This study retrospectively investigated (1) the longitudinal relationships between young handball field players’ technical throwing skills and (a) their potential nomination to youth national teams and (b) their long-term career attainment 10 years later, as well as (2) the associations between nomination status and career attainment, and the effect of nomination status as an additional predictor of career attainment were investigated retrospectively.
Retrospective Prediction of Nomination Status and Career Attainment
In summary of the binomial regression analysis, the statistically significant overall regression model for female players explained 9.2% of the variance in nomination status with a statistically significant effect for variable throwing velocity. On the other hand, the statistically significant overall regression model for male players explained 13.1% of the variance in nomination status with a statistically significant effect for variables throwing velocity and time on exercise. That is, a higher throwing velocity and a lower time on exercise were associated with being nominated to youth national teams.
In summary of the multinomial regression analysis, the statistically significant overall regression model for female players explained 9.8% of the variance in career attainment with a statistically significant effect for variable throwing velocity when comparing professional and non-professional players. In male players, the overall regression model and the variables separately showed no statistically significant effects explaining 7.1% of the variance in career attainment. That is, a higher throwing velocity was associated with becoming a professional female handball player.
Overall, technical skills appear to be on a rather homogenous level for most players in this selected age group. However, variable throwing velocity in both male and especially female players as was previously reported for female players  and variable time on exercise in male players showed predictive value. Here, variable time on exercise must be investigated further to check for its validity and practical relevance. Furthermore, higher throwing velocities leave the goalkeeper less time to react to and defend the handball, thus increasing the chance of scoring a goal. Additionally, variable throwing velocity potentially relates to overall power and thus includes other aspects of performance. Here, it is also important to note the effect of potential differences in maturation and growth influencing variable throwing velocity. In general, the high overlaps for technical throwing skills between nominated and non-nominated as well as later professional, semi-professional and non-professional players emphasize the high homogeneity in the already pre-selected sample as players were chosen by regional coaches to participate in the camp. On the one hand, this can be interpreted as high-level technical throwing skills representing an important factor already at regional levels and thus serve rather as a prerequisite than a bonus or key characteristic on national level. Here, probably the players’ age in this study (female age group 14–15, male age group 15–16 years old) also plays an important role as there are big developmental changes in this age group and differences between females and males [e.g., 23]. Especially for the male players in this study, it can be assumed that technical skills play a bigger role at the younger age of 10–14 before movement speed/explosiveness and tactical skills become more important afterward . Thus, technical skills may predict or differentiate better in younger age groups, e.g., in the phase ‘train to learn’ of the long-term athlete development model . Accordingly, the long-term development of handball players should emphasize the improvement of technical (throwing) skills early on by combining it with other performance aspects (e.g., tactical skills). In the beginning, coaches should aim for high amounts of general motor abilities before transferring to more and more handball-specific as well as position-specific skills and drills with older age groups. That is, technical (throwing) skills are an important part within a multidimensional profile and skill set that must be developed in combination with other aspects following the overall aim of ‘playing ability.’ However, it is important to note that while this approach is common practice in many TID systems, its empirical evidence to date is limited.
Furthermore, the assessment of technical skills should include, for example, more than just one throwing technique from one position. Other throwing techniques (e.g., jump shot) and other technical skills (e.g., dribbling, cutting) need to be investigated as potentially not the highly basic skill set-throw but rather throwing variations may differ between players. In addition, not only offensive but also defensive actions as well as different playing positions need to be considered when aiming to improve TID activities as both sides of the game are important  and different players have different tasks and rolls demanding different sets of skills and characteristics.
Finally, our results show that technical skills can explain 7–13% of variance in nomination status and career attainment with higher values for the former. That is, about 90% of variance remain unexplained. However, explaining 7–13% of variance with only one performance aspect appears to be a high value, especially for the career attainment with a long study period of 10 years. As Johnston et al.  have shown, longitudinal studies (in handball) aiming to explain variance of long-term success are rare. While rather isolated technical skills are a crucial part in the early phases of long-term athlete development programs, they are combined increasingly with tactical skills to train the technical–tactical application of techniques within game contexts. That is, the 87–93% of unexplained variance are probably accounted for by other factors making the multidimensional profile of performance and athlete development in handball. These include performance-related factors such as tactical and psychological skills or mental toughness that are highly important for a long and successful career. This importance of overall athlete development within a TID system is also represented by including nomination status as an additional predictor and finding an increase in explained variance (5.6% for males and 10.6% for females). Also, another factor is injuries that can have negative impacts on a player’s (long term) development and lead to unexpected attainments .
