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Acute adaptations and subsequent preservation of strength and speed measures following a Nordic hamstring curl intervention: a randomised controlled trial

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Abstract

This randomised controlled trial investigated changes in eccentric hamstring strength, 10m sprint speed, and change-of-direction (COD) performance immediately post Nordic hamstring curl (NHC) intervention and following a 3-week detraining period. Fourteen male team sports athletes were randomised to a do-as-usual control group (CG; n = 7) or to a NHC intervention group (NHC; n = 7). Isokinetic dynamometry at 180°/s evaluated eccentric hamstring strength immediately post-intervention as the primary outcome measure. Secondary outcomes included 10 m sprint time and COD. Each outcome was measured, pre, immediately post-intervention and following a 3-week detraining period. Immediately post-intervention significant group differences were observed in the NHC group for eccentric hamstring strength (31.81 Nm⁻¹ vs. 6.44 Nm⁻¹, P = 0.001), COD (−0.12 s vs. 0.20 s; P = 0.003) and sprint (- 0.06 s vs. 0.05 s; P = 0.024) performance. Performance improvements were maintained following a detraining period for COD (−0.11 s vs. 0.20 s; P = 0.014) and sprint (−0.05 s vs. 0.03 s, P = 0.031) but not eccentric hamstring strength (15.67 Nm⁻¹ vs. 6.44 Nm⁻¹, P = 0.145) These findings have important implications for training programmes designed to reduce hamstring injury incidence, whilst enhancing physical qualities critical to sport.

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... The Nordic hamstring curl (NHC) is an eccentric exercise often incorporated in HSI reduction programmes (Bahr et al., 2015;Mjølsnes et al., 2004). Efficacy of high volume NHC intervention adaptations have been reported in measures of eccentric knee flexor (KF) strength and muscle architecture for sub-elite (Alonso-Fernandez et al., 2018;Ishø et al., 2018;Siddle et al., 2019) and elite (Mendiguchia et al., 2020;Suarez-Arrones et al., 2019) male soccer players. However, elite soccer players have raised concerns regarding, fatigue, impaired performance, and injury risk because of high volume NHC training (Bahr et al., 2015). ...
... Three warm-up repetitions were performed at each speed. The dynamometer was set-up in accordance with previous literature (Siddle et al., 2019). Five maximal efforts were performed at each speed, with passive concentric knee flexion performed at 60°·s −1 between repetitions, and 60 s rest between each set. ...
... Fourteen (of 16) participants improved their COD performance post-intervention, 9 of which exceeded the MDD. These findings are consistent with previous research highlighting a 2.7-5.5% decrease in COD time following isolated (Siddle et al., 2019) andcombined NHC programmes (Tous-Fajardo et al., 2016) in sub-elite and elite male youth soccer players. Rapid changes of direction are vital for success in soccer, with players required to perform directional and speed changes that impose high metabolic and mechanical load demands (Tous-Fajardo et al., 2016), whilst a strong correlation has been identified between eccentric KF strength and COD performance (Paul et al., 2016). ...
Article
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Nordic hamstring curls (NHC) are a commonly used injury intervention method in amateur team sports. Seventeen elite male academy soccer players performed an 8-week low volume NHC programme. Pre-post intervention measures of isokinetic eccentric knee flexor (KF) strength, linear speed, COD performance, hamstring muscle thickness, pennation angle and fascicle length were recorded. No significant main effects were observed for measures of isokinetic KF strength (P ≥ 0.19), linear sprint speed (P ≥ 0.47) or hamstring muscle architecture (P ≥ 0.30). However, significance was noted for improved COD performance (P < 0.01; mean difference, -0.06, p = 0.001, 95% CI = 0.03 to 0.09; d = 0.80), exceeding the minimal detectable difference (MDD = 0.05 s). A low-volume NHC intervention may contribute to significant improvements in COD ability, independent of no significant changes in eccentric KF strength, linear sprint speed or muscle architectural properties in elite youth soccer players.
... [1][2][3] As the biarticularly working hamstrings possess a major role in locomotion, 4 Nordic Hamstring Exercise training also promotes sprint performance. [5][6][7] Within 4-to 10-weeks, NHE interventions elicited strength adaptations of moderate to large effect sizes. [8][9][10][11][12] Conversely, corresponding improvements in sprint performance were generally negligible to small [6][7][8][9] and independent of NHE-induced increased hamstring strength. ...
... [5][6][7] Within 4-to 10-weeks, NHE interventions elicited strength adaptations of moderate to large effect sizes. [8][9][10][11][12] Conversely, corresponding improvements in sprint performance were generally negligible to small [6][7][8][9] and independent of NHE-induced increased hamstring strength. 5 In contrast, NHE peak moments showed a significant, but moderate correlation to 20 m-sprint times (R 2 = 27%). ...
... 10 There is equivocal evidence about whether NHE-induced adaptations persist after 3-4 weeks of detraining 11 or not. 6,12 In contrast to traditional training which incorporates both concentric and eccentric muscle actions, eccentric-only training elicits long-lasting strength gains, especially if high intensities are implemented. 14,15 Depending on the stimuli and the athletes' performance level, the repeated bout effect lasts between several weeks up to 6 months. ...
Article
Full-text available
Nordic Hamstring Exercise (NHE) training improves eccentric hamstring strength and sprint performance. However, detraining causes rapid reductions of achieved adaptations. Furthermore, the transfer of improved hamstring capacity to swing phase mechanics of sprints is unknown. This longitudinal study aimed (1) to quantify NHE-induced adaptations by camera-based isokinetic assessments and sprint analyses, (2) to relate the magnitude of adaptations to the participants’ initial performance level, (3) to investigate the transferability to sprints, and (4) to determine strength preservations after three months. Twelve sprinters (21 y, 1.81 m, 74 kg) were analysed throughout 22 weeks. They performed maximal sprints and eccentric knee flexor and concentric knee extensor tests before and after a 4-week NHE training. Sprints and isokinetic tests were captured by ten and four high-speed cameras. The dynamic control ratio at the equilibrium point (DCRe) evaluated thigh muscle balance. High-intensity NHE training elicited significant improvements of hamstring function (p range: <0.001 to 0.011, d range: 0.44 to 1.14), thigh muscle balance (p<0.001, d range: 0.80 to 1.08) and hamstring-related parameters of swing phase mechanics (p range: <0.001 to 0.022, d range: 0.12 to 0.57). Sprint velocity demonstrated small increases (+1.4%, p<0.001, d=0.26). Adaptations of hamstring function and thigh muscle balance revealed moderate to strong transfers to improved sprint mechanics (p range: <0.001 to 0.048, R² range: 34% to 83%). The weakest participants demonstrated the highest adaptations of isokinetic parameters (p range: 0.003 to 0.023, R² range: 42% to 62%), whereas sprint mechanics showed no effect of initial performance level. Three months after the intervention, hamstring function (+6% to +14%) and thigh muscle balance (+8% to +10%) remained significantly enhanced (p<0.001, ƞp² range: 0.529 to 0.621). High-intensity NHE training induced sustained, improved hamstring function of sprinters, which can be transferred to swing phase mechanics of maximal sprints. The initial performance level, NHE training procedures and periodisation should be considered to optimize adaptations.
... Of these, seven articles were excluded: (three without a control arm (Gonzalo-Skok et al., 2017;Núñez et al., 2018;Sabido et al., 2019;Santos et al., 2010), two without an EOT arm (Coratella et al., 2018;Hoffman et al., 2005), and the remaining one with an intervention duration less than 4 weeks . In total, 11 studies met the selection criteria and were included in the qualitative synthesis (Bourgeois et al., 2017;Chaabene et al., 2020;Coratella et al., 2019;de Hoyo et al., , 2016Fiorilli et al., 2020;Lockie et al., 2014;Maroto-Izquierdo et al., 2017;Sanchez-Sanchez et al., 2019;Siddle et al., 2019;Tous-Fajardo et al., 2016) and 10 studies were included in meta-analysis (Bourgeois et al., 2017;Chaabene et al., 2020;Coratella et al., 2019;Fiorilli et al., 2020;Lockie et al., 2014;Maroto-Izquierdo et al., 2017;Sanchez-Sanchez et al., 2019;Siddle et al., 2019;Tous-Fajardo et al., 2016). Table 1 summarizes the basic characteristics of the 11 articles included in the review. ...
... Of these, seven articles were excluded: (three without a control arm (Gonzalo-Skok et al., 2017;Núñez et al., 2018;Sabido et al., 2019;Santos et al., 2010), two without an EOT arm (Coratella et al., 2018;Hoffman et al., 2005), and the remaining one with an intervention duration less than 4 weeks . In total, 11 studies met the selection criteria and were included in the qualitative synthesis (Bourgeois et al., 2017;Chaabene et al., 2020;Coratella et al., 2019;de Hoyo et al., , 2016Fiorilli et al., 2020;Lockie et al., 2014;Maroto-Izquierdo et al., 2017;Sanchez-Sanchez et al., 2019;Siddle et al., 2019;Tous-Fajardo et al., 2016) and 10 studies were included in meta-analysis (Bourgeois et al., 2017;Chaabene et al., 2020;Coratella et al., 2019;Fiorilli et al., 2020;Lockie et al., 2014;Maroto-Izquierdo et al., 2017;Sanchez-Sanchez et al., 2019;Siddle et al., 2019;Tous-Fajardo et al., 2016). Table 1 summarizes the basic characteristics of the 11 articles included in the review. ...
... Five studies recruited elite players (two elite handball players and three elite soccer players) (Chaabene et al., 2020;Fiorilli et al., 2020;De Hoyo et al., 2016;Maroto-Izquierdo et al., 2017;Tous-Fajardo et al., 2016). Five studies recruited amateur or semi-professional player: two recruited rugby players (Bourgeois et al., 2017;Siddle et al., 2019), two recruited combined team-sport players (Lockie et al., 2014;Sanchez-Sanchez et al., 2019), and one recruited amateur football players (Coratella et al., 2019). The remaining one study recruited physically active males . ...
Article
Full-text available
This study systematically reviewed and quantified evidence regarding the effectiveness of eccentric overload training (EOT) on change-of-direction speed (CODS) performance. A keyword search was performed in 30 April 2020 in eight electronic bibliographic databases: SPORTDiscus, PubMed, Web of Science, Academic Search Complete, Cochrane Library, Scopus, CINAHL and Google Scholar. A meta-analysis was conducted to estimate the pooled effect size of EOT interventions on CODS performance compared to the control group. Study heterogeneity was assessed by the I ² index. Publication bias was assessed by the Begg’s and Egger’s tests. Eleven studies, including nine randomized controlled trials, one randomized crossover trial, and one non-randomized controlled trial met the eligibility criteria and were included in the review. Time of overall change-of-direction task completion among the EOT group was 1.35 standard deviations (95% confidence interval [CI] = 0.18, 2.52) shorter than that in the control group. In conclusion, EOT was found effective in improving CODS performance compared to the control group. Future studies should adopt a randomized experimental design, recruit large and representative samples from professional team sports, and examine the effect of EOT on various measures of CODS performance among population subgroups.
... Los 11 estudios incluidos proporcionan un total de 14 grupos que realizaron entrenamiento excéntrico y que son objeto de análisis. Seis de los estudios incluidos presentaban un grupo experimental que realizó trabajo excéntrico y, además, un grupo alternativo, que trabajó de manera simultánea la fase excéntrica de distinta forma (Gonzalo-Skok et al., 2017;Nuñez et al., 2018;Sanchez-Sanchez et al., 2017), o un grupo control, que no realizó ningún tipo de entrenamiento de fuerza (Sabido, Hernández-Davó, Botella, Navarro, & Tous-Fajardo, 2017;Siddle et al., 2019). ...
... Principales efectos sobre la habilidad para cambiar de dirección Se detectaron un total de 9 estudios en los que se evaluaba el rendimiento sobre el COD (Coratella et al., 2019;Gonzalo-Skok et al., 2017;Maroto-Izquierdo et al., 2017;Nuñez et al., 2018;Raya-González et al., 2017;Sanchez-Sanchez et al., 2017;Siddle et al., 2019;Tous-Fajardo et al., 2016;Toyomura et al., 2018) de los cuáles, en dos casos no se proporcionaba información referente a los metros sobre los que se desarrollaba la prueba utilizada para evaluar dicha habilidad (Coratella et al., 2019;Maroto-Izquierdo et al., 2017). No obstante, ambos utilizaron la misma prueba para evaluar el rendimiento en el COD (la prueba T de agilidad). ...
... En esta revisión sistemática se refleja, tal y como se señala en la introducción, la capacidad para alcanzar velocidades muy altas en poca distancia de recorrido o, lo que es lo mismo, la capacidad para acelerar está directamente relacionada con la capacidad para realizar un óptimo COD. Pues existen varios casos en los que a la vez que se tienen lugar mejoras significativas en el esprint con una distancia a recorrer de 10 metros y, en la cual, se desarrolla la fase de aceleración, además se producen mejoras significativas en el COD (Siddle et al., 2019;Tous-Fajardo et al., 2016). ...
Article
Full-text available
The present systematic review aimed to review the state of the literature in relation to studies that have analysed the effects of an eccentric training program on change of direction (COD) and sprint performance in team-sports, and to explore what might be the most appropriate characteristics to achieve the greatest adaptations on performance. A search was conducted in different databases: PubMed, Scopus, SPORTDiscus and Web of Science, including articles published up to 12 February 2020. A total of 11 studies met the eligibility criteria. The sample of all the included studies was composed of healthy physically active male team-sports subjects, over 16 years old, with different level of practice. Results show that eccentric training may be an appropriate strategy to improve COD and sprint performance in team-sports. Specifically, applying the eccentric method for at least 5 weeks, with a training frequency of 2-3 days per week, could lead to the greatest improvements in COD. However, the heterogeneity of the training protocols does not allow us to determine which volume of training would be most suitable to promote improvements in COD. Likewise, applying eccentric training for at least 5 weeks, with a frequency of 1-3 days per week, with a volume of 1-4 series of 5-16 repetitions could favour improvements in sprint performance.
... [1][2][3] As the biarticularly working hamstrings possess a major role in locomotion, 4 Nordic Hamstring Exercise training also promotes sprint performance. [5][6][7] Within 4-to 10-weeks, NHE interventions elicited strength adaptations of moderate to large effect sizes. [8][9][10][11][12] Conversely, corresponding improvements in sprint performance were generally negligible to small [6][7][8][9] and independent of NHE-induced increased hamstring strength. ...
... [5][6][7] Within 4-to 10-weeks, NHE interventions elicited strength adaptations of moderate to large effect sizes. [8][9][10][11][12] Conversely, corresponding improvements in sprint performance were generally negligible to small [6][7][8][9] and independent of NHE-induced increased hamstring strength. 5 In contrast, NHE peak moments showed a significant, but moderate correlation to 20 m-sprint times (R 2 = 27%). ...
