
==== Front
Int J Sports Phys Ther
Int J Sports Phys Ther
2159
International Journal of Sports Physical Therapy
2159-2896
NASMI Website: International Journal of Sports Physical Therapy

33842041
19452
10.26603/001c.19452
Original Research
A Preseason Training Program With the Nordic Hamstring Exercise Increases Eccentric Knee Flexor Strength and Fascicle Length in Professional Female Soccer Players
Vianna Karoline Baptista 1
Rodrigues Lívia Gonçalves 1
Oliveira Nathalia Trevisol 1
Ribeiro-Alvares João Breno 1
Baroni Bruno Manfredini 1
1 Universidade Federal de Ciências da Saúde de Porto Alegre https://ror.org/00x0nkm13
Corresponding author: Bruno Manfredini Baroni; Federal University of Health Sciences of Porto Alegre (UFCSPA); Sarmento Leite St, 245 – zipcode 90050-170; Porto Alegre, Rio Grande do Sul, Brazil; Phone/fax +55 51 3303-8876; Email: bmbaroni@yahoo.com.br
1 4 2021
2021
16 2 459467
17 2 2020
4 7 2020
© The Author(s)
https://creativecommons.org/licenses/by-nc-sa/4.0/ This is an open access article distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike License (4.0) which permits non-commercial use, distribution, and reproduction in any medium, provided the original author and source are credited. If you remix, transform, or build upon this work, you must distribute your contributions under the same license as the original.

Background

Training programs that include the Nordic hamstring exercise (NHE) have been shown to increase eccentric knee flexor strength and biceps femoris fascicle length in male athletes. However, the effect of NHE on female athletes remains unknown.

Purpose

To investigate the collective and individual responses of professional female soccer players engaged in a preseason training program with the NHE regarding eccentric knee flexor strength and biceps femoris long head fascicle length.

Study Design

Quasi-experimental study.

Methods

Sixteen amateur female soccer players (without a NHE training routine) were evaluated 8-weeks apart to: (1) assess reliability of eccentric knee flexor strength and biceps femoris fascicle length measures; and (2) determine the typical error of measures that would be used to discriminate training responders and non-responders. The NHE training group had 17 professional female soccer players who performed an 8-week training program with the NHE during preseason. Within-group analysis was performed with paired sample t-tests (pre- vs. post-training), and individual responses were determined using the typical error criteria.

Results

The non-trained group’s data demonstrated that measures of strength (ICC=0.82-0.87, typical error = 12-13 N) and fascicle length (ICC=0.92-0.97; typical error = 0.19-0.38 cm) were reliable. In the NHE training group, both limbs increased the eccentric knee flexor strength (~13%; ES=0.74-0.82) and the biceps femoris fascicle length (~6%; ES=0.44-0.65). Twelve players (~71%) were considered responders to the NHE training program for the eccentric knee flexor strength, while eight athletes (~47%) were responders for the biceps femoris fascicle length.

Conclusion

The 8-week preseason training program with the NHE increased both eccentric knee flexor strength and biceps femoris fascicle length in professional female soccer players. More than two-thirds of players demonstrated a meaningful increase in eccentric strength, while nearly half achieved consistent fascicle length increases with the NHE training.

football
eccentric training
injury prevention
knee flexors
==== Body
pmcINTRODUCTION

Top-level male soccer players present injury rates of 4.1/1.000 hours of training exposure and 27.5/1.000 hours of match exposure,1 while injury rates in female players are 2.7-3.1/1.000 hours and 13.9-23.6/1.000 hours in training and matches, respectively.2–4 According data from 2016–2017 season, English Premier League male clubs suffered an average of 1410 days out due to injury and lost £45 million per season due to injury-related decrements in performance.5 The extent of the injury-related losses is not yet clear in the context of female professional soccer, but there is no doubt that injury prevention is a current priority of soccer medicine in both sexes.

Sport injuries are complex and multifactorial in nature,6 so the prevention strategies require a multidimensional approach, which includes specific exercises to enhance muscle strength, joint mobility, neuromuscular control, and movement efficiency, as well as other strategies (e.g., workload monitoring).7 Understanding of injury mechanisms and identification of potential risk factors play a key role on preventing strategies in sports.8 Therefore, soccer clubs apply a range of tests for screening intrinsic risk factors and employ specific strategies to minimize the injuries’ incidence and/or burden.9,10

The hamstring strain injury is one of the most prevalent injuries in team sports, including soccer.11 Up to 80% of hamstring injuries in soccer occur during high speed running.12 While direct evidence is still lacking, the majority of the literature suggests that the most likely timing of injury is the late swing phase, characterized by peak musculotendon strain and negative work.13 Low eccentric knee flexor strength is traditionally pointed out as a risk factor for hamstring injuries,11 which have been supported by prospective studies with soccer players,12,14–16 as well as with athletes from other sports.17–19 More recently, a prospective study evidenced that players with short fascicles in the biceps femoris long head (BFLH) are also more likely to sustain hamstring injury.12 All these studies have only focused on outcomes for male athletes.12,14–19 However, it seems reasonable that prevention programs for both sexes should address strategies to increase the eccentric knee flexor strength and the BFLH fascicle length.

