Retirement of professional soccer players - A systematic review from social sciences perspectives.

Retiring professional athletes face multifaceted changes and potential issues of adjustment, occupational development, and well-being, which raises concerns around the world. The study systematically reviewed the available research investigating professional soccer players' sport retirement from social sciences perspectives. The literature search in electronic databases and a "snowballing" procedure yielded 17 eligible studies investigating > 2,200 retired professional soccer players. The review followed the PRISMA statement. Nine studies focused on an early transition phase to retirement period; four studies investigated later periods of ten years or longer after retirement. Around half of the players reported involuntary retirement, often associated with declining performance and/or injury. Studies suggest issues of adjustment and mental health during early years after retirement, while psychological issues had apparently declined around 1-2 decades after retirement. However, available studies had notable limitations including lack of evidenced representative samples, report of measures' reliability, and control for confounders. Furthermore, while theoretical models emphasise a holistic perspective, quantitative research often took a narrow rather than holistic perspective. In summary, available knowledge is fraught with some uncertainty regarding reliability and representativeness of the population of retired professional soccer players. We offer future directions to advance the development of a theory of sport retirement.

The sky is the limit?! Evaluating the existence of a speculative bubble in European football.

In light of increasing salaries and transfer fees, the present study investigates the existence of a speculative bubble in European football. By applying the Kindleberger-Minsky model to football, we show that developments in recent years do not meet the criteria of a classic bubble. Although transfer fee spending in recent years does meet the typical pattern seen in historical bubbles, the case of football rather resembles an atypical bubble. This is because the rise in transfer fees for most clubs is largely backed by cash inflows, prompting an elevator effect for transfer fees. Typical bubbles, on the other hand, contain heavy debt-financing in the absence of respective and sustainable cash inflows. Nevertheless, despite the absence of a speculative bubble on the aggregated league level, some individual clubs seem to "live in a bubble". Furthermore, the French and especially Italian leagues should be cautious about overspending. We further discuss the main risk factors that can lead to a turning point in European football's constant revenue growth, including potential implications of a financial downturn.

Correction: The path to international medals: A supervised machine learning approach to explore the impact of coach-led sport-specific and non-specific practice.

[This corrects the article DOI: 10.1371/journal.pone.0239378.].

The path to international medals: A supervised machine learning approach to explore the impact of coach-led sport-specific and non-specific practice.

Research investigating the nature and scope of developmental participation patterns leading to international senior-level success is mainly explorative up to date. One of the criticisms of earlier research was its typical multiple testing for many individual participation variables using bivariate, linear analyses. Here, we applied state-of-the-art supervised machine learning to investigate potential non-linear and multivariate effects of coach-led practice in the athlete's respective main sport and in other sports on the achievement of international medals. Participants were matched pairs (sport, sex, age) of adult international medallists and non-medallists (n = 166). Comparison of several non-ensemble and tree-based ensemble binary classification algorithms identified "eXtreme gradient boosting" as the best-performing algorithm for our classification problem. The model showed fair discrimination power between the international medallists and non-medallists. The results indicate that coach-led other-sports practice until age 14 years was the most important feature. Furthermore, both main-sport and other-sports practice were non-linearly related to international success. The amount of main-sport practice displayed a parabolic pattern while the amount of other-sports practice displayed a saturation pattern. The findings question excess involvement in specialised coach-led main-sport practice at an early age and call for childhood/adolescent engagement in coach-led practice in various sports. In data analyses, combining traditional statistics with advanced supervised machine learning may improve both testing of the robustness of findings and new discovery of patterns among multivariate relationships of variables, and thereby of new hypotheses.

Self-Concept in Adolescents-Relationship between Sport Participation, Motor Performance and Personality Traits.

The relationship between sport participation, personality development, self-concept and self-esteem has been discussed repeatedly. In this research, a standardized written survey together with tests on motor performance were carried out with 1399 students (707 male; 692 female) in school years 7 (12.9 ± 0.6 years) and 10 (15.8 ± 0.6 years) to measure the extent of a relationship between physical self-concept (self-developed short scale) and sporting activity, measured motor performance (German motor performance test DMT (Deutscher Motorik-Test) 6⁻18) and report mark in physical education. Relationships were also analyzed between physical self-concept and general personality traits (neuroticism, extraversion, openness to experiences, compatibility, and conscientiousness, measured with NEO Five Factor Inventory (NEO-FFI)). The assessment of own physical attractiveness and own athleticism differs by sex (F(1, 962) = 35.21; p < 0.001), whereby girls assess themselves more critically. Weak significant relationships are displayed between motor performance and the assessment of own physical attractiveness (r(395) = 0.31; p < 0.01). Motor performance is given a higher predictive value with regard to a subject's own self-concept, (physical attractiveness ß = 0.37; t(249) = 5.24; p < 0.001; athleticism ß = 0.40; t(248) = 6.81; p < 0.001) than the mark achieved in physical education (physical attractiveness ß = -0.01; n.s.; athleticism ß = -0.30; t(248) = 5.10; p < 0.001). Relationships were found overall between personality traits and physical self-concept. The influence of the 'neuroticism' trait is particularly strong (physical attractiveness ß = -0.44; t(947) = -13.58; p < 0.001; athleticism ß = -0.27; t(948) = -7.84; p < 0.001). The more pronounced this trait, the lower the assessment of own physical attractiveness and own athleticism.