... 10 There is equivocal evidence about whether NHE-induced adaptations persist after 3-4 weeks of detraining 11 or not. 6,12 In contrast to traditional training which incorporates both concentric and eccentric muscle actions, eccentric-only training elicits long-lasting strength gains, especially if high intensities are implemented. 14,15 Depending on the stimuli and the athletes' performance level, the repeated bout effect lasts between several weeks up to 6 months. ...
Preprint
PURPOSE: Nordic Hamstring Exercise (NHE) training improves eccentric hamstring strength and sprint performance. However, detraining causes rapid reductions of achieved adaptations. Furthermore, the transfer of improved hamstring capacity to swing phase mechanics of sprints is unknown. This longitudinal study aimed (1) to quantify NHE-induced adaptations by camera-based isokinetic assessments and sprint analyses, (2) to relate the magnitude of adaptations to the participants’ initial performance level, (3) to investigate the transferability to sprints, and (4) to determine strength preservations after three months. METHODS: Twelve sprinters (21 y, 1.81 m, 74 kg) were analysed throughout 22 weeks. They performed maximal sprints and eccentric knee flexor (Hecc) and concentric knee extensor tests before and after a 4-week NHE training. Ten (sprints) and four (isokinetics) cameras captured all exercises. The dynamic control ratio at the equilibrium point (DCRe) evaluated thigh muscle balance. RESULTS: High-intensity NHE training elicited significant improvements of hamstring function (0.44≤d≤1.14), thigh muscle balance (0.80≤d≤1.08) and hamstring-related parameters of swing phase mechanics (0.12≤d≤0.57). Sprint velocity moderately increased (+1.4%, d=0.26). Adaptations of Hecc and DCRe revealed moderate to strong transfers to improved sprint mechanics (34%≤R²≤83%). Weakest participants demonstrated highest adaptations of isokinetic parameters (42%≤R²≤62%), whereas sprint mechanics showed no effect of initial performance level. Three months after the intervention, hamstring function and thigh muscle balance were unalteredly enhanced. CONCLUSIONS: High-intensity NHE training induced sustained, improved hamstring function of sprinters, which can be transferred to swing phase mechanics of maximal sprints. Initial performance level, NHE training procedures and periodisation should be borne in mind to optimize adaptations.
... Despite strong empirical evidence favoring the NHE for eccentric knee flexor strengthening [5][6][7][8][9], injury risk mitigation [2,3,[10][11][12][13][14][15][16][17], fascicle lengthening [5,7,8,[18][19][20][21][22][23], and performance enhancement of sprints [24][25][26][27][28][29][30] and jumps [28,29,[31][32][33][34], the exercise does not receive complete approval and appreciation by practitioners and scientists. This is particularly attributable to its challenging execution, its bilateral nature, its knee dominance, and its distinctive muscle activation patterns [34][35][36][37][38][39]. ...
... NHE assessments should present meaningful and comprehensive kinematic and kinetic data of supramaximal NHE performance [61]. It does not suffice to state that participants were instructed to oppose the increasing gravity-induced acceleration of their trunk for as long as possible by using their posterior thigh muscles as it is previously reported [12,13,24,32,37,39,41,90,114]. Instead, a quantification of how well participants fulfilled this task should be realized [40,41,43,71,82]. ...
Article
Full-text available
ABSTRACT: The objective of this scoping review is to assess Nordic Hamstring Exercise quality (ANHEQ) of assessments and interventions according to the ANHEQ rating scales and to present practical recommendations for the expedient design and reporting of future studies. A total of 71 Nordic Hamstring Exercise (NHE) assessments and 83 NHE interventions were selected from the data sources PubMed, Scopus, and SPORTDiscus. Research studies which were presented in peer-reviewed academic journals and implemented the NHE during laboratory-based assessments or multi-week interventions met the eligibility criteria. NHE assessments analyzed force (51%), muscle activation (41%), knee angle kinematics (38%), and bilateral symmetry (37%). NHE interventions lasted 4–8 weeks (56%) and implied an exercise volume of two sessions per week (66%) with two sets per session (41%) and ≥8 repetitions per set (39%). The total ANHEQ scores of the included NHE assessments and interventions were 5.0 ± 2.0 and 2.0 ± 2.0 (median ± interquartile range), respectively. The largest deficits became apparent for consequences of impaired technique (87% 0-point-scores for assessments) and kneeling height (94% 0-point-scores for interventions). The 0-point-scores were generally higher for interventions compared to assessments for rigid fixation (87% vs. 34%), knee position (83% vs. 48%), kneeling height (94% vs. 63%), and separate familiarization (75% vs. 61%). The single ANHEQ criteria, which received the highest score most frequently, were rigid fixation (66% of assessments) and compliance (33% of interventions). The quality of NHE assessments and interventions was generally ‘below average’ or rather ‘poor’. Both NHE assessments and interventions suffered from imprecise reporting or lacking information regarding NHE execution modalities and subsequent analyses. Based on the findings, this scoping review aggregates practical guidelines how to improve the design and reporting of future NHE-related research.
... Independiente de las diferentes distribuciones con las cuales se aplicaron ambos protocolos, podemos vislumbrar cuáles serían los volúmenes y densidades de entrenamiento adecuadas para conseguir mejorar el rendimiento. En la misma línea, se han reportado mejoras con volúmenes menores (115 repeticiones totales) en un periodo de 6 semanas (Siddle et al., 2018), que confirman la acepción respecto de las dosis mínimas necesarias para conseguir adaptaciones. Además, es interesante mencionar que en este estudio fueron valoradas tanto las respuestas agudas como crónicas, siendo estas últimas observables inclusive después de un periodo de desentrenamiento de tres semanas. ...
... Sin embargo, en este estudio, el tiempo para el sprint más rápido tan solo mostró mejoras para el grupo experimental (TE 0,64; p<0,05). Estos efectos son mayores a los reportados por Siddle et al., (2018), quien, después de 6 semanas de entrenamiento y 3 de desentrenamiento, evidenció la mejora de la velocidad en 10 mts con tamaños del efecto triviales (TE < 0,20) para el grupo intervenido. ...
Article
Full-text available
Introduction: The specialized literature has described the benefits of strength training on running speed. In the same way, stimulation of training based on eccentric contractions has been shown to be effective in improving this quality. Objective: To determine the effects of a training protocol based on the stretch-shortening cycle (SSC) and another on eccentric contractions (Nordic curl) on the running speed in 20 meters in adolescents from the Ñuble Region, Chile. Methodology: 42 school subjects were divided into experimental group (n = 22) and control group (n = 20). The training was developed for 6 weeks, with a frequency of 2 sessions/week, going from a volume of 8 to 32 repetitions of Nordic curl per session for the experimental group. The speed performance was evaluated in 20 meters. With photocells, the T Student's was applied to compare the pre- and post-intervention results, and the effect size (ES) was calculated. Results: Statistically significant differences were found (p <0.05) from the intervention in the experimental group (pre= 3,43 s. vs post= 3,15 s.), and a large ES (1,04). Conclusion: It is concluded that the eccentric training based on the application of Nordic Curl improves the performance of the running speed
... Independiente de las diferentes distribuciones con las cuales se aplicaron ambos protocolos, podemos vislumbrar cuáles serían los volúmenes y densidades de entrenamiento adecuadas para conseguir mejorar el rendimiento. En la misma línea, se han reportado mejoras con volúmenes menores (115 repeticiones totales) en un periodo de 6 semanas (Siddle et al., 2018), que confirman la acepción respecto de las dosis mínimas necesarias para conseguir adaptaciones. Además, es interesante mencionar que en este estudio fueron valoradas tanto las respuestas agudas como crónicas, siendo estas últimas observables inclusive después de un periodo de desentrenamiento de tres semanas. ...
... Sin embargo, en este estudio, el tiempo para el sprint más rápido tan solo mostró mejoras para el grupo experimental (TE 0,64; p<0,05). Estos efectos son mayores a los reportados por Siddle et al., (2018), quien, después de 6 semanas de entrenamiento y 3 de desentrenamiento, evidenció la mejora de la velocidad en 10 mts con tamaños del efecto triviales (TE < 0,20) para el grupo intervenido. ...
Article
Full-text available
Introducción: Los beneficios del entrenamiento de fuerza sobre la velocidad de carrera han sido descritos en la bibliografía especializada, sin embargo, la evidencia sobre la influencia de estímulos específicos, basados en contracciones excéntricas sobre la musculatura extensora de cadera, no han sido demostrados. Objetivo: Determinar los efectos de un protocolo de entrenamiento basado en contracciones excéntricas (curl nórdico) sobre la velocidad de carrera en 20 metros en adolescentes de la región de Ñuble, Chile. Metodología: 42 individuos escolares fueron divididos en grupo experimental (n=22) y grupo control (n=20). El entrenamiento se desarrolló durante 6 semanas, con una frecuencia de 2 sesiones/semana, pasando de un volumen de 8 a 32 repeticiones de curl nórdico por sesión para el grupo experimental. El rendimiento de velocidad fue evaluado en 20 metros. La prueba T de Student fue utilizada para comparar los resultados pre y post intervención y se calculó el tamaño del efecto (TE). Resultados: Se encontraron diferencias estadísticamente significativas (p<0,05) a partir de la intervención en el grupo experimental (pre= 3,43 s. vs post= 3,15 s.), y un TE grande (1,04). Conclusión: Se concluye que el entrenamiento excéntrico basado en la aplicación de Curl nórdico, mejora el rendimiento de la velocidad de carrera.
... Despite strong empirical evidence favoring the NHE for eccentric knee flexor strengthening [5][6][7][8][9], injury risk mitigation [2,3,[10][11][12][13][14][15][16][17], fascicle lengthening [5,7,8,[18][19][20][21][22][23], and performance enhancement of sprints [24][25][26][27][28][29][30] and jumps [28,29,[31][32][33][34], the exercise does not receive complete approval and appreciation by practitioners and scientists. This is particularly attributable to its challenging execution, its bilateral nature, its knee dominance, and its distinctive muscle activation patterns [34][35][36][37][38][39]. ...
... NHE assessments should present meaningful and comprehensive kinematic and kinetic data of supramaximal NHE performance [61]. It does not suffice to state that participants were instructed to oppose the increasing gravity-induced acceleration of their trunk for as long as possible by using their posterior thigh muscles as it is previously reported [12,13,24,32,37,39,41,90,114]. Instead, a quantification of how well participants fulfilled this task should be realized [40,41,43,71,82]. ...
Preprint
OBJECTIVE: Assessing Nordic Hamstring Exercise quality (ANHEQ) of assessments and interventions according to the ANHEQ rating scales and to present practical recommendations for the expedient design and reporting of future studies. DESIGN: Scoping review of 71 NHE assessments and 83 NHE interventions (12 of 131 full-text articles were applicable to both categories). DATA SOURCES: PubMed, MEDLINE and SPORTDiscus. ELIGIBILITY CRITERIA FOR SELECTING STUDIES: Research studies which were presented in peer-reviewed academic journals and implemented the NHE during laboratory-based assessments or multi-week interventions. RESULTS: The total ANHEQ scores of the analysed NHE assessments and interventions were 5.0±2.0 and 2.0±2.0 (median±IQR), respectively. Largest deficits became apparent for consequences of impaired technique (87% 0-point-scores for assessments) and kneeling height (94% 0-point-scores for interventions). The single ANHEQ criteria which received the highest score most frequently were rigid fixation (66% of assessments) and compliance (33% of interventions). CONCLUSIONS: The quality of NHE assessments and interventions was generally ‘below average’ or rather ‘poor’. Practitioners and scientists are encouraged to provide detailed information about their NHE modalities and about how their participants performed the exercise. The appropriate setup is suggested to be essential for best possible NHE performance and neuromuscular adaptations. NHE assessments should present comprehensive kinematic and kinetic data of supramaximal NHE performance, whereas NHE interventions should focus on exercise intensity and the implementation of facilitations. This scoping review aggregates practical guidelines how to improve the design and reporting of future NHE assessments and interventions to overcome the revealed limitations of current NHE-related evidences.
... The current investigation demonstrated a positive contribution of scaled NHS to speed in academy footballers (Table 3). Previous research has reported links to greater NHS and faster sprint 8,[27][28][29][30] and COD 30 performance. Markovic et al. 8 found that NHS accounted for 27% of the variance in 20m sprint performance in youth athletes; possibly, the result of architectural force generating and muscle volume 31 adaptations connected with NHS training. ...
... Limitations around single strength measures and correlational analysis could offer a potential reason for heterogeneity between our findings and those of previous research. 8,[27][28][29][30] Nordic hamstring exercises are viewed as supra-maximal, 32 suggesting a closer relationship with maximal strength and limited impact on sprinting when the time to express force is constrained to short intervals. Scaled NHS, CMJ-impulse, and hip-ADD all contributed to the COD performance. ...
Article
Full-text available
Conducting field-based strength assessments is embedded within football academy development processes. Yet, there is a limited understanding of how hip and groin strength assessments relate to vital game-based tasks such as sprinting and change of direction (COD) performance. Our aim was to explore field-based strength assessments and their relationships with both sprint and COD performance in male academy footballers. Participants (n = 146; age 14.2 ± 2.2 years; stature 166.3 ± 15.4 cm; body mass 55.6 ± 15.6 kg) performed maximal countermovement jump (CMJ), Nordic hamstring strength (NHS), isometric hip adductor (ADD)/abductor (ABD), 5m, 10m, 20m sprints and modified 505 agility test. All strength measures were allometrically scaled to account for body weight. Between limb differences were reported as imbalance scores. Principal component analysis reduced sprint and COD variables to a single ‘running ability’ component score. Scaled strength and imbalance, when controlled for age, were associated with ‘running ability’ (adjusted R² = 0.78, P < 0.001). Significant effects on ‘running ability’ included: age, CMJ-impulse, NHS and hip-ADD. When the sprint and COD variables were explored independently, age and CMJ-impulse featured in all sprint and COD models. For 10m and 20m sprint distances, hip-ADD emerged as a significant effect. Mean 505 performance was explained by age, CMJ-impulse, hip-ADD, but also with the addition of NHS. Our findings suggest that insight into the underpinning strength qualities of ‘running ability’ of academy footballers can be obtained from a suite of field-based tests.
... With regard to the measurement of ES KF in well-trained players, three studies evaluated eccentric strength using a isokinetic device at 60 • /s and 180 • /s, 18,38,42 whereas two studies 31,32 used the NordBord device. This is an important point to highlight because recently, Wiesinger et al. ...
... Note: (total n) = subjects (control + NHE group), (k) = number of studies, (*) 180 • /seg and 240 • /seg was evaluated in one study,38,42 respectively, however we did not include in the analysis because we had just one measure, n = 14. Probability of true-positive effect = see Supplementary File C for more detail. ...
