Perception and application of flywheel training by professional soccer practitioners

Abstract

Growing evidence supports use of eccentric methods for strength development and injury prevention within elite soccer, yet uncertainty remains regarding practitioners’ application of flywheel (isoinertial) methods. The aims of this study were to investigate how the flywheel training literature is perceived and applied by elite soccer practitioners, highlight gaps in knowledge and develop industry-relevant research questions. Fifty-one practitioners completed an electronic questionnaire. Fourteen Likert scale statements were grouped into topics: strength and performance; post-activation performance enhancement and methodological considerations; chronic strength; chronic performance; injury prevention. Three general questions followed, allowing more detail about flywheel training application. A Majority of the participants reported ≥ 2 years’ experience of programming flywheel training. Nearly all participants agreed that familiarisation is needed. Practitioners agree that flywheel training can improve sport performance, strength and likelihood of non-contact injury outcomes. Most practitioners prescribe 2 weekly sessions during pre- and in-season periods. Flywheel sessions mostly consist of squats but a variety of exercises (lunge, hip hinge, and open kinetic chain) are also frequently included. Practitioners are mostly unsure about differences between flywheel and traditional resistance training equipment and outcomes, practicality of flywheel equipment, and evidence-based guidelines. The investigation provides valuable insight into the perspectives and application of flywheel training within elite soccer, highlighting its perceived efficacy for strength and injury prevention.

Full text

Biology of Sport, Vol. 39 No4, 2022 3
Perception and application of ywheel training in soccer
INTRODUCTION
Professional soccer match play has shown an increasing frequency
of high intensity actions (e.g., sprints, high speed running, accelera-
tions) in recent years, highlighting the need for appropriate training
to ensure success[1]. To optimise performance of such actions in
matches, practitioners must systematically program resistance train-
ing[2], recovery[3], and injury prevention strategies[4]. Resistance
training plays an important role for enhancement of strength, per-
formance, and reduction of injury likelihood within professional soc-
cer[5,6]. However, multiple factors including prolonged national
and international travel commitments, xture congestion, and time
dedicated to technical-tactical training often limit the time for strength
training[7,8]. Practitioners have therefore tried to implement dif-
ferent strength training methodologies to efciently condition athletes.
In recent years, ywheel (isoinertial)-based exercise has become
more commonly applied by soccer and team sports practitioners as
an alternative to traditional resistance training[9,10].
The ywheel is aresistance training tool that has been employed
to enhance strength and performance with success in healthy and
Perception and application of ywheel training
by professional soccer practitioners
AUTHORS: Kevin L. de Keijzer1,2, Stuart A. McErlain-Naylor1,2, Thomas E. Brownlee3, Javier
Raya-González4, Marco Beato1,2
1 School of Health and Sports Sciences, University of Suffolk, Ipswich, United Kingdom
2 Institute of Health and Wellbeing, University of Suffolk, Ipswich, United Kingdom
3 School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University
of Birmingham, Birmingham, United Kingdom
4 Faculty of Health Sciences, Universidad Isabel I, Burgos, Spain
ABSTRACT: Growing evidence supports use of eccentric methods for strength development and injury
prevention within elite soccer, yet uncertainty remains regarding practitioners’ application of ywheel (isoinertial)
methods. The aims of this study were to investigate how the ywheel training literature is perceived and applied
by elite soccer practitioners, highlight gaps in knowledge and develop industry-relevant research questions.
Fifty-one practitioners completed an electronic questionnaire. Fourteen Likert scale statements were grouped
into topics: strength and performance; post-activation per formance enhancement and methodological
considerations; chronic strength; chronic performance; injury prevention. Three general questions followed,
allowing more detail about ywheel training application. A Majority of the participants reported ≥2years’
experience of programming ywheel training. Nearly all participants agreed that familiarisation is needed.
Practitioners agree that ywheel training can improve sport performance, strength and likelihood of non-contact
injury outcomes. Most practitioners prescribe 2 weekly sessions during pre- and in-season periods. Flywheel
sessions mostly consist of squats but avariety of exercises (lunge, hip hinge, and open kinetic chain) are also
frequently included. Practitioners are mostly unsure about differences between ywheel and traditional resistance
training equipment and outcomes, practicality of ywheel equipment, and evidence-based guidelines. The
investigation provides valuable insight into the perspectives and application of ywheel training within elite
soccer, highlighting its perceived efcacy for strength and injury prevention.
CITATION: de Keijzer KL, McErlain-Naylor SA et al. Perception and application of ywheel training by professional
soccer practitioners. Biol Sport. 2022;39(4):xx–xx.
Received: 2021-03-01; Reviewed: 2021-08-12; Re-submitted: 2021-08-14; Accepted: 2021-09-07; Published: 2021-10-xx.
athletic populations[11,12]. The user rotationally accelerates the
ywheel during the concentric phase, generating inertial torque that
must then be overcome during the eccentric phase[12]. The com-
bination of maximal concentric actions and subsequent high eccen-
tric loads experienced with ywheel training exposes athletes to unique
muscular and neural demands[6,9,10,13]. In fact, ywheel train-
ing is particularly effective for challenging the eccentric portion of
movements, which are often underloaded and difcult to overload
with traditional isotonic resistance training methods[6,9,14]. Spe-
cically, exposure to intense eccentric training has been shown to
enhance motor unit discharge rate and synchronization, as well as
selective recruitment of higher-order motor units[13]. The method-
ological advantages associated with ywheel protocols has increased
application as an injury prevention strategy with male soccer play-
ers[4,15,16]. Moreover, ywheel training has also enhanced acute
performance parameters[14,17–19] within post-activation perfor-
mance enhancement (PAPE) protocols[20]. Nonetheless, elite prac-
titioners perceive intense eccentric training methods such as the
Original Paper
DOI: https://doi.org/10.5114/biolsport.2022.109457
Key words:
Isoinertial
Strength
Injury
Football
Performance
Corresponding author:
Marco Beato
School of Health and Sports
Sciences, University of Suffolk
Ipswich, United Kingdom
E-mail: m.beato@uos.ac.uk
ORCID:
Kevin L. de Keijzer
0000-0003-1113-164X
Stuart A. McErlain-Naylor
0000-0002-9745-138X
Thomas Brownlee
0000-0002-3355-1867
Javier Raya-González
0000-0002-3570-7159
Marco Beato
0000-0001-5373-2211

