Concurrent Validity and Test-Retest Reliability of Pressure-Detecting Insoles for Static and Dynamic Movements in Healthy Young Adults.

Compared to force-plates, pressure-detecting insoles have the advantage that vertical ground reaction force (vGRF) can be estimated under field rather than laboratory conditions. However, the question arises whether insoles also provide valid and reliable results compared to a force-plate (i.e., the gold standard). The study aimed to investigate the concurrent validity and test-retest reliability of pressure-detecting insoles during static and dynamic movements. Twenty-two healthy young adults (12 females) performed standing, walking, running, and jumping movements while simultaneously collecting pressure (GP MobilData WiFi, GeBioM mbH, Münster, Germany) and force (Kistler®) data twice, 10 days apart. Concerning validity, ICC values showed excellent agreement (ICC > 0.75), irrespective of the test condition. Further, the insoles underestimated (mean bias: -4.41 to -37.15%) most of the vGRF variables. Concerning reliability, ICC values for nearly all test conditions also showed excellent agreement, and the SEM was rather low. Lastly, most of the MDC95% values were low (≤5%). The predominantly excellent ICC values for between-devices (i.e., concurrent validity) and between-visits (i.e., test-retest reliability) comparisons suggest that the tested pressure-detecting insoles can be used under field-based conditions for a valid and reliable estimation of relevant vGRF variables during standing, walking, running, and jumping.

The role of increased post-impact ball speed on plantar pressure during open and square stance groundstrokes in female tennis players.

BACKGROUND: It is firmly established that achieving a high ball speed during the execution of groundstrokes represents a relevant factor for success in tennis. However, little is known about how plantar pressure changes as post-impact ball speed is increased during open and square stance groundstrokes. The objective of the study was to determine how tennis players change the plantar pressure in each foot when they execute open versus square stance forehand groundstrokes in order to increase post-impact ball speed. METHODS: Fifteen healthy female tennis players with ITN 2 or better (mean age: 22.7 ± 7.8 years) participated in this study. The players performed open and square stance longline forehand groundstrokes (topspin) at the following four post-impact ball speed levels: 80 km/h, 90 km/h, 100 km/h, and vmax. Flexible pressure-detecting insoles were used to measure plantar pressure in each foot [i.e., dominant (equals the stroke arm) and nondominant]. RESULTS: The repeated measures ANOVA showed significant stance style × foot dominance interactions and post-hoc analyses revealed larger maximal and mean forces during open compared to square stance for the dominant but not non-dominant foot. Further, the ball speed × stance style × foot dominance interaction reached the level of significance and post-hoc analyses showed increased/decreased mean forces in the dominant/non-dominant foot during the square but not open stance when players increased their post-impact ball speed. CONCLUSION: Larger values in the open stance, but post-impact ball speed-adjusted values in square stance indicate different advantages in both styles, suggesting their situation-specific application.

Side differences in upper quarter mobility/stability are not related to serve velocity in tennis players with different levels of training experience.

OBJECTIVE: Tennis is characterised by repetitive serves and strokes predominately performed with one arm. This can lead to differences in upper quarter mobility/stability between the stroke and non-stroke arm, which could even enlarge with increasing training experience and negatively affect serve velocity. Thus, we determined side differences (i.e., limb symmetry index) in upper quarter mobility/stability and their association with flat and slice serve velocity in advanced (ITN ≤ 4) female and male tennis players (N = 42, mean age = 23.9 ± 9.3 years) with different levels of training experience (< 2 years: n = 14, 2-5 years: n = 17, 6-8 years: n = 11). RESULTS: Y Balance Test-Upper Quarter (YBT-UQ) side difference (i.e., composite score) and performances (i.e., medial reach) were largest in players with the lowest level of training experience (i.e., < 2 years). Further, YBT-UQ performances (i.e., medial reach and composite score) but not side differences were significantly correlated with flat and slice serve velocity, particularly in less experienced players. Our results suggest that significant side differences in upper quarter mobility/stability occur in less experienced players (indicative of increased injury risk) but they are not related to tennis-specific performance (i.e., serve velocity).

Biomechanical analyses of different serve and groundstroke techniques in tennis: A systematic scoping review.

