'crunches' is an exercise
that involves repeated contraction
/relaxation of abdominal (& back) mm. The most likely areas of 'strained' mms is where they attach to tendons/ligaments, which then attach to cartilage
Strain means pain.Rest those mms, exercise others. When aok, restart, this time slower and fewer, gradually increase. Then again, it could also be a gas pocket stuck in RUQ of abd-:).