4
Kevin L. de Keijzer et al.
also included, allowing practitioners to provide more detail about
their application of ywheel training.
Quantitative Analysis
Frequencies were determined for each Likert-type scale or close-
ended question response, with many of the responses also present-
ed as frequency plots. All participants were included in each analysis.
RESULTS
Practitioners experience with ywheel devices
Thirty-three participants had≥2years of experience of programming
ywheel training, with afurther 14reporting<2years of experience
and four having no experience.
Familiarisation and Post-Activation Performance Enhancement
(PAPE)
Almost all participants (n=47) agreed familiarisation is necessary to
optimise ywheel training, with few neither agreeing nor disagreeing
(n=3) and only one single participant disagreeing (Figure1). One
participant did not believe familiarisation sessions are necessary, nine
believed one session is needed, 12participants believed two sessions
were necessary, 13believed three sessions were needed, while nine
and two participants stated four and ve sessions were necessary,
respectively. Finally, ve participants also reported that they believe
familiarisation is aplayer dependent process. Amajority of participants
(n=37) believe that within the scientic literature ‘ywheel training
is well supported for acute sport performance enhancement’, with
some (n=11) unsure and few (n=3) disagreeing (Figure2).
Chronic adaptations
Practitioner opinions and perceptions regarding practicality and
strength attainment with traditional resistance training and ywheel
equipment are reported in Figure3. More than half of the participants
(n=33) agreed that an eccentric overload is necessary during y-
wheel training for acute and chronic adaptations, with some (n=16)
remaining unsure, and few (n=2) disagreeing.
The most frequently programmed ywheel exercise is the squat,
with other exercises reported in Figure4. Practitioners’ views on
ywheel familiarisation and effectiveness for increasing strength are
reported in Figure1. Practitioner application did not differ majorly
during pre- and in-season periods, is reported in Figure5.
Injury prevention
Flywheel training was considered by many (n=33) practitioners to
be an effective method of reducing non-contact muscular injuries,
with the rest (n=18) remaining unsure (Figure1). When ywheel
training was compared to traditional resistance training methods,
some (n=18) believed that ywheel methods were superior while
few (n=8) disagreed that ywheel training was superior to tradi-
tional resistance training methods (Figure3). Participants mostly
(n=25) stated they neither agreed nor disagreed with the statement.
ywheel to be very taxing and difcult to program in-season[6]. In
support of this, the current scientic literature does not provide spe-
cic considerations for load and risk management when implement-
ing ywheel training in professional soccer[16].
Although ywheel training is applied in avariety of methods in
elite team sport environments[9,12,20,21], the perceptions and
application of ywheel training methodologies amongst professional
soccer practitioners remains unknown. Addressing how ywheel train-
ing is applied by practitioners in professional soccer and highlighting
their concerns is important to reduce barriers between research and
practice[5]. Therefore, the aim of this study was to describe and
understand current application and perception of ywheel-based re-
sistance training in professional soccer for acute[20] and chronic
adaptations[11,12] as well as for reduction of non-contact inju-
ries[16].This study is the rst to contextualise the way ywheel
scientic literature is being applied in professional soccer and to iden-
tify whether gaps in current knowledge and application of ywheel
training exist. Such an approach has been utilised with avariety of
topics associated with elite athlete performance[3,6]. This study
identies difculties that practitioners face when applying ywheel
training and may be useful for the development of new research ques-
tions. Subsequent guidelines may increase practitioners’ condence
in the application of ywheel training[6], further enhancing imple-
mentation within professional soccer[4,6]. We hypothesised that
ywheel training exercise prescription and frequency would vary
amongst practitioners and would be altered throughout the season.
MATERIALS AND METHODS
Participants
Fifty-one practitioners participated in this study, including 21strength
and conditioning (S&C) coaches, 15sport scientists, 8tness coach-
es, and 7physiotherapists. Thirty-six worked with male players only,
3worked with female players only, and 12worked with males and
females. Participants were recruited via the authors’ professional
networks and social media platforms. Sample size was maximised
through chain sampling, in which participants were encouraged to
pass on investigation details to relevant persons within their high-
performance soccer networks. The questionnaire was approved by
the University of Suffolk (Ipswich, UK) research ethics committee.
All participants gave electronic informed consent prior to participation.
Experimental approach to the problem
Participants completed an electronic questionnaire (hosted online by
SurveyMonkey, California, US). A5-point Likert scale was used for
14questions, which were grouped into topics and sub-topics:
1)strength and performance, 1.1PAPE and methodological consid-
erations, 1.2chronic strength outcomes, 1.3chronic performance
outcomes; 2)injury prevention. The ve-point Likert scale (strongly
agree, agree, neither agree nor disagree, disagree, strongly disagree)
allowed participants to report their level of agreement regarding each
statement. Three general application and training questions were

