A Review of Flywheel Training

What is Flywheel Training

Flywheel training (FT) or iso-inertial training is a form of resistance training where concentric muscle effort is expended to spin a disk of known inertia. When the concentric motion is completed, the wheel begins to accelerate in the opposite direction leading to an eccentric contraction into the bottom of the exercise’s range motion. Additionally, the athlete’s ability to accelerate the flywheel dictates the force during the eccentric action, making it relatively safe to implement. In iso-inertial training, there is no resistance curve as the inertia is constant throughout the movement. This means the same force requirements are experienced throughout the whole range of motion. This may be an advantage over barbell training as some muscles may be under-stimulated due to strength and resistance curves. For example, during a squat the top ¼ of the movement is under stimulated, as the strength curve increases (optimal length-tension relationship to produce force) and resistance curve drops (required force to complete the rep decreases).

FT and Strength

Petra et al. (2018) found the largest standard mean difference (SMD) in strength measures (1.33) compared with other adaptations. Maroto-Izquierdo et al. (2017) reports a significant advantage of flywheel training over traditional training with SMD of 0.66. It should also be noted that no study used a progressive increased in inertia for strength development. Experienced trainees gained the most strength compare to novice trainees (0.41% versus 0.23% per day). This does not follow previous research in which novice trainees gain strength more rapidly (Kraemer et., 2002). Petra et al. (2018) argued that the training dose was too large for the novice trainees resulting in over training and muscle soreness, preventing realisation of their newly developed strength. I argue the adaptations occurring in iso-inertial training are due to imparting acceleration on the flywheel. More experienced trainees are stronger and can activate their muscles to a greater degree, therefore accelerating the flywheel more. Consequently, greater force is required to reverse the flywheels motion as F=MA. Novices produce less force and therefore don’t accelerate the flywheel as fast, reducing the force needed to reverse the motion. Therefore the stimulus is less and they don’t gain strength as quick. This can be likened to measuring velocity on a 200 kg deadlift; stronger athletes can get a high velocity, whereas novices can barely lift the bar, and both experience a very different strength stimulus

FT and Hypertrophy

Maroto-Izquierdo et al. (2017) found significance of P <0.0001 for preferential hypertrophy over traditional resistance training. Although the authors do acknowledge that a wide variety of methods were used to assess increases in physiological cross-sectional area. Studies in the meta-analysis using MRI found the lowest effect sizes were still between 0.44 and 0.51. Petre et al. (2018) found a similar trend and when assessing the time course of intervention and noted the time need to achieve similar levels of hypertrophy was significantly lower when compared with traditional resistance training programs.

FT and Functional Measures

In Petre et al. (2018) functional test were stratified into horizontal based (Sprint times, horizontal jump distances etc) and vertical based (countermovement jump, squat jump etc). The SMD for the two groups were 1.01 and 0.85 respectively demonstrating relatively large effects. Whilst not evaluated empirically, the authors note that iso-inertial training at high velocities had the greatest transfer to functional tests. Interestingly, several studies found double the effect sizes for change of direction tests than in jump test; 1.42 versus 0.69 and 1.44 versus 0.61 respectively (Tous-Fajardo, Gonzalo-Skok, Arjol-Serrano, & Tesch,2016; Maroto-Izquierdo, García-López, & de Paz, 2017). Improvements in kinetic parameters during a COD task were also seen in de Hoyo et al. (2016). This may be due to the relationship between eccentric strength and COD tests (Jones, Bampouras, & Marrin, 2009; Spiteri et al., 2014; Spiteri et al., 2015) with iso-inertial exercises providing a novel eccentric strength stimulus.

Additional Benefits

A tangible benefit of flywheel training is that it provides the opportunity to overload the eccentric portion of the repetition (Askling, Karlsson, & Thorstensson, 2003) with relative ease. In iso-inertial exercise, the concentric work dictates the total work due to mechanics of system. You can then overload the eccentric portion by performing the negative work over a smaller range of motion or time period (Askling et al., 2003). Alternative methods for eccentric overload are Bilateral-Unilateral and Strong-Weak concentric-eccentric variations and are still implemented easily. This is a lot more difficult with a barbell as concentric strength dictates the weight that can be lowered. As eccentric contractions are stronger than their concentric counterpart, the eccentric phases may be under stimulated. Overloading the eccentric contraction can produce unique neural and architectural adaptations that may result in increased athletic performance (Blazevitch, ) Eccentric overload was achieved with all inertias used in Martinez-Aranda and Fernandez-Gonzalo (2017) study suggesting that how repetition is carried out is of importance, however increasing the inertia did increase the percentage overload achieved until a plateau was reached at 0.05kgm2.

