Sprint and jump performance in elite male soccer players following a 10-week Nordic Hamstring exercise Protocol: A randomised pilot study

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DOI: 10.1186/s13104-017-2986-x
Cite this publication
Abstract
Objective The preseason Nordic Hamstring Protocol (NHP) reduces hamstring strain injuries in football players. Despite persisting injury rates, elite clubs are reluctant to apply the NHP often over concerns of negative impacts on performance. This pilot study investigated if sprint or jump-performance outcomes tended to increase or decrease following implementation of the NHP in elite male soccer-players. Results Nineteen male soccer players from the Danish 1st division were randomised to perform NHP (27 sessions) during pre-season, or to control group (CG). Sprint performance (30 m with 5 and 10 m split times) and countermovement jump (CMJ height) was measured before the mid-seasonal break and again after 10 weeks of performing the NHP at the end of pre-season. Dropouts were due to transfers and injuries unrelated to performing NHP (NHP = 0, CG = 5). Sprint performance on the short split distances improved for most players in the NHP (6 out of 9 improved, median changes for 5 m split: − 0.068 s; 10 m split: − 0.078 s), but not CG (2 out of 5 improved, median changes for 5 m split: + 0.1 s; 10 m split: CG: + 0.11 s), but both groups had small declines at 30 m sprint (NHP: 7 out of 9 declined, median changes: + 0.116 s; CG: 4 out of 5 declined, median changes: + 0.159 s). CMJ height mostly improved in both groups (NHP: 6 out of 9 improved, median changes: + 2.1 cm; CG: 4 out of 8 improved, median changes: + 0.55 cm). Performing the NHP in elite soccer players did therefore not seem to negatively affect sprint and vertical jump performance outcomes in the present study, while in fact showing some promise for the more explosive characteristics such as the short 5 and 10 m split-times and maximal CMJ height, which all are highly relevant performance parameters in elite football.
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Krommes et al. BMC Res Notes (2017) 10:669
https://doi.org/10.1186/s13104-017-2986-x
RESEARCH NOTE
Sprint and jump performance in elite
male soccer players following a 10-week Nordic
Hamstring exercise Protocol: a randomised pilot
study
K. Krommes1,2* , J. Petersen1, M. B. Nielsen3, P. Aagaard4, P. Hölmich1 and K. Thorborg1,2
Abstract
Objective: The preseason Nordic Hamstring Protocol (NHP) reduces hamstring strain injuries in football players.
Despite persisting injury rates, elite clubs are reluctant to apply the NHP often over concerns of negative impacts on
performance. This pilot study investigated if sprint or jump-performance outcomes tended to increase or decrease
following implementation of the NHP in elite male soccer-players.
Results: Nineteen male soccer players from the Danish 1st division were randomised to perform NHP (27 sessions)
during pre-season, or to control group (CG). Sprint performance (30 m with 5 and 10 m split times) and countermove-
ment jump (CMJ height) was measured before the mid-seasonal break and again after 10 weeks of performing the
NHP at the end of pre-season. Dropouts were due to transfers and injuries unrelated to performing NHP (NHP = 0,
CG = 5). Sprint performance on the short split distances improved for most players in the NHP (6 out of 9 improved,
median changes for 5 m split: 0.068 s; 10 m split: 0.078 s), but not CG (2 out of 5 improved, median changes for
5 m split: + 0.1 s; 10 m split: CG: + 0.11 s), but both groups had small declines at 30 m sprint (NHP: 7 out of 9 declined,
median changes: + 0.116 s; CG: 4 out of 5 declined, median changes: + 0.159 s). CMJ height mostly improved in both
groups (NHP: 6 out of 9 improved, median changes: + 2.1 cm; CG: 4 out of 8 improved, median changes: + 0.55 cm).
Performing the NHP in elite soccer players did therefore not seem to negatively affect sprint and vertical jump per-
formance outcomes in the present study, while in fact showing some promise for the more explosive characteristics
such as the short 5 and 10 m split-times and maximal CMJ height, which all are highly relevant performance param-
eters in elite football.
Keywords: Nordic Hamstring exercise, Hamstring strain injuries, Soccer, Football, Eccentric
© The Author(s) 2017. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License
(http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium,
provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license,
and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/
publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Introduction
Hamstring injuries are common in sports involving
sprinting and jumping, including different variations of
football [14]. Preventing new and recurrent hamstring
injuries in amateur and sub-elite football has effectively
been achieved in several trials by implementation of
the Nordic Hamstring Protocol, a 10-week pre-season
eccentric hamstring strength-training protocol based
on the Nordic Hamstring exercise [5, 6]. Elite clubs are
familiar with the exercise but only few utilize the full
protocol [7], more than half have reservations about the
exercise [7], and a large proportion do not employ it in
any way [8]. is is in line with epidemiological data
showing maintained or even slightly increased incidence
of hamstring injuries in elite clubs over the past decade
[9]. It is suggested that elite football environments holds
certain specific barriers to implementing preventive
measures [1012], and some have even argued that the
Nordic Hamstring exercise can decrease performance
Open Access
BMC Research Notes
*Correspondence: krommes@gmail.com
1 Sports Orthopedic Research Center-Copenhagen (SORC-C), Depar tment
of OrthopedicSurgery, Copenhagen University Hospital, Kettegaard Alle
30, Hvidovre, Denmark
Full list of author information is available at the end of the article
Page 2 of 6
Krommes et al. BMC Res Notes (2017) 10:669
and prompt injuries [13, 14]. Others propose that instead
of the Nordic Hamstring exercise, other exercises should
be employed in sprint-training and hamstring injury pre-
vention, although no data supports this claim [1517].
e Nordic Hamstring Protocol in isolation increases
eccentric hamstring strength, which is considered essen-
tial for sprint performance [18], and studies using other
means to increase eccentric hamstring strength have
indeed also reported improvements in jump [19] and
sprint [19, 20] performance. e Nordic Hamstring Pro-
tocol has not been investigated for its isolated effect on
jump or sprint outcomes but studies employing the exer-
cise in either various dosages or different timings, or
accompanying other forms of training, have indicated
either maintained or increased jump or sprint perfor-
mance, along with gains in eccentric hamstring strength
[2128]. e main purpose of this study was to pilot
implementation of the Nordic Hamstring Protocol on
team-level, in order to monitor its effect on sprinting
and jumping performance in elite male football players.
e secondary purpose was to obtain data for sample
size calculations, and other useful information for future
research.