The Nordic hamstring exercise (NHE) is a field-based exercise with focus on eccentric action of knee flexor muscles.20 The NHE was included in the injury prevention program developed by the Fédération Internationale de Football Association (FIFA), the “FIFA 11+”,21 and has been consolidated as one of the commonly used strategies to prevent hamstring injuries in top-tier soccer clubs.9,10 A recent systematic review including male and female athletic populations supports that teams using injury prevention programs that included the NHE reduces hamstring injury rates by half.22 This preventive effect seems to be related to increases on both eccentric knee flexor strength and BFLH fascicle length.23–27 However, no study has evaluated whether NHE promotes such muscular adaptations in female soccer players. Therefore, the aim of this study was to investigate the collective and individual responses of professional female soccer players engaged in a preseason training program with the NHE regarding eccentric knee flexor strength and BFLH fascicle length.

METHODS

Study design

A group of amateur female soccer players (without a NHE training routine) was recruited and evaluated twice within an 8-week interval. These data were used to: (1) assess the reliability of measures collected in this trial; and (2) determine the typical error of measures that would be used to discriminate responders and non-responders in the NHE training group.

In the NHE training group, professional female soccer players completed an eight-week NHE training program coinciding with the club preseason. The participants’ randomization into experimental and control groups was not possible due to the club requirement that all players should perform the preventive program using the NHE. Evaluations were performed one week before starting and one week after ending the training program.

The Ethics Committee of the Federal University of Health Sciences of Porto Alegre (Porto Alegre, Brazil) approved the present study. All subjects were informed about the study purpose and procedures, and provided written informed consent to participate.

Participants

Sixteen amateur female soccer players were part of the non-trained group. They were recruited through the dissemination of the study on social media and played soccer at least once a week. The NHE training group had 17 professional female soccer players from a Brazilian first national division team. They were engaged in a five-day weekly training routine, and one to two weekly games per week. Characteristics of participants are expressed in Table 1.

53641 Table 1: Characteristics of participants (mean±SD).

	Non-trained group
(amateur players)	NHE training group
(professional players)	
Age (years)	24±4	24±5	
Weight (kg)	61±4	58±6	
Height (m)	1.64±0.04	1.62±0.04	
Body mass index (kg/m2)	22.74±1.79	22.00±2.16	

The following inclusion criteria were adopted: (1) age between 18 and 40 years of age; (2) absence of thigh muscle injuries in the six months prior to the study; (3) absence of musculoskeletal injuries in lower limbs during data collection; (4) absence of any health disorders that would interfere with the NHE execution. Participants allocated in the NHE training group had to have attended a minimum of 14 training sessions (i.e., ~90% adherence) to be included in data analysis, while participants allocated in the non-trained group should have kept their usual exercise routine between the two evaluation time-points. All participants were instructed not to consume any stimulant substance, medicine or alcoholic beverages in the 24 hours before the testing sessions.

Procedures

Fascicle length evaluation

A B-mode ultrasonography system (DP-30, Mindray Medical International Ltd., Shenzhen, China) with a linear array probe (53 mm) was used to assess muscle architecture parameters of the BFLH. All ultrasound scans were taken by an experienced researcher through methods routinely used in our laboratory.24,28 The participants were assessed in prone position with the hips neutral, the knees fully extended, and the muscles relaxed. Ultrasound scans were taken at 50% of the muscle length (i.e., the midportion between the ischial tuberosity and the superior border of the fibular head). The ultrasound probe was positioned perpendicularly to the skin and following the longitudinal axis of the BFLH, with slight adjustments in probe orientation as necessary to optimize identification of the aponeuroses and fascicles.

Three ultrasound images of each limb were obtained and stored for analysis through the ImageJ software (National Institutes of Health, EUA). Image analysis was performed by an assessor blinded to group allocation. The most visible fascicle in each image was used to estimate the BFLH fascicle length using a validated equation.29 The average value between the three ultrasound images was used for statistical analyses. Previous data collected in our lab in 20 healthy active men presented acceptable test–retest reliability scores for BFLH fascicle length [intraclass correlation coefficient, 0.95 (0.86–0.98); coefficient of variation, 5.5% (4.-0–9.2); typical error, 0.48 cm (0.35–0.79)]. The non-trained group’s data were used to assess the test-retest reliability in female soccer players in the current study.

