Olaf Prieske

Neuromuscular and athletic performance following core strength training in elite youth soccer: Role of instability.

Cross‐sectional studies revealed that inclusion of unstable elements in core‐strengthening exercises produced increases in trunk muscle activity and thus potential extra stimuli to induce more pronounced performance enhancements in youth athletes. Thus, the purpose of the study was to investigate changes in neuromuscular and athletic performance following core strength training performed on unstable (CSTU) compared with stable surfaces (CSTS) in youth soccer players. Thirty‐nine male elite soccer players (age: 17 ± 1 years) were assigned to two groups performing a progressive core strength‐training program for 9 weeks (2–3 times/week) in addition to regular in‐season soccer training. CSTS group conducted core exercises on stable (i.e., floor, bench) and CSTU group on unstable (e.g., Thera‐Band® Stability Trainer, Togu© Swiss ball) surfaces. Measurements included tests for assessing trunk muscle strength/activation, countermovement jump height, sprint time, agility time, and kicking performance. Statistical analysis revealed significant main effects of test (pre vs post) for trunk extensor strength (5%, P < 0.05, d = 0.86), 10–20‐m sprint time (3%, P < 0.05, d = 2.56), and kicking performance (1%, P < 0.01, d = 1.28). No significant Group × test interactions were observed for any variable. In conclusion, trunk muscle strength, sprint, and kicking performance improved following CSTU and CSTS when conducted in combination with regular soccer training.

Effects and dose-response relationships of resistance training on physical performance in youth athletes: a systematic review and meta-analysis.

Objectives To quantify age, sex, sport and training type-specific effects of resistance training on physical performance, and to characterise dose–response relationships of resistance training parameters that could maximise gains in physical performance in youth athletes. Design Systematic review and meta-analysis of intervention studies. Data sources Studies were identified by systematic literature search in the databases PubMed and Web of Science (1985–2015). Weighted mean standardised mean differences (SMDwm) were calculated using random-effects models. Eligibility criteria for selecting studies Only studies with an active control group were included if these investigated the effects of resistance training in youth athletes (6–18 years) and tested at least one physical performance measure. Results 43 studies met the inclusion criteria. Our analyses revealed moderate effects of resistance training on muscle strength and vertical jump performance (SMDwm 0.8–1.09), and small effects on linear sprint, agility and sport-specific performance (SMDwm 0.58–0.75). Effects were moderated by sex and resistance training type. Independently computed dose–response relationships for resistance training parameters revealed that a training period of >23 weeks, 5 sets/exercise, 6–8 repetitions/set, a training intensity of 80–89% of 1 repetition maximum (RM), and 3–4 min rest between sets were most effective to improve muscle strength (SMDwm 2.09–3.40). Summary/conclusions Resistance training is an effective method to enhance muscle strength and jump performance in youth athletes, moderated by sex and resistance training type. Dose–response relationships for key training parameters indicate that youth coaches should primarily implement resistance training programmes with fewer repetitions and higher intensities to improve physical performance measures of youth athletes.

Effects of Resistance Training in Youth Athletes on Muscular Fitness and Athletic Performance: A Conceptual Model for Long-Term Athlete Development

During the stages of long-term athlete development (LTAD), resistance training (RT) is an important means for (i) stimulating athletic development, (ii) tolerating the demands of long-term training and competition, and (iii) inducing long-term health promoting effects that are robust over time and track into adulthood. However, there is a gap in the literature with regards to optimal RT methods during LTAD and how RT is linked to biological age. Thus, the aims of this scoping review were (i) to describe and discuss the effects of RT on muscular fitness and athletic performance in youth athletes, (ii) to introduce a conceptual model on how to appropriately implement different types of RT within LTAD stages, and (iii) to identify research gaps from the existing literature by deducing implications for future research. In general, RT produced small-to-moderate effects on muscular fitness and athletic performance in youth athletes with muscular strength showing the largest improvement. Free weight, complex, and plyometric training appear to be well-suited to improve muscular fitness and athletic performance. In addition, balance training appears to be an important preparatory (facilitating) training program during all stages of LTAD but particularly during the early stages. As youth athletes become more mature, specificity, and intensity of RT methods increase. This scoping review identified research gaps that are summarized in the following and that should be addressed in future studies: (i) to elucidate the influence of gender and biological age on the adaptive potential following RT in youth athletes (especially in females), (ii) to describe RT protocols in more detail (i.e., always report stress and strain-based parameters), and (iii) to examine neuromuscular and tendomuscular adaptations following RT in youth athletes.

