Defining a running overuse injury
This type of injury affects the musculoskeletal system, resulting from the combined fatigue over a period of time, beyond the capabilities of the stressed structure
All biological structures, like bones, muscles, tendons, and ligaments can adapt positively or negatively to the stress applied.
Positive adaptation required repeated stress below the mechanical limits, with adequate rest between applications.
Injury or negative adaptation occurs when stress is applied beyond the mechanical limits once - this is an acute injury or a repeated amount of time with not enough rest in between - overuse injuries.
The most commonly reported risk factors for running overuse injuries include running distance, training intensity, and stretching habits.
Increasing distance will increase the number of steps, thus increasing the number of stress applications. So running more, at the same intensity, will put you at risk of injury.
Intensity relates to running speed. So if you keep running the same distance, while increasing intensity, you are more at risk of an injury.
To sum it up, you want to let your body adapt progressively to any change in your activity. If you run faster, go for shorter runs. If you increase the run duration, decrease the speed!