This systematic scoping review aims to summarize findings regarding kinetic, kinematic, and electromyographic analyses of different characteristics (i.e., type/direction and stance style) of the tennis serve and groundstroke. A systematic search of the literature was performed on the databases PubMed, Web of Science, and SportDiscus from their inception date till May 2023. A descriptive analysis of results was conducted. The literature search identified a total of N = 899 records, 23 of which met the inclusion criteria and were analysed in this review. A total of 229 participants aged 18 to 62 years participated in the studies. The studies revealed varying results, ranging from significantly lower/higher values to no significant differences between serve/groundstroke characteristics. These inconsistent results may most likely be attributed to discrepancies in the methodological approach such as players' age (18-62 years), sex (i.e., men only or both sexes), and performance level (i.e., recreational, intermediate, or advanced) as well as the applied measurement devices (i.e., force plate or pressure-detecting insoles; motion capture system, high-speed video recordings, or IMU sensors) and used outcomes (i.e., measured or estimated force etc.). Future research is needed to provide a comprehensive biomechanical analysis of different serve/groundstroke characteristics. Specifically, it is recommended to compare different tennis serve and groundstroke types/directions and stance styles in female and male age-matched players with diverging performance levels (i.e., recreational, intermediate, advanced) using combined (i.e., kinetic, kinematic, and electromyographic) biomechanical analysis.

The role of increased post-impact ball speed on plantar pressure during topspin and slice longline forehand groundstrokes in female tennis players.

OBJECTIVE: Performing groundstrokes is a fundamental skill for tennis players. However, little is known about changes in plantar pressure when post-impact ball speed is increased during topspin and slice groundstrokes. The objective of the present study was to examine how elite (International Tennis Number ≤ 2) female tennis players (N = 15, mean age: 22.7 ± 7.8 years) change their plantar pressure in the dominant (equals the stroke arm) and non-dominant foot when executing topspin and slice longline forehand groundstrokes in order to increase post-impact ball speed (i.e., 80 km/h, 90 km/h, 100 km/h, vmax). RESULTS: The repeated measures analysis of variance revealed a significant ball speed × foot dominance interaction. Post-hoc analyses showed larger mean forces during topspin compared to slice groundstrokes for the dominant foot (p ≤ .026, d ≥ 0.34) but lower values for the non-dominant foot (p ≤ .050, d ≥ 0.28). Further, with increasing post-impact ball speed, increases in mean forces in both feet during topspin could be observed but only in the dominant foot during slice groundstrokes. Varying mean forces depending on the stroke type and foot dominance imply that specific physical exercises related to these two factors are necessary to optimise plantar pressure distribution.

Effect of stroke direction on plantar pressure in each foot during the forehand and backhand stroke among healthy adult tennis players of different performance levels.

BACKGROUND: In tennis, previous studies have shown differences in plantar pressure depending on tennis-specific movements (i.e., baseline play, serve & volley play, change of direction), playing surface (e.g., hard, grass, or clay), and serve type (e.g., slice, topspin or flat). However, the influence of stroke direction on plantar pressure in tennis players with diverging skill level is unknown. Thus, the purpose of this study was to determine the effect of stroke direction on plantar pressure in each foot during the forehand and backhand stroke among players of different performance levels. METHODS: Thirty-nine female and male healthy adult tennis players (mean ± SD age: 23.5 ± 6.4 years) representing athletes from three performance levels (recreational, intermediate, advanced) participated in this study. The players performed longline/cross forehand and backhand groundstrokes (topspin) on a clay court while plantar pressure distribution was measured in each foot using flexible instrumented insoles. RESULTS: The three-way ANOVA (performance level × stroke direction × foot dominance) showed (a) no significant differences in plantar pressure data between cross and longline strokes in almost all cases, (b) in part, significantly larger pressure values in advanced compared to intermediate and recreational players, and (c) significantly larger pressure data for the dominant compared to the non-dominant foot in nearly all comparisons. CONCLUSION: Regarding an appropriate plantar pressure distribution, our results suggest that during training of especially recreational and intermediate players attention should be paid to the feet rather than to stroke direction.

Plantar pressure is changed to increase post-impact ball speed during longline forehand and backhand groundstroke in elite female tennis players.

Introduction: Achieving high ball speed during the execution of groundstrokes represents a performance-relevant factor in tennis. However, it is unclear how plantar pressure data undergo change during the execution of groundstrokes by tennis players to achieve high postimpact ball speed. Thus, the objective of the present study is to determine how tennis players change the plantar pressure in each foot when they execute longline forehand and backhand groundstrokes in order to increase postimpact ball speed. Methods: Seventeen healthy nationally ranked female tennis players (mean age: 21.7 ± 7.7 years) participated in this study. The players performed longline forehand and backhand groundstrokes (topspin) at four postimpact ball speed levels, i.e., at 80 km/h, 90 km/h, 100 km/h, and vmax. Plantar pressure was measured in each foot [i.e., dominant (equals the stroke arm) and non-dominant] using flexible instrumented insoles. Results: Irrespective of the stroke technique, the repeated measures ANOVA procedure showed significant ball speed × foot dominance interactions. For the forehand stroke, post hoc analyses revealed significantly increased (dominant foot) and decreased (non-dominant foot) pressure values when the postimpact ball speed increased from 100 km/h to vmax. For the backhand stroke, the post hoc analyses yielded significantly decreased (dominant and non-dominant foot) plantar pressure values when the postimpact ball speed increased from 100 km/h to vmax. There were no further significant differences between the other ball speed levels. Discussion: The significantly varying plantar pressure changes depending on the stroke technique and foot dominance to increase postimpact ball speed suggest that specific physical exercises related to the foot (dominant vs. non-dominant foot) and groundstroke (forehand vs. backhand) seem to be necessary for plantar pressure optimization.

