FlexGuard: A Design Space for On-Body Feedback for Safety Scaffolding in Strength Training

Strength training carries inherent safety risks when exercises are performed without supervision. While haptics research has advanced, there remains a gap in how to integrate on-body feedback into intelligent wearables. Developing such a design space requires experiencing feedback in context, yet obtaining functional systems is costly. By addressing these challenges, we introduce FlexGuard, a design space for on-body feedback that scaffolds safety during strength training. The design space was derived from nine co-design workshops, where novice trainees and expert trainers DIY'd low-fidelity on-body feedback systems, tried them immediately, and surfaced needs and challenges encountered in real exercising contexts. We then evaluated the design space through speed dating, using storyboards to cover the design dimensions. We followed up with workshops to further validate selected dimensions in practice through a proof-of-concept wearable system prototype, examining how on-body feedback scaffolds safety during exercise. Our findings extend the design space for sports and fitness wearables in the context of strength training.