Biology of Sport, Vol. 39 No4, 2022
5
Perception and application of ywheel training in soccer
FIG. 1. Comparing practitioners’ opinions and perceptions regarding ywheel training evidence based-guidelines, necessity for
familiarisation, and for strength and injury prevention (n = 51 for each statement).
FIG. 2. Comparing practitioners’ opinions and perceptions of ywheel training for acute and chronic sport performance enhancement
(n = 51 for each statement).

6
Kevin L. de Keijzer et al.
training for acutely and chronically enhancing strength. Although
some uncertainty remained, amajority of practitioners believed that
ywheel training is useful for decreasing injury likelihood and chron-
ically enhancing change of direction, sprint, and jumping performance.
Lacking condence or awareness of ywheel training guidelines may
systematically impact efcacy and application of ywheel training in
elite soccer environments. Current perspectives shed light on practi-
cal issues and current limitations related to ywheel training for
performance enhancement and reduction of non-contact injury like-
lihood in professional soccer.
DISCUSSION
The aim of this study was to describe and compare the current
perception and application of ywheel-based resistance training
methodologies in professional soccer for performance and injury
reduction purposes. Our ndings, which partly agree with our hy-
pothesis, highlight how ywheel training varies in exercise selection
(i.e., squat, lunge) and training frequency, among other variables.
Practitioners are aware that afamiliarisation period is needed to
optimize the performance and outcomes with ywheel training. Aclear
majority of practitioners are condent in the application of ywheel
FIG. 3. Comparing practitioners’ opinions and perceptions of ywheel training and traditional resistance training (n = 51 for each
statement).
FIG. 4. Flywheel exercises that have been programmed by elite soccer practitioners (n = 51).