Sport-Induced Substance Use-An Empirical Study to the Extent within a German Sports Association.

In cooperation with the Sports Association of the Palatinate (SBP), a survey was conducted on substance use by recreational and amateur athletes. Distribution of the online questionnaire took place by means of chain-referral sampling, and questions on substance use were presented using the randomized response technique (RRT) to protect the anonymity of respondents and prevent socially desirable answers. The estimated lowest limit for the population share for use of prohibited substances during the last season (4%) and for lifetime use (3.6%) did not differ significantly. Approximately 21% of respondents had used substances for training or competitions that were taken for a purpose other than performance enhancement (e.g., to improve their mood or to help with recuperation from a minor injury or illness) in the last year. 49% had done so at some point in their life.

Socio-economic status and motor performance of children and adolescents.

The study examines the question to what extent children and adolescents differ in terms of motor performance in dependence of their socio-economic status (SES). A sample of 1389 students in Saarland (Germany) in various grades (1st grade: age 7.26 ± 0.38 years, 4th grade: 10.3 ± 0.4 years, 7th grade: 13.44 ± 0.49 years, 10th grade: 16.36 ± 0.69 years) has been examined. Their motor performance has been measured by means of 20-m sprint, standing long jump and a 6-minute run, and the SES by means of a parent survey. Based on the indicators school education, professional education, job position and household income, the SES was categorised in a three-step approach (low, middle, high). The influence on dependent variables was analysed by using multivariate analysis of variance. Students with a higher SES exhibit a higher motor performance compared with that of lower SES (results of the multivariate: Pillai's Trace = .05, F[6; 2526] = 12.56, p = .001; [Formula: see text]). In addition, the data for students of higher SES differ significantly from the data of a German reference sample (higher motor performance compared with standard values). In contrast, persons of lower SES do not differ from the reference sample, and those of middle SES differ only slightly from the reference sample. The results are relevant when considering specific prevention efforts concerning motor performance of certain groups. Especially those institutions and schools should be focused upon whose catchment area includes a high share of socially disadvantaged population groups.

Structural Analysis of Women's Heptathlon.

The heptathlon comprises the results of seven single disciplines, assuming an equal influence from each discipline, depending on the measured performance. Data analysis was based on the data recorded for the individual performances of the 10 winning heptathletes in the World Athletics Championships from 1987 to 2013 and the Olympic Games from 1988 to 2012. In addition to descriptive analysis methods, correlations, bivariate and multivariate linear regressions, and panel data regressions were used. The transformation of the performances from seconds, centimeters, and meters into points showed that the individual disciplines do not equally affect the overall competition result. The currently valid conversion formula for the run, jump, and throw disciplines prefers the sprint and jump disciplines but penalizes the athletes performing in the 800 m run, javelin throw, and shotput disciplines. Furthermore, 21% to 48% of the variance of the sum of points can be attributed to the performances in the disciplines of long jump, 200 m sprint, 100 m hurdles, and high jump. To balance the effects of the single disciplines in the heptathlon, the formula to calculate points should be reevaluated.

Strength training adaptations after cold-water immersion.

Several studies analyzed the effectiveness of cold-water immersion (CWI) to support recovery after strenuous exercise, but the overall results seem to be conflicting. Most of these studies analyzed only short-term recovery effects, whereas the adaptational aspect has been widely neglected. Therefore, we analyzed the effects of repeated cooling after training sessions (CWI) on adaptations to strength training. Seventeen trained male students volunteered the study. After a 2-week familiarization period, a pretest (T1) of 1 repetition maximum (RM) and 12RM was conducted followed by the 5-week strength training period (within-subject design). After the posttest (T2) and a 2-week detraining period, a retention test (T3) was carried out. Directly after each training session, CWI was applied for 1 randomly assigned leg. Cooling consisted of 3 4-minute intervals with a 30-second rest period. The other leg was not cooled. A significant increase in 1RM and 12RM from baseline to T2 and T3 (p < 0.001), respectively, and a further significant increase in 12RM from T2 to T3 (p ≤ 0.05) were observed. In addition, a tendency for a large leg effect with higher values for the "control leg" in both parameters (p = 0.08 each) and a moderate time × leg interaction in favor of the control leg was found (1RM: p = 0.11; 12RM: p = 0.09). The percentage change differences between both conditions were 1.6% for the increase in 1RM from T1 to T2 and 2.0% from T1 to T3 in favor of the control leg. Long-term strength training adaptations in trained subjects can be negatively affected by CWI. However, effects were small, and the practical relevance relative to possible recovery effects needs to be considered in a sports practical setting.

Considering long-term sustainability in the development of world class success.