Main text
Methods
Potential participants were 25 football players in a first
team squad from the Danish 1st Division, chosen based
on convenience sampling as one author (JP) served as
Team Doctor for the team. Injured players at the time
of pre-testing were excluded. e season in the Danish
1st Division starts in August and ends in June, includ-
ing a mid-seasonal break from December to March. All
pre-tests were performed in the week following the final
match in November 2008. e 10-week intervention was
introduced when physical training started in January.
Post-tests were performed in the week prior to the first
played match in March 2009. Besides the intervention,
both groups followed usual diet- and exercise regimes.
One author stratified all players according to age and
playing position, and subsequently randomised them to
intervention (Nordic group) or control group, by draw-
ing lots in blocks of two matched players from an opaque
envelope. e same author carried out physical tests,
and sprint and jump tests, which were all completed on
separate days. e reporting of this study follows the
Consolidated Standards of Reporting Trials (CONSORT)
statement when applicable [29].
Intervention; the Nordic Hamstring Protocol
e Nordic Hamstring Protocol consists of 27 sessions of
the Nordic Hamstring exercise, performed before regu-
lar warm-up during a 10-week period, starting with 1
weekly session of 2 sets of 5 repetitions, and ending with
3 weekly sessions with 3 sets of 12, 10 and 8 repetitions
respectively in week 5 through 10 [30]. If players were
not attending atraining session, they were instructed to
perform the protocol at home. e Nordic Hamstring
exercise is a partner exercise where the player attempts
to resist a forward-falling motion using his hamstrings to
maximize loading in the eccentric phase. e player were
asked to keep their hips fixed in a slightly flexed position
throughout the whole range of motion, and to brake the
forward fall for as long as possible using their hamstrings,
and to try keeping tension in their hamstrings even after
they have to ‘‘let go’. ey were asked to use their arms
and hands to buffer the fall, let the chest touch the sur-
face, and immediately get back to the starting position by
forcefully pushing with their hands to minimize loading
in the concentric phase. e Nordic Hamstring Protocol
has been described in detail by Mjølsnes etal. [30].
Sprint testing
Sprint performance was assessed on an indoor all-
weather-track to ensure similar ground and weather con-
ditions between sessions. A warm-up program similar to
the program used before match-play preceded the run-
ning tests, which consisted of 20min of various running
drills without ball led by the captain of the squad. Photo-
cells were positioned at 5, 10 and 30m for the sprint test,
which was conducted from a standing start on the touch
pad of an electronic timing device (Newtest, Oulu, Fin-
land). ree trials were performed, of which the fastest
time was used.
Jump testing
Vertical jump height was measured using an Accugait
force plate (Amti, USA) on the same surface for both
pre- and post-testing. To reduce the influence of shoe
properties on jump performance [31] players used the
same shoe type (Nike, Total90 Shoot-II-IC) in all tests.
A 15 min standardized warm-up procedure was used
before testing, consisting of stationary biking and sub-
maximal jumping variations. e players were instructed
to stand in an upright position with feet shoulder width
apart and keep hands on their hips throughout the
jumps. From this position the players were instructed
to do a countermovement jump by performing a rapid
downward movement by flexing the knees and hips, fol-
lowed by immediately extending the knees and hips in
order to jump as high as possible. Jumping height was
determined as the height of center of mass displacement
calculated from integration (0.001s time constant) of the
vertical ground reaction force and the measured body
mass [32]. Each individual test was repeated a minimum
of 6–8 times until a plateau of less than 5% between two
Page 3 of 6
Krommes et al. BMC Res Notes (2017) 10:669
consecutive trials was reached and the best trial was then
used.
Statistical analysis
With no predetermined level of statistical power, not-
normally distributed data with distinct outliers, and a
small final sample (5–9 players in each group for differ-
ent outcomes), no statistical testing was performed of
the dependent variables [33, 34]. Individual player data
are visualized to present the distribution and non-line-
arity of changes. Median changes is provided as a meas-
ure of central tendency [33, 35, 36]. Means and standard
deviations of group differences and combined group dif-
ferences for 30m sprint, 5- and 10m split, and counter-
movement jump are presented to supply data for future
sample size calculations [33, 35]. Baseline data from all
randomised players that completed testing in November
are displayed in Table1.
Results
Nineteen players were randomised and completed pre-
testing (Table1). Due to injuries (unrelated to perform-
ing the protocol), club-transfers and absence during
data-collection, some players did not attend post-testing
in March. Fourteen of the 19 included players completed
sprint tests with all of the dropouts occurring in the con-
trol group (n=5). Seventeen of the 19 included players
completed jump test with dropouts also only occurring
in the control group (n=2). Compliance was 100%, as
all players in the Nordic group performed the 27 sessions
and prescribed repetitions as intended.
Sprint performance on the short split distances
improved for most players in the NHP (6 out of 9
improved, median changes for 5m split: 0.068s; 10m
split: 0.078s), but not CG (2 out of 5 improved, median
changes for 5m split: +0.1s; 10m split: CG: +0.11s),
but both groups had small declines at 30m sprint (NHP:
7 out of 9 declined, median changes: + 0.116 s; CG:
4 out of 5 declined, median changes: + 0.159 s). CMJ
height mostly improved in both groups (NHP: 6 out of
9 improved, median changes: +2.1cm; CG: 4 out of 8
improved, median changes: +0.55cm) (Fig.1).
