Current guidelines for the implementation of flywheel resistance training technology in sports: a consensus statement

Current guidelines for the implementation of flywheel resistance training technology in sports: a consensus statement Marco Beato1*, Kevin L. de Keijzer1, Alejandro Muñoz-Lopez2, Javier Raya-González3, Marco Pozzo4, Björn A. Alkner5, Antonio Dello Iacono6, Jordi Vicens Bordas7,8, Giuseppe Coratella9, Sergio Maroto-Izquierdo10, Oliver Gonzalo-Skok11, Stuart A. McErlain-Naylor12, Fernando Martin-Rivera13, Jose L. Hernandez-Davo14, Luis Suarez Arrones15, Rafael Sabido16, Moises de Hoyo17, 18, Rodrigo Fernandez-Gonzalo19,20, Lena Norrbrand21 Affiliations 1. School of Allied Health Sciences, University of Suffolk, Ipswich, United Kingdom; 2. Departamento de Motricidad Humana y Rendimiento Deportivo, University of Seville, Seville, Spain; 3. Faculty of Sport Sciences, University of Extremadura, Cáceres, Spain; 4. Master de Fútbol, Universidad Pablo de Olavide, Sevilla, Spain SmartCoach Technologies, Inc.; 5. Department of Orthopaedic surgery, Eksjö, Region Jönköping County and Department of Biomedical and Clinical Sciences, Linköping University, Linköping, Sweden; 6. School of Health and Life Sciences, University of the West of Scotland; 7. Sport, Exercise, and Human Movement (SEaHM), University of Vic-Central University of Catalonia, Barcelona, Spain; 8. Sport and Physical Activity Studies Centre (CEEAF), University of Vic-Central University of Catalonia, Barcelona, Spain; 9. Department of Biomedical Sciences for Health, Università degli Studi di Milano, Milan, Italy; 10. i+HeALTH, European University Miguel de Cervantes (UEMC), Valladolid, Spain; 11. Department of Communication and Education, Universidad Loyola Andalucía, Seville, Spain; 12. School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, United Kingdom; 13. Research Group in Prevention and Health in Exercise and Sport, University of Valencia, Valencia, Spain; 14. Faculty of Health Sciences, Isabel I University, Burgos, Spain; 15. Department of Sport Sciences, Universidad Pablo de Olavide, Seville, Spain; 16. Sport Research Centre, Department of Sport Sciences, Miguel Hernández University, Elche, Spain; 17. Department of Physical Education and Sport, University of Seville, Seville, Spain. 18. Performance Department, Aston Villa Football Club, UK. 19. Department of Laboratory Medicine, Division of Clinical Physiology, Karolinska Institutet, Stockholm, Sweden. 20. Unit of Clinical Physiology, Karolinska University Hospital, Stockholm, Sweden; 21. Division of Environmental Physiology, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Solna, Sweden. *Corresponding author Marco Beato, School of Allied Health Sciences, University of Suffolk, Ipswich, United Kingdom, email: [email protected] Short title/running head: Guidelines for the implementation of flywheel resistance training technology Key Points: - Although the eccentric phase is frequently the focus of flywheel training, not all exercises, users, or training loads achieve eccentric overload. Consequently, practitioners should define this resistance method as “flywheel resistance exercise or training” instead of “eccentric overload”. - Reliable flywheel training exercise outputs are contingent upon the user’s effort, training experience (i.e., familiarization), moment of inertia (kg.m2) selected, and the mechanical characteristics of the devices used. - Practitioners can use flywheel resistance training as a valid method to develop chronic morphological adaptations in both sporting and healthy male or female populations. - Practitioners can use flywheel resistance training as a valid method to increase mechanical power and jump performance of male and female populations. Enhancements can be seen with interventions that are short and consisting of lower weekly training frequencies. - Practitioners can use flywheel resistance training as a valid method to increase athletes’ ability to perform sport specific acceleration and deceleration actions. Abstract Background: Flywheel resistance training has become more integrated within resistance training programs in a variety of sports due to the neuromuscular, strength, and task specific enhancements reported with such training. Objective: This paper aimed to present the consensus reached between internationally recognized experts during a meeting on current definitions and guidelines for the implementation of flywheel resistance training technology in sports. Methods: Nineteen experts from different countries took part in the consensus process: 16 of them were present at the consensus meeting (18th of May 2023) while 3 submitted their recommendations by e-mail. Prior to the meeting, evidence summaries were developed relating to areas of priority. This paper discusses the available evidence and consensus process from which recommendations were made regarding the appropriate use of flywheel resistance training technology in sports. The process to gain consensus had five steps: 1) performing a systematic review of systematic reviews, 2) updating the most recent umbrella review published on this topic, 3) first round discussion among a sample of the research group included in this consensus statement, 4) selection of research group members – process of the consensus meeting and formulation of the recommendation, and 5) consensus process. The systematic analysis of the literature was performed to select the most updated review papers available on the topic which resulted in 9 articles; their methodological quality was assessed according to AMSTAR 2 (Assessing the Methodological Quality of Systematic Review 2) and GRADE (Grading Recommendations Assessment Development and Evaluation). Statements and recommendations scoring 7-9 were considered appropriate. Results: The recommendations were based on evidence summary and researchers’ expertise; the consensus statement included 3 statements and 7 recommendations for the use of flywheel resistance training technology. These statements and recommendations were anonymously voted on and qualitatively analyzed. The three statements reported a range score from 8.1 to 8.8., therefore, all statements included in this consensus were considered appropriate. The recommendations (from one to seven) had a score ranging from 7.7 to 8.6, therefore, all recommendations were considered appropriate. Conclusions: Because of the consensus achieved among the experts of this project, it is suggested that practitioners and researchers should adopt the guidelines reported in this consensus statement regarding the use of flywheel resistance technology in sports. 1. Introduction The concept of using the inertia of spinning flywheels to generate resistance was used by Hill more than 100 years ago [1], whereas about 30 years ago the gravity-independent flywheel exercise device was developed for use in space to counteract muscle loss in astronauts during long-duration space flights [2]. In fact, resistance training using flywheel devices has been shown to counteract quadriceps muscle atrophy during 90 days of bedrest [3], and even induce hypertrophy during unilateral lower limb suspension [4]. The unique loading principle, allowing for variable loading within a repetition, also made the device interesting for terrestrial use. Thus, the first report of positive injury prevention outcomes with flywheel training was published 20 years ago [5]. Since then, numerous studies have been published involving athletes from various sports, demonstrating that flywheel resistance training can generate significant morphological and neuromuscular adaptations [6–10]. Flywheel devices allow for maximal or near maximal voluntary forces throughout each repetition of a set [2,11]. To initiate movement, the participant must pull, push, or curl a cord/strap connected to a fixed shaft that holds the flywheel disc(s). The force applied unwinds a strap connected to the shaft of the device, which starts to rotate. Once the whole range of motion of the concentric phase is performed, the cord/strap rewinds and the person must resist the pull of the rotating flywheel disc(s) by performing an eccentric muscle action [4,11–13]. If performed appropriately, this allows for a greater application of force during the eccentric action and thereby a mechanical eccentric overload (i.e., greater eccentric than concentric peak force or power) as well as greater muscle activation [6,13–15]. Apart from technique, it is important that the device and analysis of mechanical outputs are appropriate to optimize flywheel training [16]. The combination of repetitive maximal concentric phases and increased demands during the eccentric phase of movements may enhance physiological and mechanical adaptations and benefit athletes. Flywheel training may elicit a preferential upregulation of satellite cell activity and transcriptional pathways in fast-twitch muscle fibers, increase protein synthesis and ultimately muscular hypertrophy [17]. These effects seem to justify the acute and chronic enhancements seen with flywheel training programs. Flywheel resistance training has become more integrated within resistance training programs in a variety of sports due to the neuromuscular, strength, and task specific enhancements reported with such training [18–20]. Flywheel resistance training has been effectively implemented within post-activation performance enhancement protocols to acutely enhance sport performance [17,21–23] and for chronically enhancing strength and sport performance [8,20,24]. A recent review conducted by Raya-Gonzalez et al. [25] concluded that flywheel training may generate quicker adaptations (e.g., strength and power) than traditional resistance training programs. Moreover, flywheel training has also improved jumping [26,27], linear sprint [28,29] and change of direction [19,30] performance, which are all key variables for success in sport [18]. More recently, some recommendations for periodization of flywheel training in team sports have been provided to support the integration of flywheel training without interfering with regular sport training [31] as well as to monitor and decrease muscular asymmetries in sport [32]. The aforementioned findings highlight that flywheel training provides a valid and safe strength training method for athletic and healthy populations to enhance sport performance and strength. Although the body of literature available on flywheel resistance exercise has increased in the latest years, we still have some relevant issues when such research