Eccentric strength evaluation

The eccentric knee flexor strength during the NHE execution was measured through a custom-made device (Figure 1). This device is similar to the prototype developed by Opar et al.,30 and has been used in studies with male soccer players.31,32 Previous data collected in our lab consisting of 20 healthy active men presented acceptable test–retest reliability scores for knee flexor strength [intraclass correlation coefficient, 0.94 (0.85-0.98), coefficient of variation, 5% (3.2–6.7%); typical error, 18.54 N (13.93–22.36 N)]. The non-trained group’s data were used to assess the test-retest reliability in female soccer players in the current study.

51725 Figure 1: Assessment of eccentric knee flexor strength during the NHE execution.

Briefly, the participant was positioned to perform the NHE on a platform, and commercially available load cells (E-lastic; E-sporte Soluções Esportivas, Brasilia, Brazil) with simultaneous transference of data via Bluetooth were fastened around their ankles (right above the lateral malleolus). The participant was instructed to execute the NHE as the following: from the initial position (kneeling, the hip neutral and the torso upright), lay the torso forwards using only the knee joint (e.g., without altering the position of hips or spine), in slow speed and using the hamstring muscle eccentrically during the entire range of motion to avoid the torso acceleration to the floor. The participant should have to use their upper limbs to absorb the fall and to return to the initial NHE position. Each participant performed five NHE repetitions, with a 10-second rest between attempts. The force values were continuously registered during all repetitions, and the highest force value obtained in each lower limb was considered to statistical analysis.

NHE training program

The 8-week NHE training program (frequency and number of sets and repetitions) was based on previous studies involving NHE23,27 and provided a progressive workload increase (Figure 2). The NHE training weekly schedule was set by the coaching staff according to the games and travels, always respecting at least 48 hours between the NHE training sessions. NHE was always performed before soccer practices. A regular warm-up protocol guided by the team strength and conditioning coach was performed before the NHE execution. Players with similar anthropometric characteristics were organized in pairs to perform the NHE. A researcher supervised every NHE session to ensure correct implementation and the training volume (number of sets and number of repetitions per set) as well as proper exercise execution.

51724 Figure 2: Left: players performing the Nordic hamstring exercise (NHE); Right: the NHE training program.

Statistical analysis

Data collected in non-trained group (amateur players) were used to assess intraclass correlation coefficient (ICC), typical error (TE) and coefficient of variation (CV) of the measures. ICC values were qualitatively recorded as poor (<0.50), moderate (0.50-0.74), good (0.75-0.90), and excellent (>0.90).33 Additionally, a CV of 10% or less was set as the level at which a measure was considered reliable.30

In the NHE training group, paired sample t-tests were used to check difference between pre- and post-training in each limb. The significance level was set as 5% (α<0.05). Effect size (ES) calculation was performed using the Cohen’s d. Training effects were considered as “trivial” (ES<0.2), “small” (ES>0.2), “moderate” (ES>0.5) or “large” (ES>0.8).

The between-limbs average change (pre- to post-training) was used for calculation of individual responsiveness to NHE training. Responders and non-responders were determined using the typical error criteria: non-responders were defined as subjects who failed to achieve an increase that was greater than two times the typical error (TE) of measurement.31 Results provided by the non-trained group were used to calculate the TE of measurement. The TE for eccentric knee flexor strength was 12.18 N, thus subjects had to demonstrate at least 24.35 N of strength gain to be considered responders to the NHE training. The TE for BFLH fascicle length was 0.36 cm, thus volunteers had to demonstrate at least 0.72 cm of fascicle elongation to be considered responders to the NHE training.

RESULTS

The non-trained group’s data demonstrated that the measures used in this study were reliable (Table 2). All participants in the NHE training group attended 16 sessions (i.e., 100% adherence). The group experienced significant increases (p<0.05) in both lower limbs for the eccentric knee flexor strength (moderate to large effect sizes) and BFLH fascicle length (small to moderate effect sizes), as detailed in Table 3. Twelve players (~71%) were considered responders to the training program for the eccentric knee flexor strength, while eight athletes (~47%) were responders for the BFLH fascicle length (Figure 3). The five non-responders for the eccentric knee flexor strength were also non-responders for the BFLH fascicle length.

53642 Table 2: Reliability of eccentric knee flexor strength and biceps femoris long head fascicle length measures. Data collected in non-trained group [mean±SD (95%CI)].

