Electromyography of shoulder muscles in individuals without scapular dyskinesis during closed kinetic chain exercises on stable and unstable surfaces: a systematic review and meta-analysis.

Introduction: Unstable surfaces are commonly utilized to enhance the flexibility of the musculoskeletal system for achieving training or rehabilitation goals. However, their effects on shoulder muscle activation during various push-up (PU) exercises have not been thoroughly investigated. Therefore, the purpose of this study was to synthesize electromyography (EMG) data of shoulder muscles in individuals without scapular dyskinesis performing different PU exercises on both stable and unstable surfaces. Methods: A systematic online search was conducted in electronic databases, including Web of Science, PubMed, Scopus, and Google Scholar, up to January 16, 2024, using predefined sets of keywords. Out of the 1,971 titles and abstracts screened, 80 articles were reviewed in detail by two independent researchers to check the eligibility, of which 28 eligible studies were ultimately included. Following assessment of the quality and risk of bias, the studies were categorized based on exercises and muscle groups, and a meta-analysis using a random-effects model was performed to estimate the overall effect size. Results: The use of unstable surfaces led to a decrease in anterior deltoid activity during PU [P = 0.032; I2 = 91.34%; SMD = -0.630 (95% CI -1.205, -0.055)], an increase in pectoralis major activity during PU [P = 0.006; I2 = 63.72%; SMD = 0.282 (95% CI 0.079, 0.484)], as well as during knee PU [P = 0.018; I2 = 32.29%; SMD = 0.309 (95% CI 0.052, 0.565)], and an increase in triceps brachii activity during PU [P = 0.000; I2 = 85.05%; SMD = 0.813 (95% CI 0.457, 1.168)], knee PU [P = 0.000; I2 = 0.00%; SMD = 0.589 (95% CI 0.288, 0.891)], as well as during push-up plus [P = 0.006; I2 = 13.16%; SMD = 0.563 (95% CI 0.161, 0.965)]. However, the use of unstable surfaces did not show a significant effect on the EMG activity of the pectoralis major during push-up plus [P = 0.312; I2 = 22.82%; SMD = 0.207 (95% CI -0.194, 0.609)]. Conclusions: Unstable surfaces can modulate muscle activity in different PU exercises, while the effects on the targeted muscles depend on the type of exercise. The findings of this review provide a framework based on the level of activity of each shoulder muscle during different PU exercises, which can help coaches, trainers, and sports therapists select the most suitable type of PU for designing training or rehabilitation programs. Particularly, the most suitable exercise for increasing anterior deltoid activity is PU on a stable surface. To concurrently increase activity of the pectoralis major and triceps brachii, adding unstable surfaces under hands during knee PU and standard PU is recommended. Systematic Review Registration: PROSPERO, identifier CRD42021268465.

Little associations exist between the three commonly used functional screening tests in collegiate athletes.

Although an abundant number of studies have investigated the predictability of the commonly used functional screening tests and despite their popularity and applicability, the relationships between these tests have rarely been studied and have not been well established. This study aimed to examine the potential association between the Functional Movement Screen (FMS), Y Balance Test (YBT), and Landing Error Scoring System (LESS). Six hundred twenty-seven Iranian collegiate athletes (347 males, age = 22.63 ± 4.07, weight = 75.98 ± 13.79, height = 181.99 ± 10.15, BMI = 22.84 ± 3.16; and 280 females, age = 22.22 ± 3.37, weight = 60.63 ± 9.58, height = 166.55 ± 6.49, BMI = 21.81 ± 2.84) participated in this study. Following a 5-min warm-up, each participant underwent a standardized screening battery including the FMS, YBT, and LESS, and the scores were recorded and live coded for the statistical analysis, except for the LESS. The LESS tests were video recorded and scored by one expert examiner using an open-source 2D video analysis software (Kinovea- version 0.9.5), afterwards. The Spearman correlation was utilized as a measure for the correlation, and the Mann‒Whitney U test with a significance level of 0.05 was used to check the differences between male and female athletes. The statistical analysis was performed with RStudio 2023.03.0 using R 4.3.1. A small correlation (0.364) was observed between the FMS composite score and the YBT in male athletes. All other pairwise correlations were negligible among male and female athletes, ranging from - 0.096 to 0.294. Reducing the FMS to the component scores targeting the lower extremities did not alter the correlation to the other screening scores. The median FMS composite score in female athletes was significantly higher than that in males (p < 0.001). Negligible correlations exist between the FMS, LESS, and YBT; they do not measure the same values and therefore are irreplaceable with one another. A combination of these tests as a standardized screening battery may potentially better identify injury-predisposed athletes than the application of each test as a stand-alone screening test. Females outperformed males in the FMS test significantly, so sex must be considered a key variable in the FMS studies. Males had slightly higher LESS scores (median difference = 0.5) than females, but this difference is not clinically meaningful. Future research should continue to explore the relationships between various functional screening tests and identify the most effective combinations for comprehensive assessment in different populations and sports disciplines.

