What are the most effective strategies for regaining muscle mass and speed after a prolonged period of keto dieting, and how do these strategies differ for cyclists who have been primarily focused on endurance training versus those who have been incorporating high-intensity interval training into their regimen? Are there any specific nutritional considerations or supplements that can aid in the recovery process, and what role does periodized training play in rebuilding muscle and speed? Additionally, are there any notable differences in the recovery process for cyclists who have been doing a lot of high-mileage training versus those who have been focusing on shorter, more intense workouts?