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Objective The primary aim of this study was to investigate the effects of the Nordic Hamstring Exercise (NHE) on sprint performance (i.e., 5, 10 and 20 m) and explore associations between study characteristics and sprint outcomes in team sport players. Secondary aims were to 1) investigate the effects of the NHE on eccentric strength of knee flexors (ESKF) with categorical subgroup analysis to determine differences between recreationally, well-trained individuals and young athletes, 2) determine the relation between ESKF and sprint performance in team sport players, and (3) explore the effect of study characteristics (i.e., weekly volume, time duration and body mass) on ESKF. Methods Electronic databases were searched until the 20th of June 2020. 17 studies met the inclusion criteria. Random-effects meta-analyses were used to determine the mean difference (MD) or standardized change of mean difference (SCMD) between NHE and control group for sprint time and ESKF, respectively. Results NHE interventions showed a positive effect on sprint performance (-0.04 sec [-0.08, -0.01]). Sub-group meta-analyses indicated no significant differences in 5 and 20 m sprint performance (MDsprint(5m)= -0.02 sec [-0.10, 0.06]) and (MD sprint(20m)= -0.05 sec [-0.30, 0.19]), respectively. A significant difference was however found for 10 m sprint performance (MDsprint(10m)= -0.06 sec [-0.10, -0.01]). Meta-analysis on the effects of the NHE on ESKF showed a significant benefit of 0.83 SCMD [0.55, 1.12] in favour of the intervention group. Conclusions Studies with some concerns or high risk of bias show that training programs involving the NHE can have small beneficial effects on sprint performance in team sport players. Studies with some concerns or high risk of bias showed moderate beneficial effects on ESKF among a sample of relatively untrained individuals. However, for well-trained team sport players, the improvements in ESKF were less consistent, suggesting a higher training intensity during the NHE may be required to induce adaptations.
... Strength training of the hip extensors is crucial to the development of proficient movement in athletes with the concurrent "triple extension" of the hip, knee and ankle joints a primary characteristic of vital athletic movements such as running, jumping, and changing direction quickly (Lorenz, 2016). The Nordic Hamstring Exercise (NHE) has been shown to be an effective method with which to enhance a number of different metrics, driving positive adaptations in muscle strength (Drury et al., 2020), sprinting speed (Raya-González et al., 2021), change of direction speed (Siddle et al., 2019) and jump height (Váczi et al., 2022) in a variety of young athletic populations. In addition to the performance-enhancing benefits that the NHE offers, it is time-efficient, easy to perform and is a highly practicable exercise with no equipment required for execution, meaning it can be performed in a variety of different sporting settings (Bahr et al., 2015;Petersen et al., 2011). ...
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Purpose: This randomised controlled trial examined the effect of volume-equated programmes of Nordic hamstring exercise (NHE) training, executed at frequencies of 1- or 2-days per week, on explosive athletic tasks (30 m sprint, 15 m manoeuvrability and standing long jump [SLJ]) in male youth soccer players (mean age: 10.3 ± 0.5 years). Materials and methods: Players were divided into an experimental group (n=31) which was further subdivided into 1-day (n=16) and 2-days (n=15) per week training conditions, and a control group (n=14). Results: There were significant group-by-time interactions for 30-m sprint (p<0.001, d=0.6), SLJ (p=0.001, d=1.27) and 15 m manoeuvrability (p<0.001, d=0.61). The experimental group demonstrated small to moderate effect sizes in 30-m sprint (d=0.42, p=0.077), SLJ (d=0.97, p<0.001) and 15 m manoeuvrability (d=0.61, p<0.001). The control group showed small significant performance decrements or no change in these variables. There were no significant differences between the 1-day and 2-day training groups. In two of the three tests (30 m sprint, SLJ) the 2-day group demonstrated larger effect sizes. Conclusion: The NHE enhances explosive athletic task performance in prepubertal youth soccer players and there may be only small advantages to spreading training over two days instead of one.
... Isokinetic profiles are frequently used to identify the factors related to injuries of joints (Siddle et al., 2019;Torres-Banduc et al., 2021), including the knee (Croisier et al., 2008;Stastny et al., 2018). Indeed, the knee-joint isokinetic profile (KJIP) may predict injury risk using markers such as peak torque between agonist/antagonist muscles (i.e. ...
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Background: The knee-joint isokinetic profile (KJIP) injury risk factor may be modulated by chronological age, however, comparative data for elite male soccer players aged 25 years and older is lacking. Objective: To describe and compare the knee-joint isokinetic profile (KJIP) according to the chronological age of professional male soccer players. Method: In a cross-sectional study design, sixty-three soccer athletes from the first Chilean soccer division (A-series) were divided into younger and older groups (age ≤ 25 years; n = 35 and age > 25 years; n = 28, respectively). In both groups the IPKJ was assessed at 60°.s-1 in concentric mode. Results: The older group had lower extensor peak torque (p < .05). The younger group showed correlations between flexors peak torque and extensors mean power (p < .001). In the older group, flexors peak torque and flexors mean power were correlated. The flexors peak torque, total work, and mean power symmetric index (SI) exhibited values > 10 % for both groups. The extensors SI showed values > 10 % for mean power, although only in the older group. Conclusion: Several differences in the KJIP were noted between professional male soccer players aged ≤ 25 years and > 25 years. Current results offer injury prevention insights, discussed in the current manuscript.
... All strength and/or power training studies employed a pre-planned change of direction task as the outcome measure. Six training studies (23% of all training studies) reported a significant group by time interaction [3, 15,25,32,42,55], indicating that strength or power training significantly improved change of direction performance over time compared with a control group. Six strength and/or power training studies (23% of all training studies) reported a significant effect of time and no differences between training and control groups following the intervention [24,39,45,48,57,65]. ...
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Background Research focuses heavily upon the effect of strength and power training on change of direction performance. The objective of this scoping review is to highlight alternative approaches to training change of direction. Methods Four databases (Scopus, PubMed, Web of Science and SPORTDiscus) were searched with no date restrictions. To be included studies must (i) investigate change of direction performance following an intervention or investigate the relationships between variables of interest and change of direction performance; (ii) recruit participants > 18 years old; (iii) recruit participants involved in competitive sport. The majority of included studies investigated the effect of strength and/or power training, or, relationships between strength and/or power variables with change of direction performance. Results Despite fewer studies, alternative training methods resulted in greater improvements (compared with strength and/or power) in change of direction performance, with smaller training durations. Few studies included reactive agility as an outcome measure. Conclusion Despite much of the literature focusing on strength and/or power, there are alternative training modalities that demonstrate merit for improving change of direction performance. Future studies should investigate the effect of alternative training interventions on reactive agility performance, to provide a more valid indication of transfer to competition.
... Siddle et al. (Siddle et al., 2019)10m sprint speed, and change-of-direction (COD have tested the acute effect of Nordic hamstring exercise on speed and strength. The group consisted of 14 footballers, who were randomly divided into an intervention group (n-7) and a control group (n-7). ...
Article
Sprint is essential for successful sport performance. Acceleration is necessary for every position in football. The ability to successfully accelerate is also an important determinant for more carried gaming activities. The eccen- tric strength of the hamstrings is an important task in sprint. The aim of our study was to test the correlation between the 30 m sprint and the eccentric strength of the hamstring by NordBord. The sample consisted of 48 professional football players (23.15±4.78 yr.; 180.5±5.42 cm; 76.5±7.94 kg) of the highest Slovak football league. The correlation between 30 m performance and average eccentric hamstring strength has been -0.0826. The correlation suggests that the sprint speed and eccentric strength of the hamstrings have not been associated 0 (t=-0.5619; df=46; p=0.5769). Correlation between 30 m performance and AVG/kg was -0.1317, indicating that the correlation between average weight and speed was not been significant. The eccentric strength has not been associated with a higher speed in the 30-m sprint test. However, more intervention studies are warranted.
... Higher conKE strength has demonstrated relationships with superior jump and sprint performance (Hägglund and Waldén, 2015;Montalvo et al., 2019). Higher eccKF strength has also been associated with improved sprint performance due to the increased ability of the musculature to store and release kinetic energy (Siddle et al., 2019;Suarez-Arrones et al., 2019). However, the association between eccKF and conKE strength and dynamic control (DCR), defined as the ratio of eccKF:conKE peak torque, has yielded equivocal findings (Croisier et al., 2008;Lee et al., 2018;Van Dyk et al., 2017). ...
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The purpose of this study was to assess whether dynamic torque ratios (DCR) from isokinetic strength assessments of eccentric knee flexors (eccKF) and concentric knee extensors (conKE) display differences when stratified into specific angle-specific DCR (DCRAST) groups. Fifty-two professional female soccer players (age 21.30 ± 4.44 years; height 166.56 ± 5.17 cm; mass 61.55 ± 5.73 kg) from the English Women's Super League completed strength assessments of both lower limbs on an isokinetic dynamometer at 60°∙s-1. Angle-specific torque (AST) were used to calculate DCRAST to create sub-groups using clustering algorithms. The results identified for the dominant side that the Medium DCRAST group elicited significantly higher conKE AST when compared to Low and High DCRAST groups at increased knee extension (P ≤ 0.05). For the non-dominant side, the High DCRAST group had significantly higher and lower eccKF and conKE AST compared to the Low DCRAST group at increased knee extension (P ≤ 0.05). This study highlights that the inclusion of AST data may subsequently help practitioners to prescribe exercise that promotes strength increases at targeted joint angles. In turn, these approaches can be used to help reduce injury risk, identify rehabilitation responses and help inform return to play.
... For example, due to the high eccentric braking demands of the anterior chain during braking, coupled with the role of the passive structures within the MTU, it may be expected that positive structural and neuromuscular adaptations can be induced. Furthermore, recent advancements have highlighted the deterioration of isokinetic eccentric hamstring strength following a 3-week period of detraining, whereas linear (10 m) and COD speed (10 m approach, 180° pivot and 10 m exit) performance times were maintained [114]. This highlights a potential shift in the force-velocity characteristics underpinning these movements following a period of training cessation, which may be of concern if compensatory strategies are adopted [115]. ...
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High-intensity horizontal decelerations occur frequently in team sports and are typically performed to facilitate a reduction in momentum preceding a change of direction manoeuvre or following a sprinting action. The mechanical underpinnings of horizontal deceleration are unique compared to other high-intensity locomotive patterns (e.g., acceleration, maximal sprinting speed), and are characterised by a ground reaction force profile of high impact peaks and loading rates. The high mechanical loading conditions observed when performing rapid horizontal decelerations can lead to tissue damage and neuromuscular fatigue, which may diminish co-ordinative proficiency and an individual’s ability to skilfully dissipate braking loads. Furthermore, repetitive long-term deceleration loading cycles if not managed appropriately may propagate damage accumulation and offer an explanation for chronic aetiological consequences of the ‘mechanical fatigue failure’ phenomenon. Training strategies should look to enhance an athlete’s ability to skilfully dissipate braking loads, develop mechanically robust musculoskeletal structures, and ensure frequent high-intensity horizontal deceleration exposure in order to accustom individuals to the potentially damaging effects of intense decelerations that athletes will frequently perform in competition. Given the apparent importance of horizontal decelerations, in this Current Opinion article we provide considerations for sport science and medicine practitioners around the assessment, training and monitoring of horizontal deceleration. We feel these considerations could lead to new developments in injury-mitigation and physical development strategies in team sports.
... The clinical effect of this type of exercise is probably due to its effects on many of the previously mentioned risk factors for strain injury. Besides increasing hamstring strength (and thereby also improving hamstring to quadriceps strength ratio) it increases the length of fascicles and probably also eccentric hamstring strength capacity (Mjolsnes et al., 2004;Bourne et al., 2017;Ishøi et al., 2018;Presland et al., 2018;Ribeiro-Alvares et al., 2018;Duhig et al., 2019;Pollard et al., 2019;Siddle et al., 2019;Whyte et al., 2019;Medeiros et al., 2020). ...
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The incidence of strain injuries continues to be high in many popular sports, especially hamstring strain injuries in football, despite a documented important effect of eccentric exercise to prevent strains. Studies investigating the anatomical properties of these injuries in humans are sparse. The majority of strains are seen at the interface between muscle fibers and tendon: the myotendinous junction (MTJ). It has a unique morphology with a highly folded muscle membrane filled with invaginations of collagen fibrils from the tendon, establishing an increased area of force transmission between muscle and tendon. There is a very high rate of remodeling of the muscle cells approaching the MTJ, but little is known about how the tissue adapts to exercise and which structural changes heavy eccentric exercise may introduce. This review summarizes the current knowledge about the anatomy, composition and adaptability of the MTJ, and discusses reasons why strain injuries can be prevented by eccentric exercise.
... It is critical to choose strength training or an exercise that improves COD ability and COD deficit. For example, Nordic hamstring exercise improves COD ability [38] and plyometric exercises improve the COD performance [39]. ...
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Introduction: The aim of the study was to examine relationships between power of the lower limb and agility, speed, and change of direction (COD) deficit in professional female soccer players. Material and methods: Thirty-three elite Polish Extraliga league soccer players (aged 22 ±5 years; body height 166 ± 4 cm; body weight 58 ± 8 kg) performed the following fitness tests: lower limb muscle power (Leg Press, Half Squat, Counter Movement Jump), straight linear speed (SLS 20 m), and COD speed ( Zig-Zag test, COD deficit). Using the median value as a reference, the players were subdivided into two groups (n=17; n=16) according to their LP, HS 60% 1RM, CMJ (High values below median = stronger group and Low = weaker group ). Results: The COD deficit was calculated as the difference between the 20m speed and the Zig-Zag test. The stronger group was better than the weaker group in SLS 20m (p<0.05; ES=1.23; 0.83; 0.93), but in the Zig-Zag agility test, the difference in the results was not statistically significant (p>0.05; ES=0.48; 0.34; 0.34) and this affected the COD deficit, which was higher (p<0.05; ES=0.9; 0.73; 0.72). The most important finding was that the stronger group had a higher COD deficit and its improvement (reduction) occurs only if the results of the agility test are improved (through agility training) [Ydeficit All groups=0.10+0.87*20m - 0.83* Zig-Zag]. Increasing power (HS, LP) lead to the improvement in SLS p<0.05, not to COD abilities. Conclusion: This can be useful for coaches during agility training and to improve COD deficit in soccer players and women in general.
... Furthermore, strong relationships (r = −0.52) between eccentric hamstring strength and 20 m sprint performance were observed in highly-trained youth football players (Markovic et al., 2020). According to these relationships, intervention studies found greater 5 m to 30 m sprint performance in both amateur Mendiguchia et al., 2015;Siddle et al., 2019) and professional (Askling, Karlsson & Thorstensson, 2003) football players after a period of eccentrically focused strength training. In contrast, changes in eccentric hamstring strength were not associated with the changes in sprinting performance after a NHE intervention (17 weeks) in professional football players (Suarez-Arrones et al., 2019) compared to controls. ...