is interpreted [17]. For instance, we have several review papers that have investigated the effect of flywheel resistance training on sport parameters, however, these reviews frequently use the same studies (e.g., the same randomized controlled trials) to reach their conclusions [13,19,24], which may lead to repetitive and consequent amplification of errors derived from some of the original papers (e.g., methodological or statistical errors that lead to incorrect data interpretation) [33]. Moreover, the use of some specific terms within flywheel resistance training research is not accurate or consistent, and this is an issue that needs to be addressed. Furthermore, it has been found that on many topics there are some differences between practitioners’ perceptions and research evidence about the effect of flywheel resistance training in sport [34]. Hence, an overall consensus among researchers has not yet been reached. Given the importance of using appropriate flywheel resistance training, an internationally recognized consensus-based standard is necessary to set some specific recommendations for the use of flywheel resistance technology. The aim of this paper is to present the consensus reached between internationally recognized researchers (experts) during a meeting on current definitions and guidelines for the implementation of flywheel resistance technology in sports. 2. Methods 2.1 Consensus process The first step of this consensus statement was to synthesize and analyze the current state of the literature. Following a systematic search on PubMed/Medline and SportDiscus (only articles published in English before 30th of January 2023 were included), a total of 22 reviews or systematic reviews were found. Authors (MB and KDK) reviewed all the reviews published thus far and identified the most comprehensive and updated, which was “The effect of flywheel training on strength and physical capacities in sporting and healthy populations: An umbrella review” [20]. This paper is an umbrella review, which follows procedures to reduce the impact of limitations of individual reviews and meta-analyses. Moreover, it allows for the synthesis and appraisal of the existing evidence and thereby comparison of conclusions based on all relevant published data. Finally, this type of review allows for an analysis of possible or existing bias in the literature that can negatively affect the validity and applicability of the scientific evidence [35]. This umbrella review was selected because it is one of the latest and the most comprehensive reviews on flywheel resistance training. In addition to this, the umbrella review summarized eleven reviews previously published and scored their methodological quality according to the Assessing the Methodological Quality of Systematic Review 2 (AMSTAR 2) and Grading Recommendations Assessment Development and Evaluation (GRADE) [36,37] criteria. However, some of these selected articles were narrative reviews and were not suitable for this consensus statement procedure. Step 1: Systematic review of the systematic reviews As reported above, this consensus statement was initially based on a previous umbrella review [20], which was updated by removing any narrative reviews as well as adding any new existing systematic reviews. To do so, a new systematic search was performed using the following approach. The systematic review of the systematic reviews (SROSR) was performed according to systematic review guidelines and followed the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA, 2020) statement guidelines [38]. Systematic search: PubMed search: (flywheel exercise) OR (flywheel inertia) OR (flywheel resistance training) OR (flywheel resistance exercise) OR (variable inertial) OR (rotary inertial) OR (inertial training) OR (inertial exercise) OR (isoinertial training) OR (isoinertial exercise) OR (eccentric overload) OR (eccentric overload training) OR (enhanced eccentric) OR (gravity independent) OR (flywheel training) AND (sport performance [MeSH]) OR (muscular strength) Filters applied: Full text, Meta-Analysis, Systematic Review, English. SportDiscus search: (flywheel exercise) or (flywheel inertia) or (flywheel resistance training) or (flywheel resistance exercise) or (variable inertial) or (rotary inertial) or (inertial training) or (inertial exercise) or (isoinertial training) or (isoinertial exercise) or (eccentric overload) or (eccentric overload training) or (enhanced eccentric) or (gravity independent) or (flywheel training) or (AND (sport performance [MeSH]) OR (muscular strength). Four new reviews were found: one was a scoping review [39], two were narrative reviews [25,40], and one was a systematic review with meta-analysis [41]. Step 2: Update of the Umbrella review by De Keijzer et al., 2022 The inclusion and exclusion criteria previously used [20] were followed for this SROSR with the addition that only systematic reviews and meta-analyses could have been considered for this project. Therefore, three narrative reviews included by De Keijzer et al. [20] were excluded in this SROSR [9,15,18]. A more recent literature search was performed (Figure 1). ***Add here Figure 1 (updated flow chart)*** As stated above, three new reviews, specifically a scoping review [39] and two narrative