Biology of Sport, Vol. 39 No4, 2022
7
Perception and application of ywheel training in soccer
Flywheel exercise and PAPE
The majority of practitioners (n=37) believed that PAPE protocols
can acutely enhance performance, which is supported by the scien-
tic literature[14,17,18]. Desirable neuromuscular responses
elicited by ywheel PAPE protocols are related to effective activation
of the musculature at agreater velocity and force, improving strength
and task specic performance[20]. Nonetheless, limited research
on the effects of differing inertial intensities, volume, and exercises
on PAPE performance may have impacted practitioners’ beliefs. Some
practitioners reported they neither agreed nor disagreed (n=11)
and few others stating they disagreed (n=3) that ywheel PAPE
protocols acutely enhance sport performance. Nonetheless, com-
parisons between ywheel PAPE and traditional resistance PAPE
squat protocols report similar positive outcomes[14] with com-
parisons of different inertial loads[9] and movements[18] also at-
taining similar enhanced outcomes. The aforementioned investigations
support practitioner condence in application of ywheel PAPE pro-
tocols to enhance change of direction and jumping outcomes within
avariety of contexts[9]. Nonetheless, conclusive evidence on speed
performance (≥10m) enhancement within aywheel PAPE proto-
col is still needed.
Chronic application of ywheel training
Alarge majority of practitioners (n=45) believe that ywheel train-
ing is useful for chronically improving strength parameters. Practi-
tioners’ opinions are in agreement with research on ywheel training,
which involve several reviews and meta-analyses on various
Familiarisation
Although alarge portion of practitioners (n=47) agreed that fa-
miliarisation is necessary to optimise training, the literature suggests
it remains difcult to quantify how many sessions are necessary
to achieve reliable outcomes with ywheel devices[9,22]. Previ-
ous studies have reported using either no sessions [23],
one[14,17,18,21,24–26], two [27–30], three[10, 19], or
4–6sessions[15], and participant dependent familiarisation[31].
Alarge portion of practitioners (n=25) believe it is necessary to
program two or three familiarisation sessions, which is in line with
current guidelines[9,20]. Some practitioners (n=9) believe one
familiarisation session is sufcient, possibly due to the limited time
for strength training[5] or in reection of the majority of the lit-
erature which employs one session. An equal number of practitio-
ners (n=9) utilise 4familiarisation sessions. Such sessions may
be characterised by lower intensity or volume, as astrategy to
mitigate any negative impact of initial ywheel training sessions
on concurrent soccer training and performance– although this
cannot be conrmed. Few (n=5) practitioners believe familiarisa-
tion is dependent on the athleticism, coordination, and training
age of the athlete. Although such an approach is sensible, little is
published on the topic[9]. Such factors may be particularly im-
portant when implementing ywheel methods with youth or novice
athletes[32]. Current best practice to enhance familiarisation in-
volves pairing objective data (i.e., velocity outputs)[22], qualita-
tive feedback from the athlete’s movement and athlete condence
in execution.
FIG. 5.
Comparing practitioners’ prescription of ywheel training during the weekly micro-cycle during pre-season and in-season (n

=

51
for each statement).