Article
The aims of this study were to investigate changes in selected performance measures during an off-season period, their association, and the potential role of age and previous hamstring injury in semi-professional and amateur football players. Seventy-four male players (age: 25 ± 4 years, stature: 178.0 ± 6.6 cm, body mass: 74.9 ± 8.1 kg) were assessed at the beginning and end of the off-season summer-period for sprint, change-of-direction performance and eccentric hamstring strength. Small to medium increases in sprint times were observed at 5 (d = 0.26, p = 0.057), 10 (d = 0.42, p < 0.001) and 30 m (d = 0.64, p < 0.001). Small (d = −0.23, p = 0.033) improvements were observed for COD performance, and no changes in eccentric hamstring strength (d = 0.10, p = 0.317). The changes in the outcomes were not affected by age (p = 0.449 to 0.928) or previous hamstring injury (p = 0.109 to 0.995). The impaired sprint performance was not related to changes in eccentric hamstring strength (r = −0.21 to 0.03, p = 0.213 to 0.856), instead, changes in COD performance were associated with changes in eccentric hamstring strength (r = −0.42, p = 0.008).
... In this sense, our results indicate a protective effect of the strength training and core-stability intervention at the short-term (Phase I; i.e., 10 weeks). However, no meaningful reduction was observed at long-term (i.e., Phase II) (Table 3), perhaps due to detraining effects (Siddle et al., 2019), since in Phase II the strength-training program was not applied. In this sense, short-duration (i.e., 10 weeks) injury prevention programs may be more effective at reducing the risk of muscle injury at the short-term, during its implementation. ...
Article
Purpose: The aim of this study was to examine the short and long-term effects of a simple strength training program on muscle injury prevention in soccer players. Methods: Twenty-seven U-19 elite male soccer players participated in the study. The investigation was conducted over two consecutive and similar seasons (e.g. the same staff, players, weekly training schedule), the first being the control and the second the experimental season. The strength program was carried out 2 times per week, for 10 weeks, during part of the preseason and in-season. Injury incidence and absence days were compared between both seasons, according to the injury rate ratio (IRR), with 95% CI and the Z test. Results: A lower number of total and hamstring injuries were recorded during the experimental (9 and 2, respectively) compared to the control (15 and 7, respectively) period. During the 10 weeks intervention period, the injury rate ratio (IRR) was lower in the experimental season than in the control season (IRR= 8.12; 95% CI: 1.00–66.03; effect size (ES) = 3.30, large). In addition, there was a decline in absence days per injury and in the number of absence days/1000 h (IRR= 2.44; 95% CI: 1.90–3.14; ES = 1.12) during the experimental season. Conclusion: The results of this study suggest that this simple strength-training program could reduce the muscle injury incidence during its application period in young soccer players.
... The remaining experimental groups displaying ES > 0.8 trained with Olympic lifts [42] and different squat variations, one study training in the Nordic hamstring exercise [71]. The study implementing the eccentric Nordic hamstring exercise increased COD performance by 2.46%, supporting statements in previous research regarding the importance of eccentric hamstring strength during the deceleration phase in COD [20]. ...
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Background: The ability to perform a rapid change of direction (COD) is a critical skill in numerous court- and field-based sports. The aim of this review is to investigate the effect of different physical training forms on COD performance. Methods: A systematic review of the literature was undertaken using the following databases: PubMed, SPORTDiscus and Google Scholar. Studies were eligible if they met the following criteria: (1) a COD test measuring performance before and after the training intervention, with specific description of the test in terms of length and number of changes in a direction with specified angles, (2) involve training intervention like plyometric, strength, sprint, specific COD training, or a combination of these training forms targeting the lower extremities, (3) the study had to state training background in terms of which sport they participated in and their competitive level and a detailed methodological description. Non-English articles were excluded. Percentage difference and effect sizes were calculated in order to compare the effects of different training interventions. Results: A range of studies performing plyometrics, strength, sprint, specific COD training, training with post-activation potentiation or a combination of these training forms were examined. The percentage of change and effect size (ES) were calculated. Seventy-four studies met the inclusion criteria, comprising 132 experimental groups and 1652 unique subjects. The review revealed no clear consensus on which training form is optimal to develop COD performance. All training forms resulted in an increase in performance from almost no ES to large ES. Conclusions: The results of the study indicate that COD ability is a specific skill, whereas the COD task, the sports require determines which training form is the most effective to develop COD ability. Training targeting improvement in COD performance should address the duration of the training in line with which energy system is utilized. The complexity of the COD task with respect to the individual athlete must be considered. Consequently, the number of changes in direction and the angles of the task are relevant when organizing training.
... The inclusion of exercises to increase eccentric strength of the knee flexor muscles is considered necessary to help reducing the injury risk of the hamstrings muscles [229]. Typically, these injuries have been suggested to occur during sprinting mainly in the late swing phase in which the hamstrings are highly activated at longer lengths and therefore creating high levels of stress on the MTU [230][231][232][233]. Exercises such as the Nordic hamstrings exercise (NHE), used to strengthen the knee flexor muscles eccentrically, is deemed important not only from both an injury prevention perspective but for performance too (e.g., sprinting and change of direction) [50][51][52]234]. Furthermore, the NHE has also been shown to positively influence performance measures such as sprint speed, change of direction, and jumping in both youth males and females [235,236]. ...
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The purpose of this narrative review is to discuss the role of eccentric resistance training in youth and how this training modality can be utilized within long-term physical development. Current literature on responses to eccentric exercise in youth has demonstrated that potential concerns, such as fatigue and muscle damage, compared to adults are not supported. Considering the importance of resistance training for youth athletes and the benefits of eccentric training in enhancing strength, power, speed, and resistance to injury, its inclusion throughout youth may be warranted. In this review we provide a brief overview of the physiological responses to exercise in youth with specific reference to the different responses to eccentric resistance training between children, adolescents, and adults. Thereafter, we discuss the importance of ensuring that force absorption qualities are trained throughout youth and how these may be influenced by growth and maturation. In particular, we propose practical methods on how eccentric resistance training methods can be implemented in youth via the inclusion of efficient landing mechanics, eccentric hamstrings strengthening and flywheel inertia training. This article proposes that the use of eccentric resistance training in youth should be considered a necessity to help develop both physical qualities that underpin sporting performance, as well as reducing injury risk. However, as with any other training modality implemented within youth, careful consideration should be given in accordance with an individual's maturity status, training history and technical competency as well as being underpinned by current long-term physical development guidelines.
Article
Objectives This study aims to verify the effectiveness of different weekly frequencies of Nordic hamstring exercise (NHE) on performance and factors associated with injuries in athletes. Methods Randomised clinical trial in adult male athletes practicing intermittent sports (e.g. soccer and/or rugby). Participants will be allocated into two groups, according to the weekly frequency of NHE practice: G1, submitted to one weekly NHE session; and G2, submitted to two weekly NHE sessions. The intensity and volume will be increased progressively (repetitions and series). Intervention period ranges 10 weeks during which the participants continue with sports training in their respective modalities. One week before (baseline) and one week after the intervention (endline), the athletes will perform the single-leg bridge test, sit and reach test, 10 m sprint test, vertical countermovement jump, and 180° change-of-direction test. Muscle soreness in the hamstrings and training load will be verified on each intervention day. Discussion The findings of this study may indicate the use of reduced training volumes, especially regarding the weekly frequency of NHE application in athletes, likely increasing their adherence. Trial registration Brazilian Registry of Clinical Trials (ReBEC): RBR-8mdbmcp (03/17/2021)
Article
Background: Hamstring injuries are common among athletes. Considering the potentially prolonged recovery and high rate of recurrence, effective methods of prevention and risk factor management are of great interest to athletes, trainers, coaches, and therapists, with substantial competitive and financial implications. Purpose: To systematically review the literature concerning evidence-based hamstring training and quantitatively assess the effectiveness of training programs in (1) reducing injury incidence and (2) managing injury risk factors. Study design: Systematic review and meta-analysis; Level of evidence, 1. Methods: A computerized search of MEDLINE, CINAHL, Cochrane Central Register of Controlled Trials, and SPORTDiscus with manual screening of selected reference lists was performed in October 2020. Randomized controlled trials investigating methods of hamstring injury prevention and risk factor management in recreational, semiprofessional, and professional adult athletes were included. Results: Of 2602 articles identified, 108 were included. Eccentric training reduced the incidence of hamstring injury by 56.8% to 70.0%. Concentric hamstring strength increased with eccentric (mean difference [MD], 14.29 N·m; 95% CI, 8.53-20.05 N·m), concentric, blood flow-restricted, whole-body vibration, heavy back squat, FIFA 11+ (Fédération Internationale de Football Association), and plyometric training methods, whereas eccentric strength benefited from eccentric (MD, 26.94 N·m; 95% CI, 15.59-38.30 N·m), concentric, and plyometric training. Static stretching produced greater flexibility gains (MD, 10.89°; 95% CI, 8.92°-12.86°) than proprioceptive neuromuscular facilitation (MD, 9.73°; 95% CI, 6.53°-12.93°) and dynamic stretching (MD, 6.25°; 95% CI, 2.84°-9.66°), although the effects of static techniques were more transient. Fascicle length increased with eccentric (MD, 0.90 cm; 95% CI, 0.53-1.27 cm) and sprint training and decreased with concentric training. Although the conventional hamstring/quadriceps (H/Q) ratio was unchanged (MD, 0.03; 95% CI, -0.01 to 0.06), the functional H/Q ratio significantly improved with eccentric training (MD, 0.10; 95% CI, 0.03-0.16). In addition, eccentric training reduced limb strength asymmetry, while H/Q ratio and flexibility imbalances were normalized via resistance training and static stretching. Conclusion: Several strategies exist to prevent hamstring injury and address known risk factors. Eccentric strengthening reduces injury incidence and improves hamstring strength, fascicle length, H/Q ratio, and limb asymmetry, while stretching-based interventions can be implemented to improve flexibility. These results provide valuable insights to athletes, trainers, coaches, and therapists seeking to optimize hamstring training and prevent injury. Keywords: hamstring flexibility; hamstring injury; hamstring strength; prevention; risk factor.
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Background: As participants who engage in CrossFit training and competition perform a large volume of high intensity overhead activities, injuries to the shoulder are one of the most common in this sport. Previous research in other sports has indicated that the isokinetic force power profile of the shoulder joint (IPSJ) rotator muscles may assist in the prediction of shoulder injury. Aim: Therefore, the objective of this study was to determine the IPSJ in males engaged in CrossFit training at different competitive levels. Methods: In a cross-sectional study design, participants (age, 24.1 ± 2.7 years) classified as 'beginner' (n = 6), 'intermediate' (n = 7) or 'advanced' (n = 9) provided informed consent to participate in this study. The IPSJ assessment involved rotational and diagonal movements, including internal and external shoulder rotator muscles, at both 180°.s-1 and 300°.s-1. The variables analysed were peak torque/body mass (%), mean power (W) and the external/internal peak torque/body mass ratio (%). A Kruskal-Wallis test was used to compare the IPSJ of the three groups, with Dunn's test used for post-hoc analysis. The alpha level was set at p < 0.05. Results: The IPSJ showed greater torque and power values in those who competed at the advanced level as compared to those at a lower competitive level (i.e. intermediate, beginner). This was observed mainly for the internal rotation and internal diagonal movements at both 180°.s-1 and 300°.s-1. However, such differences between competitive levels were, in general, absent for the external rotation and external diagonal movements. Moreover, the participants from the advanced competitive level exhibited an imbalance of peak torque between the muscles responsible for the external-internal rotational and external-internal diagonal movements of the shoulder (i.e. peak torque external/internal ratio <66%), particularly in the dominant shoulder. Conclusion: These findings suggest greater development of the shoulder internal rotators and a higher probability of shoulder injury in CrossFit athletes at the advanced competitive level. Based on these results, participants engaged in CrossFit training and competition may wish to increase the volume of training for the shoulder external rotator muscles to complement the large increases in shoulder internal rotator strength that occur as a part of their regular training regimes.
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Scheduling eccentric‐based injury prevention programs (IPP) during the common 6‐day micro‐cycle in Soccer is challenged by recovery and tapering phases. This study profiled muscle damage, neuromuscular performance, and perceptual responses to a lower‐limb eccentric‐based IPP administered 1 (MD+1) versus 3 days (MD+3) post‐match. 18 semi‐professional players were monitored daily during 3 in‐season 6‐day micro‐cycles, including weekly competitive fixtures. Capillary creatine kinase concentration (CK), posterior lower limb isometric peak force (PF), counter‐movement jump (CMJ) performance, and muscle soreness were assessed 24 h prior to match‐day (baseline), and every 24 h up to 120 h post‐match. The IPP consisted of lunges, single stiff leg dead‐lifts, single leg‐squats and Nordic hamstring exercises. Performing the IPP on MD+1 attenuated the decline in CK normally observed following match‐play (CON: 142%; MD+3: 166%; small differences). When IPP was delivered on MD+3, CK was higher versus CON and MD+1 trials on both MD+4 (MD+3: 260%; CON: 146%; MD+1: 151%; moderate differences) and MD+5 (MD+3: 209%; CON: 125%; MD+1: 127%; small differences). Soreness ratings were not exacerbated when the IPP was delivered on MD+1, but when prescribed on MD+3, hamstring soreness ratings remained higher on MD+4 and MD+5 (small differences). No between trial differences were observed for PF and CMJ. Administering the IPP in the middle of the micro‐cycle (MD+3) increased measures of muscle damage and soreness, which remained elevated on the day prior to the next match (MD+5). Accordingly, IPP should be scheduled early in the micro‐cycle, to avoid compromising preparation for the following match. This article is protected by copyright. All rights reserved.
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Strength training is a valuable component of hamstring strain injury prevention programmes; however, in recent years a significant body of work has emerged to suggest that the acute responses and chronic adaptations to training with different exercises are heterogeneous. Unfortunately, these research findings do not appear to have uniformly influenced clinical guidelines for exercise selection in hamstring injury prevention or rehabilitation programmes. The purpose of this review was to provide the practitioner with an evidence-base from which to prescribe strengthening exercises to mitigate the risk of hamstring injury. Several studies have established that eccentric knee flexor conditioning reduces the risk of hamstring strain injury when compliance is adequate. The benefits of this type of training are likely to be at least partly mediated by increases in biceps femoris long head fascicle length and improvements in eccentric knee flexor strength. Therefore, selecting exercises with a proven benefit on these variables should form the basis of effective injury prevention protocols. In addition, a growing body of work suggests that the patterns of hamstring muscle activation diverge significantly between different exercises. Typically, relatively higher levels of biceps femoris long head and semimembranosus activity have been observed during hip extension-oriented movements, whereas preferential semitendinosus and biceps femoris short head activation have been reported during knee flexion-oriented movements. These findings may have implications for targeting specific muscles in injury prevention programmes. An evidence-based approach to strength training for the prevention of hamstring strain injury should consider the impact of exercise selection on muscle activation, and the effect of training interventions on hamstring muscle architecture, morphology and function. Most importantly, practitioners should consider the effect of a strength training programme on known or proposed risk factors for hamstring injury.