reviews [25,40] were excluded because of the inclusion criteria used in this SROSR. However, the authors (MB and KDK) reviewed the excluded papers to examine whether these articles could have influenced the validity of this SROSR. Based on our evaluation, these reviews would not substantially change the final evidence reported in this SROSR as well as the final recommendations and summary assessment of this consensus statement. One new systematic review with meta-analysis was included in this SROSR [41]. Quality assessment The 8 systematic reviews previously published and subsequently analyzed by De Keijzer et al. [20] were integrated with the most recent one [41], while the narrative reviews analyzed in the previous umbrella review were removed (only systematic reviews and meta-analysis were included in the current study). A new analysis of the methodological quality according to the AMSTAR 2 and GRADE was therefore performed. Once again, the final output following this procedure takes the name of SROSR and includes 9 reviews [8,13,19,24,41–45]. ***Add here Table 1 (AMSTAR 2 and GRADE) *** Results of the systematic review of systematic reviews AMSTAR 2 is a tool that allows for the assessment of methodological quality of systematic reviews [36]. In this case we reported that 7 reviews were considered moderate and 2 were rated as high quality, while none of the reviews were considered low quality [36]. GRADE is a transparent framework for developing and presenting summaries of evidence and provides a systematic approach for making clinical practice recommendations [37]. Using these GRADE principles, 1 review was rated of moderate quality (authors believe the true effect is probably close to the estimated effect), 6 of the 9 reviews were considered of high quality (authors have a lot of confidence that the true effect is like the estimated effect), while 2 reviews did not critically appraise the included primary studies and were therefore not assigned a GRADE rating Step 3: First round discussion among a sample of the research group included in this consensus statement The results of the SROSR were circulated amongst a sample of the members of the research group defined as the “leading group”, which consisted of the following researchers: MB, KDK, LN, AML, JRG. The invitation to be a member of the leading group was sent by email on the 9th of January 2023. The first meeting amongst the members of the leading group was on the 6th of February. These researchers assessed the first three stages of the process before sharing their findings of the SROSR and starting a critical analysis with the whole research group (who were selected and invited to stage 4). Step 4: Selection of research group members – process of the consensus meeting and formulation of the recommendation Selection of research group members Prior to initiating this research, the leading group set the criteria to identify potential expert group members. Researchers included in this project were selected based on their publication record (i.e., to be or to have been researchers with a minimum of 5 published peer-reviewed articles in the field of flywheel resistance technology) and to have practically applied flywheel training (i.e., use of flywheel resistance technology in applied sport settings). Potential group members were contacted via e-mail asking them if they were interested in taking part in the consensus statement. The researchers included in the first stage of the recruitment offered new potential researchers to be included in this research group. The leading group completed step 4 on the 8th of March 2023 when the new potential researchers were invited to collaborate on this consensus statement. An email asking for their availability to collaborate to this project was sent on the 10th of March and a reminder on the 17th of March 2023. Researcher/Expert group demographics All consensus meeting participants were researchers and experts in the field of flywheel resistance technology in sports. Areas of expertise among the participants included: strength and conditioning, sports science, sports medicine. The years of experience, geographic locations and gender of the experts were also recorded. Areas of priority Following this expression of interest and the final selection of the members, the following key areas were identified as priorities for consensus: definition of flywheel resistance technology, characteristics of flywheel resistance technology, exercise load monitoring, flywheel training periodization, flywheel training for hypertrophy, strength and power development, flywheel training for sprinting and change of direction performance, and flywheel training for injury prevention. Step 5: Consensus process The included expert group members were contacted via email asking for their availability to meet the rest of the leading group for an online meeting to discuss the consensus statement on the 18th of May 2023. The results of the SROSR and the first draft of the recommendations were emailed to each expert group member at least 1 week before the meeting. During the meeting, members reported their observations, and the final recommendations were made following such open discussion. The researchers that did not take part in the meeting