Improving the ecological validity of isokinetic knee tests at different hip angles: reciprocal concentric-eccentric movements as a suitable alternative for discrete tests.

Isokinetic knee tests mostly evaluate reciprocal concentric-concentric flexor-extensor movements in a seated position. Discrete tests generate higher moments, but time requirements impede their widespread implementation. This study examined if hip angle (flexed vs. extended) and test modality (discrete vs. reciprocal) affect camera-based data (100 fps). Sixteen healthy males performed concentric (con) and eccentric (ecc) isokinetic knee flexor (H) and extensor (Q) movements (60°/s). Peak moments and contractional work of discrete and reciprocal tests (QconQecc, HconHecc) strongly correlated for extended (Q:91%≥R2≥71%; H:95%≥R2≥87%) and flexed hip (Q:88%≥R2≥70%; H:81%≥R2≥75%) without significant differences (p>0.05) between test modalities. Discrete and "traditional" seated QconHcon-tests revealed substantially lower correlations for extended (Q:44%≥R2≥43%; H:55%≥R2≥54%) and flexed hip (Q:81%≥R2≥77%; H:48%≥R2≥47%). Although most mean values did not significantly differ, moderate correlations were predominant and the respective limits of agreement demonstrated considerable effects of hip angle and test modality. These insights assist practitioners in interpreting isokinetic data of different test procedures. If time constraints prevent discrete knee tests (gold standard), concentric-eccentric movements provide highly correlated outcomes, independent of the hip angle.

Synthesis and validation algorithm followed by a weighting procedure to create a detailed anthropometric dataset for the German working-age population.

For the German working-age population no publicly available and detailed anthropometric raw dataset exists, although several studies have collected anthropometric datasets. Unfortunately, the publication of raw data may be restricted by data usage regulations. This study presents a synthesis and validation algorithm to create a virtual copy of an already existing dataset. A detailed anthropometric dataset from a regional epidemiological public-health study in Germany was used for the synthesis and validation algorithm. Results revealed only minor deviations within the validation process. Compared to the original dataset, the virtual dataset was statistically almost identical. In a next step, the virtual dataset was weighted to approximate nationally representative values. In summary, the computed unweighted and weighted virtual data can be published without restrictions and used for ergonomic designing. Furthermore, the synthesis and validation algorithm is suitable for the generation of virtual copies and can be applied to other detailed anthropometric datasets.

Data usage regulations may restrict the publication of anthropometric datasets. A synthesis and validation algorithm was developed which can be applied to existing anthropometric datasets to create a virtual copy that is almost identical and can be published. In the current study this algorithm was used for data from Germany.

Electromyography of scapular stabilizers in people without scapular dyskinesis during push-ups: a systematic review and meta-analysis.