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We aim to determine the influence of sports floorings and sports shoes on impact mechanics and performance during standardised jump tasks. Twenty-one male volunteers performed ankle jumps (four consecutive maximal bounds with very dynamic ankle movements) and multi-jumps (two consecutive maximal counter-movement jumps) on force plates using minimalist and cushioned shoes under 5 sports flooring (SF) conditions. The shock absorption properties of the SF, defined as the proportion of peak impact force absorbed by the tested flooring when compared with a concrete hard surface, were: SF0 = 0% (no flooring), SF1 = 19%, SF2 = 26%, SF3 = 37% and SF4 = 45%. Shoe and flooring effects were compared using 2x5 repeated-measures ANOVA with post-hoc Bonferroni-corrected comparisons. A significant interaction between SF and shoe conditions was found for VILR only (p = 0.003). In minimalist shoes, SF influenced Vertical Instantaneous Loading Rate (VILR) during ankle jumps (p = 0.006) and multi-jumps (p<0.001), in accordance with shock absorption properties. However, in cushioned shoes, SF influenced VILR during ankle jumps only (p<0.001). Contact Time was the only additional variable affected by SF, but only during multi-jumps in minimalist shoes (p = 0.037). Cushioned shoes induced lower VILR (p<0.001) and lower Contact Time (p≤0.002) during ankle jumps and multi-jumps compared to minimalist shoes. During ankle jumps, cushioned shoes induced greater Peak Vertical Ground Reaction Force (PVGRF, p = 0.002), greater Vertical Average Loading Rate (p<0.001), and lower eccentric (p = 0.008) and concentric (p = 0.004) work. During multi-jumps, PVGRF was lower (p<0.001) and jump height was higher (p<0.001) in cushioned compared to minimalist shoes. In conclusion, cushioning influenced impact forces during standardised jump tasks, whether it was provided by the shoes or the sports flooring. VILR is the variable that was the most affected.
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Background Late-stage rehabilitation programs often incorporate ‘sport-specific’ demands, but may not optimally simulate the in-game volume or intensity of such activities as sprinting, cutting, jumping, and lateral movement. Objective The aim of this review was to characterize, quantify, and compare straight-line running and multi-directional demands during sport competition. Data SourcesA systematic review of PubMed, CINAHL, SPORTDiscus, and Cochrane Central Register of Controlled Trials databases was conducted. Study Eligibility CriteriaStudies that reported time-motion analysis data on straight-line running, accelerations/decelerations, activity changes, jumping, cutting, or lateral movement over the course of an entire competition in a multi-directional sport (soccer, basketball, lacrosse, handball, field hockey, futsal, volleyball) were included. Study Appraisal and Synthesis Methods Data was organized based on sport, age level, and sex and descriptive statistics of the frequency, intensity, time, and volume of the characteristics of running and multi-directional demands were extracted from each study. ResultsEighty-one studies were included in the review (n = 47 soccer, n = 11 basketball, n = 9 handball, n = 7 field hockey, n = 3 futsal, n = 4 volleyball). Variability of sport demand data was found across sports, sexes, and age levels. Specifically, soccer and field hockey demanded the most volume of running, while basketball required the highest ratio of high-intensity running to sprinting. Athletes change activity between 500 and 3000 times over the course of a competition, or once every 2–4 s. Studies of soccer reported the most frequent cutting (up to 800 per game), while studies of basketball reported the highest frequency of lateral movement (up to 450 per game). Basketball (42–56 per game), handball (up to 90 per game), and volleyball (up to 35 per game) were found to require the most jumping. LimitationsThese data may provide an incomplete view of an athlete’s straight-line running load, considering that only competition and not practice data was provided. Conclusions Considerable variability exists in the demands of straight-line running and multi-directional demands across sports, competition levels, and sexes, indicating the need for sports medicine clinicians to design future rehabilitation programs with improved specificity (including the type of activity and dosage) to these demands.
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To assess traditional and novel isokinetic strength characteristics of the knee flexor (eccKF) and extensor (conKE) musculature, 26 professional football players completed bilateral conKE and eccKF contractions at angular velocities of 180, 270, and 60°·s-1. Values of peak torque (PT), angle of peak torque (APT), angle-specific torque (AST) analysed every 10° between 40 and 70°), functional range (FR), and dynamic control ratios (DCR) calculated from both the PT (DCRPT) and AST data (DCRAST) were analysed. The PT, APT, and FR data elicited a significant contraction*angular velocity interactions (P< 0.001). Significant main effects for contraction*angular velocity*angle and contraction*angular velocity*limb*angle interactions (P< 0.001) were identified for AST data. The DCRPT data elicited a significant main effect for angular velocity (P< 0.001) and limb (P= 0.018), whereas the DCRAST data was significantly different across angles (P< 0.001) and elicited a significant (P= 0.002) limb*angle interaction. Traditional methods and metrics utilised for isokinetic strength assessments in football may not be appropriate and/or sensitive enough to identify injury risk and, as such, practitioners should utilise the novel metrics proposed in the current study and conduct assessments across a range of joint angles and angular velocities.
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There are three major questions about return to play (RTP) after hamstring injuries: How should RTP be defined? Which medical criteria should support the RTP decision? And who should make the RTP decision? The study aimed to provide a clear RTP definition and medical criteria for RTP and to clarify RTP consultation and responsibilities after hamstring injury. The study used the Delphi procedure. The results of a systematic review were used as a starting point for the Delphi procedure. Fifty-eight experts in the field of hamstring injury management selected by 28 FIFA Medical Centres of Excellence worldwide participated. Each Delphi round consisted of a questionnaire, an analysis and an anonymised feedback report. After four Delphi rounds, with more than 83% response for each round, consensus was achieved that RTP should be defined as 'the moment a player has received criteria-based medical clearance and is mentally ready for full availability for match selection and/or full training'. The experts reached consensus on the following criteria to support the RTP decision: medical staff clearance, absence of pain on palpation, absence of pain during strength and flexibility testing, absence of pain during/after functional testing, similar hamstring flexibility, performance on field testing, and psychological readiness. It was also agreed that RTP decisions should be based on shared decision-making, primarily via consultation with the athlete, sports physician, physiotherapist, fitness trainer and team coach. The consensus regarding aspects of RTP should provide clarity and facilitate the assessment of when RTP is appropriate after hamstring injury, so as to avoid or reduce the risk of injury recurrence because of a premature RTP.
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Purpose: Hamstring strain injury is a frequent and serious injury in competitive and recreational sports. While Nordic hamstring (NH) eccentric strength training is an effective hamstring injury-prevention method, the protective mechanism of this exercise is not understood. Strength training increases muscle strength, but also alters muscle architecture and stiffness; all three factors may be associated with reducing muscle injuries. The purpose of this study was to examine the effects of NH eccentric strength training on hamstring muscle architecture, stiffness, and strength. Methods: Twenty healthy participants were randomly assigned to an eccentric training group or control group. Control participants performed static stretching, while experimental participants performed static stretching and NH training for 6 weeks. Pre- and post-intervention measurements included: hamstring muscle architecture and stiffness using ultrasound imaging and elastography, and maximal hamstring strength measured on a dynamometer. Results: The experimental group, but not the control group, increased volume (131.5 vs. 145.2 cm(3), p < 0.001) and physiological cross-sectional area (16.1 vs. 18.1 cm(2), p = 0.032). There were no significant changes to muscle fascicle length, stiffness, or eccentric hamstring strength. Conclusions: The NH intervention was an effective training method for muscle hypertrophy, but, contrary to common literature findings for other modes of eccentric training, did not increase fascicle length. The data suggest that the mechanism behind NH eccentric strength training mitigating hamstring injury risk could be increasing volume rather than increasing muscle length. Future research is, therefore, warranted to determine if muscle hypertrophy induced by NH training lowers future hamstring strain injury risk.
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Background and Purpose: Hamstring injuries are common in sports with sprinting demands, kicking, and sudden accelerations. Rehabilitation programs aimed at the prevention of future hamstring injuries have been recommended. This study examined if Nordic hamstring (NH) exercises decreased injury rates, increased sprinting speed, and increased hamstring and quadriceps muscle strength among semi-professional soccer players. Methods: A convenience sample of level 3 and 4 male soccer players from Norway (ages 18-39) participated in the study. Participants were randomly divided into either a control group (usual warm-up exercises) or a NH group (usual warm-up plus NH exercises). Injury data was collected on 119 players for 10 months. Twenty-seven participants were evaluated twice over the same period on sprint speed, eccentric and isometric hamstring strength, and concentric hamstring and quadriceps strength. Independent t-tests compared changes in strength and speed between the control and NH groups. Paired t-tests analyzed within group changes. Statistical significance was set at P < 0.05. Findings: There was a significant difference in the number of injuries between the control (6 injuries) and NH (zero injuries) groups. No significant changes in strength or sprint speed were found between the groups. The NH group experienced a statistically significant decrease in speed, during the first 10 m of sprint testing. In addition, both groups had a significant decline in the eccentric total work of the hamstrings. Clinical Relevance: Incorporation of NH exercise protocol into regular practice sessions may be effective in reducing the number of hamstring injuries in soccer players.
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ABSTRACT: The Nordic Hamstring Exercise (NHE) is effective for selective hamstring strengthening to improve muscle balance between knee flexors and extensors. The purpose of this study (within subject design of repeated measures) was to determine the effects of a standardized 4-week NHE training on thigh strength and balance with concomitant kinetic and kinematic monitoring. Sixteen male sprinters (22 years, 181 cm, 76 kg) performed a standardised 4-week NHE training consisting of three sessions per week (each 3 x 3 repetitions). Six rope-assisted and six unassisted sessions were performed targeting at a constant knee extension angular velocity of ~15°/s across a ~90-100° knee joint range of motion. Kinetic (peak and mean moment, impulse) and kinematic parameters (e.g., ROM to downward acceleration, ROMDWA ) were recorded during selected sessions. Unilateral isokinetic tests of concentric and eccentric knee flexors and extensors quantified muscle group-, contaction mode- and velocity-specific training adaptations. Peak moments and contractional work demonstrated strong interactions of time with muscle group, contraction modes and angular velocities (η²>0.150). NHE training increased eccentric hamstring strength by 6-14% as well as thigh muscle balance with biggest adaptations at 150°/s two weeks after NHE training. Throughout the training period, significant increases (p<0.001) of peak (η²=0.828) and mean moments (η²=0.611) became apparent, whereas the impulse and the ROMDWA of unassisted NHE repetitions remained unchanged (p>0.05). A 4-week NHE training significantly strengthened the hamstrings and improved muscle balance between knee flexors and extensors. Despite the slow training velocity, biggest adaptations emerged at the highest velocity two weeks after training ended.
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Background: High-quality, evidence-based orthopaedic care relies on the generation and translation of robust research evidence. The Fragility Index is a novel method for evaluating the robustness of statistically significant findings from randomized controlled trials (RCTs). It is defined as the minimum number of patients in 1 arm of a trial that would have to change status from a nonevent to an event to alter the results of the trial from statistically significant to nonsignificant. Purpose: To calculate the Fragility Index of statistically significant results from clinical trials in sports medicine and arthroscopic surgery to characterize the robustness of the RCTs in these fields. Methods: A search was conducted in Medline, EMBASE, and PubMed for RCTs related to sports medicine and arthroscopic surgery from January 1, 2005, to October 30, 2015. Two reviewers independently assessed titles and abstracts for study eligibility, performed data extraction, and assessed risk of bias. The Fragility Index was calculated using the Fisher exact test for all statistically significant dichotomous outcomes from parallel-group RCTs. Bivariate correlation was performed to evaluate associations between the Fragility Index and trial characteristics. Results: A total of 48 RCTs were included. The median sample size was 64 (interquartile range [IQR], 48.5-89.5), and the median total number of outcome events was 19 (IQR, 10-27). The median Fragility Index was 2 (IQR, 1-2.8), meaning that changing 2 patients from a nonevent to an event in the treatment arm changed the result to a statistically nonsignificant result, or P ≥ .05. Conclusion: Most statistically significant RCTs in sports medicine and arthroscopic surgery are not robust because their statistical significance can be reversed by changing the outcome status on only a few patients in 1 treatment group. Future work is required to determine whether routine reporting of the Fragility Index enhances clinicians' ability to detect trial results that should be viewed cautiously.
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We have previously argued that there may actually be no significant eccentric, but rather predominantly an isometric action of the hamstring muscle fibres during the swing phase of high-speed running when the attachment points of the hamstrings are moving apart. Based on this we suggested that isometric rather than eccentric exercises are a more specific way of conditioning the hamstrings for high-speed running. In this review we argue that some of the presumed beneficial adaptations following eccentric training may actually not be related to the eccentric muscle fibre action, but to other factors such as exercise intensity. Furthermore, we discuss several disadvantages associated with commonly used eccentric hamstring exercises. Subsequently, we argue that high-intensity isometric exercises in which the series elastic element stretches and recoils may be equally or even more effective at conditioning the hamstrings for high-speed running, since they also avoid some of the negative side effects associated with eccentric training. We provide several criteria that exercises should fulfil to effectively condition the hamstrings for high-speed running. Adherence to these criteria will guarantee specificity with regards to hamstrings functioning during running. Practical examples of isometric exercises that likely meet several criteria are provided.
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Background Hamstring injuries are among the most common non-contact injuries in sports. The Nordic hamstring (NH) exercise has been shown to decrease risk by increasing eccentric hamstring strength. Objective The purpose of this systematic review and meta-analysis was to investigate the effectiveness of the injury prevention programs that included the NH exercise on reducing hamstring injury rates while factoring in athlete workload. Methods Two researchers independently searched for eligible studies using the following databases: the Cochrane Central Register of Controlled Trials via OvidSP, AMED (Allied and Complementary Medicine) via OvidSP, EMBASE, PubMed, MEDLINE, SPORTDiscus, Web of Science, CINAHL and AusSportMed, from inception to December 2015. The keyword domains used during the search were Nordic, hamstring, injury prevention programs, sports and variations of these keywords. The initial search resulted in 3242 articles which were filtered to five articles that met the inclusion criteria. The main inclusion criteria were randomized controlled trials or interventional studies on use of an injury prevention program that included the NH exercise while the primary outcome was hamstring injury rate. Extracted data were subjected to meta-analysis using a random effects model. ResultsThe pooled results based on total injuries per 1000 h of exposure showed that programs that included the NH exercise had a statistically significant reduction in hamstring injury risk ratio [IRR] of 0.490 (95 % confidence interval [CI] 0.291–0.827, p = 0.008). Teams using injury prevention programs that included the NH exercise reduced hamstring injury rates up to 51 % in the long term compared with the teams that did not use any injury prevention measures. Conclusions This systematic review and meta-analysis demonstrates that injury prevention programs that include NH exercises decrease the risk of hamstring injuries among soccer players. A protocol was registered in the International Prospective Register of Systematic Reviews, PROSPERO (CRD42015019912).