Discussion
Performing the full 10-week Nordic Hamstring Protocol
during preseason in elite soccer players did not seem to
negatively affect sprint and vertical jump performance
outcomes, while in fact showing some promise for the
more explosive characteristics such as the short 5 and
10 m split-times and maximal countermovement jump
height compared to control group or baseline measures.
e data from the present study are in line with previ-
ous findings of either maintained or increased sprint
and jump performance when performing the Nordic
Hamstring exercise with smaller dosage or as part of
additional strength training [2128]. Previous stud-
ies on sprint performance in elite male football players
have demonstrated a difference in maximum mean 10m
sprint times between the top and bottom 25th percen-
tile of 0.08s [37], suggesting the median improvement of
0.078s (mean 0.14s) observed in the intervention group
could be clinically relevant if replicated in adequately
powered future trials. As such, this study can provide
data for such trials to obtain appropriate statistical power
and make pre-determined decisions regarding analyses
(Table2). e standard deviation of changes of, e.g. the
10m split for both groups, were 0.13s, so in order to
show a mean between-group difference of 0.14s, as in the
present study (corresponding to a large effect size), with
a power of 80% and alpha level at 0.05 using a two-tailed
paired t test, a sample with 16 players in each group
would be needed (G*Power 3.1.9.2) (Table2).
e data can be of use if future research on the effect of
the Nordic Hamstring exercise on either injury rates or
performance outcomes in an elite football setting should
come across reluctant coaching- or medical staff with
reservations about impacts of the Nordic Hamstring Pro-
tocol on performance measures. e protocol of such a
future trial can be designed in accordance with the pre-
sent study, as it was simple to execute, and participat-
ing players and staff reported no compliance issues or
adverse events, while the effort of the individual players
was also deemed acceptable.
Table 1 Baseline data of the intervention and control
group
Group mean values and standard deviations obtained in November 2008. BMI
body mass index, RM repetition maximum. The Cooper test is a 12-min running
test of physical fitness. The squat was performed as a full barbell squat with
the femurs parallel to the ground. Some measures involved different number
of players; the Cooper test (n = 8 in both groups); the sprint test (n = 9 in the
Nordic group and n = 8 in the control group); the countermovement jump test
(CMJ; n = 9 in both groups); and Squat 1RM (n = 7 in the Nordic group and
n = 4 in the control group)
Nordic group (n = 9) Control group (n = 10)
Age (years) 23.0 ± 3.9 25.1 ± 4.9
Body mass (kg) 73.1 ± 5.8 77.9 ± 9.9
Height (m) 1.83 ± 0.05 1.81 ± 0.07
BMI (kg/m2) 21.8 ± 1.6 23.7 ± 2.0
Cooper test (m) 3052.5 ± 291.4 3102.5 ± 363.2
Squat 1RM load (kg) 93.6 ± 25.1 111.3 ± 8.5
30 m sprint (s) 4.101 ± 0.159 4.036 ± 0.095
5 m split (s) 0.904 ± 0.108 0.838 ± 0.027
10 m split (s) 1.686 ± 0.152 1.599 ± 0.047
CMJ (cm) 43.8 ± 3.7 42.6 ± 6.7
Page 4 of 6
Krommes et al. BMC Res Notes (2017) 10:669
Conclusion
Conducting the simple 10-week pre-season Nordic Ham-
string Protocol in elite soccer players did not negatively
affect sprint and vertical jumping performance, respec-
tively. Signs of improved explosive acceleration charac-
teristics as evaluated by 5 and 10m split times, and the
-0.5
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
Nordic groupControl group
seconds
Median difference 30 m sprint
3.7
3.8
3.9
4.0
4.1
4.2
4.3
4.4
4.5
4.6
November March November March
Nordic groupControl group
seconds
30 m sprint times
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
Nordic groupControl group
seconds
Median difference 5 m split
0.6
0.7
0.8
0.9
1
1.1
1.2
November March November March
Nordic groupControl group
seconds
5 m split times
-0.5
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
Nordic groupControl group
seconds
Median difference 10 m split
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2.0
November March November March
Nordic groupControl group
seconds
10 m split times
-10
-8
-6
-4
-2
0
2
4
6
8
Nordic groupControl group
cm
Median difference CMJ
30
35
40
45
50
55
November March November March
Nordic groupControl group
cm
CMJ height
Fig. 1 30 m sprint with 5 and 10 m split times, and Countermovement Jump height. Individual pre and post data, and median differences (black
bars). CMJ Countermovement jump
Page 5 of 6
Krommes et al. BMC Res Notes (2017) 10:669
maximal countermovement jump height were noted,
which represent highly relevant skills in top level foot-
ball. e effect of Nordic Hamstring exercise on maxi-
mal acceleration, sprint and jump performance therefore
should be examined more thoroughly in future large
scale studies, with focus on shorter sprinting distances,
and vertical jumping. Such studies can be designed based
of data and other relevant information obtained during
the present investigation.
Limitations
e sample in the current study was small and warrants
testing in future trials to estimate effect with adequate sta-
tistical power and room for dropouts. Only 19 players were
randomised from the full team of 25 due to injuries, trans-
fers or abstaining. Additional players dropped out during
the study period for similar reasons, resulting in a high rate
of dropouts from the full squad for the different outcomes
(sprint: n=1144%; CMJ: n=728%). It is suggested
that data collection is done just prior to and after the inter-
vention period, and preferably not spread out over several
days to minimize this. As this team played in the second
highest tier in Denmark and was mostly comprised of
part-time professional players, conducting the study with
full-time professionals might be expected to also reduce
dropouts. e standard deviations of changes and indi-
vidual measures were high. It does, however, seem plau-
sible that smaller standard deviations would be observed
when examining larger groups, as when looking at the dis-
tribution of individual data-points, distinct outliers can be
observed. Some risk of potential bias was present, as the
same author did stratification, randomisation, group allo-
cation and managed outcome assessments, although the
type of outcomes measures were objective and the author
could have little to no potential impact on the assessment
[38]. No clear objectives were pre-determined as currently
recommended when designing pilot studies [39, 40], and
no quantifiable data therefore exists on objectives such as
adverse events, acceptability of effort by staff and players,
muscle soreness, cost-effectiveness etc.