Background: Push-up (PU) is widely considered an effective exercise to stabilize the scapular, especially if performed on unstable surfaces. However, available studies cover a wide range of exercise variations and differ according to exercise prescription, muscle selection and study design. Therefore, findings are contradictory, and conclusions for a proper application of the PU are difficult to draw. Objective: To synthesize the available literature on the changes in the activity of the periscapular muscles in individuals without scapular dyskinesis while performing different types of PU on unstable surfaces. Search procedure: Four online databases were searched from the earliest publications to 9 August 2023, using predefined keywords. Out of the 2,850 potential references identified in the primary search, 92 studies were reviewed in detail, of which 38 met the inclusion criteria and were included. Methodological quality was evaluated using a standardized form based on the Newcastle‒Ottawa scale for observational studies. Data combination was performed using CMA (v3), and the random-effects model was used to calculate the standardized mean difference (SMD) with a 95% confidence interval (CI). Results: The use of unstable surfaces in people without scapular dyskinesis led to increased activity of the upper trapezius during the PU (p = 0.017; I2 = 84.95%; SMD = 0.425 [95% CI 0.077, 0.773]) and knee PU (p = 0.023; I2 = 70.23%; SMD = 0.474 [95% CI 0.066, 0.882]) exercises and increased activity of the middle trapezius (MT) (p = 0.003; I2 = 64.50%; SMD = 0.672 [95% CI 0.225, 1.119]) and serratus anterior (SA) (p = 0.039; I2 = 4.25%; SMD = 0.216 [95% CI 0.011, 0.420]) muscles during the push-up plus (PUP) exercise. Conclusion: Using an unstable support base during PU does not necessarily increase the activity of all scapular stabilizers. The amount of muscle activity depends on the type of PU other than the type of support base. If an unstable surface is used, PUP exercise appears to be the most effective modality to increase the quality of training, improve performance, and prevent the occurrence of scapular dyskinesis due to the increase in the activity of the MT and SA muscles. Systematic Review Registration: http://www.crd.york.ac.uk/PROSPERO, CRD42021268465.

Acute effects of the FIFA11+ and Football+ warm-ups on motor performance. A crossover randomized controlled trial.

INTRODUCTION: Few studies including contradictory results have addressed the acute effects of the 11+ on motor performance, indicating a potentially reduced applicability of the program for warming up before competitions. This study aims to compare the acute effects of a soccer-specific warm-up (Football+) and the 11+ on motor performance. MATERIALS AND METHODS: Thirty-eight volunteer collegiate players (22 males; age = 21.1±1.9 years, height = 1.81± 0.06 m, weight = 73.4± 9.5 kg; 16 females; age = 21.3±1.5 years; height = 1.71± 0.07 m, weight = 67.8± 8.5 kg) underwent the 11+ and the Football+ in a randomized crossover design with a one-week washout. The Football+ starts with a self-estimated 40-50 percent running, followed by dynamic stretching of the hip muscles, shoulder contact, controlled lunge, Copenhagen exercise, and modified Nordic hamstring exercise. The second part involves roughly intensive small-sided games, followed by plyometric and anaerobic exercises in the third part. The warm ups' effects on performance were determined by a linear sprinting test (20 m), countermovement jump performance (CMJ), Illinois agility (IA), and dribbling speed (DS) tests. Within-subject differences were reported as the means and SD. Pairwise t tests at the significance level of p<0.05 were used to calculate the significant differences. RESULTS: Overall, except for the CMJ (mean = -0.43±3.20 cm, p = 0.21, d = -0.13), significant differences for the 20 m sprint (mean = 0.04±0.10 s, p = 0.005, d = 0.42), IA (mean = 0.65±0.45 s, p = 0.01, d = 1.43), and DS (mean = 0.60±1.58 s, p = 0.012, d = 0.38) were observed. In females, significant differences observed only for IA (mean difference = 0.52±0.42 s, p<0.001, d = 1.24) and DS (mean difference = 1.29±1,77 s, p = 0.005, d = 0.73), with the Football+ showing superiority. In males, significant differences were found only for 20 m sprinting (mean difference = 0.06±0.09, p = 0.005, d = 0.60) and IA (mean difference = 0.74±0.46, p<0.001, d = 1.62), with the Football+ having superiority. DISCUSSION: Although practicable for injury prevention, the 11+ may not optimize acute performance and prepare players for high-intensity physical tasks as well as a well-structured, roughly intensive warm-up. Further gender-specific studies should evaluate the long-term effects of the Football+ on performance and injury prevention.

