Micro-CT analysis and mechanical properties of low dimensional CFR-PEEK specimens additively manufactured by material extrusion.

Material extrusion of thermoplastic polymers enables the realization of complex specific designs with high performance composites. The present study aims at evaluating the mechanical properties of carbon fiber-reinforced semi-crystalline thermoplastic polymer polyether ether ketone (CFR-PEEK) manufactured by material extrusion and correlating them with results obtained by micro-CT. Samples in the shape of small bars were provided by Kumovis (Munich, Germany). The determination of surface roughness and density was followed by three-point bending tests. To reveal the pore distribution as well as the fusion quality of CFR PEEK when applied with external forces, micro-CT scans were performed with an X-ray microscope before and after the mechanical test to localize the sites where the fracture is generated. The density of CFR-PEEK bars indicated that they had superior mechanical properties compared with our previous study on unfilled 3D printed PEEK (bending modulus: (5.4 ± 0.5) GPa vs. (1.05 ± 0.05) GPa to (1.48 ± 0.10) GPa; bending strength: (167 ± 11) MPa vs. (51 ± 15) to (193 ± 7) MPa). Micro-CT analyses revealed the local 3D-distribution of voids. Voids of 30 µm diameter are nearly spherical and make up the main part of the total porosity. The larger the voids, the more they deviate from a spherical shape. Significant lack-of-fusion voids are located between the deposited filaments. By growing and merging, they act as seeds for the forming fracture line in the region of the flexural specimens where the maximum local tensile stresses occurred under bending load. Our work provides a detailed analysis of printed PEEK with fiber additive and relates this with mechanical properties.

Physical determinants, intercorrelations, and relevance of movement speed components in elite junior tennis players.

Movement speed is considered essential for success in elite tennis. The aim of the present study was to develop a model of movement speed components and quantify their age - and gender-related relevance for tennis performance. Physical testing data obtained from 1,434 nationally ranked junior squad tennis players were divided according to the age at peak height velocity (YPHV) into two age groups (pre-PHV: n=103 girls, 11.7 ± 0.6 yrs.; n=466 boys, 12.7 ± 1.0 yrs.; post-PHV: n=524 girls, 14.2 ± 1.4 yrs.; n=344 boys, 15.3 ± 1.2 yrs.). After assessing anthropometrics and maturity status, all players passed a series of standardized physical tests on an indoor hard court. All data were z-standardized, filtered and sorted by gender, maturity level, and ranking position. The structuring of the speed-related performance parameters resulted in four factors ("Elementary Speed", "Jumping Power", "Linear Speed", and "COD Speed"), which were then confirmed by factor analysis. The correlation of these factors to the national ranking position was mostly significant but rather low, with "Linear Speed" reaching the lowest (r=0.10-0.18) and "COD Speed" the highest correlation (r=0.22-0.34). Path analytic models revealed "COD Speed" as the most important factor, which is strongly influenced by "Jumping Power" and "Linear Speed," with medium effect sizes, while "Elementary Speed" affects this factor only slightly. It can be concluded that the relationship between movement speed and junior players' tennis ranking is lower than expected. The development of "COD Speed" should be prioritized during testing, training, and talent identification, independent of age group and gender.Highlights Performance parameters for 1,434 junior players with national rankings were analyzed and assigned to four superior factors.The impact of the factors on the ranking position, as well as the internal causal relationships, were investigated via path analysis."COD Speed" was the most impactful factor for tennis performance and was strongly influenced by "Linear Speed" and "Jumping Power."

Impact of Physical Performance and Anthropometric Characteristics on Serve Velocity in Elite Junior Tennis Players.

Fett, J, Ulbricht, A, and Ferrauti, A. Impact of physical performance and anthropometric characteristics on serve velocity in elite junior tennis players. J Strength Cond Res 34(1): 192-202, 2020-This study aimed to investigate the impact of physical performance components and anthropometric characteristics on serve velocity (SV) in elite junior tennis players depending on the sex and age group. A sample of the best 1,019 (male = 625, female = 394) junior squad tennis players of the German Tennis Federation participated in the study involving complex anthropometric measurements (body height, body mass, sitting height, and arm span) and physical tests (e.g., SV, medicine ball throws [MBTs], hand grip strength, push-ups, back extension, countermovement jumps [CMJs], horizontal jumps, 20-m sprint, and tennis-specific endurance). Of all the anthropometric and physical characteristics analyzed, the MBTs (r = 0.49-0.60♂; r = 0.20-0.60♀), hand grip strength (r = 0.43-0.59♂; r = 0.27-0.37♀), arm span (r = 0.37-0.56♂; r = 0.24-0.36♀), body height (r = 0.31-0.52♂; r = 0.26-0.38♀), and body mass (r = 0.44-0.57♂; r = 0.35-0.39♀) were particularly closely correlated with SV. The results of the multiple regression analysis indicated that the combination of selected predictors (e.g., MBTs, grip strength, arm span, and body mass) explained 41-66% of the variance in SV of boys and 19-45%, respectively, for girls. The results reinforce that service speed is dependent on physical abilities and anthropometric characteristics but also strongly on additional factors (i.e., technical components). In particular, the upper-body power/strength is important to the junior players' service, especially in athletes with a greater body height and arm span (i.e., biomechanical advantages), whereas purely lower-body power (e.g., CMJ) is less important. To this effect, talent identification and intervention programs focusing on the specific requirements are recommended.

Impact of Fitness Characteristics on Tennis Performance in Elite Junior Tennis Players.