e-mailed their feedback and suggestions to the leading group, who integrated such feedback into the final recommendations. Experts that did not participate to the meeting and did not submit their feedback were excluded from the final authors’ list. Following the conclusion of the meeting and when the recommendations were made, the expert group members voted on the final recommendations of this consensus statement. This process was conducted in an anonymous format, following the procedure and scoring system used in a previous consensus statement [46]. The score was performed using a 9-point Likert scale, where 1 was the minimum and 9 was the maximum. Overall, scores from 1–3 were considered and defined as inappropriate, scores of 4–6 were considered uncertain, and scores of 7–9 were considered appropriate. The final consensus statement was written based on the evidence reported in the SROSR and expert group members’ votes. 3. Results Twenty-five potential experts were contacted by email and 19 of them completed the survey and took part in this project. Researchers included in this research were selected based on their previous publications on the topic and to have been/being flywheel practitioners. Researchers identified (multiple selections were allowed) as experts in strength and conditioning (n =13), sports science (n =17), medical doctors (n =1) or biomechanics (n =1). Experts had a mean of 12 (range: 4-26) years of experience in the use of flywheel resistance technology. Their geographical location was Europe (n = 19). The participants identified as men (n =18) and a woman (n = 1). The consensus meeting took place on the 18th of May 2023 in an online format. Of the 19 experts involved in this process, 16 took part in this event while 3 submitted their recommendations by e-mail to the leading group. Therefore, all experts were included in the consensus voting process, which was concluded on the 23rd of June, and they were listed as authors of this paper. The consensus voting statement and qualitative analysis of the recommendations are reported in Figure 2. “Please, add here Figure 2 (vote on the final recommendations)” 4. DISCUSSION The aim of this consensus statement was to present a consensus reached between internationally recognized researchers (experts) during a meeting on current definitions and guidelines for the implementation of flywheel resistance training technology in sports. The consensus-based standard set some specific statements and recommendations for the use of flywheel resistance technology: Statement 1: Flywheel resistance training is characterized by the use of rotating flywheel discs or cones to provide resistance. The concentric action is initiated by pulling the strap connected to the shaft of the device, spinning (accelerating) the flywheel/cone. Once the strap rewinds around the shaft, an eccentric action is performed to decelerate the flywheel/cone rotation. The inertia of a flywheel or cone provides the resistance when using flywheel resistance technology [20]. The concentric action is initiated by pulling a strap connected to the shaft, setting the flywheel/cone into rotation [13]. When the strap rewinds around the shaft, an eccentric action (braking force) decelerates the flywheel/cone rotation [47,48]. Hence, the training method is characterized by increasing or decreasing the stored kinetic energy of a rotating flywheel or cone [6]. The intensity of the movement can be adjusted by changing the flywheels or the cone, and thereby changing the moment of inertia. It usually consists of one or more stacked discs or a cone with radially mounted masses. During the concentric phase, the kinetic energy can be calculated as follows: Ek = ½ I  2, where Ek = kinetic energy (J), I = flywheel moment of inertia (kgm2) and  = angular velocity (rad/s). tensiomyography [48]. Practitioners can use different moments of inertia (e.g., 0.029–0.11 kg·m2), based on the exercise selected, and multi-set exercises (e.g., 2–3 sets) to enhance sportspecific performance [15,17]. Regarding the post-activation performance enhancement timewindow, acute fatigue is dominant in the early part of the recovery period (e.g., 30 s), while potentiation is dominant in the second part (e.g., after 3 min) [15], thus it is suggested to practitioners to plan a recovery period between the flywheel post-activation performance enhancement protocol and the subsequent exercises to facilitate transfer effects on athletic performance [17]. Recommendation 6: Practitioners can use flywheel resistance training as a valid method to increase athletes’ ability to perform sport specific braking and accelerating actions. Indeed, the systematic use of flywheel training within training will enhance acceleration, deceleration, sprint, and change of direction ability in sporting populations. Further studies are needed to evaluate the dose-response relationship between flywheel training and sprint performance amongst sport populations that typically adopt a low resistance training frequency per week (e.g., football). Flywheel resistance training has been commonly used to improve sprint and change of direction ability in sport [18,20]. A meta-analysis reported that both sprinting and change of direction ability increase following short training