What are the most effective Zwift races for high-intensity training, and how can riders tailor their training to get the most out of these events? Are there specific routes or events that are better suited for sprint training, hill repeats, or endurance building? How do Zwifts various race formats, such as criteriums, road races, and time trials, lend themselves to different types of high-intensity training? Are there any particular Zwift features, such as the ability to join a group ride or compete against other riders, that can enhance the effectiveness of high-intensity training? Can riders use Zwifts data analytics and training plans to optimize their high-intensity training, and if so, how? Are there any Zwift-specific training protocols or workouts that have been developed to target specific physiological adaptations, such as increasing lactate threshold or improving anaerobic capacity? How can riders balance the need for high-intensity training with the risk of overreaching or burnout, and are there any specific Zwift features or strategies that can help mitigate this risk?