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Paul Ritsche, Thomas Bernhard, Ralf Roth, Eric Lichtenstein, Martin Keller, Sabrina Zingg, Martino V. Franchi, and Oliver Faude

Purpose: Hamstring muscle architecture may be associated with sprint performance and the risk of sustaining a muscle injury, both of which increase during puberty. In this study, we investigated the m. biceps femoris long head (BFlh) cross-sectional area (ACSA), fascicle length (FL) and pennation angle (PA), and sprint performance as well as their relationship in under 13 to 15 youth soccer players. Methods: We measured 85 players in under-13 (n = 29, age = 12.5 [0.1] y, height = 155.3 [6.2] cm, weight = 43.9 [7.6] kg), under-14 (n = 25, age = 13.5 [0.3] y, height = 160.6 [7.7] cm, weight = 47.0 [6.8] kg), and under-15 (n = 31, age = 14.4 [0.3] y, height = 170.0 [7.7] cm, weight = 58.1 [8.8] kg) teams. We used ultrasound to measure BFlh ACSA, FL and PA, and sprint tests to assess 10- and 30-m sprint time, maximal velocity  (v max), and maximal acceleration (α max). We calculated Pearson r to assess the relationship between sprint ability and architectural parameters. Results: All muscle architectural parameters increased from the under-13 to the under-15 age group (BFlh ACSA = 37%, BFlh FL = 11%, BFlh PA = 8%). All sprint performance parameters improved from the under-13 to under-15 age categories (30-m time = 7%, 10-m time = 4%, v max = 9%, α max = 7%). The BFlh ACSA was correlated with 30-m sprint time (r = −.61 (95% compatibility interval [CI] [−.73, −.45]) and v max (r = .61, 95% CI [.45, .72]). A combination of BFlh ACSA and age best predicted 30-m time (R² = .47 [.33, .62]) and 10-m time (R² = .23 [.08, .38]). Conclusions: Muscle architectural as well as sprint performance parameters increase from the under-13 to under-15 age groups. Even though we found correlations for all assessed architectural parameters, BFlh ACSA was best related to the assessed sprint parameters.

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Iván Peña-González, José M. Sarabia, Alba Roldan, Agustín Manresa-Rocamora, and Manuel Moya-Ramón

In regular football, the players’ selection process involves an objective assessment based on their anthropometric and physical performance. However, available literature focused on players’ selection process in cerebral palsy (CP) football is scarce. Purpose: To describe the anthropometrical and physical performance profiles of the International Spanish CP footballers and to compare them with the remaining CP football players from the national competition. Method: A total of 75 CP football players from the Spanish CP Football National Competition (classified into the 3 existing classes: football class [FT] 1 = 38; FT2 = 29; FT3 = 8) participated in the study. Participants were divided into 2 groups: selected players (n = 15) and nonselected players (n = 60) for the national team. Anthropometrical data and physical performance (countermovement jump, 20-m sprint, modified agility T-test [MAT], and dribbling test) were collected. Results: There were significant differences in the 20-m sprint, MAT, and dribbling for the total sample and in MAT and dribbling for FT2 and FT3 classes between selected players and nonselected players (P < .05), but there were no differences for FT1. The MAT and dribbling showed a positive correlation and a high percentage of player selection prediction. Conclusion: Change-of-direction ability (ie, MAT) and dribbling skills are important when performing the selection process, as they allow the evaluation of important aspects of the game, but they may also provide the technical staff with an idea of the functionality and the physical performance of the players in each sport class.

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Satoshi Aikawa and Hideaki Takai

Athletes believe imagery is essential for high-quality performance. It is essential to identify what type of imagery significantly contributes to performance. The purpose of this study was to examine the relationship between imagery ability and gymnastics performance, as well as self-efficacy and thoughts during competitions that are related to performance. Fifty-two gymnasts were recruited for this study. Participants were measured for imagery ability, self-efficacy, thoughts during competitions, and performance. Results indicated that skill imagery significantly predicts worry and disengagement in a negative manner, and mastery imagery is positively related to self-efficacy. Moreover, goal imagery has a significant positive relationship to self-efficacy, disengagement, confidence, and performance. In conclusion, the ability to easily image an ideal performance, such as the success of one’s performance or the image of a perfect performance, might increase confidence in the competition and lead to the success of the performance.

