It is true, if you are tense, few muscles contract and give you pain. Do not stop breathing while masturbating. keep your self relaxed/( learn relaxing each part/muscles of the body. Use lubricated hand.Do not feel guilty about masturbating. Keep your perineum relaxed. Masturbation per Se does not cause Headache or muscular pain.
Hi are you tense when masturbating that will give you pain in the area's you say about , you must learn to relax and not tense up , just let things happen and not let you body stiffen up , Take care ,