Current Guidelines for the Implementation of Flywheel Resistance Training Technology in Sports: A Consensus Statement

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 this training.

OBJECTIVE

This paper aimed to present the consensus reached by 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 (18 May 2023) while three 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 recommendations, and (5) the consensus process. The systematic analysis of the literature was performed to select the most up-to-date review papers available on the topic, which resulted in nine 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 the evidence summary and researchers' expertise; the consensus statement included three statements and seven 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 score ranging from 8.1 to 8.8, and therefore, all statements included in this consensus were considered appropriate. The recommendations (1-7) had a score ranging from 7.7 to 8.6, and therefore, all recommendations were considered appropriate.

CONCLUSIONS

Because of the consensus achieved among the experts in 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.

Perception and use of flywheel resistance training amongst therapists in sport

Flywheel (isoinertial) resistance training is a valid strength training method that has been incorporated in sport for decades, yet little is known about how therapists working in sport apply flywheel resistance training. We aimed to describe and understand current application and perception of flywheel resistance training amongst therapists working in sport. Seventy- three therapists (13 ± 10 years of experience) started part of this survey with 52 completing the entire electronic questionnaire. Nine multiple choice questions on application and perceptions of flywheel training (prerequisites, use of technology, barriers, and upper- and lower-body exercises) preceded two 6-point Likert scale statements on strength and reduction of injury likelihood. Most therapists (47/73) either used or intended to use flywheel training with their athletes and stated familiarisation would be a priority prior to initiating training. Although more than half suggested they were confident flywheel training could enhance strength (27/52) and muscular prehabilitation outcomes (40/52), many remained unsure. Nonetheless, it appears that therapists would mostly include flywheel training within prehabilitation (40/52) or during the later stages of rehabilitation (37/52). To monitor progress, therapists slightly prefer power (30/52) over velocity outputs, while few would not use them at all. Although therapists would prescribe most exercises - the squat, rotational exercise, and unilateral leg curl would be the most selected. Meanwhile, therapists reported remain most unsure or would avoid prescribing the lateral squat and unilateral hip extension. The biggest perceived barriers to flywheel training are equipment cost/space, evidence, and scheduling. The investigation provides valuable insight into the application and perception of flywheel training amongst therapists working in sport.

Hypertrophic adaptations to a 6-week in-season barbell vs. flywheel squat added to regular soccer training

BACKGROUND

The aim of this study was to compare the hypertrophic adaptations to barbell or flywheel squat exercise added to regular in-season soccer training.

METHODS

Quadriceps' (rectus femoris [RF], vastus medialis [VM] and vastus lateralis [VL]) cross-sectional area (CSA) in its portions (proximal [PROX], middle [MID], and distal [DIST]) was measured on both legs before and after a 6-week barbell (80 to 90% one-maximum repetition; N.=7) or flywheel (0.0611 to 0.0811 kg·m²; N.=7) in an U19 professional soccer team using a 3T magnetic resonance imaging. Both groups underwent 5 sets × 6 reps per session of squat separated by 3-min rest, while controlling the time under tension (within 0.5 and 0.8 s).

RESULTS

The barbell squat group experienced moderate CSA increments in the VM<inf>MID</inf> and the VL<inf>DIST</inf> of the right leg (d=0.98-0.99). Additionally, the flywheel group experience large CSA increments in the RF<inf>MID</inf>, VL<inf>PROX</inf> and VL<inf>MID</inf> of the right leg (d=1.00-1.84). On average, flywheel squat training largely produced greater force during exercise compared to the barbell squat training (29.2 vs. 12.2 N·kg^-1; d=5.95), whereas the barbell squat training produced moderately greater power output (10.5 vs. 9.7; d=0.52).

CONCLUSIONS

Barbell squat training seems to be more effective for VM hypertrophy whereas flywheel squat triggers greater RF and VL hypertrophy as complementary to regular field-based soccer practice and competition within a short range of time (6 weeks) during the in-season. These findings can be considered also from either strength or reconditioning perspective based on the increase in the quadriceps muscles' CSA as mechanism underlying strength/power adaptations.