Abbreviations
CONSORT: Consolidated Standards of Reporting Trials; BMI: body mass index;
RM: repetition maximum.
Authors’ contributions
KT, JP, PA, PH and MBN contributed to planning of the study. JP collected all
data. KK drafted the manuscript and analyzed the data. All authors contributed
to interpretation of the data andrevision of the manuscript. All authors read
and approved the final manuscript.
Author details
1 Sports Orthopedic Research Center-Copenhagen (SORC-C), Department
of Orthopedic Surgery, Copenhagen University Hospital, Kettegaard Alle 30,
Hvidovre, Denmark. 2 Physical Medicine & Rehabilitation Research-Copenha-
gen (PMR-C), Department of Physical and Occupational Therapy, University
of Copenhagen, Copenhagen, Denmark. 3 Department of Radiology, Section
of Ultrasound, Diagnostic Centre, Rigshospitalet, Faculty of Health Sciences, Uni-
versity of Copenhagen, Copenhagen, Denmark. 4 Department of Sports Science
and Clinical Biomechanics, University of Southern Denmark, Odense, Denmark.
Acknowledgements
The authors thank Thomas Christensen, and club staff and players for their
time and effort in data collection and supervision of the intervention.
Competing interests
The authors declare that they have no competing interests.
Availability of data and materials
The data that support the findings of this study are available from Jesper
Petersen in his capacity as Team Doctor of the participating club, but restric-
tions apply to the availability of these data, and so are not publicly available.
Data are however available from the authors upon reasonable request and
with permission of the participating club.
Consent for publication
Not applicable.
Ethics approval and consent to participate
The Danish Ethics Committee of the Capital Region (H-A-2007-0062) and The
Danish Data Protection Agency (2007-41-0275) approved the study. All par-
ticipants signed written consent in accordance with the Helsinki-declaration
before being enrolled in the study.
Funding
There were no specific grants or funding for the present study.
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in pub-
lished maps and institutional affiliations.
Received: 9 March 2017 Accepted: 23 November 2017
Table 2 Sprint and jump performance for intervention and control group before and after mid-seasonal training period
Group mean values and standard deviations. Only values for players who completed pre and post tests are presented. All between-group differences are in favor of
the Nordic group. The sprint test performed was 30 meters sprint with standing start and split times after 5 and 10 meters (n = 9 in the intervention group and n = 5
in the control group). The jump test performed was a counter movement jump (CMJ; n = 9 in the intervention group and n = 8 in the control group)
Nordic group Control group Between-group mean
difference of changes
Nov Mar Δ (%) Nov Mar Δ (%)
30 m (s) 4.10 ± 0.15 4.20 ± 0.14 + 0.09 (+ 2.42%) ± 0.20 4.00 ± 0.09 4.16 ± 0.20 + 0.15 (+3.88%) ± 0.15 0.04
5 m split (s) 0.90 ± 0.10 0.81 ± 0.10 0.08 ( 9.40%) ± 0.15 0.83 ± 0.02 0.85 ± 0.14 + 0.02 (+3.21%) ± 0.12 0.10
10 m split (s) 1.68 ± 0.15 1.58 ± 0.13 0.09 ( 5.77%) ± 0.15 1.58 ± 0.04 1.63 ± 0.15 + 0.05 (+3.17%) ± 0.11 0.14
CMJ (cm) 43.82 ± 3.67 44.97 ± 3.89 + 1.15 (+ 2.63%) ± 4.20 44.47 ± 5.38 43.48 ± 5.85 0.98 ( 2.22%) ± 5.60 2.13
Page 6 of 6
Krommes et al. BMC Res Notes (2017) 10:669
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  • ... In addition to its potential role in preventing posterior thigh muscle strains, hamstring muscle strength has been suggested as an important factor to improve sprinting performance in soccer as a horizontal force producer [15,16]. During the acceleration phase of sprinting, forward orientation of ground reaction force (GRF) has been shown to be the most powerful determinant of field sprint performance compared to the overall magnitude of vertical or resultant GRF [17]. ...
    ... Different types of hamstring-focused strength training have been proposed in the literature to improve sprint performance in soccer players [14,16] but the direct, individual relationship between improvements in single joint hamstring strength and sprint performance and mechanics remains unclear. Interestingly, to date, no study exists about the effect of sprint practice (recently suggested as a potentially preventive method in adequate doses) [19,20], as a complementary training on the muscle architecture of soccer players. ...
    ... Although hamstrings play a role in the forward orientation of the ground reaction force, especially at high running speed (when their torque capability and electrical activity are both considered), the results of this study showed no benefits (and even small negative changes) of a NHE force program added to regular soccer practice on sprint mechanical outputs and performance. This is consistent with previous results [14], and contrasts with two very similar recent studies reporting small to moderate improvements (with high inter-individual variability) in sprint performance after NHE training in a group of soccer players [15,16]. Although sprint acceleration mechanical properties were not analyzed in these studies [15,16], the time of realization of the program (pre-season versus in-season), and match and training high running speed exposure, internal and external training load may explain the differences between studies. ...
    Article
    Full-text available
    Aims The purpose of this study was to compare the effects of hamstring eccentric (NHE) strength training versus sprint training programmed as complements to regular soccer practice, on sprint performance and its mechanical underpinnings, as well as biceps femoris long head (BFlh) architecture. Methods In this prospective interventional control study, sprint performance, sprint mechanics and BFlh architecture variables were compared before versus after six weeks of training during the first six preseason weeks, and between three different random match-pair groups of soccer players: “Soccer group” (n = 10), “Nordic group” (n = 12) and “Sprint group” (n = 10). Results For sprint performance and mechanics, small to large pre-post improvements were reported in “Sprint group” (except maximal running velocity), whereas only trivial to small negative changes were reported in “Soccer group” and “Nordic group”. For BFlh architecture variables, “Sprint” group showed moderate increase in fascicle length compared to smaller augment for the “Nordic” group with trivial changes for “Soccer group”. Only “Nordic” group presented small increases at pennation angle. Conclusions The results suggest that sprint training was superior to NHE in order to increase BFlh fascicle length although only the sprint training was able to both provide a preventive stimulus (increase fascicle length) and at the same time improve both sprint performance and mechanics. Further studies with advanced imaging techniques are needed to confirm the validity of the findings.
