01).

Conclusions: In standing tennis, force must be transferred from the lower limb to the upper limb to ensure strong serve (David, 1988). However, in wheelchair sitting, this kinetic chain is difficult to achieve and thought to decreaseserve velocity. Wheelchair tennis players tend to increase shoulder joint horizontal flexion during the serve motion (Tanabe et al., 2018), and the muscle activity of the serratus anterior increases with horizontal flexion in the flexed shoulder joint position (Decker et al., 1999). This serve motion caused the difference inthe muscleactivities betweenthe two conditions. Increased horizontal flexion increases tensile stress applied to the posterior shoulder joint (Kimura et al., 2012). Because serratus anterior dysfunction leads to scapular instability (Kurosawa, 2008), the excessive anterior deltoid and serratus anterior muscle activities may affect shoulder joint disorders in wheelchair tennis.

Implications: These results suggest that the excessive shoulder muscle activity during the serving motion in wheelchair tennis compared to the standing motion might cause an imbalance in shoulder joint motion, which may lead to shoulder joint disorders.

Funding acknowledgements: We have no funding acknowledgment in this study.

Keywords:
Wheelchair tennis
Tennis serve motion
Shoulder joint muscle activities

Topics:
Sport & sports injuries
Musculoskeletal: upper limb
Musculoskeletal

Did this work require ethics approval? Yes

Institution: Hiroshima University

Committee: The Ethics Committee of Hiroshima University

Ethics number: E-3290