Whats the most effective approach to incorporating interval training into a triathlon preparation plan, and how can athletes avoid the common pitfalls of overtraining and burnout when implementing this type of high-intensity training? Are there specific interval protocols that are more beneficial for triathletes, such as HIIT or polarized training, and how should these be periodized throughout the training season to maximize performance gains? Furthermore, what role should a coach or experienced athlete play in designing and implementing an effective interval training plan, and what metrics or data should be used to measure the success of this type of training? Can anyone share their experience with using interval training in triathlon preparation, and what specific challenges or obstacles did they encounter, and how were these overcome? Additionally, what are some common misconceptions about interval training that triathletes should be aware of, and how can these be avoided in order to maximize the benefits of this type of training?