8
Kevin L. de Keijzer et al.
populations[11,12,33,34] and specically in soccer players[35].
Specically, the overloaded eccentric phase is perceived to be crucial
for most practitioners (n= 33) when applying ywheel training.
Although some practitioners neither agreed nor disagreed (n=16)
and others disagreed (n=2), the perceived importance of ahigh
intensity eccentric contraction can be attributed to the vast evidence
supporting its use and well established benets[9,12,34]. Practi-
tioners working within soccer may be particularly attracted to the
ability of eccentric training to preferentially recruit high threshold
motor units and increase cortical activity– which may boost strength
adaptations[13,25]. In support of current practitioners’ application
(Figure5), weekly and bi-weekly ywheel training has enhanced
hamstring strength outcomes with professional and semi-profession-
al soccer players[15,28,36]. Although information is still severely
lacking on female soccer populations, arecent systematic review
highlighted the positive effects of ywheel training on strength re-
lated outcomes in females[34].
Exercise prescription
Ahigh proportion of practitioners (n=40) program squats, which is
in agreement with reports of squat-biased eccentric exercise prescrip-
tion in elite sport[6]. Specically, few investigations have utilised
unilateral[31] and lateral[27,29,37,38] squats, with most pre-
scribing bilateral squats[14,17–19,22–25,29,30,36,39,40].
Reverse[27] and forward lunges[24,37], although utilised by many
practitioners (n=30), have not been investigated as thoroughly as
squats. Nonetheless, bi- and uni-lateral eccentric capacity has been
enhanced via ywheel multi-planar movements[27,29], supporting
use of ywheel lunge and multi-directional training (Figure4). Prac-
titioner utilisation (n=19) of open kinetic chain exercises is sup-
ported by effective flywheel leg extension [10] and leg
curl[15,21,30,36] protocols in the literature. Even though hamstring
based protocols (e.g., leg curl) enhanced performance and injury re-
lated outcomes[15,21,30,36], such open-kinetic chain exercises
are not as frequently utilised as squats (Figure4). Training purpose,
athlete compliance and experience may all impact exercise selection–
although equipment availability is most likely the reason for reduced
implementation of open kinetic chain exercises amongst practitio-
ners[5,31]. Nonetheless, the continued use of evidence based pro-
grams involving multiple exercises are recommended for male sport-
ing populations[4,28,30,35].
Dierences between pre- and in-season
The present investigation highlights that amajority of practitioners
prescribe flywheel training 2–3times per week (n = 44) and
1–2times per week (n=46) during the pre- and in-season period,
respectively (Figure5). The reduced training frequency applied from
pre- to in-season periods by practitioners is in line with present
guidelines[11] and reects key changes between tactical, technical
and physical objectives throughout the soccer season[6,20]. Apart
from athlete, coach, and environmental factors (e.g., team timetables),
considerations for exercise choice, intensity, and volume are impor-
tant for determining optimal training frequency[9, 11,12]. The
application of low volume ywheel protocols[17,19,23,24,27,38]
may be particularly important during the initial stages of the in-
season period if athletes are not accustomed to ywheel training.
Careful consideration of training frequency and volume may be im-
portant for reducing injury risk[9,13] and for maintenance of mus-
cle strength and sport performance in-season[38].
Flywheel training for enhancement of sport specic capacities
Chronic performance enhancement of jumping, sprinting, and change
of direction have been achieved with 1–3weekly training sessions over
a 6–10 week period involving 3–6 sets of 6–10 repeti-
tions[15,24,26,36–38]. Practitioners (n=31) mostly agree that
jumping, an important capacity in team sports[31], can be enhanced
by ywheel training. Although ywheel training has improved jumping
performance in highly-trained youth[27,31,36–38], semi-profes-
sional, and professional male team sport players[23,24,26,28],
some practitioners (n=19) stated they neither agreed nor disagreed,
while one practitioner disagreed with such statement (Figure2). Some
of the practitioners (n=16) prescribing weekly training sessions dur-
ing the in-season period may also be encouraged by the literature
showing how such exposure can specically enhance unilateral verti-
cal and horizontal jumping ability after 7–10weeks of training with
youth soccer players[24,38]. Such alow dose approach may be
aviable short-term alternative to precede more comprehensive and
time demanding protocols[5] or as along-term method to maintain
vertical jumping performance over a24week period with an athletic
population at risk of patellar tendinopathies[23].
Most practitioners (n=31) agreed that ywheel training can
enhance sprint speed (Figure2), with evidence supporting such an
approach with male youth and professional soccer players and profes-
sional handball players[15,26,36]. Nonetheless, the rest of the
practitioners (n=20) stated they neither agreed nor disagreed, re-
ecting some inconsistency in the literature[27,28,38]. Interest-
ingly, the weekly or bi-weekly exposure utilised in the ywheel soccer
literature[15,27,28,36] has also been adopted by many practitio-
ners in the present investigation (Figure5)– even if such an approach
has not always been successful in enhancing performance[27,28,38].
Alarge portion of practitioners (n=36) agree that ywheel train-
ing can improve change of direction performance, an important de-
terminant of soccer match play performance[28]. Importantly, prac-
titioner views are in line with evidence supporting ywheel trainingfor
enhancement of change of direction performance[15,27–29,36,38].
Eccentric strength, one of several factors associated with successful
change of direction performance, can be improved by ywheel train-
ing[41]. Investigations lasting 6–11weeks have enhanced change
of direction with semi-professional male soccer players[28], athletes
with limited training experience[27], and professional handball play-
ers[26]. Nonetheless, some practitioners (n=14) neither agreed nor
disagreed and one disagreed that ywheel training can enhance

