No one has ever told me that they feel they have injured their (fill in the blank here) because they are too strong. I agree with this article in The Globe and Mail on two tenets of strength training.
I would also emphasize that form is important, and breathing is even more important, especially with core work. Ideally with every exercise you want to perform a core breath, which is actively engaging the pelvic floor muscles as you exhale. This manages the increase in abdominal pressure as you are working your core muscles, and prevents that pressure from being forced downward to your pelvic floor muscles.