Additionally, the harness and pully systems in flywheel type exercise provide an alternative to heavy spinal loading associated with traditional resistance exercise. This makes it a joint friendly option for athlete who maybe loading-sensitive or rehabilitating current injuries.

Potential Drawbacks

Little research has been carried out with regards using specific inertias and speeds to target specific biomotor abilities. Martinez-Aranda and Fernandez-Gonzalo, (2017) found that a lower inertia resulted in a significantly higher power output than higher inertias, more than likely due to increased ease to impart velocity to the implement. Consequently, increasing the inertia requires more force to accelerate the flywheel and therefore may target maximum strength capabilities. Perhaps certain velocities or power zones illicit specific adaptations similar Velocity Based Training, but further research needs to be performed before this is a viable prescription strategy.

A non-negotiable of resistance training is progressive overload. A stronger stimulus is necessary in order to continue to elicit positive adaptations. Whilst prescription for iso-inertial training may not be straight forward, Table 1 shows simple potential overload strategies for flywheel training .

Similarities exist between progressive overload in traditional resistance training and iso-inertial training. Anecdotally, practitioners who typically employ iso-inertial training as a novel stimulus without thought of overload or desired adaptation.

Conclusion

FT offers a unique and potent stimulus for experienced resistance trainees that may be superior to traditional resistance training. Strength, hypertrophy and power can all be trained effectively with higher flywheel velocities or powers results in great transfer to athletic movements. However, there is a lack of consensus on how to periodise and apply progressive overload to FT and ensure it is more than just a novel stimulus. Until further research is completed to ascertain dose- response relationships, FT may have limited applicability to training contexts.

References

Askling, C., Karlsson, J., & Thorstensson, A. (2003). Hamstring injury occurrence in elite soccer players after preseason strength training with eccentric overload. Scandinavian journal of medicine & science in sports, 13(4), 244-250.

de Hoyo, M., Sañudo, B., Carrasco, L., Mateo-Cortes, J., Domínguez-Cobo, S., Fernandes, O., ... & Gonzalo-Skok, O. (2016). Effects of 10-week eccentric overload training on kinetic parameters during change of direction in football players. Journal of sports sciences, 34(14), 1380-1387.

Petré, H., Wernstål, F., & Mattsson, C. M. (2018). Effects of flywheel training on strength-related variables: A meta-analysis. Sports medicine-open, 4(1), 55.

Jones, P., Bampouras, T., & Marrin, K. (2009). An investigation into the physical determinants of change of direction speed. Journal of Sports Medicine and Physical Fitness, 49(1), 97-104.

Kraemer, W. J., Adams, K., Cafarelli, E., Dudley, G. A., Dooly, C., Feigenbaum, M. S., ... & Newton, R. U. (2002). American College. of Sports Medicine. American College of Sports Medicine position stand. Progression models in resistance training for healthy adults. Med Sci Sports Exerc, 34(2), 364-80.

Maroto-Izquierdo, S., García-López, D., & de Paz, J. A. (2017a). Functional and muscle-size effects of flywheel resistance training with eccentric-overload in professional handball players. Journal of human kinetics, 60(1), 133-143.

Maroto-Izquierdo, S., García-López, D., Fernandez-Gonzalo, R., Moreira, O. C., González-Gallego, J., & de Paz, J. A. (2017b). Skeletal muscle functional and structural adaptations after eccentric overload flywheel resistance training: a systematic review and meta-analysis. Journal of science and medicine in sport, 20(10), 943-951.

Martinez-Aranda, L. M., & Fernandez-Gonzalo, R. (2017). Effects of inertial setting on power, force, work, and eccentric overload during flywheel resistance exercise in women and men. The Journal of Strength & Conditioning Research, 31(6), 1653-1661.

Tous-Fajardo, J., Gonzalo-Skok, O., Arjol-Serrano, J. L., & Tesch, P. (2016). Enhancing change-of-direction speed in soccer players by functional inertial eccentric overload and vibration training. International journal of sports physiology and performance, 11(1), 66-73.

Spiteri, T., Nimphius, S., Hart, N. H., Specos, C., Sheppard, J. M., & Newton, R. U. (2014). Contribution of strength characteristics to change of direction and agility performance in female basketball athletes. The Journal of Strength & Conditioning Research, 28(9), 2415-2423.

Spiteri, T., Newton, R. U., Binetti, M., Hart, N. H., Sheppard, J. M., & Nimphius, S. (2015). Mechanical determinants of faster change of direction and agility performance in female basketball athletes. The Journal of Strength & Conditioning Research, 29(8), 2205-2214.