Is the idea of combining endurance training with speed work on the same day a recipe for disaster, or can it actually be an effective way to improve overall cycling fitness, and if so, whats the most effective way to structure such a workout, considering the widely varying opinions on the matter, with some coaches advocating for a high-intensity interval session followed by a longer, steady-state ride, while others recommend the opposite, and what are the potential pitfalls of trying to cram too much into a single workout, such as overtraining, decreased performance, or even injury, and how can cyclists balance the need for endurance training with the desire to improve speed and power without sacrificing one for the other.