Whats the most effective way to incorporate high-intensity interval training (HIIT) workouts into a Zwift ERG mode plan, considering the modes focus on precise power output, and how can riders balance the need for explosive power with the steady-state efforts that ERG mode is designed for? Are there any specific workout structures or protocols that can help riders maximize the benefits of HIIT while still taking advantage of ERG modes precision? Additionally, how can riders adjust their cadence and gearing to optimize power output during high-intensity intervals in ERG mode, given that the mode is designed to maintain a consistent power output regardless of cadence or gearing?