	Measure 1	Measure 2	ICC	CV	TE	p-value	
Eccentric strength (N)							
Right limb	235±35 (217-254)	243±32 (227-260)	0.87	5%	12.74 N	0.112	
Left limb	230±29 (215-244)	235±24 (223-248)	0.82	5.3%	11.97 N	0.185	
Fascicle length (cm)							
Right limb	9.43±1.86 (8.47-10.39)	9.46±1.71 (8.58-10.34)	0.97	3.8%	0.19 cm	0.824	
Left limb	9.78±1.28 (9.12-10.44)	9.93±1.21 (9.31-10.55)	0.92	4.2%	0.38 cm	0.279	
N, Newtons, cm, centimeters, ICC, intraclass correlation coefficient; CV, coefficient of variation; TE, typical error.

53643 Table 3: Eccentric knee flexor strength and biceps femoris long head fascicle length of the NHE training group [mean±SD (95%CI)].

	Pre-training	Post-training	Δ	Δ%	ES	p-value	
Eccentric strength (N)							
Right limb	263±41 (242-284)	298±48 (274-323)	35.31	13.41	0.82C	0.003	
Left limb	254±44 (231-276)	289±53 (261-316)	34.9	13.76	0.74B	0.001	
Fascicle length (cm)							
Right limb	9.90±1.44 (9.16-10.64)	10.51±1.45 (9.76-11.26)	0.61	6.16	0.44A	<0.001	
Left limb	9.57±1.09 (9.01-10.13)	10.20±0.89 (9.74-10.66)	0.63	6.58	0.65B	<0.001	
N, Newtons, cm, centimeters, Δ, mean absolute change; Δ%, mean percent change; ES, effect size;

A small effect size; B moderate effect size; C large effect size.

51723 Figure 3: Individual responsiveness to the NHE training program. Black lines indicate individual responses, and vertical grey bars show the group average values. Δ = absolute and percent changes of responders and non-responders.

DISCUSSION

This is the first study to investigate the effects of a NHE training program on hamstring injury risk factors in professional female soccer players. The main findings were that the NHE training program implemented here increased both the eccentric knee flexor strength and the BFLH fascicle length. More than two-thirds of players demonstrated a meaningful increase in eccentric strength, while nearly half achieved consistent fascicle length increases with the NHE training.

Measures of eccentric knee flexor strength have been performed through isokinetic dynamometers for decades, and those devices are considered the gold standard tool for assessing human strength through joint torque measures. A few years ago, Opar et al.30 validated a prototype allowing a cheaper and faster assessment of the eccentric knee flexor strength during the NHE execution. While a large cohort study found no clinical value of strength tests with isokinetic dynamometry or the NHE device for predicting risk of hamstring injury,34 cohort studies with soccer,12,14–16 Australian football,19 rugby,18 and sprinters17 have demonstrated that athletes with eccentric knee flexor weakness are more susceptible to hamstring injury. For this reason, eccentric strength was selected as the primary outcome of the current study, and findings demonstrated that an 8-week NHE training program improved eccentric strength of the knee flexor muscles of female soccer players.

Professional male soccer players have demonstrated eccentric knee flexor strength values ranging from ~299 N to ~411 N during the NHE,34,35 while female players in the present study had ~258 N. Previous studies involving 6-10 weeks of NHE training have found increases of 7-11% on the eccentric knee flexor strength in well-conditioned male athletes.23,27,36,37 Therefore, the average increase of ~13% presented by female professional players in the current study suggest a satisfactory response to the NHE training program. It has been suggested that for every 10 N increase in eccentric knee flexor strength, the risk of hamstring injury can be reduced by 9% in male soccer players.12 Although the same numbers should not be assumed for female players, it is plausible to speculate that the approximate 35 N increase in eccentric strength found in our study may have aided the prevention of hamstring injury along the season.

A prospective cohort study found that soccer players with shorter BFLH fascicles were four times more likely to suffer a subsequent hamstring injury than those with longer fascicles.12 The mechanism by which shorter fascicles predispose athletes to injury is not entirely clear, but a reasonable hypothesis suggests that short fascicles (i.e., fewer in series sarcomeres) may be more susceptible to excessive stretching and subsequent injury during eccentric high-intensity contractions,38 such as those performed during high-speed running. The fascicle lengthening in response to the NHE training was expected in the present study because it has been consistently reported in both active subjects24 and well-conditioned athletes.23,27 However, it is curious that female players in the present study increased their BFLH fascicle length (~7% or ~0.6 cm) with a slightly lower magnitude compared to male athletes submitted to the same training program periodization (~9-10% or ~1 cm).23,27