Predictive modeling of lower extremity injury risk in male elite youth soccer players using least absolute shrinkage and selection operator regression.

PURPOSE: To (1) identify neuromuscular and biomechanical injury risk factors in elite youth soccer players and (2) assess the predictive ability of a machine learning approach. MATERIAL AND METHODS: Fifty-six elite male youth soccer players (age: 17.2 ± 1.1 years; height: 179 ± 8 cm; mass: 70.4 ± 9.2 kg) performed a 3D motion analysis, postural control testing, and strength testing. Non-contact lower extremities injuries were documented throughout 10 months. A least absolute shrinkage and selection operator (LASSO) regression model was used to identify the most important injury predictors. Predictive performance of the LASSO model was determined in a leave-one-out (LOO) prediction competition. RESULTS: Twenty-three non-contact injuries were registered. The LASSO model identified concentric knee extensor peak torque, hip transversal plane moment in the single-leg drop landing task and center of pressure sway in the single-leg stance test as the three most important predictors for injury in that order. The LASSO model was able to predict injury outcomes with a likelihood of 58% and an area under the ROC curve of 0.63 (sensitivity = 35%; specificity = 79%). CONCLUSION: The three most important variables for predicting the injury outcome suggest the importance of neuromuscular and biomechanical performance measures in elite youth soccer. These preliminary results may have practical implications for future directions in injury risk screening and planning, as well as for the development of customized training programs to counteract intrinsic injury risk factors. However, the poor predictive performance of the final model confirms the challenge of predicting sports injuries, and the model must therefore be evaluated in larger samples.

Analyses of Isokinetic Thigh Muscle Strength: Camera-Based Assessment Alters the Magnitude, but Not the Message.

Background: Thigh muscle strength capacities are major modifiable risk factors for knee and thigh muscle injuries. Therefore, their valid assessment is essential. Most isokinetic knee tests are conducted in a seated position and rely on dynamometer-based data. However, their accuracy is doubtful because axis alignment is erroneous. Purpose: This study investigated if hip angle (flexed vs. extended) and assessment method (dynamometer-based vs. camera-based) affect isokinetic outcome parameters. Methods: Sixteen healthy male participants (27 years, 184 cm, 80 kg) performed discrete isokinetic tests of the knee flexors and extensors (60°/s) while their kinematics were captured (100 fps). Results: Both assessment methods revealed very strong linear relationships (94% ≤ R2 ≤ 98%) although peak moments (d ≤ 0.87), contractional work (d ≤ 1.26), and functional knee flexor:extensor ratios (d ≤ 0.81) significantly differed. Seated knee flexor tests demonstrated the largest knee trajectory center's misalignment (x = 4.0 cm, z = -2.5 cm; 1.37 ≤ d ≤ 4.74). Conclusion: Hip-angle induced kinematic changes did not affect the relation between the lever arms, thus causing highly proportional deviations of kinetic parameters. The assessment method altered the magnitude, but not the message of isokinetic knee tests, which should be preferentially performed with extended hip joint to improve axis alignment. Knowledge of these kinetic and kinematic interactions assists practitioners and scientists with isokinetic tests and/or rehabilitation training to ensure reasonable interpretations of gathered isokinetic outcomes.

Effects of a seat-integrated mobilization system on long-haul truck drivers motion activity, muscle stiffness and discomfort during a 4.5-h simulated driving task.

OBJECTIVE: The aim of this study is to evaluate the effects of a seat-integrated mobilization system on motion activity, muscle stiffness and discomfort during prolonged driving. METHOD: During a 4.5-h driving task, motion activity, muscle stiffness and discomfort (measured subjectively and objectively) of long-haul truck drivers were determined and compared intra-individually in a test condition with mobilization (seat-integrated stimulation) and a control condition under standardized conditions in a simulated driving study (N = 16). RESULTS: In the experimental condition, participants showed a significantly increased motion activity and a reduced muscle stiffness compared to the control condition. Furthermore, discomfort occurred significantly more frequently in the control condition. CONCLUSION: The mobilization system increased motion activity and reduced discomfort as well as muscle stiffness. Therefore, it provides considerable potential to counteract negative effects of prolonged sitting and to promote truck driver's health.

