Development of a test rig and a testing procedure for bicycle frame stiffness measurements

The stiffness measuring method for bicycle frames is not standardized, leading to a wide variety of test setups; they differ in many aspects such as applied load, support constraints and frame deflection measurement. The aim of this paper is to draw attention to this problem and to quantify the perturbing, unwanted side effects that influence the stiffness measurement of the bicycle frame. This is illustrated by developing a multi-purpose rating test method for bicycle frame stiffness. The proposed test rig design considers different aspects which should be taken into account when measuring the bicycle frame stiffness. In the experimental setup, it is observed that the contribution of the test bench compliance led to 21% difference in the frame stiffness results; the influence due to the head, the tube-bearing type the corresponding preload resulted in up to 19% difference in the stiffness results between the lowest and highest stiffness values measured; hysteresis effects caused by pulleys are estimated to introduce errors up to 11%; and the influence due to the operator variability and sensor accuracy is estimated to be less than 3%.     

Free kick goals in football: an unlikely success between failure and embarrassment

We develop and use a numerical model to investigate the window of opportunity of free kicks in association football. The planar multibody forward dynamics model comprises a two segment leg model with joint actuations, a football, a wall and the turf. Contact mechanics is defined to model the impact of the foot and the ball’s interaction with the different elements in the environment. The optimum kick is determined using the global optimization algorithm differential evolution, requiring millions of kick simulations. The sensitivity of various solutions to parameter perturbation is investigated. It is concluded that toe kicks are theoretically superior to instep kicks, but are difficult to perform reliably. The results also show that small perturbations in parameters can lead to embarrassingly failed kicks.     

Roller skiing biomechanical information analysis using GPS,IMU, and atmospheric pressure sensors: a case study

The purpose of this research was to propose a method to acquire the three-dimensional movement of a roller skiing athlete utilizing a global positioning system (GPS), an atmospheric pressure sensor (APS), and an inertial measurement unit (IMU) to distinguish between diagonal skiing and double poling techniques. In this study, we developed a lightweight wearable sensor that was composed of a GPS, APS, and IMU. For the data collection, two national level athletes roller skied a 1700 m long course where the maximum difference in elevation was 5.3 m. The planar positions of the athletes were based on the longitudinal and latitudinal data provided by the GPS, and the altitude was calculated by the International barometric formula and Laplace transform from the APS. The longitudinal and latitudinal data acquired through GPS had errors within 2 m range at each point. The altitude of Laplace transform from the APS showed errors of less than 1 m at each point. The range of motion of pelvis from the IMU was 34.0?±?3.8° for diagonal skiing, which is wider than the 21.2?±?6.9° for double poling.     

League design and sporting challenge as factors in amateur golf players’ satisfaction

The organization of individual sports into leagues has received little attention in research, but its practical relevance has increased. This article aims to elucidate the role of competitive balance and league design elements in a sports league with less spectator demand from a player perspective. The analysis focuses on the reformed German Golf League. Because this league is an amateur league with no payment for players and currently few spectators, a change in perspective is appropriate. The empirical results of the stated preference approach highlight the relevance of perceived competitive balance as well as several league characteristics for the players. The findings thus show that governing bodies of sports leagues should focus on both the development of an optimal league design and soft aspects to deliver attractive and challenging competition from a player’s perspective.     

Change-of direction deficit in elite young soccer players

Change-of-direction (COD) ability is an essential physical component for soccer. This study examined the relationships between conventional speed–power assessments and COD performance in elite young soccer players. Twenty-five under-20 male players from the same club (age: 17.6?±?0.8 years, height: 178.1?±?6.7?cm, body mass [BM]: 72.2?±?7.9?kg) performed sprint speed tests, vertical jumps, loaded jump squats, half squats, and Zigzag COD assessments. Moreover, the COD deficit was calculated as the difference between 20-m sprint velocity and Zigzag COD test velocity. A Pearson correlation analysis was used to determine the correlations between Zigzag COD performance and COD deficit with speed and power outputs. Although no significant relationships between speed–power variables and COD ability were present, there were still strong positive correlations between traditional neuromechanical measures and COD deficit. Briefly, it seems that higher performances in speed and power tests are not necessarily related to better performances in specific COD maneuvers. Therefore, it is recommended that coaches and technical staff include specific COD drills in soccer player routines to optimize the transference from speed and power capacities to specific COD performance.     

Muscle and tendon tissue properties of competitive soccer goalkeepers and midfielders

The purpose of this pilot study was to investigate the effect of playing-position-dependent training routines in soccer on the various muscle–tendon parameters. We hypothesized that there would be differences in such parameters between competitive goalkeepers and midfielders. According to their playing position, 21 healthy volunteers were assigned to goalkeeper (n?=?7), midfielder (n?=?7), and control (n?=?7) groups. To investigate the muscle–tendon parameters, we determined the maximum dorsiflexion range of motion and the corresponding muscle thickness, fascicle length, and pennation angle of the gastrocnemius medialis. Passive resistive torque and maximum voluntary contraction were measured with a dynamometer. Observation of muscle–tendon junction displacement with ultrasound allowed us to determine length changes in the tendon and muscle, respectively, and hence to calculate stiffness. There was no significant difference in range of motion, passive resistive torque, muscle–tendon stiffness, and the examined structural parameters (e.g., tendon stiffness) between the three groups. However, we found a significant difference in maximum voluntary contraction torque between the goalkeepers and midfielders vs. the controls, but not between the athlete groups. Habitual training leads to higher muscle strength in soccer players compared to less active persons. However, soccer training does not lead to specific muscle and tendon architecture adaptations according to playing position or when compared to less active persons.     