The Role of Instability with Plyometric Training in Sub-elite Adolescent Soccer Players

The purpose of this study was to investigate the effects of plyometric training on stable (SPT) vs. highly unstable surfaces (IPT) on athletic performance in adolescent soccer players. 24 male sub-elite soccer players (age: 15±1 years) were assigned to 2 groups performing plyometric training for 8 weeks (2 sessions/week, 90 min each). The SPT group conducted plyometrics on stable and the IPT group on unstable surfaces. Tests included jump performance (countermovement jump [CMJ] height, drop jump [DJ] height, DJ performance index), sprint time, agility and balance. Statistical analysis revealed significant main effects of time for CMJ height (p<0.01, f=1.44), DJ height (p<0.01, f=0.62), DJ performance index (p<0.05, f=0.60), 0-10-m sprint time (p<0.05, f=0.58), agility (p<0.01, f=1.15) and balance (p<0.05, 0.46≤f≤1.36). Additionally, a Training group×Time interaction was found for CMJ height (p<0.01, f=0.66) in favor of the SPT group. Following 8 weeks of training, similar improvements in speed, agility and balance were observed in the IPT and SPT groups. However, the performance of IPT appears to be less effective for increasing CMJ height compared to SPT. It is thus recommended that coaches use SPT if the goal is to improve jump performance.

Effectiveness of Traditional Strength vs. Power Training on Muscle Strength, Power and Speed with Youth: A Systematic Review and Meta-Analysis

Numerous national associations and multiple reviews have documented the safety and efficacy of strength training for children and adolescents. The literature highlights the significant training-induced increases in strength associated with youth strength training. However, the effectiveness of youth strength training programs to improve power measures is not as clear. This discrepancy may be related to training and testing specificity. Most prior youth strength training programs emphasized lower intensity resistance with relatively slow movements. Since power activities typically involve higher intensity, explosive-like contractions with higher angular velocities (e.g., plyometrics), there is a conflict between the training medium and testing measures. This meta-analysis compared strength (e.g., training with resistance or body mass) and power training programs (e.g., plyometric training) on proxies of muscle strength, power, and speed. A systematic literature search using a Boolean Search Strategy was conducted in the electronic databases PubMed, SPORT Discus, Web of Science, and Google Scholar and revealed 652 hits. After perusal of title, abstract, and full text, 107 studies were eligible for inclusion in this systematic review and meta-analysis. The meta-analysis showed small to moderate magnitude changes for training specificity with jump measures. In other words, power training was more effective than strength training for improving youth jump height. For sprint measures, strength training was more effective than power training with youth. Furthermore, strength training exhibited consistently large magnitude changes to lower body strength measures, which contrasted with the generally trivial, small and moderate magnitude training improvements of power training upon lower body strength, sprint and jump measures, respectively. Maturity related inadequacies in eccentric strength and balance might influence the lack of training specificity with the unilateral landings and propulsions associated with sprinting. Based on this meta-analysis, strength training should be incorporated prior to power training in order to establish an adequate foundation of strength for power training activities.

