In this disorder a person is preoccupied with thoughts concerning appearance, especially musculature. Muscle dysmorphia is strictly connected with selective attention: individuals selectively focus their attention on perceived defect (too skinny body, underweight etc.). They are hypervigilant to even small deviations from perceived ideal and they ignore information that their body image is not consistent with reality. There is also a hypothesis that individuals repeat negative and distorted self-statements concerning their appearance to such extent that they become automatic. Muscle dysmorphia influences person's mood often causing depression or feelings of disgust. This is often connected with constant comparing person's body to unattainable ideal.
To be diagnosed as muscle dysmorphic, the person must exhibit symptoms of the type and degree outlined in the Diagnostic and Statistical Manual for body dysmorphic disorder, and not merely appear over-interested in physique or engage in behaviors other people would find unwise. Muscle dysmorphia is fairly rare and not just a simple obsession with working out.
Muscle dysmorphia is most common in males and often starts in the late teens. Olivardia and others found in a 2000 study that the average onset age was 19.4 years. It most often occurs in those who are already considered by others to be muscular and is often accompanied by depression.
There are also a few different hypotheses regarding the etiology of muscle dysmorphia. The Cognitive explanation is one of the most common theories. It searches for possible causes of the disorder in a cognitive vicious circle of dysfunctional thoughts. When a person has a negative appraisal of internal body image, it influences the external representation of appearance. That triggers processing self as an aesthetic object which results in negative internal body image. To sum up: people are not only sensitive to bodily cues, but also threatened by them. In people vulnerable to somatoform disorders it can imply an overinterpretation of bodily imperfections.
The psychodynamic explanation states that these are unresolved conflicts from childhood and extremely difficult feelings that are responsible for the disorder. The disorder provides a means for people to express their emotions that otherwise would be too difficult to express. In this case emotions are converted into more tolerable physical symptoms. The purpose of such conversion is to communicate extreme feelings in 'physical language'. Therefore a preoccupation with musculature could be treated as an individual's unconscious displacement of sexual or emotional conflict (or feelings of guilt, or even poor self-image).
According to the biological explanation a serotonin irregularity is mostly responsible for the disorder.
Finally, the cognitive-behavioral explanation combines a few approaches. It states that the responsibility for muscle dysmorphia is shared by: cultural factors, biological predispositions, psychological vulnarabilities and early childhood experiences. Cultural factors manifest themselves in an exaggerated emphasis on appearance, physical strength and attractiveness. People compare themselves with others and even little deviations from the pattern perceived as ideal lead to extremely negative appraisals. In his 2000 book The Adonis Complex for example, the Harvard psychiatrist Harrison "Skip" Pope Jr. argues that muscle dysmorphia is fueled by the portrayal of overly fit characters of unattainable musculature in children's cartoons, such as G.I. Joe. Next, some people are biologically predisposed to a constant drive for perfection. Psychological vulnerability is mostly based on low self-esteem. Childhood experiences connected with the disorder are: unharmonious family background, bullying, teasing. This may produce feelings of being unloved, insecure and rejected.