Modulating the Nordic Hamstring Exercise From "Zero to Hero": A Stepwise Progression Explored in a High-Performance Athlete.

BACKGROUND: The Nordic hamstring exercise (NHE) is commonly implemented to selectively improve eccentric knee-flexor strength. However, the standard version of the exercise (leveled shanks, extended hip joint) is too strenuous for most individuals, whose muscle activity rapidly decreases at extended knee angles. Hitherto, a gradual approach to the exercise has been missing. In this exploratory case study, we investigated elite performance to introduce a stepwise progression to the NHE. OBJECTIVE: To determine the extent to which exercise modifications (shank inclination, additional load, hip flexion) altered NHE mechanics. DATA COLLECTION AND ANALYSIS: One male long jumper (age = 33 years, height = 171 cm, mass = 69 kg) with high-level expertise in the NHE performed 20 exercise variations. The corresponding kinematics, kinetics, and electromyographic activity of the biceps femoris long head (BFlh) and semitendinosus (ST) muscles were evaluated. RESULTS: Exercise variations demonstrated gradually increased peak moments from 69% (zigzag pose) to 154% (inclined bent single-legged version) versus a standard NHE. Shank inclination and additional load elicited small to moderate effects on peak moments, BFlh, and ST (0.24 ≤ d ≤ 0.72), whereas hip flexion largely affected all tested variables (2.80 ≤ d ≤ 6.66), especially muscle activity (BFlh = -63%; ST = -55% of maximal voluntary isometric contraction). COMMENTARY: These insights will help practitioners and scientists design multifaceted stepwise NHE progressions by creating differentiated stimuli that best match the strength capacities of individuals and address their specific needs.

Effects of the FIFA 11+ program on performance, biomechanical measures, and physiological responses: A systematic review.

BACKGROUND: The side effects of the FIFA 11+ program on performance have not been generally reviewed. The objective of this study was to synthesize the literature on the effects of the 11+ on players' performance. METHODS: Five online databases (PubMed, Scopus, ScienceDirect, Springer, and Google Scholar) were searched (from April 2006 to March 2022) using predefined keywords and sub-keywords. The potential references were primarily recorded through Endnote and imported to Covidence. Out of the 123 references screened by 2 blinded researchers through the software, 59 full texts were assessed for eligibility, 33 of which were ultimately included. The quality of the studies and the risk of bias were then assessed. Study ID, title, place, aim, design, start/end dates, population description, study criteria, statistical analysis, and outcomes were extracted. RESULTS: Studies were conducted on male and female players aged 10-32 years old. The quality of the studies was moderate to high, and except for unclear bias for blinding outcome assessment, the risk of bias for all domains was low. Long-term application of the 11+ improved most biomechanical measures and physiological responses except for lower extremity stability, ankle evertors time latency, ankle dorsiflexion, and proprioception. Conversely, the 11+ showed acute negative effects on physical performance compared to dynamic warm-ups and non-significant effects on technical abilities. CONCLUSION: Mid-to-long-term implementation of the 11+ improved the majority of biomechanical and a couple of physical measures but showed no effects on technical skills. Precaution must be observed for using the 11+ before competitions, as it could acutely decrease physical/technical performance. Given the contradictory nature of the literature, further studies should evaluate the short-to-mid-term effects of the 11+. Further studies are required to address ankle responses to the 11+ intervention.

Effects of the FIFA 11+ and a modified warm-up programme on injury prevention and performance improvement among youth male football players.