  • ... Elite junior or academy athletes were recruited in four studies [20][21][22][23]. Athletes from professional or Division I sport organisations were recruited in six studies [19,[24][25][26][27][28]. The remainder of studies recruited semi-professional or lower division athletes. ...
    ... These authors prescribed intensity based on percentage of one repetition maximum (1RM) [30], percentage of bodyweight [31] or through a familiarisation protocol [23]. The remaining studies verbally encouraged participants to produce a maximal effort either against a flywheel device of varying inertial resistance [15,20,21,24,28], or during the eccentric phase of bodyweight exercise [19,22,26,29,32]. Compliance to the training intervention was reported in all but three studies [22,24,30]. ...
    ... Five of the nine studies used an isokinetic dynamometer to perform the strength assessment. Training interventions utilised inertial flywheel devices [20,21,23,24,27,28,33], traditional isoinertial equipment [30,31] or exercises performed with bodyweight [19,22,25,26,29]. Mendiguchia et al. [31] used both isoinertial and bodyweight exercises. ...
    Article
    Full-text available
    Eccentric resistance training has been shown to improve performance outcomes in a range of populations, making it a popular choice for practitioners. Evidence suggests that neuromuscular adaptations resulting from eccentric overload (EO) and accentuated eccentric loading (AEL) methods could benefit athletic populations competing in team sports. The purpose of this review was to determine the effects of eccentric resistance training on performance qualities in trained male team sport athletes. A systematic review was conducted using electronic databases PubMed, SPORTDiscus and Web of Science in May 2019. The literature search resulted in 1402 initial articles, with 14 included in the final analysis. Variables related to strength, speed, power and change of direction ability were extracted and effect sizes were calculated with a correction for small sample size. Trivial, moderate and large effect sizes were reported for strength (−0.17 to 1.67), speed (−0.08 to 1.06), power (0.27 to 1.63) and change of direction (0.48 to 1.46) outcomes. Eccentric resistance training appears to be an effective stimulus for developing neuromuscular qualities in trained male team sport athletes. However, the range of effect sizes, testing protocols and training interventions suggest that more research is needed to better implement this type of training in athletic populations.
  • ... 12 The increased hamstrings strength has previously been demonstrated to elicit beneficial effects on speed and jumping performances. 10,13 In contrast to the high number of studies on injury prevention 8,10 , there is only scarce information available on the effects of NHE training on measures of physical performance. Krommes et al. 13 studied the effects of a 10-week pre-season NHE training on sprint and jump performances in elite male soccer players. ...
    ... 10,13 In contrast to the high number of studies on injury prevention 8,10 , there is only scarce information available on the effects of NHE training on measures of physical performance. Krommes et al. 13 studied the effects of a 10-week pre-season NHE training on sprint and jump performances in elite male soccer players. These authors reported improvements in both, sprint (i.e., 5-m and 10-m sprint-time) and jump (i.e., countermovement-jump [CMJ]) performances. ...
    ... Despite the small body of literature relating to the effects of NHE on performance outcomes, the results of the few available studies are promising. 10,13 To the authors' knowledge, no study has examined the impact of NHE training on measures of physical performance in females. Therefore, this study aimed to investigate the effects of an in-season progressive NHE training program on components of physical performance (i.e., linear sprint-time, jumping, CoD, and RSA) in young female handball players. ...
    Article
    Purpose: This study examined the effects of an 8-week Nordic-hamstring exercise (NHE) training on components of physical performance in young female handball players. Methods: Participants were allocated to an experimental (EG; n=10; age: 15.9 ± 0.2 years) and a control group (CG; n=9; age: 15.9 ± 0.3 years). The EG performed NHE (2-3 sessions/week) in replacement of some handball-specific drills whereas the CG followed regular handball training. Pre- and post-training, tests were carried-out for the assessment of sprint speed (5 m, 10 m, 20 m), jump performance (countermovement jump [CMJ] height), change-of-direction (CoD [T-test]), and repeated-sprint-ability (RSA total-time [RSAtotal], RSA best-time [RSAbest], RSA fatigue-index [RSAFI]). Data were analyzed using magnitude-based inferences. Results: Within-group analyses for the EG showed moderate performance improvements for 5 m, 10 m, 20 m (effect-size [ES] = 0.68-0.82), T-test (ES=0.74), and CMJ (ES=0.85). Trivial-to-small improvements were observed for RSA (ES=-0.06-0.35). For the CG, within-group outcomes showed performance decrements with moderate (T-test [ES=0.71]), small (5 m [ES=0.46], and RSAbest [ES=0.20]), and trivial magnitude (10 m [ES=0.10], 20 m [ES=0.16] and RSAtotal [ES=0.00]). Further, trivial-to-small performance improvements were found for CMJ (ES=0.10) and RSAFI (ES=0.5). Between-group analyses revealed small-to-large effects in favor of EG for 5 m (ES=1.07), 10 m (ES=0.66), 20 m (ES=0.53), T-test (ES=1.38), and RSA (ES=0.68 to 0.78). A trivial between-group difference was demonstrated for CMJ (ES=-0.01). Conclusions: The NHE training intervention, in replacement of some handball-specific drills, was more effective than regular handball training in improving physical performance (i.e., linear sprint-time, jumping, CoD, and RSA) in young female handball players.