Positive environments in youth football

Derived from Basic Psychological Needs Theory (BPNT) is the notion that the social environment may promote athletes’ basic psychological needs, which are considered important for positive development and optimal motivational functioning. The present study investigated the predictive value of perceived justice and coach feedback on basic needs satisfaction in the context of youth football. Participants were Norwegian youth football players (N?=?532) participating in a national tournament. During the initial stage of the tournament, players completed the Coaching Feedback Questionnaire, Perceived Justice in Sport Questionnaire and Basic Psychological Needs in Exercise Scale under supervision. Regression analysis showed that perceived justice and positive/instructive coaching feedback positively predicted players’ needs satisfaction, while negative feedback and non-reinforcement/ignoring mistakes were not significant predictors of needs satisfaction. Together, perceptions of justice and coach feedback explained 24% of the variance in athletes’ needs satisfaction. The findings thereby indicate that athletes’ perceptions of fairness and coach feedback are important in understanding youth athletes’ needs satisfaction.     

Relationships between performance test and match-related physical performance parameters

Background

The purpose of this study was to analyze the relationship between performance test parameters and match-related physical performance in professional soccer players.

Methods

To determine physical capacity, 28 male soccer players underwent several performance tests at the start of the seasons 2013/2014, 2014/2015, and 2015/2016. The following parameters were assessed: maximum running velocity (v_max), fixed (v_4mmol/l) and individual anaerobic threshold (v_IAS) during an incremental treadmill test; 30-m sprint time in a linear sprint test (LS_30m); in a repeated-sprint test, the 30-m sprint time (RST_30m) and performance decrement (RST_decr); and countermovement jump height (CMJ). Match physical performance was quantified during the first ten official matches of each season using a computerized, camera-based tracking system. The following measures of match physical performance were considered: top running speed (TS), mean running speed (v_Ø), total distance covered (TD), number of sprints (SP), number of high-intensity running (HIR), and aerial duels won (AD+). Pearson correlation coefficients were used for statistical analysis.

Results

Moderate to very large correlations were found between the majority of performance test parameters and match performance variables, with a variability of correlations across the three seasons. Large relationships across all three seasons were only observed between v_max and TD, v_max and v_Ø, LS_30m and TS as well as RST_30m and TS.

Conclusion

This study demonstrates the relationship between several performance test parameters and match-related physical performance in professional soccer players, thereby supporting the test parameters’ criterion validity. v_max, LS_30m, and RST_30m seem to be the most consistent parameters.

     

Residents’ perceptions of mega sport event legacies and impacts

The purpose of this study was to examine perceptions of local residents prior to the public referendum for the 2024 Hamburg Olympic bid and to assess their level of support for the bid. The representative survey conducted amongst Hamburg residents reveals a high level of support but also a strong perception of negative legacies. A comparison between the perceived positive and negative legacies shows that the negative legacies outweigh the positive legacies. When examining factors that influence support, statistical analysis reveals the perception of positive legacies as the strongest predictor of support. The survey also indicates that residents attach great importance to the costs of the Games and feel no personal benefit from hosting them. The findings suggest that Games organizers and authorities should mostly rely on positive legacies while negative legacies ought to be mitigated.     

Stabilität der physischen Fitness im Kindesalter

Monitoring of physical fitness (PF) in childhood is important from a societal as well as individual perspective to ensure and support healthy child development. Hence, the German Standing Conference of the Ministers of Education and Cultural Affairs together with the German Olympic Federation recommend the usage of motor tests, for instance in schools, to implement targeted interventions. Results of motor assessments are interpreted using reference categories to prevent overinterpretation of small but meaningless intra- and inter individual differences. Furthermore, temporal trends can influence the validity of these reference categories. The aims of the study are (1) to examine short- and medium-term changes in PF in middle childhood (2) to evaluate implications for reference values and the validity of the construct PF, (3) to provide valid reference values for eight- to nine-year-old children. In the school years 2011–2016, over 20,000 third-graders completed the German Motor Test (GMT) in the project “Berlin has Talent”. Possible temporal trends are examined using regressions and cross-tables. Implications of these changes on the construct PF are analyzed using Rasch measurement. Four out of seven tasks showed temporal changes. However, the validity and unidimensionality of the GMT are confirmed (p?>?0.90), if balancing backwards is excluded from the model. On the one hand, task-related changes of children’s motor performance within five years support the requirement of a comprehensive continuous monitoring to enable early interventions. On the other hand, they call for continuous evaluation of reference values of the GMT, which should rely on representative and sufficiently large samples.