The Effect of Flywheel Inertia on Peak Power and Its Inter-session Reliability During Two Unilateral Hamstring Exercises: Leg Curl and Hip Extension

This study investigated the effect of flywheel moment of inertia (0.029, 0.061, and 0.089 kg·m2) on concentric and eccentric peak power and eccentric:concentric peak power ratio during unilateral flywheel leg curl and hip extension exercises. Moreover, the inter-session reliability of peak power was analyzed during both exercises. Twenty amateur male soccer athletes attended five visits-performing three sets of eight repetitions of either unilateral leg curl or hip extension (all three moments of inertias) during each visit. For the unilateral leg curl, there were no differences in any measure between moments of inertia (p = 0.479) but a higher eccentric than concentric peak power for all moments of inertia (p < 0.001). For the unilateral hip extension, differences between moments of inertia were reported for all measures (p < 0.05). Specifically, the lowest moment of inertia elicited the greatest concentric peak power (p = 0.022), there were no differences with the medium inertia (p = 0.391), and the greatest moment of inertia obtained the greatest eccentric peak power (p = 0.036). Peak power measures obtained acceptable to excellent reliability while the eccentric:concentric ratio reported unacceptable to good reliability for both exercises. A variety of moments of inertia can elicit high eccentric knee flexor demands during unilateral leg curls, whereas higher moments of inertia are needed to achieve an eccentric-overload in peak power during hip extensions. Different exercises may have different inertia-power relationships. Concentric and eccentric peak power measures should continue to inform training, while the eccentric:concentric ratio should not be used.

Assessment of anterior thigh muscle size and fat infiltration using single-slice CT imaging versus automated MRI analysis in adults

OBJECTIVES

We examined the longitudinal and cross-sectional relationship between automated MRI-analysis and single-slice axial CT imaging for determining muscle size and muscle fat infiltration (MFI) of the anterior thigh.

METHODS

Twenty-two patients completing sex-hormone treatment expected to result in muscle hypertrophy (n = 12) and atrophy (n = 10) underwent MRI scans using 2-point Dixon fat/water-separated sequences and CT scans using a system operating at 120 kV and a fixed flux of 100 mA. At baseline and 12 months after, automated volumetric MRI analysis of the anterior thigh was performed bilaterally, and fat-free muscle volume and MFI were computed. In addition, cross-sectional area (CSA) and radiological attenuation (RA) (as a marker of fat infiltration) were calculated from single slice axial CT-images using threshold-assisted planimetry. Linear regression models were used to convert units.

RESULTS

There was a strong correlation between MRI-derived fat-free muscle volume and CT-derived CSA (R = 0.91), and between MRI-derived MFI and CT-derived RA (R = -0.81). The 95% limits of agreement were ±0.32 L for muscle volume and ±1.3% units for %MFI. The longitudinal change in muscle size and MFI was comparable across imaging modalities.

CONCLUSIONS

Both automated MRI and single-slice CT-imaging can be used to reliably quantify anterior thigh muscle size and MFI.

ADVANCES IN KNOWLEDGE

This is the first study examining the intermodal agreement between automated MRI analysis and CT-image assessment of muscle size and MFI in the anterior thigh muscles. Our results support that both CT- and MRI-derived measures of muscle size and MFI can be used in clinical settings.

The effect of flywheel training on strength and physical capacities in sporting and healthy populations: An umbrella review

The aim of this umbrella review was to provide a detailed summary of how flywheel training enhances strength and physical capacities in healthy and athletic populations. The eleven reviews included were analyzed for methodological quality according to the Assessing the Methodological Quality of Systematic Review 2 (AMSTAR 2) and the Grading of Recommendations Assessment, Development and Evaluation (GRADE) criteria. Two were systematic reviews, six were systematic reviews with meta-analyses and three were narrative reviews. Although the included reviews support use of flywheel training with athletic and healthy populations, the umbrella review highlights disparity in methodological quality and over-reporting of studies (38 studies were included overall). Flywheel post-activation performance enhancement protocols can effectively enhance strength and physical capacities acutely with athletes and healthy populations. All relevant reviews support flywheel training as a valid alternative to traditional resistance training for enhancing muscular strength, power, and jump performance with untrained and trained populations alike. Similarly, reviews included report flywheel training enhances change of direction performance—although conclusions are based on a limited number of investigations. However, the reviews investigating the effect of flywheel training on sprint performance highlight some inconsistency in attained improvements with elite athletes (e.g., soccer players). To optimize training outcomes, it is recommended practitioners individualize (i.e., create inertia-power or inertia-velocity profiles) and periodize flywheel training using the latest guidelines. This umbrella review provides an analysis of the literature’s strengths and limitations, creating a clear scope for future investigations.