Physical fitness and stroke performance in healthy tennis players with different competition levels: A systematic review and meta-analysis.

Differences in variables of physical fitness and stroke performance by competition level (i.e., elite vs. sub-elite players) have not been systematically investigated yet. Thus, the objective of the systematic review with meta-analysis was to characterize and quantify competition-level dependent differences in physical fitness and stroke performance in healthy tennis players. A systematic literature search was conducted in the databases PubMed, Web of Science, and SportDiscus from their inception date till May 2022. Studies were included if they investigated healthy tennis players and reported at least one measure of physical fitness (e.g., lower extremity muscle power, endurance, agility, speed) or stroke performance (e.g., stroke velocity). Weighted standardized mean differences (SMD) were calculated and reported according to their magnitude. The search identified a total of N = 12,714 records, 16 of which met the inclusion criteria. Competition-level dependent differences in physical fitness and stroke performance were investigated by 11 and 10 studies, respectively. For physical fitness, moderate (lower extremity muscle power: SMD = 0.53; endurance: SMD = 0.59; agility: SMD = 0.54) and small (speed: SMD = 0.35) effects were detected; all in favour of elite tennis players. However, sub-group analyses revealed an influence of players' age showing higher SMD-values for adult than for young players. Further, a large effect (SMD = 1.00) was observed for stroke performance again in favour of elite tennis players. Lastly, a larger but not significantly different association between physical fitness and stroke performance was observed for elite (r = 0.562) compared to sub-elite (r = 0.372) tennis players. This systematic review and meta-analysis revealed better physical fitness and stroke performances in healthy elite compared to sub-elite tennis players. The greatest differences by competition level were shown in measures of lower extremity muscle power, endurance, and agility. Thus, training programs for sub-elite tennis players should place a special focus on these physical components.

Effects of athletic training on physical fitness and stroke velocity in healthy youth and adult tennis players: A systematic review and meta-analysis.

Better physical fitness and stroke velocity in healthy elite compared to sub-elite tennis players have been shown in previous studies. However, evidence-based knowledge regarding the effectiveness of athletic training on physical fitness and stroke velocity is currently lacking. Thus, the objective of this systematic review with meta-analysis was to characterize, aggregate, and quantify athletic training effects on measures of physical fitness and stroke velocity in healthy youth and adult tennis players. A computerized systematic literature search was performed in the databases PubMed, Web of Science, and SportDiscus from their inception date to August 2022. Studies were included, among others, if the intervention period lasted a minimum of four weeks and if at least one parameter of physical fitness (i.e., speed, agility, lower-extremity muscle power, upper-extremity muscle power/strength, endurance, balance, flexibility) or stroke performance (i.e., stroke velocity) was tested. Initially, 11,511 articles were identified, after removing duplicates and assessing abstracts and full texts, 24 articles were used to calculate weighted standardized mean differences (SMD). For measures of physical fitness, athletic training resulted in small (speed: SMD = 0.44), moderate (endurance: SMD = 0.61, upper-extremity muscle power: SMD = 0.72; flexibility: SMD = 0.63), and large (agility: SMD = 0.93, lower-extremity muscle power: SMD = 0.88; upper-extremity muscle strength: SMD = 0.90; balance: SMD = 0.88) effects. Further, a large effect (SMD = 0.90) on stroke velocity was detected. The additionally performed sub-analyses showed differences in the effectiveness of athletic training on variables of physical fitness and stroke speed when considering players' age (i.e., youth players: <18 years; adult players: ≥18 years). Precisely, there was a high potential for training-related adaptations in adult players with respect to lower-extremity muscle power, upper-extremity muscle strength, and stroke velocity and in youth players with respect to endurance. Interventions to promote physical fitness and stroke velocity in healthy tennis players revealed varying levels of effectiveness ranging from small to large and these were additionally affected by players' age. Therefore, future studies should investigate modalities to increase training efficacy in youth and adult tennis players, especially for fitness components that showed small- to moderate-sized changes.