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Flywheel Resistance Training (FRT) has gained popularity for its ability to produce high mechanical tension and eccentric overload, which has shown to be beneficial for athletic performance and rehabilitation. However, the high mechanical loads inherent in machines FRT pose significant engineering challenges regarding durability and user experience (UX). Current belt-lock systems (BLS) and auto-retract mechanisms (ARM) often face premature material failure and user interactions that are inconsistent. This study aims to explore and propose a redesigned BLS and ARM that prioritizes durability, sustainability through Life Cycle Assessment (LCA), and UX. This is achieved by identifying critical UX factors for these subsystems and designing a solution that improves technical performance and decreases environmental impact compared to an existing model. The following research questions were answered in the study:

RQ1: What UX factors are important in a BLS and ARM for FRT equipment?

RQ2: How could a BLS and ARM be designed for FRT equipment to have increased durability, UX and decreased environmental impact compared to a previous solution?

The study followed an abductive research approach, iterating between theoretical frameworks and empirical data. A narrative literature review established a basis for the relevant theoretical areas related to the research questions. An in-depth single-case study was conducted at Exxentric AB, where a generic product development process was combined with Design Thinking (DT) tools. Data was collected through semi-structured interviews with seven users of different experience levels and through workshops with the company's R&D team. The proposed solution was evaluated using Finite Element Analysis (FEA), fatigue simulations, and a simplified LCA with a “Cradle-to-Gate” (CTG) scope.

The conducted study proposes a final prototype transitioning from a friction-based "belt-bite" system to a mechanical ratchet and pawl mechanism that locks directly on the belts axle. This shift eliminates abrasive wear on the drive-belt, a primary cause of failure in previous designs. Simulations confirmed a load capacity exceeding 1500 N and a lifespan of at least 200,000 cycles. UX improvements include a doubled retraction force of the belt (1.9 N) and an increased ergonomic unlocking button surface (314 mm²). While the initial carbon footprint increased to 2.09 kg CO2 eq, the design offers superior long-term sustainability by eliminating the material waste associated with frequent belt replacements. The study concludes that functional efficiency on the behavioral level is the main driver of user satisfaction in FRT equipment. The proposed axle-lock mechanism successfully fulfills critical requirements for safety, performance, and brand quality.