With a view to monitoring external load, the combination of miniature inertial sensors and machine learning offers a practical and automated method of quantifying shot counts and discriminating shot types in elite tennis players.

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Background Low back pain (LBP) is pervasive among elite junior tennis players. Previous research has explored the relationship between serving mechanics and LBP, though the participants in these studies had already experienced LBP. Therefore, it is unclear whether their serving mechanics caused the LBP or are a result of having LBP. Thus, the purpose of this study was to compare the flat and kick serve kinematics of asymptomatic elite adolescent male and female tennis players with and without lumbar spine abnormalities. Twenty-four players (nine of which had confirmed lumbar spine abnormalities) carried out a series of flat and kick serves, while marker trajectories were recorded by a 3D motion capture system. Pelvis and lumbar spine kinematics (anterior/posterior tilt, lateral tilt, axial rotation and flexion/extension, lateral flexion and axial rotation respectively) were compared between players with and without lumbar spine abnormalities, genders, and serve types using a mixed-effects model. Exploratory data pertaining to the order and timing of key serve events was also collected. Results Males had significantly greater posterior pelvis tilt than females during the drive phase of both flat (M, − 7.1 ± 5°; F, 4 ± 5.5°) and kick serves (M, − 8.6 ± 5.1°; F, 2.1 ± 5.8°). Independent of serve type, males also impacted the ball ~ 15 cm further into the court than females, while all players contacted flat serves significantly further forward (~ 17 cm). There were no effects for abnormality in the magnitude of pelvis and trunk kinematics. The order and timing of key serve events, however, did tend to differ between those with and without lumbar spine abnormalities. Players with abnormalities entered peak front knee flexion and initiated pelvis rotation earlier than players without abnormalities. Lastly, the timing of pelvis rotation was highly variable among females though not males. Conclusion Pelvis and ball toss kinematics vary with gender and serve type but not necessarily abnormality in the elite adolescent serve. There is evidence to suggest that the order and timing of key serve events might help to identify those at risk of lumbar spine abnormalities; however, further research is needed to investigate the statistical significance of the timing of these events.

Background Lumbar spine abnormalities, in particular stress fractures to the pars interarticularis, are common in elite junior tennis players, though the difference in prevalence between males and females remains unclear. Further, facet joint orientation appears to be a possible option for recognizing which players might go on to present with a pars stress fracture. Given the link between pars stress fractures and low back pain in tennis players, it appears logical to explore the link between facet joint angle and pars abnormalities. Thus, the purpose of this study was to describe the prevalence of lumbar spine abnormalities and explore the relationship between facet joint orientation and pars abnormalities in elite adolescent tennis players. Methodology Lumbar spine MRI images of 25 elite junior tennis players were obtained and distributed between five radiologists for analysis. Descriptive comparisons and confidence intervals were used to describe the prevalence of the abnormalities. A generalized linear regression model was conducted to investigate the relationship between lumbar pars abnormalities and lumbar facet joint angles. Results Sixteen (64%) of 25 players were found to have at least one lumbar spine abnormality. Pars abnormalities affected 36% of players while bone marrow edema was found in 24% of players. Disc herniation, disc degeneration, and facet joint degeneration were diagnosed in 20%, 44%, and 24% of players respectively. Lastly, one player (4%) was diagnosed with spondylolisthesis. Females had significantly larger facet joint angles across L3/4 L5/S1 compared to males (p < 0.01). Further, those who had pars abnormalities had larger facet joint angles compared to those who did not (p < 0.001). Conclusion Disc degeneration, pars abnormalities, including bone marrow edema, and facet joint degeneration were common findings among elite adolescent tennis players. Additionally, this study is the first to discover that pars abnormalities are linked to facet joint angle in elite adolescent tennis players. This finding might assist in identifying tennis players at a greater risk of developing lumbar spine pars abnormalities in the future.