The impact of fitness characteristics on tennis performance in adolescent players is not clearly understood. Therefore, the aim of the present study was to test whether physical characteristics are related to players' competitive level (i.e., national youth ranking). A secondary aim was to compare adolescent tennis players by performance level (i.e., regional selected players and the national team). A total of 902 male and female junior players (aged, 11-16 years) in Germany were evaluated using a physical testing battery: grip strength; countermovement jump; 10 and 20-m sprint; tennis-specific sprint; overhead, forehand, and backhand medicine ball throws (MBT); serve velocity and tennis-specific endurance test (hit and turn tennis test). Results showed that serve velocity (r = -0.43 to 0.64 for female subjects [♀]; r = -0.33 to 0.49 for male subjects [♂]) and upper-body power (e.g., MBT r = -0.26 to -0.49 ♀; r = -0.20 to -0.49 ♂) were the most correlated predictors of tennis performance (i.e., national youth ranking) in both female and male tennis players. Moreover, national selected players showed better performance levels than their regional counterparts, mainly in the most predictive physical characteristics (i.e., serve velocity: effect size [ES], 0.78-1.04 ♀; ES 0.92-1.02 ♂, MBT: ES, 0.66-0.88 ♀; ES, 0.67-1.04 ♂) and specific endurance (ES, 0.05-0.95 ♀; ES, 0.31-0.73 ♂). The present findings underline the importance of certain physical attributes, especially serve velocity and strength- and power-related variables (upper body), and suggest the need to include these parameters in the area of training, physical testing, and talent identification of young tennis players.

The Relative Age Effect and Physical Fitness Characteristics in German Male Tennis Players.

The aims of the study were to test: 1) whether the relative age effect (RAE) was prevalent in young (U12-U18) German male tennis players; 2) the potential influence of age and/or skill level on RAE and 3) whether maturity, anthropometric and fitness measures vary according to birth date distribution in elite youth tennis players. For the present study the following male populations were analysed: Overall German population (n = 3.216.811), all players affiliated to the German Tennis Federation (DTB) (n = 120.851), players with DTB official ranking (n = 7165), regional (n = 381) and national (n = 57) squads (11-17 years old), as well as the top 50 German senior players were analyzed. RAEs were more prevalent at higher competitive levels with more players born in the first quarter of the year compared with the reference population for ranked (29.6%), regional (38.1%) and national (42.1%) players. No systematic differences were found in any of the maturity, anthropometric and fitness characteristics of the regional squad players born across different quarters. RAEs are present in the DTB competitive system and it was more pronounced at higher competitive levels. Compared with early born, late born players who were selected into elite squads did not differ in maturation, anthropometric and fitness characteristics. Key pointsRAEsexist in the selection of youth tennis players in Germany, a greater percentage of players analyzed was born in the 1st quarter compared to all licensed tennis players in the country, and more pronounced with an increased competition level in youth players.Players born later in the selection year and still selected in elite squads were likely to be similar across a range of physical fitness attributes compared with those born earlier in the year.The selection process should be reevaluated and changed to reduce the impact of RAEs on tennis players.

Fitness testing of tennis players: how valuable is it?

In tennis, sport-specific technical skills are predominant factors, although a complex profile of physical performance factors is also required. The fitness test batteries assist in examining tennis players' capabilities for performance at different levels in the laboratory as well as in the field, in the junior or elite level. While laboratory tests can be, and are, used to evaluate basic performance characteristics of athletes in most individual sports, in a more specific approach, field-based methods are better suited to the demands of complex intermittent sports like tennis. A regular test battery performed at different periods of the year allows to obtain an individual's performance profile, as well as the ability to prescribe individual training interventions. Thus, the aim of the present review was to describe and evaluate the different physical tests recommended and used by practitioners, sports scientists and institutions (national tennis federations).

Effects of a 6-week junior tennis conditioning program on service velocity.

This study examined the effects of a 6-week strength-training program on serve velocity in youth tennis players. Thirty competitive healthy and nationally ranked male junior tennis players (13 years of age) were randomly and equally divided into control and training groups. The training group performed 3 sessions (60-70 min) weekly for 6 weeks, comprising core strength, elastic resistance and medicine ball exercises. Both groups (control and training) also performed a supervised stretching routine at the end of each training session, during the 6 week intervention. Service velocity, service accuracy and shoulder internal/external rotation were assessed initially and at the end of the 6-week conditioning program for both, control and training groups. There was a significant improvement in the serve velocity for the training group (p = 0. 0001) after the intervention, whereas in the control group there were no differences between pre and post-tests (p = 0.29). Serve accuracy was not affected in the training group (p = 0.10), nor in the control group (p = 0.15). Shoulder internal/external rotation ROM significantly improved in both groups, training (p = 0.001) and control (p = 0.0001). The present results showed that a short- term training program for young tennis players, using minimum equipment and effort, can result in improved tennis performance (i.e., serve velocity) and a reduction in the risk of a possible overuse injury, reflected by an improvement in shoulder external/internal range of motion. Key PointsA short-term training program for young tennis players, using minimum equipment and effort, can result in improved tennis performance and a reduction in the risk of a possible overuse injury, reflected by an improvement in shoulder external/internal range of motionA combination of core stabilization, elastic resistance exercises, and upper body plyometric exercises (i.e., medicine ball throws), focussing on the primary muscle groups and stabilizers involved in tennis specific movement patterns, could be appropriate for development tennis playersStretching exercises are recommended in the cool-down phase following matches or training sessions.