protocols (5-10 weeks) [45]. Flywheel training involves repetitive maximal concentric and eccentric contractions and may lead to sportspecific improvements by enhancing muscular size, muscular strength, and capacity to exert force during change of direction actions [17,51]. Another meta-analysis (involving 11 studies) found that flywheel training improves change of direction performance (e.g., 180 change of direction) more so than control groups in professional team sports [42]. This was further confirmed by a recent systematic review with meta-analysis that reported that change of direction ability can be improved in less than 12 weeks of training [41]. Instead, another metaanalysis [19] that assessed male soccer players found that flywheel resistance training presents contrasting evidence regarding its efficacy for enhancing sprint performance. This could be related to the low training dose that is usually prescribed in soccer studies, for instance most of the interventions used a training frequency of 1-2 sessions a week or with an overall low flywheel resistance training volume [19]. However, it is not possible to provide a definitive explanation of this due to the number of contextual factors that play a role in speed (and physical) training in football. In contrast, the same review confirmed findings of previous reviews stating that flywheel resistance training is suitable for enhancing change of direction ability in football players [19]. Therefore, the experts involved in this consensus statement, after the evaluation of the SROSR, suggest practitioners use flywheel resistance training to improve the braking and accelerating actions that athletes experience when performing changes of direction as well as to improve sprinting capacity in sporting populations. However, it is our opinion that a greater understanding of low-dose flywheel training for the enhancement of sprint performance in sport (e.g., football) populations is still necessary. Recommendation 7: Further well-designed intervention studies (i.e., randomized controlled trials) are needed to verify the ability of flywheel resistance technology-based training interventions to reduce the likelihood of muscular (e.g., hamstring) and articular (e.g., anterior cruciate ligament) injuries in sport populations; moreover, further research is needed to evaluate its validity as a rehabilitation tool following an injury. One of the main advantages of flywheel resistance training is the mechanical work that can be performed during the eccentric phase [9]. Eccentric training can stimulate specific neuromuscular and morphological adaptations [82], which can lead to a reduction in likelihood of lower limb injuries (e.g., hamstring) [83]. However, adaptations and related benefits of flywheel training span from the combination of both concentric and eccentric contractions [6,25]. As previously reported, the concentric phase of the movement is an indispensable requirement to generate a demanding eccentric phase [17,51,55,56]. Therefore, it is clear that the acute mechanical load generated during flywheel resistance exercises and the related chronic benefits are related to the combination of both actions [14,28,51]. Regarding injury prevention using flywheel resistance training devices, it was found that the use of 1-2 flywheel resistance exercises, using moments of inertia ranging from 0.05 to 0.145 kg·m2, volume of 6-8 repetitions for 3-6 sets, training 2 times per week, reduced lower limb injuries in soccer players [5,7,57]. Although some evidence exists, the current body of literature about the capacity of flywheel resistance training programs to actually reduce the likelihood of muscular injuries is quite limited. Moreover, little is also known regarding its validity within rehabilitation; a recent paper showed that flywheel resistance training can be successfully used in populations with patellar tendinopathy [84] but more research in this field is needed. On this basis, no flywheel specific evidence-based guidelines can be provided to practitioners until this area is further explored. Nonetheless, we suggest practitioners integrate flywheel resistance training in a progressive and systematic manner (like how other resistance training methods are used) to improve athletes’ strength and obtain training adaptations. Intensity and volume should therefore be progressed (ideally with monitoring of mechanical outputs) for both injury prevention and rehabilitation objectives [66]. We suggest combining different flywheel exercises (e.g., squats, leg curls) with other suitable training methods to enhance injury prevention programs rather than relying solely on one training methodology [32,75,85]. Quality of evidence (AMSTAR/GRADE) Of the nine included reviews, two were systematic reviews and seven were systematic reviews with meta-analyses. While two reviews were considered of high quality, seven were considered of moderate quality using the AMSTAR 2 checklist (Table 1). Future studies should aim to provide explicit statements wherein methods are established a priori (item 2), justify study inclusion/exclusion (with rationale) (item 7), assess individual studies’ risk of bias (item 9), clearly report funding/conflicts of interest (item 10 and 16), and consider