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Background Resistance training is an integral component of physical preparation for athletes. A growing body of evidence indicates that eccentric strength training methods induce novel stimuli for neuromuscular adaptations. Objective The purpose of this systematic review was to determine the effects of eccentric training in comparison to concentric-only or traditional (i.e. constrained by concentric strength) resistance training. Methods Searches were performed using the electronic databases MEDLINE via EBSCO, PubMed and SPORTDiscus via EBSCO. Full journal articles investigating the long-term (≥4 weeks) effects of eccentric training in healthy (absence of injury or illness during the 4 weeks preceding the training intervention), adult (17–35 years), human participants were selected for the systematic review. A total of 40 studies conformed to these criteria. ResultsEccentric training elicits greater improvements in muscle strength, although in a largely mode-specific manner. Superior enhancements in power and stretch-shortening cycle (SSC) function have also been reported. Eccentric training is at least as effective as other modalities in increasing muscle cross-sectional area (CSA), while the pattern of hypertrophy appears nuanced and increased CSA may occur longitudinally within muscle (i.e. the addition of sarcomeres in series). There appears to be a preferential increase in the size of type II muscle fibres and the potential to exert a unique effect upon fibre type transitions. Qualitative and quantitative changes in tendon tissue that may be related to the magnitude of strain imposed have also been reported with eccentric training. Conclusions Eccentric training is a potent stimulus for enhancements in muscle mechanical function, and muscle-tendon unit (MTU) morphological and architectural adaptations. The inclusion of eccentric loads not constrained by concentric strength appears to be superior to traditional resistance training in improving variables associated with strength, power and speed performance.
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Most common preventive eccentric-based exercises, such as Nordic hamstring do not include any hip flexion. So, the elongation stress reached is lower than during the late swing phase of sprinting. The aim of this study was to assess the evolution of hamstring architectural (fascicle length and pennation angle) and functional (concentric and eccentric optimum angles and concentric and eccentric peak torques) parameters following a 3-week eccentric resistance program performed at long (LML) versus short muscle length (SML). Both groups performed eight sessions of 3-5x8 slow maximal eccentric knee extensions on an isokinetic dynamometer: the SML group at 0° and the LML group at 80° of hip flexion. Architectural parameters were measured using ultrasound imaging and functional parameters using the isokinetic dynamometer. The fascicle length increased by 4.9% (p
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The study evaluated the effect of transcranial direct current stimulation (tDCS) applied over prefrontal cortex on the oxygen uptake (V˙ O 2 ) at rest and during post-exercise recovery. The V˙ O 2 was assessed in eleven healthy subjects before, during tDCS (sham or anodal tDCS, 2 mA, 20 min), and 30-min following isocaloric aerobic exercise (~200 kcal). During tDCS, no changes were observed on V˙ O 2 compared to baseline (P=0.95) and sham condition (P=0.85). The association between isocaloric exercise and anodal tDCS increased the V˙ O 2 throughout 30-min recovery compared to sham condition (P 2 and energy expenditure at least for 30-min of recovery.
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Purpose: To investigate the kinematic and muscle activation adaptations during performance of the Nordic hamstring exercise (NHE) to a 6-week eccentric hamstring training programme using the NHE as the sole mode of exercise. Methods: Twenty-nine healthy males were randomly allocated to a control (CG) or intervention (IG) group. The IG participated in a 6-week eccentric hamstring exercise programme using the NHE. Results: The findings of the present study were that a 6-week eccentric hamstring training programme improved eccentric hamstring muscle strength (202.4 vs. 177.4 nm, p = 0.0002, Cohen's d = 0.97) and optimized kinematic (longer control of the forward fall component of the NHE, 68.1° vs. 73.7°, p = 0.022, Cohen's d = 0.90) and neuromuscular parameters (increased electromyographic activity of the hamstrings, 83.2 vs. 56.6 % and 92.0 vs. 54.2 %, p < 0.05, Cohen's d > 1.25) associated with NHE performance. Conclusion: This study provides some insight into potential mechanisms by which an eccentric hamstring exercise programme utilizing the NHE as the mode of exercise may result in an improvement in hamstring muscle control during eccentric contractions.
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Recent literature supports the importance of horizontal ground reaction force (GRF) production for sprint acceleration performance. Modeling and clinical studies have shown that the hip extensors are very likely contributors to sprint acceleration performance. We experimentally tested the role of the hip extensors in horizontal GRF production during short, maximal, treadmill sprint accelerations. Torque capabilities of the knee and hip extensors and flexors were assessed using an isokinetic dynamometer in 14 males familiar with sprint running. Then, during 6-s sprints on an instrumented motorized treadmill, horizontal and vertical GRF were synchronized with electromyographic (EMG) activity of the vastus lateralis, rectus femoris, biceps femoris, and gluteus maximus averaged over the first half of support, entire support, entire swing and end-of-swing phases. No significant correlations were found between isokinetic or EMG variables and horizontal GRF. Multiple linear regression analysis showed a significant relationship (P = 0.024) between horizontal GRF and the combination of biceps femoris EMG activity during the end of the swing and the knee flexors eccentric peak torque. In conclusion, subjects who produced the greatest amount of horizontal force were both able to highly activate their hamstring muscles just before ground contact and present high eccentric hamstring peak torque capability.
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Background/aim: To investigate the role of eccentric knee flexor strength, between-limb imbalance and biceps femoris long head (BFlh) fascicle length on the risk of future hamstring strain injury (HSI). Methods: Elite soccer players (n=152) from eight different teams participated. Eccentric knee flexor strength during the Nordic hamstring exercise and BFlh fascicle length were assessed at the beginning of preseason. The occurrences of HSIs following this were recorded by the team medical staff. Relative risk (RR) was determined for univariate data, and logistic regression was employed for multivariate data. Results: Twenty seven new HSIs were reported. Eccentric knee flexor strength below 337 N (RR=4.4; 95% CI 1.1 to 17.5) and possessing BFlh fascicles shorter than 10.56 cm (RR=4.1; 95% CI 1.9 to 8.7) significantly increased the risk of a HSI. Multivariate logistic regression revealed significant effects when combinations of age, history of HSI, eccentric knee flexor strength and BFlh fascicle length were explored. From these analyses the likelihood of a future HSI in older athletes or those with a HSI history was reduced if high levels of eccentric knee flexor strength and longer BFlh fascicles were present. Conclusions: The presence of short BFlh fascicles and low levels of eccentric knee flexor strength in elite soccer players increases the risk of future HSI. The greater risk of a future HSI in older players or those with a previous HSI is reduced when they have longer BFlh fascicles and high levels of eccentric strength.
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BACKGROUND: The Fédération Internationale de Football Association (FIFA) 11+ program has been shown to be an effective injury prevention program in the female soccer cohort, but there is a paucity of research to demonstrate its efficacy in the male population. HYPOTHESIS: To examine the efficacy of the FIFA 11+ program in men's collegiate United States National Collegiate Athletic Association (NCAA) Division I and Division II soccer. STUDY DESIGN: Randomized controlled trial; Level of evidence, 1. METHODS: Before the commencement of the fall 2012 season, every NCAA Division I and Division II men's collegiate soccer team (N = 396) was solicited to participate in this research study. Human ethics review board approval was obtained through Quorum Review IRB. Sixty-five teams were randomized: 34 to the control group (CG; 850 players) and 31 to the intervention group (IG; 675 players). Four teams in the IG did not complete the study, reducing the number for analysis to 61. The FIFA 11+ injury prevention program served as the intervention and was utilized weekly. Athlete-exposures (AEs), compliance, and injury data were recorded using a secure Internet-based system. RESULTS: In the CG, 665 injuries (mean ± SD, 19.56 ± 11.01) were reported for 34 teams, which corresponded to an incidence rate (IR) of 15.04 injuries per 1000 AEs. In the IG, 285 injuries (mean ± SD, 10.56 ± 3.64) were reported for 27 teams, which corresponded to an IR of 8.09 injuries per 1000 AEs. Total days missed because of injury were significantly higher for the CG (mean ± SD, 13.20 ± 26.6 days) than for the IG (mean ± SD, 10.08 ± 14.68 days) (P = .007). There was no difference for time loss due to injury based on field type (P = .341). CONCLUSION: The FIFA 11+ significantly reduced injury rates by 46.1% and decreased time loss to injury by 28.6% in the competitive male collegiate soccer player (rate ratio, 0.54 [95% CI, 0.49-0.59]; P < .0001) (number needed to treat = 2.64).
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This study examined the effects of a novel iso-inertial eccentric overload and vibration training (EVT) paradigm on change of direction speed and multiple performance tests applicable to soccer. Twenty-four young, male players were assigned to EVT (n=12) or conventional combined (CONV, n=12) group, once weekly for 11 weeks. EVT consisted of 2 sets of 6-10 repetitions in 5 specific and 3 complementary exercises. CONV used comparable volume (2 sets of 6-10 reps in 3 sequences of 3 exercises) of conventional combined weight, plyometric and linear speed exercises. Pre- and post intervention tests included 25-m sprint with 4 x 45° change of direction (COD) every 5th m (V-cut test), 10- and 30-m sprints, repeat sprint ability (RSA), countermovement jump (CMJ) and hopping (RJ5). Group comparison showed very likely to likely better performance for EVT in the COD (effect size; ES=1.42), 30-m (ES=0.98), 10-m (ES=1.17), and average power (ES=0.69) and jumping height (ES=0.69) during RJ5. There was a large (r=-0.55) relationship between the increase in average hopping power and the reduced V-cut time. As EVT, not CONV, improved COD ability but also linear speed and reactive jumping, this "proof-of-principle" study suggests this novel exercise paradigm performed once weekly, could serve as a viable adjunct to improve performance tasks specific to soccer.
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Team sports are increasingly popular, with millions of participants worldwide. Athletes engaged in these sports are required to repeatedly produce skilful actions and maximal or near-maximal efforts (eg, accelerations, changes in pace and direction, sprints, jumps and kicks), interspersed with brief recovery intervals (consisting of rest or low-intensity to moderate-intensity activity), over an extended period of time (1–2 h). While performance in most team sports is dominated by technical and tactical proficiencies, successful team-sport athletes must also have highly-developed, specific, physical capacities. Much effort goes into designing training programmes to improve these physical capacities, with expected benefits for team-sport performance. Recently, some team sports have introduced altitude training in the belief that it can further enhance team-sport physical performance. Until now, however, there is little published evidence showing improved team-sport performance following altitude training, despite the often considerable expense involved. In the absence of such studies, this review will identify important determinants of team-sport physical performance that may be improved by altitude training, with potential benefits for team-sport performance. These determinants can be broadly described as factors that enhance either sprint performance or the ability to recover from maximal or near-maximal efforts. There is some evidence that some of these physical capacities may be enhanced by altitude training, but further research is required to verify that these adaptations occur, that they are greater than what could be achieved by appropriate sea-level training and that they translate to improved team-sport performance.
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It has been proposed that match congestion in elite soccer results in residual fatigue and underperfor-mance in ensuing competition due to insufficient recovery time. In this article, matters relating to match congestion and running performance in elite soccer competition are discussed. We suggest a need to determine the extent to which elite players are, in reality, exposed to periods of match congestion and hence to potential declines in performance. Despite evidence of exercise-induced muscle damage combined with a decline in physical performance up to 72 h post-match, research using time–motion analyses suggests that running performance represented by distances covered is unaffected over periods of match congestion. We recommend analysis of alternative movement variables including accelerations, decelerations and turns that are taxing metabolically and contribute greatly to muscle damage. Moreover, a holistic approach combining subjective ratings with biochemical, hormonal and immunological responses to exercise would be pertinent, especially in players frequently exposed to match congestion. Contemporary practitioners typically implement various post-match recovery treatments during dense schedules in an attempt to accelerate recovery and ensure that subsequent running performance is not unduly affected. However, empirical evidence to support their efficacy in maintaining running performance is lacking and we recommend controlled intervention studies using match simulations in an attempt to verify their effectiveness. These points are critically addressed using findings from the current scientific literature, while gaps in the current body of knowledge and future directions for research are highlighted.
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Purpose Little is known about injury prevention practices in professional football clubs. The purpose of this study was therefore to determine the current perceptions and practices of premier league football clubs internationally concerning risk factors, testing and preventative exercises for non-contact injuries. Methods A survey was administered to 93 premier league football clubs internationally. The survey included four sections: (1) persons involved in the injury prevention programme: position, quantity, role, qualification; (2) perceptions regarding non-contact injury risk factors; (3) tests used to identify non-contact injury risk and (4) non-contact injury prevention exercises used, their perceived effectiveness and implementation strategies. Results 44 surveys were successfully returned (47%). The position of physiotherapist was the most represented position in the injury prevention programme. The top five perceived risk factors in rank order were previous injury, fatigue, muscle imbalance, fitness and movement efficiency. The five most commonly used tests to identify injury risk (in rank order) were functional movement screen, questionnaire, isokinetic dynamometry, physical tests and flexibility. The top five exercises used by clubs were (also in rank order) eccentric exercise, balance/proprioception, hamstring eccentric, core stability and, sharing the fifth position, Nordic hamstring and gluteus activation. Conclusions The survey revealed the most common perceptions and practices of premier league football clubs internationally regarding risk factors, testing and preventative exercises. The findings can enable reduction of the gap between research and practice.
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This study examined the evolution of physical and technical soccer performance across a 7-season period in the English Premier League. Match performance observations (n=14700), collected using a multiple-camera computerised tracking system and controlled for season, phase of season, position and standard were analysed for emergent trends. Total distance covered during a match was ~2% lower in 2006-07 compared to 2012-13. Across seven seasons, high-intensity running distance increased by ~30% (890±299 vs 1151 ± 337 m, p<0.001; ES: 0.82) and high-intensity running actions by ~50% (118±36 vs 176±46, p<0.001; ES: 1.41). Sprint distance increased by ~35% across the timeframe (232±114 vs 350±139 m, p<0.001; ES: 0.93) with a concomitant increase in the number of sprints (31±14 vs 57±20, p<0.001; ES: 1.46). Mean sprint distance was shorter in 2012-13 compared to 2006-07 (5.9±0.8 vs 6.9±1.3 m, p<0.001; ES: 0.91), with the proportion of explosive sprints increasing (34±11 vs 47±9%, p<0.001; ES: 1.31). Players performed ~40% more passes (35±17 vs 25±13, p<0.001; ES: 0.66), with a greater percentage of successful passes in 2012-13 compared to 2006-07 (83±10% vs 76±13%, p<0.001; ES: 0.60). The increased number of short and medium passes followed a similar pattern to total passes (p<0.001; ES>0.6), whereas the number of long passes varied little between seasons (p<0.001; ES: 0.11). This data demonstrates evolution of physical and technical parameters in the English Premier League, and could be used to aid talent identification, training preparation and injury prevention.