Resistance training induces similar adaptations of upper and lower-body muscles between sexes

The purpose of the study was to compare sex adaptations in hypertrophy, strength and contractile properties of upper and lower-body muscles induced by resistance training (RT). Eighteen RT untrained male (MG) and female (FG) students (aged 24.1 ± 1.7 years, height: 1.75 ± 0.08 m, weight: 70.4 ± 12.3 kg) undervent 7 weeks of biceps curl and squat training (2 days/week, 60–70% repetition maximum, 3–4 sets, 120 s rest intervals, reps until muscular failure). At baseline and final measurement, thickness and cross-section area, one-repetition maximum and tensiomyography parameters (contraction time − Tc and radial displacement − Dm) of elbow flexors (biceps brachii) and knee extensors (4 quadriceps muscles) were evaluated. Although MG tends to display greater absolute strength gains for upper- (p = 0.055) and lower-body (p = 0.098), for relative changes ANCOVA revealed no sex-specific differences for either of the tested variables. Significant hypertrophy was observed for all tested muscles, except for vastus intermedius in FG (p = 0.076). The Dm significantly decreased for biceps brachii (MG by 12%, p < 0.01 and FG by 13.1%, p < 0.01) and rectus femoris (MG by19.2%, p < 0.01 and FG by 12.3%, p < 0.05), while Tc values remain unchanged. These results indicate that initial morphological, functional and contractile alterations following RT are similar for males and females, and that there are no specific sex adaptations either for the upper- or lower-body muscles. The study was registered with ClinicalTrials.gov (NCT04845295).

The Maximum Flywheel Load: A Novel Index to Monitor Loading Intensity of Flywheel Devices

BACKGROUND

The main aim of this study was (1) to find an index to monitor the loading intensity of flywheel resistance training, and (2) to study the differences in the relative intensity workload spectrum between the FW-load and ISO-load.

METHODS

twenty-one males participated in the study. Subjects executed an incremental loading test in the squat exercise using a Smith machine (ISO-load) or a flywheel device (FW-load). We studied different association models between speed, power, acceleration, and force, and each moment of inertia was used to find an index for FW-load. In addition, we tested the differences between relative workloads among load conditions using a two-way repeated-measures test.

RESULTS

the highest r2 was observed using a logarithmic fitting model between the mean angular acceleration and moment of inertia. The intersection with the x-axis resulted in an index (maximum flywheel load, MFL) that represents a theoretical individual maximal load that can be used. The ISO-load showed greater speed, acceleration, and power outcomes at any relative workload (%MFL vs. % maximum repetition). However, from 45% of the relative workload, FW-load showed higher vertical forces.

CONCLUSIONS

MFL can be easily computed using a logarithmic model between the mean angular acceleration and moment of inertia to characterize the maximum theoretical loading intensity in the flywheel squat.

A Randomized Crossover Trial on the Acute Cardiovascular Demands During Flywheel Exercise

In a randomized crossover trial, we examined whether age plays a role in the mean arterial pressure (MAP) response during a vigorous flywheel exercise of varying load. We hypothesized that the magnitude of increase in the MAP during the flywheel exercise would increase in proportion to advancing age, thereby imposing a significant challenge to the cardiovascular system. A total of 30 participants of both sexes (age range from 20-55 y, 37% women) underwent a detailed medical examination, and their maximal oxygen uptake was determined. They performed a squat exercise (2 sets × 7 repetitions) on a flywheel ergometer at three randomly assigned moments of inertia set at 0.025, 0.05, and 0.075 kg m², while the cardiovascular response was continuously recorded via a Task force monitor. Compared to the resting values, robust rises in the MAP were observed during all three flywheel loads, reaching the highest value of 179 ± 4 mmHg (p = 0.001) during the highest load. In parallel, the cardiac index (cardiac output normalized by the body surface area) was two-fold greater during all the flywheel loads compared to rest, and at a high load, exclusively, the total peripheral resistance increased by 11% (p = 0.001). The rise in heart rate compensated for a load-dependent drop in the stroke index (stroke volume normalized by the body surface area). In our study population, no correlations were observed between the relative increase in the MAP and the participants' age for the three flywheel loads. The present findings suggest that the larger moments of inertia impose a substantial burden to the cardiovascular system, without apparent associated age-differences of the relative magnitude of MAP rise throughout the exercise.