The developmental practice patterns leading to the highest levels of success remain a subject of debate. The present study purposes to extend the body of empirical research by analysing athletic biographies from a large sample of German national squad athletes across all Olympic sports (n=1558; 57% male, 43% female). In a combined retrospective and longitudinal study utilising postal questionnaires, we evaluated the age at onset, volume, domain-specificity, variability in training and competition and success attained at different ages. Developmental practice patterns leading to rapid adolescent success and long-term senior success were inconsistent, and in some aspects contradictory. An early start-age for training and competition, early specialisation, high-intensity specific practice in the respective domain sport and little or no involvement in other sports (OS) favoured early adolescent success. Juvenile success, however, did not contribute to individual differences in success achieved at a senior age (-0.09

Motor performance and bodyweight of children and adolescents in Saarland -- status quo.

The motor performance of children and adolescents has been a subject of controversial discussion. As part of a pilot project, 839 schoolchildren from 14 different schools in Saarland were studied and their height, weight and sport motor performance were measured using the German motor performance test DMT 6-18. The results show a slight increase in the number of overweight children compared to reference samples. However, these discrepancies are minor and cannot be judged to be practically relevant because of the weakness of the effects. The average motor test performances of the Saarland schoolchildren were above the average performance of the reference samples in almost all individual performances. There are also hardly any weaker performances in comparison to older studies. The current results for motor performance of Saarland children and adolescents do not, therefore, give any great reason for concern. Further evaluation steps will be needed to clarify the influences that might be associated with adverse characteristics for motor performance (socio-economic status, living situation, leisure behaviour, school performance, etc.).

Outcome effects of single-set versus multiple-set training--an advanced replication study.

The starting point of this review is the assumption that single-set training (SST) can be regarded as an equal alternative to multiple-set strength training. On the basis of 72 primary studies, the meta-analysis dealt with the problem of single-set vs. multiple-set training (MST). The effectiveness of these training methods was examined depending on various interventions. Apart from qualitative decision aspects, the effectiveness was checked on the basis of effect size. Generally speaking, it can be stated that MST, depending on factors like age, training experience, duration of the study, etc., offers several advantages over single-set regimes (F = 3.71; df = 1; p = 0.06; eta(2) = 0.02), especially when combined with periodization strategies, and it can be applied very successfully for increasing maximal strength in long-time effects. Therefore, the outcome effects of both methods are the same in short-time interventions. For longer-time interventions (F = 15.74; df = 1; p < 0.05; eta(2) = 0.12) and for advanced subjects with the goal of optimizing their strength gain, however, multiple-set strategies are superior (F = 7.32; df = 1; p < 0.05; eta(2) = 0.06).

Situated health promotion: reflections on implementing situated learning approaches in health promotion.

Handing down health knowledge and behavior patterns is a main objective of health promotion. Often, interventions do not bring about the intended change of behavior. This could be due, among other things, to the fact that the majority of intervention programs are not based on principles of instructional design to bridge the gap between knowledge and action. A situated design of health promotion measures is to be considered particularly suitable. That accounts for the fact that the acquisition and application of knowledge is an active construction process on the part of the individuals involved, and one that includes the possibility to improve the quality of learning processes in the area of health promotion, and thus increases the probability that acquired knowledge can be applied in real situations. In the context of the problem that most health promotion interventions frequently do not show the desired permanent behavioral changes of the participating individuals, from a pedagogical perspective, it is crucial that current didactic-methodological principles be taken into account. This, too, should be taken into account in connection with an empirical analysis of the reflections in this article. In the following paper, various suggestions for implementation are explained and discussed.

Training methods and intensity distribution of young world-class rowers.

PURPOSE: To describe the distribution of exercise types and rowing intensity in successful junior rowers and its relation to later senior success. METHODS: 36 young German male rowers (31 international, 5 national junior finalists; 19.2 +/- 1.4 y; 10.9 +/- 1.6 training sessions per week) reported the volumes of defined exercise and intensity categories in a diary over 37 wk. Training categories were analyzed as aggregates over the whole season and also broken down into defined training periods. Training organization was compared between juniors who attained national and international senior success 3 y later. RESULTS: Total training time consisted of 52% rowing, 23% resistance exercise, 17% alternative training, and 8% warm-up programs. Based on heart rate control, 95% of total rowing was performed at intensities corresponding to <2 mmol x L(-1), 2% at 2 to 4 mmol x L(-1), and 3% at >4 mmol x L(-1) blood lactate. Low-intensity work remained widely unchanged at approximately 95% throughout the season. In the competition period, the athletes exhibited a shift within <2 mmol exercise toward lower intensity and within the remaining approximately 5% of total rowing toward more training near maximal oxygen consumption (VO(2max)) intensity. Retrospectively, among subjects going on to international success 3 y later had their training differed significantly from their peers only in slightly higher volumes at both margins of the intensity scope. CONCLUSION: The young world-class rowers monitored here exhibit a constant emphasis on low-intensity steady-state rowing exercise, and a progressive polarization in the competition period. Possible mechanisms underlying a potential association between intensity polarization and later success require further investigation.