INTRODUCTION: The effects of the FIFA11+ programme (the 11+) on ankle and groin injuries and performance have remained questionable. The latter, particularly, has potentially reduced the implementation rate and applicability of the programme. This study aimed to evaluate the mid-to-long-term effects of the 11+ and a modified programme including football-specific exercises on injury prevention and performance improvement. MATERIALS AND METHODS: Three teams of the Iranian Youth League (division two) volunteered to participate in this study and were randomly assigned to two intervention groups (F11+; n = 29, M11+; n = 31) and a control group (n = 30). The F11+ followed the FIFA 11+ programme, whereas the M11+ performed modified exercises three times weekly as a warm-up protocol before training and competition through a football season. The control group carried out its routine warm-ups, including joggings, basic football drills, and static stretches, while having no injury prevention approaches. Lower extremity injuries, as well as exposure time for each player, were recorded. The football-specific performance was assessed using the Illinois Agility and Slalom Dribbling tests. ANOVA, Fisher Freeman Halton, and chi-square tests were used to analyze the data. RESULTS: Injury incidences differed significantly between groups (p = 0.02, C = 0.40), with M11+ reporting the lowest incidence. Significant differences between the pre- and posttest as well as differences between the groups for development over time were revealed for the Illinois agility and dribbling speed (p≤0.01). Both performance tests demonstrated a large time effect, as the effect sizes for time in agility and dribbling speed were 0.74 (CI = [0.66; 0.79]) and 0.86 (CI = [0.79; 0.87]), respectively. The effect size for the interaction can be categorized as medium, with 0.38 (CI = [0.25; 0.49]) for agility and 0.52 (CI = [0.40; 0.61]) for dribbling speed. M11+ showed the largest improvement in both. DISCUSSION: Mid-to-long-term application of a structured dynamic warm-up that integrates injury prevention and performance approaches may lower injury incidences and improve youth subelite players' performance. Although additional studies with larger samples are needed to prove the results of the current study, the amateur clubs/teams could integrate such twofold dynamic warm up into their routine training plan and benefit its advantages on injury prevention and performance improvement.

The dynamic control ratio masks bilateral asymmetries - A gender-specific analysis of 264 healthy and ACL-injured athletes.

Isokinetic strength tests are frequently applied to assess anterior cruciate ligament (ACL) rehabilitation processes. However, diverging methodologies cause misleading conclusions. This cross-sectional study evaluated the effects of gender (male vs. female), group (healthy vs. ACL-injured) and limb (dominant/healthy vs. non-dominant/ACL-injured) on thigh muscle balance of 138 female and 126 male athletes (50% ACL-injured, averagely 12.8 months after surgery). Balance was analysed between legs (bilateral asymmetry) and between concentric knee extensor (Qcon) and eccentric knee flexor strength (Hecc) (DCR = dynamic control ratio, DCRe = DCR at the equilibrium point). Females were generally 17-27% weaker than males. Independent of gender and time after surgery, ACL-injured athletes demonstrated bilateral asymmetries (7-20%) in peak (PMQcon, PMHecc) and DCRe moments (p ≤0.030; 0.018≤ηp2≤0.215). ACL-injured athletes' affected (24-28%) and unaffected (12-24%) hamstrings and quadriceps peak moments were significantly weaker compared to healthy athletes (p<0.001; 0.061≤ηp2≤0.362). The bilateral asymmetries of PMQcon significantly decreased from early to late self-reported rehabilitation phases (p<0.001; ηp2=0.158). Peak and DCRe moments detected bilateral asymmetries, whereas DCR revealed ~50% false negative attributions. This knowledge provides guidance for future design and interpretation of isokinetic tests.

Evaluation of the Functional Movement Screen (FMS) in Identifying Active Females Who are Prone to Injury. A Systematic Review.