likelihood of publication bias (item 15) [36]. In accordance with the adapted GRADE principles, six reviews were considered high quality (>2 high quality studies), one was considered moderate quality (>1 high or >2 moderate quality studies), while two did not critically appraise the included primary studies and were therefore not assigned a GRADE rating. Future reviews should aim to include high quality studies to enhance the conclusions of their research [20]. Final considerations and practical application section This consensus statement presents for the first time a consensus reached between internationally recognized researchers (experts) during a meeting on current definitions and guidelines for the implementation of flywheel resistance technology in sports. Firstly, a systematic analysis of the literature was performed to select the most updated review papers available on the topic which resulted in 9 articles [8,13,19,24,41–45] – this process can be found in the flow chart (Figure 1). Secondly, the researchers involved in this project assessed the methodological quality of them according to AMSTAR 2 and GRADE, which can be found in Table 1. Regarding these reviews, all of the review papers were considered of moderate or high quality (AMSTAR 2), while considering the GRADE, 7 were considered of moderate or high quality; following that, the reviews selected in this consensus statement were used to discuss the main areas of priority and subsequently to formulate the recommendations for flywheel resistance training. Based on the current scientific evidence and researchers’ expertise, the consensus statement included 3 statements and 7 recommendations for the use of flywheel resistance training technology. These statements and recommendations were anonymously voted on and qualitatively analyzed (see Figure 2). Statement one, two and three reported an average score of 8.8  0.3, 8.7  0.4, and 8.1  0.8, respectively, therefore, all statements included in this consensus were considered appropriate. The recommendations (from one to seven) reported a score of 7.7  1.0, 8.2  0.7, 8.4  0.7, 8.6  0.5, 8.4  0.7, 8.3  0.9 and 8.6  0.6, respectively, therefore, all recommendations included in this consensus were considered appropriate (scores of 7–9 were). Because of the consensus achieved among the researchers (experts) of this project, it is suggested that practitioners and researchers should adopt the guidelines reported in this consensus statement regarding the use of flywheel resistance training technology in sports. Limitations and future directions This consensus statement is not without limitations. Firstly, the expert group was from Europe, limiting the cultural diversity of the group. Secondly, only one woman was present in this expert group. Future meetings should try to improve diversity and involve researchers, experts, athletes, and other stakeholders. The selection of the areas of interest regarding flywheel resistance training was made by the experts involved in this research, therefore some form of bias (e.g., confirmation bias, reporting bias) could be present; future research should try to limit the effect of these biases. Another limitation is related to the researchers’ inclusion process, which was based on two criteria: the researcher’s publication record (i.e., a minimum of 5 published peer-reviewed articles in the field of flywheel resistance technology) and the researcher’s expertise in applied flywheel training (i.e., use of flywheel resistance technology in applied sport settings). The first inclusion criterion does not consider the quality and impact of these publications, which is a limitation. Lastly, some recommendations were made using the current evidence and the current experts’ opinions, therefore, such recommendations should be step-by-step updated when new high-quality pieces of evidence are produced (i.e., new systematic review and meta-analysis, high-quality randomized controlled trials). 5. Conclusions This consensus statement is the first paper of its type for flywheel resistance training technology in sports. The definitions and guidelines for the implementation of flywheel resistance training technology in sports were reached in this consensus statement between internationally recognized experts. Three statements and seven recommendations were voted on and qualitatively considered as appropriate. Practitioners and researchers that use flywheel resistance technology in sports settings should adopt the guidelines reported in this consensus statement. 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Int J Sports Physiol Perform [Internet]. 2016;11:66–73. Available from: http://www.ncbi.nlm.nih.gov/pubmed/25942419 Authors contribution All authors contributed to the generation of the statements and recommendations made in this article. All authors also read and approved the final version. Funding Javier Raya-González was supported by a Ramn y Cajal postdoctoral fellowship (RYC2021- 031072-I) given by the Spanish Ministry of Science and Innovation, the State Research Agency (AEI) and the European Union (NextGenerationEU/PRTR). Conflict of interest The authors declare no conflict of interest for this paper. Data availability statement This manuscript does not have associated data.