The definition of a mi I split is a type of running workout that is designed to help improve speed and endurance. It involves running at a set pace for a certain distance, then increasing the pace for a shorter distance. For example, a runner might run a mile at a comfortable pace, then increase the pace for the next quarter mile, then return to the original pace for the final quarter mile. This type of workout is great for those who are looking to improve their speed and endurance, as it allows them to gradually increase their speed while still getting a good workout. It also helps to prevent burnout, as it allows the runner to vary their pace and keep their body from becoming too accustomed to a single pace. Mi I splits are a great way to improve running performance and can be used by both beginner and experienced runners alike.