Fast-paced fitness training (e.g. aerobics, Bodycombat, step workouts) is one of the most popular activities at fitness clubs worldwide because it is beneficial for physical health and it can enhance participants' motivation and engagement of fitness training. Yet, their fast pace and required coordination make it difficult for some participants, especially for beginners and those with coordination problems, to follow the class. Here we present the design, implementation and qualitative user evaluation of TwinkleBands, a piece of wearable technology that provides real-time support with trainees' movement and coordination learning by providing discriminative visual cues on the extremities. We show that TwinkleBands helps movement imitation and coordination in several ways. Based on this, we discuss key design takeaways for future technology design to support movement teaching and learning in fast-paced activities.