The individual responsiveness is an interesting analysis for professionals working in the medical departments and coaching staffs of team sports. Although the average values give us an idea of the team’s behavior, it is important to note that individual responses varied. In the present study, 71% of players had consistent muscle strength gains with the NHE training, which is a similar percentage of responders than those found in male soccer players engaged in a NHE training program during preseason (19 out of 25 players, 76%).31 Conversely, half of players engaged in the NHE training program in the current study did not experience fascicle length enhancement. All players were engaged in the same soccer training routine and all of them attended every NHE training session, thus adherence issues cannot explain the non-responders. Baseline status also does not seem to explain the training responses, as illustrated by the similar pre-training levels between responders and non-responders in Figure 3. Interestingly, all non-responders for the eccentric strength were also non-responders for the BFLH fascicle length. Further investigation is needed to understand why some athletes respond to NHE training and others do not. In addition, it would be a sports medicine breakthrough if future studies could determine if responders and non-responders have different injury rates during the season.

Like all sport injuries, muscle strains are complex and multifactorial in nature,6 and most soccer players present multiple risk factors for sustaining a hamstring injury.28 According prospective data,12 eccentric knee flexor strength and BFLH fascicle length account for approximately 30% of the risk associated with hamstring injury occurrence, thus the other 70% cannot be undervalued. The posterior chain flexibility,39 hamstring-to-quadriceps strength ratios,14,16 and proximal neuromuscular control40 are examples of modifiable factors also associated with hamstring injury. Therefore, despite the present study focused the effects of a single exercise on only two of those risk factors (eccentric knee flexor strength and BFLH fascicle length), a comprehensive approach is recommended for preventive programs.41

The current study has limitations. First, this is not a randomized controlled trial. It means that the NHE cannot be assumed as the single factor responsible for changes observed on muscle strength and architecture, despite previous evidence in male players has demonstrated that regular soccer training does not affect the outcomes assessed here.25,36 Second, it was not possible to follow the injury rates of the professional players along the subsequent season, which would allow us to verify whether the individual responsiveness to the NHE training program had an influence on the hamstring injuries or not. Third, the number of participants in the current study is small, and caution is recommended regarding the percent distribution of responders and non-responders to the NHE training program. Despite these limitations, this study presents high ecological validity because it was done within the real-world of competitive soccer.

CONCLUSION

The results of this study indicate that an 8-week NHE training program performed twice a week during preseason increases the eccentric knee flexor strength and the BFLH fascicle length in professional female soccer players. The positive effects on two injury risk factors for hamstring strain injury support the adoption of the NHE within a prevention program. Medical and coaching staffs must be attentive and monitor individual responses because not all players benefit from the NHE intervention.

Conflicts of Interest

The authors declare that there is no conflict of interest.

