pressuring the bladder can cause leakage, because it's a bladder: if you squeeze it stuff can happen.

Hitting the pubis really hard generally means you have groin pain to worry about, or if you take some kinda super severe hit a bruised or broken pubis that can make walking a pain or at worst cause horrific permanent injury.

TL:DR? Musashi's cruel and groin hits range from comically painful to 'serious medical problem' to 'might never walk again'.