Inertial Flywheel Training
By Daniel Cobian MS, CSCS, RSCC*D, CES, Chicago White Sox
Eccentric resistance training is an effective means of preventing muscle damage and enhancing performance through inertial flywheel training devices. Meta-analysis data indicates that inertial flywheel training produced significantly greater improvements in concentric and eccentric strength, muscle power, muscle hypertrophy, vertical jump height and running speed than conventional resistance training (2). Additional research indicated that Initial training sessions may allow athletes to become accustomed to flywheel training in regards to obtaining stabilization measures while regular performance training protocols may elicit high concentric peak power output and greater eccentric overloads depending on the inertial loads (3). The greater eccentric overloads may contribute to higher motor unit activation compared to the concentric activation rates associated with traditional multi-joint movements that make flywheel training an optimal conditioning stimulus to induce the effects of post-activation potentiation (PAP) (1). Along with the positive effects on variables such as speed, jump height, and change of direction performance, flywheel training may elicit muscle activation, muscle length, and tendon stiffness that are ideal during the implementation in a rehabilitation setting (4)
Flywheel devices are designed to provide inertial concentric and eccentric forces that are generated by the rotating flywheels with varied resistance depending on their diameter and thickness (Figure 1). The athlete’s concentric muscle action initiates the flywheel’s rotation, with a cord or strap connected to the shaft, through kinetic energy that is followed by an eccentric action that brings the flywheel to a stop leading to the next concentric-eccentric cycle (Figures 2 & 3). The delay in braking forces during the eccentric phase of the movement results in eccentric overloading.
A systematic review of nine studies involving 275 subjects by Maroto-Izquierdo et al. (2) highlighted the skeletal muscle adaptations associated with flywheel eccentric overload training. To inclusion criteria included peer-reviewed randomized controlled trials of athletes or physically active individuals without any prior injury and were compared against controls or another intervention group. The findings showed that maximal dynamic strength was significantly greater with flywheel training devices compared to traditional resistance exercise programs by greater eccentric overloads inducing greater forces from lower inertia or higher velocities. Greater improvements in hypertrophy adaptations were also observed in flywheel training compared to traditional resistance training while larger effect sizes were observed in well-trained athletes. Muscular power showed the greatest improvements of all the variables analyzed with the eccentric overload properties of flywheel training. The improvements in power were associated with the maximization of the stretch-shortening cycle from optimal joint angles during the eccentric phase just prior to the concentric phase resulting in higher velocities during the entire movement (2).
An understanding of the time requirements necessary for familiarization before flywheel training is essential to ensure safe and efficient technique while optimal programming may be developed after acknowledging how varied power may be produced under different loads. When 24-high level athletes (age=25.1±4.6-years) completed four sessions consisting of 4-sets of 10-reps of the flywheel quarter-squat under different inertial loads (0.025, 0.050, 0.075, & 0.100-kg·m²), higher concentric peak power values were observed with the lowest inertial loads (0.025-kg·m²) while greater eccentric power was observed with 0.025 and 0.050-kg·m² (Sabido et al., 2018). Also, a greater eccentric-concentric ratio was exhibited with the 0.075-kg·m² load. In regards to familiarization, three sessions were believed to be optimal as good reliability measures were observed on the third testing day compared to the first two sessions. These findings provide a rationale for determining inertial loads depending on the training objective in regards to peak concentric power and greater eccentric overload.
Given that greater PAP effects are elicited depending on the type of conditioning, flywheel training may provide a stimulus with higher more unit discharge during eccentric overloads. Stronger potentiation effects are produced as greater eccentric forces are generated leading to greater power outputs (Beato et al., 2020). Furthermore, the increased kinetic output positively improves the stretch-shortening cycle resulting in greater athletic tasks such as sprinting and jumping. However, optimal PAP effects through flywheel training may be observed with biomechanically similar conditioning and athletic performance variables (e.g., half-squat & countermovement jumps/ hip thrusts & sprinting).
The heightened eccentric component associated with flywheel inertial training produces efficient forces with low energy requirements that may be ideal for rehabilitation training settings. Lower risk of hamstring injuries has been associated with eccentric overload training while flywheel training over six-weeks has been shown to improve hamstring eccentric-concentric torque that may reduce the likelihood of anterior cruciate ligament injury (Wonders, 2019). Because flywheel training includes concentric and eccentric phases it may be a suitable method during the rehabilitation of tendinosis. With that said, flywheel squats, for example, have been shown to reduce pain through eccentric exercise while improving patellar and Achilles tendon quality (Wonders, 2019). During the second week after an initial calf muscle strain, flywheel training may also improve the structural components of the gastrocnemius.
In conclusion, flywheel inertial training may be a more effective alternative to resistance training for improvements in strength, power, and hypertrophy gains, through eccentric overloading. The increased eccentric durations involved with flywheel training lead to more motor unit activity and potentiation effects producing greater subsequent power outputs observed in specific athletic tasks. After athletes become familiarized with up to three sessions of flywheel training, proper training protocols may be programmed from understanding that lower inertial loads (0.025-kg·m²) are associated with higher concentric power output and greater eccentric power is accomplished with loads of 0.025 and 0.050-kg·m² (Sabido et al., 2018). Flywheel training may also benefit rehabilitation protocols as the eccentric and concentric combination provides an efficient stimulus to improve tendon and hamstring strengthening qualities beneficial for reduction of injury and improving the rate of return to play.
- Beato, M., McErlain-Naylor, S. A., Halperin, I., & Iacono, A. D. (2020). Current evidence and practical applications of flywheel eccentric overload exercises as post activation potentiation protocols: A brief review. International Journal of Sports Physiology and Performance, 15, 154-161.
- Maroto-Izquierdo, S., Garcia-Lopez, D., Fernandez-Gonzalo, R., Moreira, O. C., Gonzalez-Gallego, J. and Paz, J. A. (2017). 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, 943-951.
- Sabido, R., Hernandez-Davo, J. L., & Pereyra-Gerber, G. T. (2018). Influence of different inertial loads on basic training variables during the flywheel squat exercise. International Journal of Sports Physiology and Performance, 13, 482-489.
- Wonders, J. (2019). Flywheel training in musculoskeletal rehabilitation: A clinical commentary. The International Journal of Sports Physical Therapy, 14(6), 994-1002.
Daniel Cobian MS, CSCS, RSCC*D, CES is the AZL and rehab strength coach for the Chicago White Sox.