BACKGROUND: The validity of the Functional Movement Screen (FMS) in identifying active females who are predisposed to injury has not been specifically reviewed. This study aims to synthesize the literature on the ability of the FMS to identify at-risk active females. METHODS: Six online databases, including PubMed, Medline, Web of Science, Science Direct, SPORTDiscus and Google Scholar, were searched for the period of April 2006 to September 2021. Out of the 61 potential references, 17 were reviewed in detail with respect to the inclusion criteria; ten were ultimately included. The risk of bias, applicability and level of the studies were then identified using the QUADAS-2 and a checklist for assessing methodological quality. The following data were obtained from the included studies: year of publication, title, study type, participants' demographic, sample size, FMS cutoff point, injury definition, statistical analyses used, FMS results and study level. RESULTS: Generally, the quality of eight studies was poor to moderate due to both small sample sizes and short follow-up periods. Except for a study on military members, all studies were carried out on team sports players. The overall bias of the studies was low, but there was an unclear amount of bias for participant selection. Two studies reported no predictive validity for the FMS, while three defended its predictive validity; the rest partially supported the FMS as a valid diagnostic tool. The reliability of the recommended cutoff point was confirmed, though cutoffs higher than 14 were significantly associated with the predictive ability of the FMS. CONCLUSION: Although the FMS is reliable for clinical practice, and the current literature shows promise regarding the predictive ability of the FMS among active females, concerns remain regarding its validity in identifying at-risk females. Given the lack of clarity in the literature on the use of the FMS in females, further well-organized studies with larger sample sizes and longer monitoring periods are highly recommended. The sensitivity and specificity of the recommended cutoff of ≤ 14 has considerably decreased , and higher cutoff values should be applied to increase the FMS predictive ability. Level of evidence The level of evidence was determined to be 2b.

Identification of Neuromuscular Performance Parameters as Risk Factors of Non-contact Injuries in Male Elite Youth Soccer Players: A Preliminary Study on 62 Players With 25 Non-contact Injuries.

Introduction: Elite youth soccer players suffer increasing numbers of injuries owing to constantly increasing physical demands. Deficits in neuromuscular performance may increase the risk of injury. Injury risk factors need to be identified and practical cut-off scores defined. Therefore, the purpose of the study was to assess neuromuscular performance parameters within a laboratory-based injury risk screening, to investigate their association with the risk of non-contact lower extremity injuries in elite youth soccer players, and to provide practice-relevant cut-off scores. Methods: Sixty-two elite youth soccer players (age: 17.2 ± 1.1 years) performed unilateral postural control exercises in different conditions, isokinetic tests of concentric and eccentric knee extension and knee flexion (60°/s), isometric tests of hip adduction and abduction, and isometric tests of trunk flexion, extension, lateral flexion and transversal rotation during the preseason period. Non-contact lower extremities injuries were documented throughout 10 months. Risk profiling was assessed using a multivariate approach utilizing a Decision Tree model [Classification and Regression Tree (CART) method]. Results: Twenty-five non-contact injuries were registered. The Decision Tree model selected the COP sway, the peak torque for knee flexion concentric, the functional knee ratio and the path of the platform in that hierarchical order as important neuromuscular performance parameters to discriminate between injured and non-injured players. The classification showed a sensitivity of 0.73 and a specificity of 0.91. The relative risk was calculated at 4.2, meaning that the risk of suffering an injury is four times greater for a player, who has been classified as injured by the Decision Tree model. Conclusion: Measuring static postural control, postural control under unstable condition and the strength of the thigh seem to enable a good indication of injury risk in elite youth soccer players. However, this finding has to be taken with caution due to a small number of injury cases. Nonetheless, these preliminary results may have practical implications for future directions in injury risk screening and in planning and developing customized training programs to counteract intrinsic injury risk factors in elite youth soccer players.

Null Effects of Different Amounts of Task Variation in Both Contextual Interference and Differential Learning Paradigms.

Various motor learning approaches, such as Schema Theory, Contextual Interference or Differential Learning, have proposed that varying the task during skill acquisition prompts superior learning. However, past research has mainly compared task variation in an experimental group to no task variation in a control group. Past research has more rarely compared specific intervention groups and/or addressed how varying amounts of task variation may affect skill learning. Our aim in this study was to compare motor learning of golf putting across four groups of novice golfers randomly assigned to these conditions: (a) a contextual interference group who putted at varied putting distances and had varied repetitive weekly schedule patterns, (b) a differential learning group who putted at multiple putting distances, putting amplitudes, and putting movements and had no repetitions, (c) an identical differential learning as in (b) except that participants also varied the putter, and (d) a control group who experienced no practice variations. Participants were 42 university students randomly divided into the four groups. All groups completed eight training sessions of 36 putts per session over four weeks, a pretest, posttest, two retention tests (one and three weeks after posttest) and transfer tasks (different floor). Average hit ratios and minimal distances to the hole were captured and analyzed by Scheirer-Ray-Hare test and Mann-Whitney post-hoc tests. Results showed improved hit ratios from pre- to post-test for all groups, and a stable retention performance for the variable training groups in contrast to the control group (p = .003). Transfer performance was low for all variable training groups with a significantly lower control group performance on transfer test 2 (p = .008). In conclusion, variable training schedules in all experimental groups benefited motor learning relative to controls, and differences in the amount of task variation between groups with variable training schedules did not affect skill acquisition.