Intrasession and intersession reliability in maximal and explosive isometric torque production of the elbow flexors

Abstract Prieske, O, Wick, D, and Granacher, U. Intrasession and intersession reliability in maximal and explosive isometric torque production of the elbow flexors. J Strength Cond Res 28(6): 1771–1777, 2014—The purpose of this study was to assess intrasession and intersession reliability of maximal and explosive isometric torque production of the elbow flexors and its respective neuromuscular activation pattern. Subjects (13 men, age: 24.8 ± 3.1 years, height: 1.9 ± 0.1 m, body mass: 83.7 ± 12.7 kg; and 6 women, age: 26.5 ± 1.4 years, height: 1.7 ± 0.1 m, body mass: 62.7 ± 7.0 kg) were tested and retested 2–7 days later performing unilateral maximal isometric elbow flexions. Absolute (coefficient of variation [CV], test-retest variability [TRV], Bland-Altman plots with 95% limits of agreement) and relative reliability statistics (intraclass correlation coefficient) were calculated for various mechanical (i.e., maximal isometric torque, rate of torque development, impulse) and electromyographical measures (i.e., mean average voltage) at different time intervals relative to onset of torque (i.e., 30, 50, 100, 200, 300, 400, 100–200 ms). Intraclass correlation coefficient values were ≥0.61 for all mechanical and electromyographical measures and time intervals indicating good to excellent intrasession and intersession reliability. Bland-Altman plots confirmed these findings by showing that only 0–2 (⩽13.3%) data points were beyond the limits of agreement. Regarding torque and electromyographic measures, CV (11.9–32.3%) and TRV (18.4–53.8%) values were high during the early intervals of torque development (⩽100 ms) indicating high variability. During the later intervals (>100 ms), lower CV (i.e., 5.0–29.9%) and TRV values (i.e., 5.4–34.6%) were observed indicating lower variability. The present study revealed that neuromuscular performance during explosive torque production of the elbow flexors is reproducible in time intervals >100 ms after onset of isometric actions, whereas during earlier time intervals variability is high.

Sex-Specific effects of surface instability on drop jump and landing biomechanics

This study investigated sex-specific effects of surface instability on kinetics and lower extremity kinematics during drop jumping and landing. Ground reaction forces as well as knee valgus and flexion angles were tested in 14 males (age: 23±2 years) and 14 females (age: 24±3 years) when jumping and landing on stable and unstable surfaces. Jump height was found to be significantly lower (9%, p<0.001) when drop jumps were performed on unstable vs. stable surface. Significantly higher peak ground reaction forces were observed when jumping was performed on unstable versus stable surfaces (5%, p=0.022). Regarding frontal plane kinematics during jumping and landing, knee valgus angles were higher on unstable compared to stable surfaces (19-32%, p<0.05). Additionally, at the onset of ground contact during landings, females showed higher knee valgus angles than males (222%, p=0.027). Sagittal plane kinematics indicated significantly smaller knee flexion angles (6-35%, p<0.05) when jumping and landing on unstable vs. stable surfaces. During drop jumps and landings, women showed smaller knee flexion angles at ground contact compared to men (27-33%, p<0.05). These findings imply that knee motion strategies were modified by surface instability and sex during drop jumps and landings.

Effects of fatigue and surface instability on neuromuscular performance during jumping

It has previously been shown that fatigue and unstable surfaces affect jump performance. However, the combination thereof is unresolved. Thus, the purpose of this study was to examine the effects of fatigue and surface instability on jump performance and leg muscle activity. Twenty elite volleyball players (18 ± 2 years) performed repetitive vertical double‐leg box jumps until failure. Before and after a fatigue protocol, jump performance (i.e., jump height) and electromyographic activity of selected lower limb muscles were recorded during drop jumps (DJs) and countermovement jumps (CMJs) on a force plate on stable and unstable surfaces (i.e., balance pad on top of force plate). Jump performance (3–7%; P < 0.05; 1.14 ≤ d ≤ 2.82), and muscle activity (2–27%; P < 0.05; 0.59 ≤ d ≤ 3.13) were lower following fatigue during DJs and CMJs, and on unstable compared with stable surfaces during DJs only (jump performance: 8%; P < 0.01; d = 1.90; muscle activity: 9–25%; P < 0.05; 1.08 ≤ d ≤ 2.54). No statistically significant interactions of fatigue by surface condition were observed. Our findings revealed that fatigue impairs neuromuscular performance during DJs and CMJs in elite volleyball players, whereas surface instability affects neuromuscular DJ performance only. Absent fatigue × surface interactions indicate that fatigue‐induced changes in jump performance are similar on stable and unstable surfaces in jump‐trained athletes.