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S. Sofie Lövdal, Ruud J.R. Den Hartigh, and George Azzopardi

Purpose: Staying injury free is a major factor for success in sports. Although injuries are difficult to forecast, novel technologies and data-science applications could provide important insights. Our purpose was to use machine learning for the prediction of injuries in runners, based on detailed training logs. Methods: Prediction of injuries was evaluated on a new data set of 74 high-level middle- and long-distance runners, over a period of 7 years. Two analytic approaches were applied. First, the training load from the previous 7 days was expressed as a time series, with each day’s training being described by 10 features. These features were a combination of objective data from a global positioning system watch (eg, duration, distance), together with subjective data about the exertion and success of the training. Second, a training week was summarized by 22 aggregate features, and a time window of 3 weeks before the injury was considered. Results: A predictive system based on bagged XGBoost machine-learning models resulted in receiver operating characteristic curves with average areas under the curves of 0.724 and 0.678 for the day and week approaches, respectively. The results of the day approach especially reflect a reasonably high probability that our system makes correct injury predictions. Conclusions: Our machine-learning-based approach predicts a sizable portion of the injuries, in particular when the model is based on training-load data in the days preceding an injury. Overall, these results demonstrate the possible merits of using machine learning to predict injuries and tailor training programs for athletes.

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Stephen S. Cheung

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Veronique Richard, Justin Mason, Stacey Alvarez-Alvarado, Inbal Perry, Benoit Lussier, and Gershon Tenenbaum

The aim of the present study was to compare the effectiveness of a learned preperformance routine (PPR) with an intuitively developed one before a simulation race on advanced swimmers’ speed and motor efficiency, as well as self-efficacy and emotional regulation. In total, 46 National Collegiate Athletic Association Division I swimmers were stratified to either the control (intuitively developed PPR) or the PPR condition, which included four instructional sessions aimed at developing a PPR. A simulated competitive race was organized before and after the intervention. For each simulation, speed and motor efficiency were measured during the race, and self-efficacy and emotions, after the completion of the race. Nonsignificant effects were revealed for speed, motor efficiency, and self-efficacy following the intervention. However, performing a learned PPR prior to racing significantly influenced the swimmers’ emotional state. These results provide some support for the effect of a PPR on emotional regulation prior to a swimming race.

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Lasse Ishøi, Kasper Krommes, Mathias F. Nielsen, Kasper B. Thornton, Per Hölmich, Per Aagaard, Juan J.J. Penalver, and Kristian Thorborg

Purpose: Increasing age, high quadriceps strength, and low hamstring muscle strength are associated with hamstring strain injury in soccer. The authors investigated the age-related variation in maximal hamstring and quadriceps strength in male elite soccer players from under-13 (U-13) to the senior level. Methods: A total of 125 elite soccer players were included from a Danish professional soccer club and associated youth academy (first tier; U-13, n = 19; U-14, n = 16; U-15, n = 19; U-17, n = 24; U-19, n = 17; and senior, n = 30). Maximal voluntary isometric force was assessed for the hamstrings at 15° knee joint angle and for the quadriceps at 60° knee joint angle (0° = full extension) using an external-fixated handheld dynamometer. Hamstring-to-quadriceps strength (H:Q) ratio and hamstring and quadriceps maximal voluntary isometric force levels were compared across age groups (U-13 to senior). Results: Senior players showed 18% to 26% lower H:Q ratio compared with all younger age groups (P ≤ .026). Specific H:Q ratios (mean [95% confidence interval]) were as follows: senior, 0.45 (0.42–0.48); U-19, 0.61 (0.55–0.66); U-17, 0.56 (0.51–0.60); U-15, 0.59 (0.54–0.64); U-14, 0.54 (0.50–0.59); and U-13, 0.57 (0.51–0.62). Hamstring strength increased from U-13 to U-19 with a significant drop from U-19 to the senior level (P = .048), whereas quadriceps strength increased gradually from U-13 to senior level. Conclusion: Elite senior soccer players demonstrate lower H:Q ratio compared with youth players, which is driven by lower hamstring strength at the senior level compared with the U-19 level combined with a higher quadriceps strength. This discrepancy in hamstring and quadriceps strength capacity may place senior-level players at increased risk of hamstring muscle strain injuries.