Independent influence of age on heart rate recovery after flywheel exercise in trained men and women

The present study examined whether differences in the heart rate recovery following flywheel exercise cessation were associated with differences in maximal oxygen uptake (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{\text{V}}}$$\end{document}V˙O₂ max.), age and sex in trained adults. Eleven men (age range 22–49 years, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{\text{V}}}$$\end{document}V˙O₂ max. = 43.6 ± 7.6 mL kg min⁻¹) and ten women (age range 20—53 years, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{\text{V}}}$$\end{document}V˙O₂ max. = 38.0 ± 5.7 mL kg min⁻¹) were randomly assigned to complete a squat-exercise on the flywheel ergometer set at three different moments of inertia, while their cardiovascular responses were continuously monitored. During the flywheel exercise the mean arterial pressure rose by ~ 35 to 40% (p = .001), and the increment was more robust in men than women. The cardiac index was two-fold greater across both sexes compared to the baseline (p = .001), while the rise in heart rate (~ 144 bpm) was more pronounced in women to compensate for their load-dependent stroke index decline (p = .001). The load-independent time-course changes in heart rate recovery markers were comparable between the sexes. When these indicators were pooled, a stepwise regression revealed age as the only relevant predictor of both fast and slow components of the heart rate recovery (~ 30% of the shared variance explained, p = .014). The present data suggest that the heart rate recovery declines with age, irrespective of sex, or well-preserved cardiorespiratory fitness in moderately-trained adults.

Acute flywheel exercise does not impair the brachial artery vasodilation in healthy men of varying aerobic fitness

BACKGROUND

The cardiovascular response to variable load exercise on a flywheel ergometer is still unknown.

OBJECTIVE

This study examined the effects of flywheel exercise on cardiovascular response and brachial artery vasodilation capacity in healthy, active men.

METHODS

In this cross-sectional study, nineteen men (20-57 years old) completed three laboratory visits, including a ramp exercise test to determine their maximal oxygen uptake JOURNAL/blpmo/04.03/00126097-202106000-00008/inline-graphic1/v/2021-04-27T091817Z/r/image-tiff max, and exercise intervention on a flywheel ergometer set at 0.075 kg·m2 moment of inertia. After the ramp test cessation, all participants were allocated into aerobically untrained (n = 10) and trained (n = 9) groups. Throughout the flywheel exercise, cardiovascular demands were continuously monitored via Finapres, while a pre/postflow-mediated dilation (FMD) assessment was performed using ultrasound imaging.

RESULTS

There were no differences observed between the groups in their anthropometrics, age or resting brachial artery diameter, while the JOURNAL/blpmo/04.03/00126097-202106000-00008/inline-graphic2/v/2021-04-27T091817Z/r/image-tiff max was ~15% higher (P = 0.001) in trained compared to aerobically untrained group. The cardiovascular response to the flywheel exercise was similar between the groups, with peak mean arterial pressure and heart rate readings reaching ~160 mmHg and ~140 bpm, respectively. The flywheel exercise did not impair the FMD (%) response, which was comparable between the groups (P = 0.256). When these data were pooled, the regression analysis showed an inverse relationship among FMD (%), age (β = -0.936, P = 0.001) and JOURNAL/blpmo/04.03/00126097-202106000-00008/inline-graphic3/v/2021-04-27T091817Z/r/image-tiffmax. (β = -0.359, P = 0.045).

CONCLUSION

Although aerobic fitness alone does not directly explain the FMD response to flywheel exercise, aerobically untrained individuals, as they get older, tend to have lower brachial artery FMD.

The effects of free weights and iso-inertial resistance during semi-squatting exercise on amateur soccer players' physical performance indicators: a randomized controlled study

BACKGROUND

The aim was to compare the effects of two lower extremity strengthening programs using iso-inertial resistance or free weights on amateur soccer players' physical performance indicators.