Acknowledgements

BMB thank CNPq-Brazil for the research productivity fellowship.
==== Refs
Injury incidence and injury patterns in professional football: The UEFA injury study British Journal of Sports Medicine Ekstrand J. Hägglund M. Waldén M. 2011
45 7 553 558 0306-3674 10.1136/bjsm.2009.060582 10.1136/bjsm.2009.060582 19553225
Injuries in female soccer players: A prospective study in the German national league The American Journal of Sports Medicine Faude Oliver Junge Astrid Kindermann Wilfried Dvorak Jiri SAGE Publications 11 2005
33 11 1694 1700 0363-5465 10.1177/0363546505275011 10.1177/0363546505275011
Injuries among Swedish female elite football players: A prospective population study Scandinavian Journal of Medicine and Science in Sports Jacobson I. Tegner Y. 2007
17 1 84 91 0905-7188 10.1111/j.1600-0838.2006.00524.x 10.1111/j.1600-0838.2006.00524.x 17305943
Injuries in Norwegian female elite soccer: A prospective one-season cohort study Knee Surgery, Sports Traumatology, Arthroscopy Tegnander Agnar Olsen Odd Egil Moholdt Trine Tegdan Engebretsen Lars Bahr Roald Springer Science and Business Media LLC 2008
16 2 194 198 0942-2056 10.1007/s00167-007-0403-z 10.1007/s00167-007-0403-z
Estimation of injury costs: Financial damage of English Premier League teams’ underachievement due to injuries BMJ Open Sport & Exercise Medicine Eliakim Eyal Morgulev Elia Lidor Ronnie Meckel Yoav BMJ 5 2020
6 1 e000675 2055-7647 10.1136/bmjsem-2019-000675 10.1136/bmjsem-2019-000675 32537241
Complex systems approach for sports injuries: Moving from risk factor identification to injury pattern recognition-narrative review and new concept British Journal of Sports Medicine Bittencourt N F N Meeuwisse W H Mendonça L D Nettel-Aguirre A Ocarino J M Fonseca S T BMJ 21 7 2016
50 21 1309 1314 0306-3674 10.1136/bjsports-2015-095850 10.1136/bjsports-2015-095850
An injury prevention pyramid for elite sports teams British Journal of Sports Medicine Coles Philip Alexander BMJ 2018
52 15 1008 1010 0306-3674 10.1136/bjsports-2016-096697 10.1136/bjsports-2016-096697 28343160
Understanding injury mechanisms: A key component of preventing injuries in sport British Journal of Sports Medicine Bahr R Krosshaug T. 1 6 2005
39 6 324 329 0306-3674 10.1136/bjsm.2005.018341 10.1136/bjsm.2005.018341 15911600
Risk factors, testing and preventative strategies for non-contact injuries in professional football: Current perceptions and practices of 44 teams from various premier leagues British Journal of Sports Medicine McCall Alan Carling Chris Nedelec Mathieu Davison Michael Le Gall Franck Berthoin Serge Dupont Gregory BMJ 16 5 2014
48 18 1352 1357 0306-3674 10.1136/bjsports-2014-093439 10.1136/bjsports-2014-093439
Strategies for injury prevention in Brazilian football: Perceptions of physiotherapists and practices of premier league teams Physical Therapy in Sport Meurer Maurício Couto Silva Marcelo Faria Baroni Bruno Manfredini 11 2017
28 1 8 1466-853X 10.1016/j.ptsp.2017.07.004 10.1016/j.ptsp.2017.07.004
Hamstring strain injuries: Factors that lead to injury and re-injury Sports Medicine Opar David A. Williams Morgan D. Shield Anthony J. 3 2012
42 3 209 226 0112-1642 10.2165/11594800-000000000-00000 10.2165/11594800-000000000-00000 22239734
Short biceps femoris fascicles and eccentric knee flexor weakness increase the risk of hamstring injury in elite football (soccer): A prospective cohort study British Journal of Sports Medicine Timmins Ryan G Bourne Matthew N Shield Anthony J Williams Morgan D Lorenzen Christian Opar David A BMJ 2016
50 24 1524 1535 0306-3674 10.1136/bjsports-2015-095362 10.1136/bjsports-2015-095362 26675089
Late swing or early stance? A narrative review of hamstring injury mechanisms during high‐speed running Scandinavian Journal of Medicine & Science in Sports Kenneally‐Dabrowski Claire J. B. Brown Nicholas A. T. Lai Adrian K. M. Perriman Diana Spratford Wayne Serpell Benjamin G. Wiley 22 5 2019
29 8 1083 1091 0905-7188 10.1111/sms.13437 10.1111/sms.13437
Strength imbalances and prevention of hamstring injury in professional soccer players: A prospective study The American Journal of Sports Medicine Croisier Jean-Louis Ganteaume Sebastien Binet Johnny Genty Marc Ferret Jean-Marcel SAGE Publications 8 2008
36 8 1469 1475 0363-5465 10.1177/0363546508316764 10.1177/0363546508316764 18448578
Intrinsic risk factors of non-contact quadriceps and hamstring strains in soccer: A prospective study of 100 professional players British Journal of Sports Medicine Fousekis K. Tsepis E. Poulmedis P. Athanasopoulos S. Vagenas G. 2011
