Flywheel Training and the Assumption of Eccentric Overload

A recent review by Spudić and Nosaka (2026) in Sports Medicine – Open challenges a common assumption in the field: that flywheel devices inherently provide eccentric overload. While flywheel training is recognized for its unique neuromuscular and structural benefits, the authors highlight that achieving true eccentric overload—where eccentric mechanical quantities exceed concentric ones—is highly dependent on execution technique and equipment constraints.

The Mechanical Constraint of Passive Flywheel Systems

In traditional passive flywheel systems, eccentric loading is mechanically constrained by the preceding concentric action. The energy stored in the flywheel during the concentric phase dictates the maximum eccentric resistance that can be applied during the braking phase.

For practitioners, this means that unless specific strategies are used, such as delaying braking until the final third of the range of motion, eccentric outputs may only match rather than exceed concentric outputs. When braking is initiated too early or distributed across the full range, the result can be a more controlled but submaximal eccentric stimulus.

This distinction matters. Without sufficient eccentric overload, the neuromuscular and architectural adaptations commonly attributed to flywheel training may be blunted, particularly in well-trained or elite populations.

Bypassing These Constraints with Exerfly Motorized Technology

Exerfly is the only flywheel device on the market offering true eccentric overload. Our motorized flywheel technology is designed to address these research-identified gaps:

• Decoupled loading: An integrated motor allows eccentric loads to exceed concentric output by up to 80%, ensuring a supramaximal eccentric stimulus even when concentric force production declines.
• Quantifiable Loading: Enables practitioners to precisely measure and prescribe the magnitude of eccentric overload, moving away from the "user-dependent" variability often seen in passive devices.
• Consistency: Motorized assistance ensures that high-threshold motor units are targeted throughout every repetition, regardless of concentric fatigue.

In practical terms, this allows coaches to reliably expose athletes to high eccentric forces without relying solely on perfect technique or maximal concentric intent.

This video demonstrates how the motorized system provides consistent, intense resistance during the eccentric phase of a leg curl, ensuring the user experiences true overload and more closely mimicking game like conditions.

Exerfly Motorized Technology Explained

Practical Takeaway for Coaches

Flywheel training remains a highly effective training modality, but its effectiveness depends on how eccentric loading is achieved. Coaches using passive systems should place particular emphasis on braking strategy and monitor mechanical outputs where possible. Exerfly Motorized systems offer an alternative by ensuring eccentric overload is delivered consistently and measurably.

‍

Full article: Spudić & Nosaka (2026), Sports Medicine – Open
https://doi.org/10.1186/s40798-025-00974-y