METHODS

Thirty-five amateur soccer players (average age 22.6±5.1 years) were randomly assigned to iso-inertial group (n=11) or free-weight group (n=11), or control group (n=13). The groups performed two training sessions per week for six weeks. Before and after the strengthening implementation, physical performance indicators were evaluated, including the isokinetic knee extensors and flexors' strength, power, speed, and agility. The significance level was set at p<0.05.

RESULTS

The iso-inertial training resistance led to an increase in the hamstrings' eccentric strength at 60°/s and 150°/s (p<0.05) compared to the free-weight resistance (p>0.05) and the controls (p>0.05). No other significant adaptations were observed in the other isokinetic strength, power, speed (10-m, p=0.052) and agility measurements (Illinois agility test, p=0.059). In ratio (knee flexors/knee extensors) the only differences observed was at 150 o/s for iso-inertial group (p<0.05).

CONCLUSIONS

Iso-inertial resistance training during semi squatting can enhance the hamstrings' eccentric performance andthe soccer players' speed and agility compared to the classic free-weight training program, which should considered when designing strength and injury prevention programs.

Effects of flywheel training on strength-related variables in female populations. A systematic review

This study aimed to evaluate the effect of flywheel training on female populations, report practical recommendations for practitioners based on the currently available evidence, underline the limitations of current literature, and establish future research directions. Studies were searched through the electronic databases (PubMed, SPORTDiscus, and Web of Science) following the preferred reporting items for systematic reviews and meta-analysis statement guidelines. The methodological quality of the seven studies included in this review ranged from 10 to 19 points (good to excellent), with an average score of 14-points (good). These studies were carried out between 2004 and 2019 and comprised a total of 100 female participants. The training duration ranged from 5 weeks to 24 weeks, with volume ranging from 1 to 4 sets and 7 to 12 repetitions, and frequency ranged from 1 to 3 times a week. The contemporary literature suggests that flywheel training is a safe and time-effective strategy to enhance physical outcomes with young and elderly females. With this information, practitioners may be inclined to prescribe flywheel training as an effective countermeasure for injuries or falls and as potent stimulus for physical enhancement.

Eccentric Resistance Training in Youth: Perspectives for Long-Term Athletic Development

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.

Implementing Eccentric Resistance Training-Part 2: Practical Recommendations

The purpose of this review is to provide strength and conditioning practitioners with recommendations on how best to implement tempo eccentric training (TEMPO), flywheel inertial training (FIT), accentuated eccentric loading (AEL), and plyometric training (PT) into resistance training programs that seek to improve an athlete's hypertrophy, strength, and power output. Based on the existing literature, TEMPO may be best implemented with weaker athletes to benefit positional strength and hypertrophy due to the time under tension. FIT may provide an effective hypertrophy, strength, and power stimulus for untrained and weaker individuals; however, stronger individuals may not receive the same eccentric (ECC) overload stimulus. Although AEL may be implemented throughout the training year to benefit hypertrophy, strength, and power output, this strategy is better suited for stronger individuals. When weaker and stronger individuals are exposed to PT, they are exposed to an ECC overload stimulus as a result of increases in the ECC force and ECC rate of force development. In conclusion, when choosing to utilize ECC training methods, the practitioner must integrate these methods into a holistic training program that is designed to improve the athlete's performance capacity.

Implementing Eccentric Resistance Training-Part 1: A Brief Review of Existing Methods

The purpose of this review was to provide a physiological rationale for the use of eccentric resistance training and to provide an overview of the most commonly prescribed eccentric training methods. Based on the existing literature, there is a strong physiological rationale for the incorporation of eccentric training into a training program for an individual seeking to maximize muscle size, strength, and power. Specific adaptations may include an increase in muscle cross-sectional area, force output, and fiber shortening velocities, all of which have the potential to benefit power production characteristics. Tempo eccentric training, flywheel inertial training, accentuated eccentric loading, and plyometric training are commonly implemented in applied contexts. These methods tend to involve different force absorption characteristics and thus, overload the muscle or musculotendinous unit in different ways during lengthening actions. For this reason, they may produce different magnitudes of improvement in hypertrophy, strength, and power. The constraints to which they are implemented can have a marked effect on the characteristics of force absorption and therefore, could affect the nature of the adaptive response. However, the versatility of the constraints when prescribing these methods mean that they can be effectively implemented to induce these adaptations within a variety of populations.