45 9 709 714 0306-3674 10.1136/bjsm.2010.077560 10.1136/bjsm.2010.077560 21119022
Eccentric hamstring strength deficit and poor hamstring-to-quadriceps ratio are risk factors for hamstring strain injury in football: A prospective study of 146 professional players Journal of Science and Medicine in Sport Lee Justin W.Y. Mok Kam-Ming Chan Hardaway C.K. Yung Patrick S.H. Chan Kai-Ming 8 2018
21 8 789 793 1440-2440 10.1016/j.jsams.2017.11.017 10.1016/j.jsams.2017.11.017 29233665
Strength deficits identified with concentric action of the hip extensors and eccentric action of the hamstrings predispose to hamstring injury in elite sprinters Journal of Orthopaedic & Sports Physical Therapy Sugiura Yusaku Saito Tomoyuki Sakuraba Keishoku Sakuma Kazuhiko Suzuki Eiichi Journal of Orthopaedic & Sports Physical Therapy (JOSPT) 8 2008
38 8 457 464 0190-6011 10.2519/jospt.2008.2575 10.2519/jospt.2008.2575 18678956
Eccentric knee flexor strength and risk of hamstring injuries in Rugby Union: A prospective study The American Journal of Sports Medicine Bourne Matthew N. Opar David A. Williams Morgan D. Shield Anthony J. SAGE Publications 2 9 2015
43 11 2663 2670 0363-5465 10.1177/0363546515599633 10.1177/0363546515599633
Eccentric hamstring strength and hamstring injury risk in Australian footballers Medicine & Science in Sports & Exercise Opar David A. Williams Morgan D. Timmins Ryan G. Hickey Jack Duhig Steven J. Shield Anthony J. 4 2015
47 4 857 865 0195-9131 10.1249/mss.0000000000000465 10.1249/mss.0000000000000465 25137368
Human hamstring muscles adapt to eccentric exercise by changing optimum length Medicine and Science in Sports and Exercise Brockett CAMILLA L. Morgan DAVID L. Proske UWE 5 2001
33 5 783 790 0195-9131 10.1097/00005768-200105000-00017 10.1097/00005768-200105000-00017 11323549
FIFA 11+: An effective programme to prevent football injuries in various player groups worldwide-a narrative review British Journal of Sports Medicine Bizzini Mario Dvorak Jiri BMJ 15 4 2015
49 9 577 579 0306-3674 10.1136/bjsports-2015-094765 10.1136/bjsports-2015-094765 25878073
Including the Nordic hamstring exercise in injury prevention programmes halves the rate of hamstring injuries: A systematic review and meta-analysis of 8459 athletes British Journal of Sports Medicine van Dyk Nicol Behan Fearghal P Whiteley Rod BMJ 26 2 2019
53 21 1362 1370 0306-3674 10.1136/bjsports-2018-100045 10.1136/bjsports-2018-100045
Effect of weekly training frequency with the Nordic hamstring exercise on muscle strain risk factors in football players: A randomized trial International Journal of Sports Physiology and Performance Medeiros Thales M. Ribeiro-Alvares João B. Fritsch Carolina G. Oliveira Gabriel S. Severo-Silveira Lucas Pappas Evangelos Baroni Bruno M. 1 8 2020
15 7 1026 1033 1555-0265 10.1123/ijspp.2018-0780 10.1123/ijspp.2018-0780
Four weeks of Nordic hamstring exercise reduce muscle injury risk factors in young adults Journal of Strength and Conditioning Research Ribeiro-Alvares João Breno Marques Vanessa B. Vaz Marco A. Baroni Bruno M. 5 2018
32 5 1254 1262 1064-8011 10.1519/jsc.0000000000001975 10.1519/jsc.0000000000001975 28459795
Hamstring injury prevention in soccer: Before or after training? Scandinavian Journal of Medicine & Science in Sports Lovell R. Knox M. Weston M. Siegler J. C. Brennan S. Marshall P. W. M. Wiley 2018
28 2 658 666 0905-7188 10.1111/sms.12925 10.1111/sms.12925 28544170
‘Nordic’ Hamstrings Exercise – Engagement characteristics and training responses International Journal of Sports Medicine Iga J. Fruer C. Deighan M. Croix M.D. James D.V. 15 8 2012
33 12 1000 1004 0172-4622 10.1055/s-0032-1304591 10.1055/s-0032-1304591
Progressive workload periodization maximizes effects of Nordic hamstring exercise on muscle injury risk factors Journal of Strength and Conditioning Research Severo-Silveira Lucas Dornelles Maurício P. Lima-E-Silva Felipe X. Marchiori César L. Medeiros Thales M. Pappas Evangelos Baroni Bruno M. 22 10 2018
Publish Ahead of Print 1064-8011 10.1519/jsc.0000000000002849 10.1519/jsc.0000000000002849
Prevalence of hamstring strain injury risk factors in professional and under-20 male football (soccer) players Journal of Sport Rehabilitation Ribeiro-Alvares João Breno Dornelles Maurício Pinto Fritsch Carolina Gassen de Lima-e-Silva Felipe Xavier Medeiros Thales Menezes Severo-Silveira Lucas Marques Vanessa Bernardes Baroni Bruno Manfredini 1 3 2020