Association Between Nomination Status and Career Attainment
Both chi-square tests showed a statistically significant association between nomination status at the end of the camp and the career attainment 10 years after camp with a medium effect size for female and a small effect size for male players. That is, the nomination status at the end of the camp is associated with the players’ career attainment afterward. This might indicate that coaches are to some degree able to recognize ‘talented’ and in the future successful players as was shown before [e.g., 11]. Vice versa, it also might indicate that the nomination to national teams and with that entering the talent development system of the DHB could increase the chance of becoming a professional player. Here, the multinomial regression analyses for career attainment including nomination status as an additional predictor showing statistically significant effects in combination with highly increased explained variances (9.8% to 20.3% for female, 7.1% to 12.7% for male) probably is an indication that advantages of nomination to the youth national team, e.g., greater quality and quantity of practice, better social networks and surroundings, influence future performance in both female and male handball. As the Odds ratio of the chi-square test show, the chance of making it to the professional level when being nominated 10 years earlier is increased by a factor of 7.24 and 2.83 in female and male players, respectively. Of those 74 players (31 females, 43 males) identified as ‘talented’ and thus nominated by coaches at the camp in 2009, 37 players (18 females, 19 males) ended up playing professional handball while 11 players (1 female, 10 males) played only semi-professionally and 26 players (12 females, 14 males) only non-professionally (see Fig. 1). That is, results show that coaches overall were able to identify (or quasi predict) 38.1% of all later professional handball players (37 of 96) as ‘talented.’ Here, their TID decisions at the camp in 2009 were more ‘successful’ (sensitivity) in females than in males as 58.1% (18 of 31) and 44.2% (19 of 43) of nominated players, respectively, made it to the highest level in their careers. Accordingly, half of the players (37 of 74) identified as ‘talented’ played only semi- or non-professional handball in their careers. The fact that the effect size and the Odds ratios in the chi-square test, the additional explained variance by nomination status in the regression analyses, and the descriptive numbers are higher for females than for males may be explained by the national TID system playing a bigger and more crucial role in female than in male handball. In the latter, there is a more complete and comprehensive talent system at the club level allowing more players to become professional even without the national TID system whereas the national TID system acts as a ‘gatekeeper’ to better development possibilities even more in female handball . Here, further research is needed to investigate the gender data gap in talent research, e.g., regarding differences between female and male TID systems and players’ career chances .
Results on inter-rater reliability (intraclass correlation coefficient; ICC) within the technique rating process showed poor reliability (ICC[1, 3] = 0.02, p = 0.42) between the two raters that might have led to variable technique rating showing no statistically significant effects. Despite similar training beforehand coaches may still have slightly different ideas of throwing technique and assessed certain elements differently, especially within a binary scale. For example, the technical element ‘hand behind the ball’ can be rated differently depending on how far the hand has to be behind the handball to rate this as fulfilled/1 instead of not fulfilled/0. Here, a rating with more than two options could allow for a more detailed assessment. Also, the possibility to assess certain weights to specific elements relating to their importance could improve validity. Furthermore, better training including precise prime examples of categories fulfilled/1 and not fulfilled/0 could improve rater reliability. In addition, rating quality could potentially be increased by presenting videos in slow motion (e.g., 1/4 playback speed) to allow raters to percept movements in more detail . Accordingly, further research regarding the optimal design of observation sheets, quality of video clips, presentation modus, preparation of the coaches and their usage is needed. While other studies showed video observations in combination with technical observations sheets are an effective tool for technique assessment, this has to be restricted based on these findings. Potentially, this downside of observations sheet could be counterbalanced by conducting more objective, biomechanical movement analyses as part of the technique evaluation [30, 31]. Furthermore, future research should consider technique assessments during talent selection activities. However, it is important that assessments are not interfering with camp activities and/or other coach tasks during talent selection.
There are some other limitations to the longitudinal design and analysis of this study. First, changes and developments within a sport and its culture, e.g., tactical approaches or rule adaptions, can influence the role of certain skills or characteristics over time, especially when analyzing data longitudinally. Second, data on maturation and growth as well as potential ‘relative age effects’ were not analyzed in this study, but could have affected the technical throwing skill assessments, e.g., differences in throwing velocity. Future studies should include this information in their analysis. Third, potentially there are errors with some of our assessment tools. Especially the variable technique rating and its assessment process based on an observation sheet must be advanced and improved to allow for high-quality data from a ‘technique-related’ method type. In addition, using the players’ highest league as a proxy for career attainment may have reduced the players’ performance to a rather tight variable. Here, future studies should consider other measurements of career attainment, e.g., games played , titles won, goals scored or other game statistics. Fourth, as mentioned above, future studies should include technical skills as one dimension in a multidimensional approach. Last, including players with no information on their highest league in the group of non-professional players during the analysis may have introduced some error and future studies could try to incorporate potential reasons for lower career attainments, e.g., injury.