  • ... Recent research findings on the links between eccentric strength, hamstring muscles fascicle a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 length and injury risk have promoted the use of Nordic Hamstring exercise (NHE) to enhance maximal eccentric hamstring strength (EHS), measured during the NHE, and increase the biceps femoris long head fascicle length as an effective strategy to reduce the risk of a future hamstring strain injury [3,4]. However, and despite its simplicity and proposed efficacy, it appears that the vast majority of professional clubs do not include the NHE protocol as part of their injury prevention strategy [5][6][7]. This might be due to sports medicine and coaching professionals labeling the NHE as ineffective for injury prevention and performance [8]. ...
    ... This might be due to sports medicine and coaching professionals labeling the NHE as ineffective for injury prevention and performance [8]. In regards to performance, two recent studies investigated changes in sprint performance after an injury-prevention NHE protocol, showing significant improvements in sprint performance [7,9] and EHS using the NHE [10]. Ishoi et al. (2017) reported that 10-weeks of training with NHE resulted in significant improvements in 10 m sprint performance (2.6%) and repeatedsprint performance (1.8%) in amateur male football players. ...
    ... Ishoi et al. (2017) reported that 10-weeks of training with NHE resulted in significant improvements in 10 m sprint performance (2.6%) and repeatedsprint performance (1.8%) in amateur male football players. On the other hand, Krommes et al. (2017) found significant improvements in 5-m (9.4%) and 10-m (5.8%) sprint performance in elite male Danish football players after the 10-week NHE protocol. Considering that straight sprinting is one of the most game-deciding physical action in professional football [11] and the predominant injury condition in hamstring strain injuries [9,12] the inclusion of the NHE protocol can be a very time efficient and effective training intervention targeting both the injury prevention and performance sites. ...
    Article
    Full-text available
    The aim of the present study was to evaluate the consequence of implementing a Nordic Hamstring exercise (NHE) protocol during the first 15 to 17 weeks of the season to assess the effect on sprinting and NHE strength (NHEs) in professional football players. The study examined 50 healthy male professional football players (age 18.8±0.8yr; height 176.8±6.9cm; weight 71.3±5.7kg) belonging to 3 of the reserve squads of three Spanish La-Liga clubs divided in 2 intervention teams [Nordic-Group1 (NG-1) and Nordic-Group2 (NG-2, extensive experience in NHE)] and 1 team as a control-group (CG). NHEs and linear sprint (T5, T10, T20-m) were evaluated at the beginning of the season and at the end of an intervention period of conditioning and football training, supplemented with a NHE protocol (24 sessions for NG-1 and 22 sessions for NG-2) or without using the NHE at all (CG). Sprint times were substantially improved in all groups (ES from -2.24±0.75 to -0.60±0.37). NHEs was enhanced absolute and relative to body-mass only in NG-1 after the training period (ES from 0.84±0.32 to 0.74±0.26), while in the NG-2 there were only improvements in average NHEs relative to body-mass (ES = 0.39±0.36). The improvements in T20-m were substantially greater in NG-2 vs. NG-1, and there were no differences in sprint performance changes between NG-1 and CG. Changes in sprinting performance and NHEs were unrelated. NHEs was largely correlated with the body-mass of the players. Results indicate that the improvements in sprint are not dependent on the NHEs changes, with no relationships between NHEs and sprint performance, and between sprint changes and changes in NHEs.
  • ... As such, the present study findings provide novel insights regarding the role of explosive hamstring muscle force as an important determinant for sprint acceleration performance, thereby adding to the growing body of evidence on this topic. [8][9][10] Positive associations of medium strength were observed between early phase (0-100 ms) hamstring RTD and mechanical sprint acceleration parameters (FH0 and Pmax), whereas no associations were observed for late phase (0-200 ms) hamstring RTD or hamstring peak torque. This observation may be explained by the very short duration of the propulsive stance phase during sprint acceleration lasting 86-171 ms. ...
    ... The present study findings contribute to elucidate potential mechanisms associated with improved sprint acceleration performance observed following hamstring muscle training in football players. 9,10 More specifically, Ishøi et al. 9 and Krommes et al. 10 reported clinically International Journal of Sports Physiology and Performance © 2018 Human Kinetics, Inc. relevant improvements in 0-10 m sprint time (2.6-5.8%) and maximal eccentric hamstring muscle strength (+19.2%) following ten weeks of eccentric hamstring muscle training using the Nordic Hamstring exercise. ...
    ... However, recent randomized controlled trials focusing on increasing eccentric hamstring muscle strength using the Nordic Hamstring exercise reported consistent improvements in sprint acceleration performance. 9,10 Secondly, the present study was explorative with no pre-specified hypothesizes. As three regression analyses for each dependent variable were performed this may have resulted in an elevated risk of false positive findings (statistical type-1 errors). ...
    Purpose:: This cross-sectional study aimed to investigate the association between hamstring muscle peak torque and rapid force capacity (rate of torque development: RTD) versus sprint performance in elite youth football players. Methods:: Thirty elite academy youth football players (16.75 ± 1.1 years, 176.9 ± 6.7 cm, 67.1 ± 6.9 kg) were included. Isometric peak torque (Nm/kg) and early (0-100 ms) and late (0-200 ms) phase RTD (RTD100, RTD200) (Nm/s/kg) of the hamstring muscles were obtained as independent predictor variables. Sprint performance was assessed during a 30-m sprint trial. Mechanical sprint variables (maximal horizontal force production (FH0) (N/kg); maximal theoretical velocity (V0) (m/s); maximal horizontal power output (Pmax) (W/kg)) and sprint split times (0-5 m; 0-15 m; 0-30 m; 15-30 m) (s) were derived as dependent variables. Subsequently, linear regression analysis was conducted for each pair of dependent and independent variables. Results:: Positive associations were observed between hamstring RTD100 and FH0 (r2=0.241, p=0.006) and Pmax (r2=0.227, p=0.008). Furthermore, negative associations were observed between hamstring RTD100 and 0-5 m (r2=0.206, p=0.012), 0-15 m (r2=0.217, p=0.009) and 0-30 m sprint time (r2=0.169, p=0.024). No other associations were observed. Conclusion:: The present data indicate that early-phase (0-100 ms) rapid force capacity of the hamstring muscles plays an important role for the acceleration capacity in elite youth football players. In contrast, no associations were observed between hamstring muscle function and maximal sprint velocity. This indicates that strength training focusing on improving early-phase hamstring rate of force development may contribute to enhance sprint acceleration performance in this athlete population.