29 3 339 345 1056-6716 10.1123/jsr.2018-0084 10.1123/jsr.2018-0084
Validity of architectural properties of the hamstring muscles: Correlation of ultrasound findings with cadaveric dissection Journal of Biomechanics Kellis Eleftherios Galanis Nikiforos Natsis Konstantinos Kapetanos George 11 2009
42 15 2549 2554 0021-9290 10.1016/j.jbiomech.2009.07.011 10.1016/j.jbiomech.2009.07.011
A novel device using the Nordic hamstring exercise to assess eccentric knee flexor strength: A reliability and retrospective injury study Journal of Orthopaedic & Sports Physical Therapy Opar David A. Piatkowski Timothy Williams Morgan D. Shield Anthony J. Journal of Orthopaedic & Sports Physical Therapy (JOSPT) 9 2013
43 9 636 640 0190-6011 10.2519/jospt.2013.4837 10.2519/jospt.2013.4837 23886674
A four-week training program with the Nordic hamstring exercise during preseason increases eccentric strength of male soccer players International Journal of Sports Physical Therapy de Oliveira Nathalia Trevisol Medeiros Thales Menezes Vianna Karoline Baptista Oliveira Gabriel Santos de Araujo Ribeiro-Alvares João Breno Baroni Bruno Manfredini 5 2020
15 4 571 578 2159-2896 10.26603/ijspt20200571 10.26603/ijspt20200571 33354390
Eccentric knee flexor strength of professional football players with and without hamstring injury in the prior season European Journal of Sport Science Ribeiro-Alvares João Breno Oliveira Gabriel Dos Santos De Lima-E-Silva Felipe Xavier Baroni Bruno Manfredini 26 3 2020
21 1 131 139 1746-1391 10.1080/17461391.2020.1743766 10.1080/17461391.2020.1743766
A guideline of selecting and reporting intraclass correlation coefficients for reliability research Journal of Chiropractic Medicine Koo Terry K. Li Mae Y. 6 2016
15 2 155 163 1556-3707 10.1016/j.jcm.2016.02.012 10.1016/j.jcm.2016.02.012 27330520
A comprehensive strength testing protocol offers no clinical value in predicting risk of hamstring injury: A prospective cohort study of 413 professional football players British Journal of Sports Medicine van Dyk Nicol Bahr Roald Burnett Angus F Whiteley Rod Bakken Arnhild Mosler Andrea Farooq Abdulaziz Witvrouw Erik BMJ 29 7 2017
51 23 1695 1702 0306-3674 10.1136/bjsports-2017-097754 10.1136/bjsports-2017-097754
The effect of body mass on eccentric knee-flexor strength assessed with an instrumented Nordic hamstring device (Nordbord) in football players International Journal of Sports Physiology and Performance Buchheit Martin Cholley Yannick Nagel Mark Poulos Nicholas 9 2016
11 6 721 726 1555-0265 10.1123/ijspp.2015-0513 10.1123/ijspp.2015-0513 26638728
A 10-week randomized trial comparing eccentric vs. concentric hamstring strength training in well-trained soccer players Scandinavian Journal of Medicine and Science in Sports Mjølsnes Roald Arnason Arni Østhagen Tor Raastad Truls Bahr Roald 10 2004
14 5 311 317 0905-7188 10.1046/j.1600-0838.2003.367.x 10.1046/j.1600-0838.2003.367.x
Hamstring eccentric strengthening program: Does training volume matter? International Journal of Sports Physiology and Performance Lacome Mathieu Avrillon Simon Cholley Yannick Simpson Ben M. Guilhem Gael Buchheit Martin 1 1 2020
15 1 81 90 1555-0265 10.1123/ijspp.2018-0947 10.1123/ijspp.2018-0947
New insights into the behavior of muscle during active lengthening Biophysical Journal Morgan D.L. 2 1990
57 2 209 221 0006-3495 10.1016/s0006-3495(90)82524-8 10.1016/s0006-3495(90)82524-8 2317547
Muscle flexibility as a risk factor for developing muscle injuries in male professional soccer players. A prospective study The American Journal of Sports Medicine Witvrouw Erik Danneels Lieven Asselman Peter D'Have Thomas Cambier Dirk 1 2003
31 1 41 46 0363-5465 10.1177/03635465030310011801 10.1177/03635465030310011801
Proximal neuromuscular control protects against hamstring injuries in male soccer players: A prospective study with electromyography time-series analysis during maximal sprinting The American Journal of Sports Medicine Schuermans Joke Danneels Lieven Van Tiggelen Damien Palmans Tanneke Witvrouw Erik SAGE Publications 1 3 2017
45 6 1315 1325 0363-5465 10.1177/0363546516687750 10.1177/0363546516687750
Recommendations for hamstring injury prevention in elite football: Translating research into practice British Journal of Sports Medicine Buckthorpe Matthew Wright Steve Bruce-Low Stewart Nanni Gianni Sturdy Thomas Gross Aleksander Stephan Bowen Laura Styles Bill Della Villa Stefano Davison Michael Gimpel Mo BMJ 2019
53 7 449 456 0306-3674 10.1136/bjsports-2018-099616 10.1136/bjsports-2018-099616 30413424
