Involuntary muscle contractions are involuntary body movements that happen without conscious control during orgasm. They can be physical manifestations of pleasure and excitement that cause the body to contract, twitch, tremble, spasm, or shudder. These involuntary reactions typically occur in certain areas of the body like the pelvic area or genitals but may extend to other parts such as the face and hands during an intense climax. During orgasm, various muscles contract and relax rapidly creating sensations of tightening and release, resulting in pleasurable feelings for both partners involved. The intensity of these contractions varies depending on factors like age, health status, sexual arousal level, type of stimulation used, etc.
During penile-vaginal intercourse, it's common for males to experience facial contortions when they ejaculate due to involuntary muscular contractions caused by semen expulsion from their penis. This is known as 'male orgasmic facies,' which refers to visible signs of extreme pleasure like grimacing, grinning, flushed skin, bulging eyes, frowns, or clenched teeth. On the contrary, women tend to display less facial involuntary muscle contraction than men because most of them don't experience facial muscle tension during orgasm. However, some females have reported experiencing slight facial expressions during orgasm like smiling or even screaming while enjoying intense intimate moments with their partner(s). In addition to this, a handful of people report experiencing minor twitches or jerks in their hands after climaxing intensely - especially if they are using manual masturbation techniques like squeezing or rubbing themselves vigorously before reaching orgasm.
Overall, involuntary muscle contractions during orgasm can be exciting and add another layer of pleasure to an already thrilling sexual encounter between two consenting adults who understand each other well enough to explore new possibilities together safely without any emotional harm or physical risk. They also help build trust within relationships by showing partners how much you care about them while expressing your desire through uncontrollable body movements that speak louder than words ever could.