Biology of Sport, Vol. 39 No4, 2022
9
Perception and application of ywheel training in soccer
were not condent that differences existed between the two meth-
odologies. To the best of the authors knowledge, no longitudinal
investigation currently exists comparing ywheel training and tra-
ditional resistance training for the ability to decrease injury likelihood
in athletes[16]. Investigating differences between ywheel and
traditional resistance training methods should be performed with
elite populations to generate useful evidence for application by
practitioners[6]. Nonetheless, amajority of the practitioners
(n= 33) agreed that ywheel training can help reduce risk and
alleviate burden of injuries, with the rest (n=18) neither agreeing
nor disagreeing (Figure1). The importance of consistent intense
eccentric training throughout the soccer season is highlighted by
the increased risk of muscle damage and injury associated with its
prolonged absence (e.g.,>4weeks)[21]. Although the importance
of intense eccentric training is clearly understood by practitioners
and researchers alike[4,13], limited practical evidence exists on
practical application of ywheel training with athletic popula-
tions[15,21,36]. Within soccer, only two such investigations
currently exist, with both investigating the efcacy of ywheel train-
ing for reducing hamstring injury risk[15,36]. The investigations
prescribed weekly or bi-weekly ywheel squats and/or hamstring
curl training protocols[15,16,36], which are among the more
commonly prescribed exercises by practitioners (Figure4).
Guidelines and Application
Nearly half of the practitioners (n=24) stated they were not satis-
ed with the current guidelines for ywheel training within soccer
(Figure1). Our ndings support previous suggestions that alack of
longer duration (i.e.,>12weeks) protocols and investigations involv-
ing elite soccer participants limit practitioner satisfaction with the
amount or quality of evidence for males [23]. Flywheel strength
training protocols involving female soccer players are also needed to
enhance implementation[34]. Specically investigating training fre-
quency, intensity, exercise choice, and volume may be useful to
practitioners– with particular attention also to tracking movement
velocity as ameans to understand if it can help optimise training
outcomes with avariety of movements and devices[22]. Within
aPAPE context, future studies investigating the effect of ywheel
PAPE protocols on speed performance (≥10m) may enhance prac-
titioner application. Further evidence for enhancement of jumping,
change of direction, and sprinting capabilities with elite[41] and
female soccer players[20] may also benet implementation. Since
practitioners commonly prescribe training weekly (Figure5), further
investigation into the efcacy of such protocols for sport performance
enhancement is also necessary[23,24,27]. Such an approach with
the objective of enhancing coach/player buy-in and applicability
within soccer environments[5] may be aviable short-term alternative
or step to progression towards greater weekly application and train-
ing outcomes[26]– although this must be thoroughly investigated.
Finally, it is possible that some of the practitioners (n= 18) who
remain unsure about the efcacy of ywheel training for reducing
change of direction performance. Considering the evidence supporting
the use of ywheel training for enhancing muscle activation and the
ability to sustain greater intense deceleration and stabilisation with
athletes[27,30]– it remains unclear why practitioners are lacking
condence in ywheel training for enhancing change of direction per-
formance.
Comparison between ywheel vs. traditional resistance training
Several practitioners (n=14) believed that ywheel methods were
superior to traditional resistance training methods for increasing
strength, while the majority (n=28) neither agreed nor disagreed
with the statement. Uncertainty amongst practitioners reects the
state of the research[9,12]. Primarily, alack of evidence impacts
the conclusions drawn[12], with largely contrasting ndings also
presented[9,12,33]. Future high quality study designs (e.g., ran-
domised control trials) are necessary to determine the relative effect
of either training modality on strength outcomes. Other comparisons,
such as equipment practicality, remain more divided between prac-
titioners– with some (n=20) agreeing, others neither agreeing nor
disagreeing (n=19), and fewer practitioners disagreeing (n=12)
that isoinertial equipment is more practical than traditional resistance
equipment. Although research dedicated to developing application
and safety of ywheel training among athletes exists[9], a divide
still exists amongst practitioners regarding equipment practicality
between the two training modalities (Figure3). Validated and reliable
measures highlighting concentric and eccentric strength during y-
wheel training might not replace traditional strength testing (e.g.,
isokinetic dynamometry) but may be practically valuable to practi-
tioners due to ease of access[22,39]. Although quantication of
load requires little equipment or time[14,22], differences between
devices and inertial loads may present issues regarding reliability,
impacting its applicability[9]. Importantly, ywheel training may
also be perceived as asafer and more manageable method than
traditional resistance training methods for practitioners working with
populations less accustomed or willing to perform intense eccentric
training, although opinions may differ between practitioners due to
familiarity with ywheel devices[6]. Flywheel devices do not require
third-party assistance following an adequate familiarization (e.g.,
coach) or implements (e.g., chains), enhancing both practicality and
safety[6]. In support of this, amajority of practitioners (n=37)
believe that ywheel devices provide an eccentric load that is difcult
to achieve with traditional resistance training, which is in line with
the literature [9]. Although evidence supports such a state-
ment[10,14], several practitioners neither agreed nor disagreed
(n=9) or disagreed (n = 5). Differences between devices and
techniques may alter eccentric load achieved– possibly swaying
practitioners’ opinion on this issue[6,9,10].
Flywheel training and injury prevention
When ywheel training was compared to traditional resistance
training for injury prevention, the majority of practitioners (n=25)