Effects of drop height and surface instability on neuromuscular activation during drop jumps

The purpose of this study was to examine whether drop height‐induced changes in leg muscle activity during drop jumps (DJ) are additionally modulated by surface condition. Twenty‐four healthy participants (23.7 ± 1.8 years) performed DJs on a force plate on stable, unstable, and highly unstable surfaces using different drop heights (i.e., 20 cm, 40 cm, 60 cm). Electromyographic (EMG) activity of soleus (SOL), gastrocnemius (GM), tibialis anterior (TA) muscles and coactivation of TA/SOL and TA/GM were analyzed for time intervals 100 ms prior to ground contact (preactivation) and 30–60 ms after ground contact [short latency response (SLR)]. Increasing drop heights resulted in progressively increased SOL and GM activity during preactivation and SLR (P < 0.01; 1.01 ≤ d ≤ 5.34) while TA/SOL coactivation decreased (P < 0.05; 0.51 ≤ d ≤ 3.01). Increasing surface instability produced decreased activities during preactivation (GM) and SLR (GM, SOL) (P < 0.05; 1.36 ≤ d ≤ 4.30). Coactivation increased during SLR (P < 0.05; 1.50 ≤ d ≤ 2.58). A significant drop height × surface interaction was observed for SOL during SLR. Lower SOL activity was found on unstable compared to stable surfaces for drop heights ≥40 cm (P < 0.05; 1.25 ≤ d ≤ 2.12). Findings revealed that instability‐related changes in activity of selected leg muscles are minimally affected by drop height.

Tests for the Assessment of Sport-Specific Performance in Olympic Combat Sports: A Systematic Review With Practical Recommendations

The regular monitoring of physical fitness and sport-specific performance is important in elite sports to increase the likelihood of success in competition. This study aimed to systematically review and to critically appraise the methodological quality, validation data, and feasibility of the sport-specific performance assessment in Olympic combat sports like amateur boxing, fencing, judo, karate, taekwondo, and wrestling. A systematic search was conducted in the electronic databases PubMed, Google-Scholar, and Science-Direct up to October 2017. Studies in combat sports were included that reported validation data (e.g., reliability, validity, sensitivity) of sport-specific tests. Overall, 39 studies were eligible for inclusion in this review. The majority of studies (74%) contained sample sizes <30 subjects. Nearly, 1/3 of the reviewed studies lacked a sufficient description (e.g., anthropometrics, age, expertise level) of the included participants. Seventy-two percent of studies did not sufficiently report inclusion/exclusion criteria of their participants. In 62% of the included studies, the description and/or inclusion of a familiarization session (s) was either incomplete or not existent. Sixty-percent of studies did not report any details about the stability of testing conditions. Approximately half of the studies examined reliability measures of the included sport-specific tests (intraclass correlation coefficient [ICC] = 0.43–1.00). Content validity was addressed in all included studies, criterion validity (only the concurrent aspect of it) in approximately half of the studies with correlation coefficients ranging from r = −0.41 to 0.90. Construct validity was reported in 31% of the included studies and predictive validity in only one. Test sensitivity was addressed in 13% of the included studies. The majority of studies (64%) ignored and/or provided incomplete information on test feasibility and methodological limitations of the sport-specific test. In 28% of the included studies, insufficient information or a complete lack of information was provided in the respective field of the test application. Several methodological gaps exist in studies that used sport-specific performance tests in Olympic combat sports. Additional research should adopt more rigorous validation procedures in the application and description of sport-specific performance tests in Olympic combat sports.