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The FIFA 11+ is a structured warm-up programme specially designed to prevent injuries among football players from age 14 years and above. However, studies to prove its efficacy are generally few and it is yet to be tested in male youth footballers and among African players. The purpose of the study was to examine the efficacy of the FIFA 11+ programme in reducing the risk of injuries among male youth football players of the Lagos Junior League. A cluster randomised controlled trial was conducted. All the 20 teams (414 players aged 14 -19 years) in the Premier League division were block-randomised into either an intervention (INT) or a control (CON) group. The INT group performed the FIFA 11+ exercises as warm-up during training sessions and the CON group performed usual warm-up. Participating teams were prospectively followed through an entire league season of 6 months in which they were visited every week to assess injured players for time-loss injuries in both groups. The primary outcomes were any injury to the players, injuries by type of exposure and injuries specific to the lower extremities. The secondary outcomes were injuries reported by body location, aetiology, mechanism and severity. In total, 130 injuries were recorded affecting 104 (25%) of the 416 players. Team and player compliance with the INT was 60% and 74% respectively. Based on the primary outcome measures of the study, the FIFA 11+ programme significantly reduced the overall rate of injury in the INT group by 41% [RR = 0.59 (95% CI: 0.40 - 0.86; p = 0.006)] and all lower extremity injuries by 48% [RR = 0.52 (95% CI: 0.34 - 0.82; p = 0.004)]. However, the rate of injury reduction based on secondary outcomes mostly did not reach the level of statistical significance. The FIFA 11+ programme is effective in reducing the rates of injuries in male youth football players.
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Hamstring injuries are the most common muscle injuries in male amateur soccer. Eccentric strength of the hamstrings is recognized as an important modifiable risk factor, leading to the development of preventive exercises such as the Nordic Hamstring Exercise. This study aims to investigate the preventive effect of the Nordic Hamstring Exercise on the incidence and severity of hamstring injuries in male amateur soccer players. Cluster-randomized controlled trial with soccer teams as the unit of cluster. Dutch first class amateur field soccer. Male amateur soccer players (mean age 24.5 years, SD 3.8 years) from 40 teams were allocated to intervention (n=309 players) or control group (n=310 players). The intervention group was instructed to perform 25 sessions of the Nordic Hamstring Exercise within a period of 13 weeks during the first months of 2013. Both the intervention group and control group performed regular soccer training and were followed for hamstring injury incidence and severity during the calendar year 2013. At baseline, personal characteristics (e.g. age, injury history, field position) were gathered from all participants via questionnaire. Primary outcomes are initial and recurrent hamstring injury incidence (number of hamstring injuries) and injury severity (number of days injured). Interim analysis after intervention (2 months follow-up) show a total of 2 hamstring injuries in intervention group vs 12 hamstring injuries in control group (χ(2)=7.5, P<.05). Regarding injury severity, no difference was found between intervention and control group (t=0.3, P=.77). Preliminary analyses during the summer break show substantial hamstring injury incidence reduction by incorporating the Nordic Hamstring Exercise in regular training. With a total follow-up of 9 months, final analyses (survival analyses including the number of injuries per 1000 playing hours) will be performed in January 2014.
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Objectives A P-value <0.05 is one metric used to evaluate the results of a randomized controlled trial (RCT). We wondered how often statistically significant results in RCTs may be lost with small changes in the numbers of outcomes. Study Design and Setting A review of RCTs in high-impact medical journals that reported a statistically significant result for at least one dichotomous or time-to-event outcome in the abstract. In the group with the smallest number of events, we changed the status of patients without an event to an event until the P-value exceeded 0.05. We labeled this number the Fragility Index; smaller numbers indicated a more fragile result. Results The 399 eligible trials had a median sample size of 682 patients (range: 15–112,604) and a median of 112 events (range: 8–5,142); 53% reported a P-value <0.01. The median Fragility Index was 8 (range: 0–109); 25% had a Fragility Index of 3 or less. In 53% of trials, the Fragility Index was less than the number of patients lost to follow-up. Conclusion The statistically significant results of many RCTs hinge on small numbers of events. The Fragility Index complements the P-value and helps identify less robust results.
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Implementing objective methods to assess physical performance has become an invaluable component of athlete or player development, monitoring, and talent identification in distinct sports. Many sports depend heavily upon muscular strength, muscle power output and sprint performance especially at competition level. Therefore, the aim of this study was to examine the relationships between 10-m time and several kinetic and kinematic parameters variables related to a weighted countermovement jump using a linear transducer in a large sample of trained sportsmen. A group of 32 trained sportsmen volunteered to participate in the study (mean ± SD: age 21.4 ± 1.5 yr, body mass 67.5 ± 4.8 kg, body height 1.74 ± 0.02 m). The major findings of this study were the significant associations between 10 m sprint time and peak velocity during jumping (r= 0.630; p<0.01); and also the non-significant associations between sprint and of force, mechanical impulse and rate of force development. These results underline the important relationship between 10 m sprint and maximal lower body strength, as assessed by the force, power and bar velocity displacement. It is suggested that sprinting time performance would benefit from training regimens aimed to improve these performance qualities.
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Abstract Understanding the magnitude of forces and lower body kinematics that occur during a change of direction (COD) task can provide information about the biomechanical demands required to improve performance. To compare the magnitude of force, impulse, lower body kinematics and post-COD stride velocity produced between athletes of different strength levels during a COD task, 12 stronger (8 males, 4 females) and 12 weaker (4 males, 8 females) recreational team sport athletes were recruited. Strength levels were determined by relative peak isometric force of the dominant and non-dominant leg. All athletes performed 10 pre-planned 45° changes of direction (5 left, 5 right) while three-dimensional motion and ground reaction force (GRF) data were collected. Differences in all variables for the dominant leg were examined using a one-way analysis of variance (ANOVA) with a level of significance set at p ≤0.05. The stronger group displayed significantly faster post-COD stride velocity and greater vertical and horizontal braking forces, vertical propulsive force, vertical braking impulse, horizontal propulsive impulse, angle of peak braking force application, hip abduction and knee flexion angle compared to the weaker group. The results suggest that individuals with greater relative lower body strength produced higher magnitude plant foot kinetics and modified lower body positioning while producing faster COD performances. Future investigations should determine if strength training to enable athletes to increase plant foot kinetics while maintaining or adopting a lower body position results in a concomitant increases in post-COD stride velocity.
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Field sport coaches must use reliable and valid tests to assess change-of-direction speed in their athletes. Few tests feature linear sprinting with acute change- of-direction maneuvers. The Change-of-Direction and Acceleration Test (CODAT) was designed to assess field sport change-of-direction speed, and includes a linear 5-meter (m) sprint, 45° and 90° cuts, 3- m sprints to the left and right, and a linear 10-m sprint. This study analyzed the reliability and validity of this test, through comparisons to 20-m sprint (0-5, 0-10, 0-20 m intervals) and Illinois agility run (IAR) performance. Eighteen Australian footballers (age = 23.83 ± 7.04 yrs; height = 1.79 ± 0.06 m; mass = 85.36 ± 13.21 kg) were recruited. Following familiarization, subjects completed the 20-m sprint, CODAT, and IAR in 2 sessions, 48 hours apart. Intra-class correlation coefficients (ICC) assessed relative reliability. Absolute reliability was analyzed through paired samples t-tests (p ≤ 0.05) determining between-session differences. Typical error (TE), coefficient of variation (CV), and differences between the TE and smallest worthwhile change (SWC), also assessed absolute reliability and test usefulness. For the validity analysis, Pearson's correlations (p ≤ 0.05) analyzed between-test relationships. Results showed no between-session differences for any test (p = 0.19-0.86). CODAT time averaged ~6 s, and the ICC and CV equaled 0.84 and 3.0%, respectively. The homogeneous sample of Australian footballers meant that the CODAT's TE (0.19 s) exceeded the usual 0.2 x standard deviation (SD) SWC (0.10 s). However, the CODAT is capable of detecting moderate performance changes (SWC calculated as 0.5 x SD = 0.25 s). There was a near perfect correlation between the CODAT and IAR (r = 0.92), and very large correlations with the 20-m sprint (r = 0.75-0.76), suggesting that the CODAT was a valid change-of-direction speed test. Due to movement specificity, the CODAT has value for field sport assessment. Key pointsThe change-of-direction and acceleration test (CODAT) was designed specifically for field sport athletes from specific speed research, and data derived from time-motion analyses of sports such as rugby union, soccer, and Australian football. The CODAT features a linear 5-meter (m) sprint, 45° and 90° cuts and 3-m sprints to the left and right, and a linear 10-m sprint.The CODAT was found to be a reliable change-of-direction speed assessment when considering intra-class correlations between two testing sessions, and the coefficient of variation between trials. A homogeneous sample of Australian footballers resulted in absolute reliability limitations when considering differences between the typical error and smallest worthwhile change. However, the CODAT will detect moderate (0.5 times the test's standard deviation) changes in performance.The CODAT correlated with the Illinois agility run, highlighting that it does assess change-of-direction speed. There were also significant relationships with short sprint performance (i.e. 0-5 m and 0-10 m), demonstrating that linear acceleration is assessed within the CODAT, without the extended duration and therefore metabolic limitations of the IAR. Indeed, the average duration of the test (~6 seconds) is field sport-specific. Therefore, the CODAT could be used as an assessment of change-of-direction speed in field sport athletes.
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Purpose To determine the time course of architectural adaptations in the biceps femoris long head (BFLH) following high or low volume eccentric training. Methods Twenty recreationally active males completed a two week standardised period of eccentric Nordic hamstring exercise (NHE) training, followed by four weeks of high (n=10) or low volume (n=10) training. Eccentric strength was assessed pre and post intervention and following detraining. Architecture was assessed weekly during training and after two and four weeks of detraining. Results After six weeks of training, BFLH fascicles increased significantly in the high (23 ± 7%, P<0.001, d=2.87) and low volume (24 ± 4%, P<0.001, d=3.46) groups, but reversed following two weeks of detraining (high volume, ‐17 ± 5%, P<0.001, d=‐2.04; low volume, ‐15 ± 3%, P<0.001, d=‐2.56) after completing the intervention. Both groups increased eccentric strength after six weeks of training (high volume, 28 ± 20%, P=0.009, d=1.55; low volume, 34 ± 14%, P<0.001, d=2.09) and saw no change in strength following a four week period of detraining (high volume, ‐7 ± 7%, P=0.97, d=‐0.31; low volume, ‐2 ± 5%, P=0.99, d=‐0.20). Conclusions Both low and high volume NHE training stimulate increases in BFLH fascicle length and eccentric knee flexor strength. Architectural adaptations reverted to baseline levels within two weeks after training, but eccentric strength is maintained for at least four weeks. These observations provide novel insight into the effects of training volume and detraining on BFLH architecture, and may provide guidance for the implementation of NHE programmes. This article is protected by copyright. All rights reserved.
Article
This assessor-blinded, randomized controlled superiority trial investigated the efficacy of the 10-week Nordic Hamstring exercise (NHE) protocol on sprint performance in football players. Thirty-five amateur male players (age: 17–26 years) were randomized to a do-as-usual control group (CG; n = 17) or to 10-weeks of supervised strength training using the NHE in-season (IG; n = 18). A repeated-sprint test, consisting of 4 × 6 10 m sprints, with 15 s recovery period between sprints and 180 s between sets, was conducted to evaluate total sprint time as the primary outcome. Secondary outcomes were best 10 m sprint time (10mST) and sprint time during the last sprint (L10mST). Additionally, peak eccentric hamstring strength (ECC-PHS) and eccentric hamstring strength capacity (ECC-CAPHS) were measured during the NHE. Ten players were lost to follow-up, thus 25 players were analyzed (CG n = 14; IG n = 11). Between-group differences in mean changes were observed in favor of the IG for sprint performance outcomes; TST (−0.649 s, p = 0.056, d = 0.38), 10mST (−0.047 s, p = 0.005, d = 0.64) and L10mST (−0.052 s, p = 0.094, d = 0.59), and for strength outcomes; ECC-PHS (62.3 N, p = 0.006, d = 0.92), and ECC-CAPHS (951 N, p = 0.005, d = 0.95). In conclusion, the NHE showed small-to-medium improvements in sprint performance and large increases in peak eccentric hamstring strength and capacity. Trial Registration Number: NCT02674919
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Background: Agility is a fundamental performance element in many sports, but poses a high risk of injury. Hierarchical modelling has shown that eccentric hamstring strength is the primary determinant of agility performance. Purpose: The purpose of this study was to investigate the relationship between knee flexor and extensor strength parameters and a battery of agility tests. Study design: Controlled laboratory study. Methods: Nineteen recreational intermittent games players completed an agility battery and isokinetic testing of the eccentric knee flexors (eccH) and concentric knee extensors (conQ) at 60, 180 and 300°·s-1. Peak torque and the angle at which peak torque occurred were calculated for eccH and conQ at each speed. Dynamic control ratios (eccH:conQ) and fast:slow ratios (300:60) were calculated using peak torque values, and again using angle-matched data, for eccH and conQ. The agility test battery differentiated linear vs directional changes and prescriptive vs reactive tasks. Results: Linear regression showed that eccH parameters were generally a better predictor of agility performance than conQ parameters. Stepwise regression showed that only angle-matched strength ratios contributed to the prediction of each agility test. Trdaitionally calculated strength ratios using peak torque values failed to predict performance. Angle-matched strength parameters were able to account for 80% of the variation in T-test performance, 70% of deceleration distance, 55% of 10m sprint performance, and 44% of reactive change of direction speed. Conclusions: Traditionally calculated strength ratios failed to predict agility performance, whereas angle-matched strength ratios had better predictive ability and featured in a predictive stepwise model for each agility task. Level of evidence: 2c.
Article
Eccentric strength training alters muscle architecture, but it is also an important factor for the prevention of hamstring injuries. The purpose was to determine the architectural adaptations of the Biceps Femoris long head (BFlh) after eccentric strength training with Nordic Hamstring exercise (NHE), followed by a subsequent detraining period. The participants in this intervention (n = 23) completed a period of 13 weeks consisting of a first week of control and prior training, followed by 8 weeks of eccentric strength training with NHE, and concluding with a 4-week period of detraining. The architectural characteristics of the BFlh were measured at rest using two-dimensional ultrasound before (M1 – week 1) and after (M2 – week 9) the eccentric strength training, and at the end of the detraining period (M3 – week 13). The muscle fascicle length significantly increased (t = -7.73, d = 2.28, P < .001) in M2 compared to M1, as well as the muscle thickness (t = -5.23, d = 1.54, P < .001), while the pennation angle presented a significant decrease (t = 7.81, d = 2.3, P < .001). The muscle fascicle length decreased significantly (t = 6.07, d = 1.79, P < .001) in M3 compared to M2, while the pennation angle showed a significant increase (t = -4.63, d = 1.36, P < .001). The results provide evidence that NHE may cause alterations in the architectural conditions of the BFlh and may have practical implications for injury prevention and rehabilitation programs. This article is protected by copyright. All rights reserved.