10
Kevin L. de Keijzer et al.
injury likelihood may benet from seeing further investigation on this
topic with elite athletes[16].
Limitations and future directions
This study is not without limitations. Although this research may not
allow for generalisations to all soccer practitioners due to various
types of bias (affecting respondent participation and responses given),
it increases awareness of perceived limitations and supports imple-
mentation of ywheel training. For example, practitioners, who
mostly had≥2years of experience of programming ywheel training
and predominantly worked with males, perceived ywheel methods
as effective to generate acute and chronic physical adaptations in
soccer environments. Such views are mostly supported by the litera-
ture, which boasts several methodological advantages (e.g., combi-
nation of repeated maximal concentric and eccentric contractions).
Although aclear majority of practitioners agreed on topics such as
familiarisation and strength enhancement– mixed responses regard-
ing reduction of injury likelihood, sport performance enhancement,
and comparison between methodologies exist. Such uncertainty es-
pecially highlights the need for further research into the effects of
ywheel training for reduction of injury likelihood and comparison
between ywheel and other training methodologies. Furthermore,
practitioners believe that evidence-based guidelines are lacking, which
may heavily inuence the efcacy of ywheel training within soccer.
The present investigation does not report different familiarisation nor
programming strategies when utilising ywheel training with youth
or adult soccer players. Nonetheless, further work dedicated to de-
veloping evidence-based recommendations for ywheel training
implementation within male and female soccer is needed.
CONCLUSIONS
Practitioners agree that ywheel training can improve sport perfor-
mance, strength, and likelihood of non-contact injury outcomes. Most
practitioners prescribe 2weekly sessions during pre- and in-season
periods. Flywheel sessions mostly consist of squats, but avariety of
exercises (lunge, hip hinge, and open kinetic chain) are also fre-
quently included. Practitioners are mostly unsure about differences
between ywheel and traditional resistance training outcomes, prac-
ticality of ywheel equipment, and evidence-based guidelines. The
investigation provides valuable insight into the perspectives and ap-
plication of ywheel training within elite soccer, highlighting its per-
ceived efcacy for strength and performance outcomes.
Practical Applications
Flywheel training is utilised by practitioners for various purposes
within soccer environments. Practitioners initially dedicate 2–3y-
wheel training sessions to familiarisation, especially if the athlete
lacks ywheel training experience. The pairing of ywheel devices
and technology (e.g., tablets) to permit instantaneous feedback may
enhance individualisation and outcomes– especially during familia-
risation. Although ywheel and traditional resistance training are both
deemed valid for enhancing performance and strength parameters,
advantages of one methodology over the other remain unclear. Prac-
titioners typically prescribe 2–3 and 1–2weekly ywheel sessions
during the pre- and in-season period, respectively. Within these ses-
sions, practitioners condently utilise avariety of exercises for chron-
ically enhancing performance and strength– while also prescribing
ywheel PAPE protocols to acutely enhance performance. Although
some evidence supports use of ywheel training (i.e., leg curl proto-
cols) to reduce injury risk amongst soccer players, limited use by
practitioners highlights potential practical issues related to imple-
mentation (e.g., time or equipment available).
Acknowledgments
We would like to thank all participating practitioners and clubs for
their cooperation and support. The authors declare that there is no
conict of interest.
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