Upper Extremity Kinematics and Electromyographic Activity in Uninjured Tennis Players

Comparison of Grip Strength, Forearm Muscle Activity, and Shock Transmission between the Forehand Stroke Technique of Experienced and Recreational Tennis Players Using a Novel Wearable Device

Upper limb tennis injuries are primarily chronic, resulting from repetitive overuse. We developed a wearable device which simultaneously measures risk factors (grip strength, forearm muscle activity, and vibrational data) associated with elbow tendinopathy development resulting from tennis players' technique. We tested the device on experienced (n = 18) and recreational (n = 22) tennis players hitting forehand cross-court at both flat and topspin spin levels under realistic playing conditions. Using statistical parametric mapping analysis, our results showed that all players showed a similar level of grip strength at impact, regardless of spin level, and the grip strength at impact did not influence the percentage of impact shock transfer to the wrist and elbow. Experienced players hitting with topspin exhibited the highest ball spin rotation, low-to-high swing path brushing action, and shock transfer to the wrist and elbow compared to the results obtained while hitting the ball flat, or when compared to the results obtained from recreational players. Recreational players exhibited significantly higher extensor activity during most of the follow through phase compared to the experienced players for both spin levels, potentially putting them at greater risk for developing lateral elbow tendinopathy. We successfully demonstrated that wearable technologies can be used to measure risk factors associated with elbow injury development in tennis players under realistic playing conditions.

Upper Extremity Muscle Activation during Drive Volley and Groundstroke for Two-Handed Backhand of Female Tennis Players

Drive volley is one of the essential backhand stroke technique trends seen in recent women's tennis competitions. Although movements of the drive volley and groundstroke are similar, activation of the internal muscles vary due to different incoming ball conditions. Most previous studies only focused on the groundstroke, however. The current study investigates the different muscle activation patterns in the upper extremity muscle during the two-handed backhand drive volley as well as the groundstroke for female tennis players. Ten elite female tennis players were measured in the muscle activation of the flexor carpi radialis (FCR), extensor carpi radialis (ECR), biceps brachii (BB), and triceps brachii (TB) from both upper extremities. Racket-head speed at impact, swing duration of each phase, and racket-head average velocity in both strokes were also recorded. Significant differences were found between the drive volley and groundstroke in the velocity profile of racket tip, swing duration of each phase (preparation, early follow-through, and late follow-through), activation patterns of upper extremity muscles, and flexor/ extensor ratios of wrist and elbow in both upper extremities. Different racket trajectory strategies were also observed between the two strokes, with greater horizontal racket velocity recorded in the groundstroke but greater vertical velocity in the drive volley. ECR and TB muscle activation during the drive volley preparation phase was greater than the groundstroke when completing a quicker backswing. In the early acceleration phase, the greater FCR leading arm activation in the drive volley assisted wrist stabilization in preparation for impact. In the late follow-through phase, less TB leading arm activity and higher ECR trailing arm activity in the drive volley showed more forward compression movement in racket contact with the ball. As it is essential for the drive volley to complete a quicker backswing and to increase shot efficiency at the end of the forward movement, coaches should consider the two strokes' muscle activation and technique differences to enhance specific techniques and fitness training programs.

High-accuracy tennis players linearly adjust racket impact kinematics according to impact height during a two-handed backhand stroke

We hypothesised that high-accuracy players more linearly coordinate racket kinematics with impact heights under random height conditions than low-accuracy players. We compared the adjustments of racket kinematics according to impact height between high- and low-accuracy players. Fourteen male tennis players hit the incoming balls with a two-handed backhand at different impact heights (21-108% of body height) to a target area. The cluster analysis on accuracy divided participants into high- (n = 7, 48.6 ± 2.4%) and low- (n = 7, 32.4 ± 4.8%) accuracy groups. Most of the high-accuracy players linearly decreased the horizontal velocity, increased the vertical velocity, and increased the face angle of racket (R2 = 0.42, 0.36, 0.66) as impact heights increased, while the low-accuracy group only linearly increased face angle (R2 = 0.46) but not linearly adjusted horizontal and vertical velocities (R2 = 0.02, 0.14). The linearities between horizontal velocity and face angle and between vertical velocity and face angle in high-accuracy group (R2 = 0.40, 0.26) were significantly stronger than those in low-accuracy group (R2 = 0.07, 0.08). We found that the high-accuracy players coordinate more racket kinematics and adopt a set of consistent solutions of adjustment according to impact heights. We suggest that players linearly adjust the velocities and the face angles of rackets according to impact heights when prioritising the accuracy.