  • ... However, studies investigating the effect of the NHE on sprint performance are lacking. To date, only a single pilot study from our group has investigated sprint performance using the Mjølsnes 10-week injury-prevention NHE protocol (Mjolsnes et al., 2004), and reported improved 10 m sprint performance (Krommes et al., 2017). Therefore, this trial aimed to investigate the efficacy of a 10-week in-season NHE training intervention on sprint performance in male football players. ...
    ... The likely-to-very likely small-to-medium effect size improvements suggest a clinically relevant effect of both repeated-and 10 m sprint performance (Hopkins et al., 2009). As such, the present study confirms our preliminary findings on improved 10 m sprint performance using an identical NHE protocol (Krommes et al., 2017). Previous studies have reported either improved performance (Campos-Vazquez et al., 2015) or no performance enhancing effect (Buchheit et al., 2010) on repeated-sprint ability in football players following progressive heavy strength training using loaded squat exercise or explosive strength training using body weight loaded exercises, respectively. ...
    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
  • ... The idea of an interplay between fascicle length and injury incidence was also supported by a recent review (Kellis, 2018). Based on these observations, several studies investigated in adults if muscle architecture could be altered in response to a training regimen and if this also affects the occurrence of muscle injuries (Mendiguchia et al., 2020, Pollard et al., 2019, Bourne et al., 2018, Krommes et al., 2017. BFlh architecture may also impact sprint performance. ...
    Preprint
    Background. It has been proposed that muscle architecture can be associated with sprint performance and the risk of sustaining a muscle injury. During puberty, sprint performance as well as muscle injury risk increases in young soccer players. In this study, we investigated the changes in m. biceps femoris long head (BFlh) cross-sectional area (ACSA), fascicle length (FL) and pennation angle (PA) and sprint performance as well as their relationship in under 13 to 15 youth soccer players. Methods. In total, we measured 85 youth soccer players in under 13 (n=29, age=12.5 y (SD=0.1), height=155.3 cm (6.2), weight=43.9 kg (7.6)), under 14 (n=25, age=13.5 y (0.3), height=160.6 y (7.7), weight=47.0 kg (6.8)) and under 15 (n=31, age=14.4 y (0.3) , height=170.0 cm (7.7), weight=58.1 kg (8.8) ) teams of three high level soccer clubs. We used ultrasound to measure BFlh ACSA, FL and PA. We performed sprint tests to assess 10m and 30m sprint time, maximal velocity (vmax) and maximal acceleration (amax). We calculated Pearson’s r and 95% compatibility intervals to assess the relationship between sprint ability, maturity ratio, chronological age and architectural parameters. In addition, we calculated the best set of predictors for sprint ability using multiple regression models.Results. All muscle architectural parameters increased from the under 13 to the under 15 age group (BFlh ACSA: 37%, BFlh FL: 11%, BFlh PA: 8%). All sprint performance parameters improved from the under 13 to under 15 age categories (30m time: 7%, 10m time: 4%, vmax: 9%, amax: 7%). BFlh ACSA was correlated with 30m sprint time (r = -0.61 (95% CI = -0.73, -0.45)) and vmax (r= 0.61 (0.45, 0.72)). The correlation for maturity ratio with assessed parameters were larger compared to the correlation for chronological age. A combination of BFlh ACSA, FL, chronological age and height best predicted sprint parameters. Discussion. Parallel to improvements in sprint performance, muscle architectural parame-ters increase from the under 13 to under 15 age groups. BFlh ACSA seems to be related to sprint performance in youth soccer players. BFlh ACSA and chronological age are the main predictors of most sprint parameters.
  • Chapter
    Hamstring function is influenced by a number of neural, architectural and morphological factors, and the adaptability of these characteristics has important implications for optimizing performance and reducing injury risk. High rates of maximal or near-maximal hamstring force development are required to generate peak horizontal velocities during running, and this is largely determined by the extent to which these muscles can be voluntarily activated. Greater eccentric hamstring strength also correlates with better acceleration capacity and likely improves the ability to decelerate the lower limb during the presumably injurious terminal swing phase of high-speed running. The intra- and intermuscular coordination of the hamstrings appears to influence both hamstring muscle fatiguability and the risk of muscle strain injury. Muscle volume and architectural features such as fascicle length and pennation angle also influence hamstring function, and these vary considerably between hamstring muscles, between individuals and with training status. The adaptability of these features has been explored to a significant extent in recent times, and careful exercise selection allows selective targeting of individual hamstring muscles or muscle segments and this appears to influence the pattern of chronic adaptations such as muscle hypertrophy. Short fascicles within the often-injured long head of biceps femoris may predispose athletes to strain injury but these appear to respond in a contraction-mode-specific manner; lengthening after eccentric training and shortening after concentric training of 4 or more weeks. Conventional training with eccentric and concentric phases in each repetition can also lengthen fascicles, possibly in an excursion (muscle length)-dependent manner. A large biceps femoris muscle to proximal aponeurosis width ratio has been proposed as a potential risk factor for hamstring strain injury, although this is only supported by biomechanical modelling at the time of writing. High levels of anterior pelvic tilt and lateral trunk flexion during sprint running may also predispose athletes to hamstring strain injury, although the quantity of evidence for this is small at the moment. At present, the optimal methods for altering coordination and running technique are not known.