Effects of a seat-integrated mobilization system during passive driver fatigue.

OBJECTIVE: The aim of this study is to evaluate the effectiveness of a seat-integrated mobilization system for maintaining vigilance under monotonous driving situations. METHOD: For this purpose, vigilance indicators were compared intra-individually in a test condition with mobilization (seat-integrated stimulation) and a placebo condition under standardized conditions in a real driving study (N = 31). During a monotonous two-hour ride, physiological (brain activity by the EEG alpha spindle rate), performance-based (reaction times) and subjective indicators were recorded. RESULTS: The necessary precondition for the paradigm of inducing fatigue through monotony was confirmed by a significant increase in the EEG alpha spindle rate and the subjective vigilance indices. The mobilization system had a significant impact on the most fatigue-sensitive parameter of the alpha spindle rate, whereas the other parameters of vigilance did not reflect a significant effect of mobilization. CONCLUSION: The Mobilization Seat is an effective measure to prevent drivers' fatigue during monotonous situations.

Comment on "Hurdle Clearance Detection and Spatiotemporal Analysis in 400 Meters Hurdles Races Using Shoe-Mounted Magnetic and Inertial Sensor".

The recent paper "Hurdle Clearance Detection and Spatiotemporal Analysis in 400 Meters Hurdles Races Using Shoe-Mounted Magnetic and Inertial Sensor" (Sensors 2020, 20, 354) proposes a wearable system based on a foot-worn miniature inertial measurement unit (MIMU) and different methods to detect hurdle clearance and to identify the leading leg during 400-m hurdle races. Furthermore, the presented system identifies changes in contact time, flight time, running speed, and step frequency throughout the race. In this comment, we discuss the original paper with a focus on the ecological validity and the applicability of MIMU systems for field-based settings, such as training or competition for elite athletes.

Acute physical exercise affected processing efficiency in an auditory attention task more than processing effectiveness.

Research on effects of acute physical exercise on performance in a concurrent cognitive task has generated equivocal evidence. Processing efficiency theory predicts that concurrent physical exercise can increase resource requirements for sustaining cognitive performance even when the level of performance is unaffected. This hypothesis was tested in a dual-task experiment. Sixty young adults worked on a primary auditory attention task and a secondary interval production task while cycling on a bicycle ergometer. Physical load (cycling) and cognitive load of the primary task were manipulated. Neither physical nor cognitive load affected primary task performance, but both factors interacted on secondary task performance. Sustaining primary task performance under increased physical and/or cognitive load increased resource consumption as indicated by decreased secondary task performance. Results demonstrated that physical exercise effects on cognition might be underestimated when only single task performance is the focus.

Identification of interindividual and intraindividual movement patterns in handball players of varying expertise levels.

The authors examined the movement patterns of 5 left-handed handball players (ranging from beginner to national level) who threw a handball to different sections of a goal as if a goalkeeper were present. The authors used time-continuous, 3-dimensional kinematic data to assess interindividual movement patterns and considered participants' intraindividual differences relative to different targets. Cluster analysis yielded the highest assignment rates for level of expertise; a mean of 92% of trials was correctly assessed. The authors observed an interaction with expertise for the intraindividual movement patterns. Variability in the novice throwers was increased, whereas (a) advanced throwers experienced a period of stability, and (b) the expert thrower's variability was increased. The results indicate that random variability characterizes novice motor performance, whereas active functional variability may exemplify expert motor performance.