The aims of this systematic review were to critically examine evidence as to whether OCPD traits and/or OCD are associated with excessive exercise in patients with AN, and to determine the nature of relationships between these constructs. The results of the systematic review indicated a positive relationship between excessive exercise and obsessive-compulsive personality traits. However, the relationship between OCD and excessive exercise in AN patients is less clear with studies producing varying results.
Davis et al.  proposed a theoretical model of the relationship between starvation, physical activity and obsessive-compulsiveness in the development of eating disorders for some patients. This model works on the understanding that significantly reduced dietary intake and increased physical activity, combined with OCD features, create a mutually reinforcing, destructive mechanism which may play an integral role in the development and maintenance of an eating disorder . The results of this review also seem consistent with the theory of “activity anorexia” , providing preliminary evidence for this phenomenon in human samples. Results have also supported the notion that high level exercising and reduced dietary intake alter the functioning of 5-HT with increased OCD symptomatology , creating a cycle whereby the individual undertakes an even higher level of physical activity and decreases their dietary intake as their obsessions increase .
Furthermore, the findings of Naylor et al.  are consistent with research examining the reduction in quality of life for these patients  and descriptions of their exercise being “out of control” . Having obsessive beliefs and compulsions was a significant predictor in the regression model for exercise beliefs, after controlling for BMI and eating disorder psychopathology . Such findings are consistent with the premise that obsessionality plays a causal role in the development and maintenance of excessive exercise .
Bewell-Weiss and Carter  reported a negative relationship between OCD symptomatology and excessive exercise. The researchers concluded that it may have been that their regression model was more comprehensive than those used in previous studies, or that obsessive-compulsive symptomatology had shared variance with another variable that had not been explored with previous studies . Additionally, they used different OCD measures than those used in other studies . Penas-Lledo et al.  found a trend only for increased obsessive compulsive symptomatology in exercising patients using the SCL-90-R. Finally, Hotlkamp et al.  found no direct relationship between obsessive-compulsiveness and levels of physical activity, also assessed using the SCL-90-R. It may be that this measure is not as sensitive as other measures, or that OCD features affect cognitions or beliefs about exercise .
Davis et al.  speculated that it could be that greater obsessive-compulsive personality traits are exacerbated by the combination of starvation and high level exercise, or that these patients choose to combine dietary restraint with excessive exercise. It may be the case that patients who have obsessive tendencies are more likely to undertake exercise as an additional method to prevent weight gain (on top of restricted diet, purging behaviour) or to neutralise fears of changes in their body weight and shape . Alternatively, patients may be using exercise to alleviate or reduce anxiety , or as a means of neutralising predominant weight or food related obsessions .
Anderluh et al.  found that participants with childhood traits of rigidity, extreme cautiousness and perfectionism underwent more severe food restriction and higher levels of excessive exercise, and experienced longer periods of underweight status. Their research identified the possibility of homogenous phenotypes of AN and demonstrates that premorbid obsessive-compulsive personality traits in childhood may influence the course of the eating disorder later in life, potentially contributing to a more severe form of restricting AN, which could be extremely resistant to treatment .
There are a number of limitations that were evident in the reviewed literature. The number of studies examined in the review (10) is small, and results must be interpreted with some caution as some of the studies did not support the association between OCD and excessive exercise. A number of the reviewed studies did not clearly differentiate between OCD and OCPD constructs in their presentation of results. Nine different types of measures were employed across the studies to assess OCPD traits and OCD symptomatology, many of these being self-report questionnaires, which may increase the incidence of socially desirable response styles. Others involved expert clinical assessment in the form of an interview (for example, the EATATE interview in Anderluh et al. ). These various instruments assess different constructs, and some measures may have provided more detailed information, both of which may have biased the results. In one study, the use of the SCL-90 may have been inappropriate, as it had been normed for participants aged 14 years and older, yet a proportion of their sample were aged between 13 and 14 years. It would thus be beneficial for future studies to utilise the most current and comprehensive assessment tools in the field to enable more reliable inter-study comparisons.
Denial commonly occurs in anorexia nervosa, and subjective measures may have underestimated the amount of physical activity completed by patients. Such underestimation may have led to significant bias and consequently inaccuracy of data regarding the extent of exercise, and its relationships with coexisting OCD and/or OCPD. This potential room for bias has led to the utilisation of more objective means of assessing for physical activity in patients with AN, for example accelerometers [77, 78]. Yet no study included in the review used such devices. Numerous measures of exercise were utilised across studies, reflecting both the variety of measures available, and the time period over which the studies were undertaken (1995–2011). However, there is also a pervasive issue in this field regarding the lack of consensus on what defines excessive exercise, how it should be measured and how it should be managed in patients with AN .
There are also a number of limitations in regards to participants utilised in the studies. The small sample size of Holtkamp et al.  affected their capability to generalise their results, whilst the use of informants may have been beneficial for Anderluh et al.  to confirm retrospective data provided by participants and to limit memory bias effects. Participants across studies who were inpatients were not exercising at the time of completing study assessments and questionnaires, and it is unknown what effect this may have had on response style. Other participants (for example outpatients) would not have such intense restrictions. The research reviewed also did not take into account other factors which may be important in the study of obsessive-compulsive symptomatology with excessive exercisers, such as motivational factors and specific reasons for exercising (other than the use of CET in Naylor et al., ). Finally, across studies, the patients were recruited mostly from secondary and tertiary referral services, i.e. inpatient and outpatient eating disorder services. Thus, the findings from the review cannot be generalised to people with AN who are currently not seeking treatment, or whose eating disorder pathology is not as severe as those patients in hospital treatment.
As the vast majority of the studies employed a cross-sectional design, only relationships between variables could be determined, and there can be no demonstration of the direction of such associations. Acute starvation syndrome and severity of eating disorder psychopathology both have significant impact upon level of obsessive-compulsive symptoms and exercise . There was also no information about how obsessionality might affect prognosis and treatment outcome for AN patients who exercise excessively.
Whilst this review has focused on the relationships between OCPD traits and/or OCD symptomatology with excessive exercise in patients with AN, it would be remiss not to mention the significant relationships which excessive exercise shares with other psychopathologies, which have important implications for treatment. Studies included in the review demonstrated that AN patients who exercised excessively demonstrated lower minimum BMI and lower novelty seeking, but higher harm avoidance, persistence and cooperativeness . In other studies, these patients demonstrated higher levels of anxiety and food restriction ; higher levels of depression, self-esteem and dietary restraint ; higher addictive personality traits ; higher weight preoccupation ; and higher levels of bulimic and eating disorder psychopathology .