Article
Background The architectural and morphological adaptations of the hamstrings in response to training with different exercises have not been explored. Purpose To evaluate changes in biceps femoris long head (BFLH) fascicle length and hamstring muscle size following 10-weeks of Nordic hamstring exercise (NHE) or hip extension (HE) training. Methods 30 recreationally active male athletes (age, 22.0±3.6 years; height, 180.4±7 cm; weight, 80.8 ±11.1 kg) were allocated to 1 of 3 groups: (1) HE training (n=10), NHE training (n=10), or no training (control, CON) (n=10). BFLH fascicle length was assessed before, during (Week 5) and after the intervention with a two-dimensional ultrasound. Hamstring muscle size was determined before and after training via MRI. Results Compared with baseline, BFLH fascicles were lengthened in the NHE and HE groups at mid-training (d=1.12-1.39, p<0.001) and post-training (d=1.77-2.17, p<0.001) and these changes did not differ significantly between exercises (d=0.49-0.80, p=0.279-0.976). BFLH volume increased more for the HE than the NHE (d=1.03, p=0.037) and CON (d=2.24, p<0.001) groups. Compared with the CON group, both exercises induced significant increases in semitendinosus volume (d=2.16-2.50, ≤0.002) and these increases were not significantly different (d=0.69, p=0.239). Conclusion NHE and HE training both stimulate significant increases in BFLH fascicle length; however, HE training may be more effective for promoting hypertrophy in the BFLH. © 2016 BMJ Publishing Group Ltd & British Association of Sport and Exercise Medicine.
Article
Purpose: To assess the residual fatigue response associated with the completion of two successive soccer-specific exercise protocols (SSEP). Methods: Twenty male soccer players were pair-matched before completing SSEPs, interspersed by either 48 or 72 h. Outcome variables were measured every 15 mins, and comprised uni-axial measures of PlayerLoad, mean (HR) and peak heart rate (HRpeak), blood lactate concentration, mean and peak (V̇O2peak) oxygen consumption, and rating of perceived exertion (RPE). Results: No significant (P>0.05) group interactions were identified for any outcome variables. Uni-axial (and total) PlayerLoad exhibited a significant (P<0.05) main effect for time, with the exception of the relative contribution of medial lateral PlayerLoad. Total PlayerLoad during the final 15mins (222.23 ± 15.16 a.u) was significantly higher than all other time points. All other outcome variables also exhibited a significant main effect for time, with HR, HRpeak and V̇O2peak also exhibiting significantly higher values in the first trial. There was also a significant (P=0.003) trial*time interaction for RPE. Conclusions: With equivalence at baseline, there was no difference in the fatigue response associated with two SSEPs interspersed by either 48 or 72 h recovery. The current study has implications for the design and micro management of training and competition schedules Key words: Fixture Congestion, Physiology, Biomechanics, PlayerLoad
Article
The aim of the current study was to analyse the effect of 10-week eccentric overload training on kinetic parameters during change of direction (COD) in U-19 football players. The outcome measured included relative peak braking (rPB) and propulsive force (rPF), contact time (CT), time spent during braking (BT) and propulsive phase (PT), relative total (rTOT_IMP), braking (rB_IMP) and propulsive (rP_IMP) impulses. Between-group results showed a substantial better improvement (likely) in CT (ES: 0.72) and BT (ES: 0.74) during side-step cutting, and in rPB (ES: 0.84) and rB_IMP (ES: 0.72) during crossover cutting, in the experimental group (EXP) in comparison to control group (CON). Within-group analysis showed a substantially better performance (likely to almost certain) in CT (ES: 1.19), BT (ES: 1.24), PT (ES: 0.70), rPB (ES: 0.75), rPF (ES: 0.68), rTOT_IMP (ES: 0.48) and rB_IMP (ES: 0.50) in EXP during side-step cutting. Regarding crossover cutting, within-group analysis showed a substantial better performance (likely to almost certain) in CT (ES: 0.75), rPB (ES: 0.75), rPF (ES: 1.34), rTOT_IMP (ES: 0.61), rB_IMP (ES: 0.76) and rP_IMP (ES: 0.46) in EXP. In conclusion, the eccentric overload-based programme led to an improvement in kinetic parameters during COD football tasks.
Article
Background There are limited data on hamstring injury rates over time in football. Aim To analyse time trends in hamstring injury rates in male professional footballers over 13 consecutive seasons and to distinguish the relative contribution of training and match injuries. Methods 36 clubs from 12 European countries were followed between 2001 and 2014. Team medical staff recorded individual player exposure and time-loss injuries. Injuries per 1000 h were compared as a rate ratio (RR) with 95% CI. Injury burden was the number of lay off days per 1000 h. Seasonal trend for injury was analysed using linear regression. Results A total of 1614 hamstring injuries were recorded; 22% of players sustained at least one hamstring injury during a season. The overall hamstring injury rate over the 13-year period was 1.20 injuries per 1000 h; the match injury rate (4.77) being 9 times higher than the training injury rate (0.51; RR 9.4; 95% CI 8.5 to 10.4). The time-trend analysis showed an annual average 2.3% year on year increase in the total hamstring injury rate over the 13-year period (R2=0.431, b=0.023, 95% CI 0.006 to 0.041, p=0.015). This increase over time was most pronounced for training injuries—these increased by 4.0% per year (R2=0.450, b=0.040, 95% CI 0.011 to 0.070, p=0.012). The average hamstring injury burden was 19.7 days per 1000 h (annual average increase 4.1%) (R2=0.437, b=0.041, 95% CI 0.010 to 0.072, p=0.014). Conclusions Training-related hamstring injury rates have increased substantially since 2001 but match-related injury rates have remained stable. The challenge is for clubs to reduce training-related hamstring injury rates without impairing match performance.
Article
This study aimed to determine: (a) the spatial patterns of hamstring activation during the Nordic hamstring exercise (NHE); (b) whether previously injured hamstrings display activation deficits during the NHE; and (c) whether previously injured hamstrings exhibit altered cross-sectional area (CSA). Ten healthy, recreationally active men with a history of unilateral hamstring strain injury underwent functional magnetic resonance imaging of their thighs before and after six sets of 10 repetitions of the NHE. Transverse (T2) relaxation times of all hamstring muscles [biceps femoris long head (BFlh); biceps femoris short head (BFsh); semitendinosus (ST); semimembranosus (SM)] were measured at rest and immediately after the NHE and CSA was measured at rest. For the uninjured limb, the ST's percentage increase in T2 with exercise was 16.8%, 15.8%, and 20.2% greater than the increases exhibited by the BFlh, BFsh, and SM, respectively (P < 0.002 for all). Previously injured hamstring muscles (n = 10) displayed significantly smaller increases in T2 post-exercise than the homonymous muscles in the uninjured contralateral limb (mean difference -7.2%, P = 0.001). No muscles displayed significant between-limb differences in CSA. During the NHE, the ST is preferentially activated and previously injured hamstring muscles display chronic activation deficits compared with uninjured contralateral muscles. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.
Article
The Nordic hamstring (NH) exercise programme was introduced in 2001 and has been shown to reduce the risk of acute hamstring injuries in football by at least 50%. Despite this, the rate of hamstring injuries has not decreased over the past decade in male elite football. To examine the implementation of the NH exercise programme at the highest level of male football in Europe, the UEFA Champions League (UCL), and to compare this to the Norwegian Premier League, Tippeligaen, where the pioneer research on the NH programme was conducted. Retrospective survey. 50 professional football teams, 32 from the UCL and 18 from Tippeligaen. A questionnaire, based on the Reach, Efficacy, Adoption, Implementation and Maintenance framework, addressing key issues related to the implementation of the NH programme during three seasons from 2012 through 2014, was distributed to team medical staff using electronic survey software. The response rate was 100%. Of the 150 club-seasons covered by the study, the NH programme was completed in full in 16 (10.7%) and in part in an additional 9 (6%) seasons. Consequently, 125 (83.3%) club-seasons were classified as non-compliant. There was no difference in compliance between the UCL and Tippeligaen in any season (χ(2): 0.41 to 0.52). Adoption and implementation of the NH exercise programme at the highest levels of male football in Europe is low; too low to expect any overall effect on acute hamstring injury rates. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.
Article
To investigate the hierarchical contributions of anthropometry, strength and cognition to a battery of prescriptive and reactive agility tests. Nineteen participants (mean ± S.D.; age: 22.1 ± 1.9 years; height: 182.9 ± 5.5 cm; body mass: 77 ± 4.9 kg) completed four agility tests: a prescriptive linear sprint, a prescriptive change-of-direction sprint, a reactive change-of-direction sprint, and a reactive linear deceleration test. Anthropometric variables included body fat percentage and thigh girth. Strength was quantified as the peak eccentric hamstring torque at 180, 300, and 60°∙s-1. Mean reaction time and accuracy in the Stroop word-colour test was used to assess perceptual and decision making factors. There was little evidence of inter-test correlation with the strongest relationship observed between 10m sprint and T-test performance (r2 = 0.49, P<0.01). Anthropometric measures were not strong predictors of agility, accounting for a maximum 23% (P=0.12) in the prescriptive change-of-direction test. Cognitive measures had a stronger correlation with the reactive (rather than prescriptive) agility tests, with a maximum 33% (P=0.04) of variance accounted for in the reactive change-of-direction test. Eccentric hamstring strength accounted for 62% (P=0.01) of the variance in the prescriptive change-of-direction test. Hierarchical ordering of the agility tests revealed that eccentric hamstring strength was the primary predictor in 3 of the 4 tests, with cognitive accuracy the next most common predictor. There is little evidence of inter-test correlation across a battery of agility tests. Eccentric hamstring strength and decision making accuracy are the most common predictors of agility performance.
Article
The objective of this study was to examine the effects of a neuromuscular training program combining eccentric hamstring muscle strength, plyometrics, and free/resisted sprinting exercises on knee extensor/flexor muscle strength, sprinting performance, and horizontal mechanical properties of sprint running in football (soccer) players. Sixty footballers were randomly assigned to an experimental group (EG) or a control group (CG). Twenty-seven players completed the EG and 24 players the CG. Both groups performed regular football training while the EG performed also a neuromuscular training during a 7-week period. The EG showed a small increases in concentric quadriceps strength (ES = 0.38/0.58), a moderate to large increase in concentric (ES = 0.70/0.74) and eccentric (ES = 0.66/0.87) hamstring strength, and a small improvement in 5-m sprint performance (ES = 0.32). By contrast, the CG presented lower magnitude changes in quadriceps (ES = 0.04/0.29) and hamstring (ES = 0.27/0.34) concentric muscle strength and no changes in hamstring eccentric muscle strength (ES = −0.02/0.11). Thus, in contrast to the CG (ES = −0.27/0.14), the EG showed an almost certain increase in the hamstring/quadriceps strength functional ratio (ES = 0.32/0.75). Moreover, the CG showed small magnitude impairments in sprinting performance (ES = −0.35/−0.11). Horizontal mechanical properties of sprint running remained typically unchanged in both groups. These results indicate that a neuromuscular training program can induce positive hamstring strength and maintain sprinting performance, which might help in preventing hamstring strains in football players.
Article
Context: The winter break in the top 2 German professional soccer leagues was shortened from 6.5 to 3.5 weeks in the 2009-2010 season. Objective: To investigate whether this change affected injury characteristics by comparing the second half of the 2008-2009 (long winter break) with the equivalent period in the 2009-2010 season (short winter break). Design: Prospective cohort study. Setting: German male professional soccer leagues. Patients or other participants: Seven professional German male soccer teams (184 players in the 2008-2009 season, 188 players in the 2009-2010 season). Main outcome measure(s): Injury incidences and injury characteristics (cause of injury, location, severity, type, diagnosis), including their monthly distribution, were recorded. Results: A total of 300 time-loss injuries (2008-2009 n = 151, 2009-2010 n = 149) occurred. The overall injury incidence per 1000 soccer hours was 5.90 (95% confidence interval = 5.03, 6.82) in 2008-2009 and 6.55 (5.58, 7.69) in 2009-2010. Match injuries per 1000 hours were 31.5 (25.0, 38.0) in the first season and 26.5 (20.2, 32.7) in the second season; the corresponding training values were 2.67 (2.08-3.44) and 3.98 (3.19-4.95), respectively. The training injury incidence (incidence rate ratio = 1.49 [95% confidence interval = 1.07, 2.08], P = .02) and the risk of sustaining a knee injury (incidence rate ratio = 1.66 [1.00, 2.76], P = .049) were higher in 2009-2010 after the short winter break; the incidence of moderate and severe injuries (time loss >7 days) trended higher (incidence rate ratio = 1.34 [0.96, 1.86], P = .09). Conclusions: Shortening the winter break from 6.5 to 3.5 weeks did not change the overall injury incidence; however, a higher number of training, knee, and possibly more severe injuries (time loss >7 days) occurred.
Article
The aim of this study was to determine whether declines in knee flexor strength following overground repeat sprints were related to changes in hamstrings myoelectrical activity. Seventeen recreationally active men completed maximal isokinetic concentric and eccentric knee flexor strength assessments at 180°/s before and after repeat sprint running. Myoelectrical activity of the biceps femoris (BF) and medial hamstrings (MHs) was measured during all isokinetic contractions. Repeated measures mixed model [fixed factors = time (pre- and post-repeat sprint) and leg (dominant and nondominant), random factor = participants] design was fitted with the restricted maximal likelihood method. Repeat sprint running resulted in significant declines in eccentric, and concentric, knee flexor strength (eccentric = 26 ± 4 Nm, 15% P < 0.001; concentric 11 ± 22 Nm, 10% P < 0.001). Eccentric BF myoelectrical activity was significantly reduced (10%; P = 0.035). Concentric BF and all MH myoelectrical activity were not altered. The declines in maximal eccentric torque were associated with the change in eccentric BF myoelectrical activity (P = 0.013). Following repeat sprint running, there were preferential declines in the myoelectrical activity of the BF, which explained declines in eccentric knee flexor strength.
Article
Good kicking technique is an important aspect of a soccer player. Therefore, understanding the biomechanics of soccer kicking is particularly important for guiding and monitoring the training process. The purpose of this review was to examine latest research findings on biomechanics of soccer kick performance and identify weaknesses of present research which deserve further attention in the future. Being a multiarticular movement, soccer kick is characterised by a proximal-to-distal motion of the lower limb segments of the kicking leg. Angular velocity is maximized first by the thigh, then by the shank and finally by the foot. This is accomplished by segmental and joint movements in multiple planes. During backswing, the thigh decelerates mainly due to a motion-dependent moment from the shank and, to a lesser extent, by activation of hip muscles. In turn, forward acceleration of the shank is accomplished through knee extensor moment as well as a motion-dependent moment from the thigh. The final speed, path and spin of the ball largely depend on the quality of foot-ball contact. Powerful kicks are achieved through a high foot velocity and coefficient of restitution. Preliminary data indicate that accurate kicks are achieved through slower kicking motion and ball speed values.