In ERG mode, if you slow your cadence the trainer increases resistance to hold the target watts, and vice versa. This makes hitting exact power targets effortless — 250W means 250W whether you pedal at 70 or 100 RPM. Best for threshold and sweet spot work. Turn it off for VO2max intervals where you want to surge naturally. Available on all modern smart trainers (Wahoo KICKR, Tacx NEO, etc.).