  • Article
    Full-text available
    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
    Full-text available
    La prevención de lesiones es un pilar de intervención de profesionales como preparadores físicos, licenciados en educación física y fisioterapeutas, en equipos profesionales de fútbol. Con ella se busca reducir la incidencia de lesiones deportivas a través del incremento de componentes neuromusculares y motores implicados en el rendimiento deportivo. Objetivo: formular una propuesta de protocolo de prevención de lesiones por habilidad en jugadores de fútbol profesional, a partir de una revisión sistemática de literatura. Método: la revisión se realizó en bases de datos científicas indexadas, con los términos MeSH: rehabilitation, training, injuries, sports medicine, prevention, soccer. Resultados: se evidenció que la prevención de lesiones implica habilidades específicas como carrera, fuerza, flexibilidad, balance, propiocepción, velocidad, agilidad, salto y potencia, que garantizan la reducción de riesgo de lesiones musculares, ligamentosas y articulares. Conclusión: el trabajo conjunto entre preparación física y fisioterapia, da como resultado la creación de protocolos de prevención de lesiones que garantizan el adecuado rendimiento y estado deportivo de futbolistas profesionales, que llevarán a incrementar las posibilidades de la obtención de títulos deportivos a nivel nacional e internacional.
  • Article
    Full-text available
    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.
  • Research describing load monitoring techniques for team sport is plentiful. Much of this research is conducted retrospectively, and typically involves recreational or semi-elite teams. Load monitoring research conducted on professional team sports is largely observational. Challenges exist for the practitioner in implementing peer-reviewed research into the applied setting. These challenges include match scheduling, player adherence, manager/coach buy-in, sport traditions, and staff availability. External load monitoring often attracts questions surrounding technology reliability and validity, while internal load monitoring makes some assumptions about player adherence as well as having some uncertainty around the impact these measures have on player performance This commentary outlines examples of load monitoring research, discusses the issues associated with the application this research in an elite team sport setting, and suggests practical adjustments to the existing research where necessary.
  • Article
    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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    It is widely assumed that there is an eccentric hamstring muscle fibre action during the swing phase of high-speed running. However, animal and modelling studies in humans show that the increasing distance between musculotendinous attachment points during forward swing is primarily due to passive lengthening associated with the take-up of muscle slack. Later in the swing phase, the contractile element (CE) maintains a near isometric action while the series elastic (tendinous) element first stretches as the knee extends, and then recoils causing the swing leg to forcefully retract prior to ground contact. Although modelling studies showed some active lengthening of the contractile (muscular) element during the mid-swing phase of high-speed running, we argue that the increasing distance between the attachment points should not be interpreted as an eccentric action of the CE due to the effects of muscle slack. Therefore, there may actually be no significant eccentric, but rather predominantly an isometric action of the hamstrings CE during the swing phase of high-speed running when the attachment points of the hamstrings are moving apart. Based on this, we propose that isometric rather than eccentric exercises are a more specific way of conditioning the hamstrings for high-speed running.
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    Data presentation for scientific publications in small sample size studies has not changed substantially in decades. It relies on static figures and tables that may not provide sufficient information for critical evaluation, particularly of the results from small sample size studies. Interactive graphics have the potential to transform scientific publications from static reports of experiments into interactive datasets. We designed an interactive line graph that demonstrates how dynamic alternatives to static graphics for small sample size studies allow for additional exploration of empirical datasets. This simple, free, web-based tool (http://statistika.mfub.bg.ac.rs/interactive-graph/) demonstrates the overall concept and may promote widespread use of interactive graphics.
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    The optimal scheduling of Nordic Hamstring exercises (NHEs) relative to football training sessions is unknown. We examined the acute neuromuscular and performance responses to NHE undertaken either before (BT) or after (AT) simulated football training. Twelve amateur players performed six sets of five repetitions of the NHE either before or after 60 min of standardised football-specific exercise (SAFT60). Surface electromyography signals (EMG) of the hamstring muscles were recorded during both the NHE, and maximum eccentric actions of the knee flexors (0.52 rad · s–1) performed before and after the NHE programme, and at 15 min intervals during SAFT60. Ten-metre sprint times were recorded on three occasions during each 15 min SAFT60 segment. Greater eccentric hamstring fatigue following the NHE programme was observed in BT versus AT (19.8 %; very likely small effect), which was particularly apparent in the latter range of knee flexion (0–15°; 39.6%; likely moderate effect), and synonymous with hamstring EMG declines (likely small–likely moderate effects). Performing NHE BT attenuated sprint performance declines (2.0–3.2%; likely small effects), but decreased eccentric hamstring peak torque (–14.1 to –18.9%; likely small effects) during football-specific exercise. Performing NHE prior to football training reduces eccentric hamstring strength and may exacerbate hamstring injury risk.
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    Background There are well-known challenges to implementing injury prevention strategies in amateur soccer, but information from other soccer settings is scarce. This cross-sectional survey analysed the injury prevention perceptions of soccer coaches, fitness coaches and physiotherapists from 4 male teams in a professional youth soccer academy. Methods The respondents (n=18) completed a web-based survey relating to lower limb (LL) soccer injuries, the value and practicality of injury prevention exercise programmes (IPEPs) in general and, more specifically, the IPEP endorsed by FIFA, the FIFA 11+. Results There were very high levels of agreement regarding players’ susceptibility to LL injury and the seriousness of these injuries. Respondents agreed unanimously that players should perform evidence-based injury prevention exercises. Despite 61% of respondents having previously heard of the FIFA 11+, just 6% reported current use of the full programme, with a further 22% reporting modified use. 22% believed the FIFA 11+ contained adequate variation and progression for their team and 78% felt it needed improvement. Respondents identified multiple barriers and facilitators to maintaining IPEPs, relating either to the programme content (eg, exercise variation), or the delivery and support of the programme (eg, coach acceptance). Conclusions The coaches, fitness coaches and physiotherapists of professional youth teams support the use of IPEPs, but enhancing their impact requires tailoring of programme content, along with adequate delivery and support at multiple levels. The findings suggest that the FIFA 11+ needs modification for use in professional youth soccer teams.
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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.