Introduction
Schizophrenia is a complex mental health condition characterized by both positive and negative symptoms severe enough to compromise social and occupational functioning. People with schizophrenia may experience delusions and hallucinations, disorganized behavior and/or speech, apathy, and social withdrawal (3). The condition has a lifetime prevalence of 0.30% to 0.66% and is the fifth leading cause of disability-adjusted life years (24,36).
People with schizophrenia experience a substantial reduction in life expectancy compared with the general population, as a result of poor physical health. The rates of impaired respiratory function, cardiovascular disease, and diabetes are two- to threefold higher in people with schizophrenia and schizoaffective disorder compared with that in the general population (8,13). Furthermore the mortality risk from cardiovascular disease is almost twice that of the general population (25). In addition to the negative impact of antipsychotic medication, behaviors such as inactivity, smoking, and poor nutrition, coupled with health care inadequacies including poorer access to primary health care and a reduced quality of cardiometabolic heath care, contribute to this disparity in cardiovascular risk for people with schizophrenia (9,13).
The first-line treatment strategy for people with schizophrenia is antipsychotic drugs. First-generation medications such as chlorpromazine or haloperidol now have been replaced largely by second-generation drugs such as clozapine and olanzapine, which minimize the motor system side effects while treating the positive symptoms with equal efficacy. However the effect on negative symptoms is unchanged largely; therefore people with schizophrenia may continue to experience depressive episodes. Moreover while second-generation antipsychotics may offer equal positive symptom outcomes, the burden of metabolic complications associated with these medications is raised significantly in people with schizophrenia (19,38).
One strategy to ameliorate metabolic dysregulation as a consequence of antipsychotic medication is exercise (21). Studies have reported positive outcomes in physical health (32,37), mental health (5), or both physical and mental health (23,31) for people with schizophrenia and related conditions, as a result of participation in exercise programs. For example, Schwee et al. (32) reported improvements in maximal oxygen uptake and peak power in 63 male and female adults with schizophrenia spectrum disorder following 6 months of once to twice weekly combined resistance and cardiovascular exercise compared with no improvements in nonexercising controls. While people with schizophrenia demonstrated lower maximal oxygen uptake compared with people without schizophrenia, the magnitude of improvement as a result of the intervention appears similar to that in the general population. Moreover this study showed a decline in maximal aerobic capacity during the intervention period in nonexercising participants. This should be of significant concern for all clinicians who treat people with schizophrenia and other mental illnesses, given that a low maximal aerobic capacity is an independent risk factor for cardiovascular disease (20).
Less vigorous exercise programs such as yoga also have been demonstrated to improve the mental health of people with schizophrenia. Behere et al. (5) randomized 91 adults with schizophrenia (stabilized on antipsychotic medication) to a yoga program, a calisthenic-style exercise program, or a wait list control group. Yoga and exercise participants received 1 month of supervised training, then completed 2 further months of yoga or exercise at home. Baseline to second month and baseline to final assessment showed significant improvements in positive and negative symptoms score in the yoga group only, with baseline to 2-month follow-up showing the greatest improvement. Interestingly only the yoga group demonstrated positive changes in facial emotion recognition deficits (FERD). FERD are a component of social cognition and may impair interpersonal communication and social interactions and are associated with poor overall functioning in people with schizophrenia. Thus yoga as an add-on therapy for people with schizophrenia may offer benefits that other exercise protocols do not.
Lastly in a small pilot study, Marzaloni et al. (23) demonstrated significant improvements in aerobic capacity (6-min walk test), muscular strength (1-repetition maximum bicep curl), and mental health (Mental Health Inventory) in 8 adults randomized to 12 wk of community-based combined aerobic conditioning and muscle-strengthening exercises. Participants in the exercise group attended a community-based facility for supervised exercise twice weekly for approximately 90 min per session. Adherence to the protocol was 72%, with all participants attending at least 50% of the exercise classes. Although hampered by a small sample size, this pilot study demonstrates that a program of supervised combined resistance and cardiovascular exercise undertaken on a regular basis over 12 wk can contribute to improved outcomes for adults with schizophrenia.
Collectively these and other studies demonstrate the potential for various forms of exercise as an add-on therapy for people with schizophrenia and related conditions. Nonetheless the heterogeneous nature of the studies, measures of physical and mental health outcomes, and settings make firm conclusions regarding the most effective exercise program for people with schizophrenia difficult.
Supporting the outcomes from individual studies, a number of systematic reviews have reported beneficial effects of exercise in people with schizophrenia. For example, Ellis et al. (12) reviewed 10 qualitative, quantitative, and mixed-method studies including case studies, quasi-experimental, and randomized controlled trial (RCT) designs. Despite only including one RCT (4), having a limited number of participants from case studies and quasi-experimental studies, and observing differing methods of investigation, the authors suggest that exercise may result in clinically meaningful and statistically significant improvement in physical and mental health of people with schizophrenia and other mental disorders.
More recently, Holley et al. (17) reviewed both qualitative and quantitative studies on physical activity and exercise in people with schizophrenia, schizoaffective disorder, and schizophreniform disorder. Like the review of Ellis et al. (12), only one RCT investigating the effect of yoga therapy in people with schizophrenia was included (11). The reviewers suggest that despite finding beneficial effects of physical activity and exercise from a range of interventions, the variability of study designs and interventions may affect their reviews credibility negatively and make it difficult to conclude what type of activity offers the greatest benefit.
Vancampfort et al. (35) undertook a systematic review of physical activity recommendations contained within clinical practice guidelines (CPG) for the prevention of cardiometabolic complications in people with schizophrenia. Using the Appraisal of Guidelines for Research and Evaluation (2), only one CPG statement could be recommended for use without provisos (10). More specifically, of the 12 articles reviewed, only 4 included advice on specific program variables such as duration and frequency of exercise and only one met the basic requirements of the “frequency, intensity, time, and type” principle of exercise prescription (10). Furthermore the recommendations contained in the CPG of De Hert et al. (10) are not dissimilar to those recommended for a healthy population (14). No CPG reviewed indicated an appropriate delivery method or the need, or otherwise, of supervision.
A recent Cochrane review (15) found substantial disparity in the included studies with respect to exercise type, delivery, and outcome measures. While only three studies met the inclusion criteria, the authors concluded that successful RCT of exercise interventions in people with schizophrenia are possible and that exercise can impact physical and mental health positively without adverse outcomes. The authors also concluded that data reporting was inconsistent, biases were evident, and dropout rates were high and that these factors should be addressed in future research.
The most recent review of exercise and schizophrenia by Bernard and Ninot (6) considered quantitative studies investigating the effect of physical activity on the physical or mental health of individuals with schizophrenia. From the 19 studies meeting the inclusion criteria, the authors concluded that aerobic exercise may be beneficial for both positive and negative symptoms; however most studies are of short duration and long-term data are lacking.
Thus while the results from RCT and systematic reviews on the effect of exercise in people with schizophrenia are encouraging, the exact exercise program variables such as exercise frequency, intensity, duration, and type, which result in positive mental health outcomes for people with schizophrenia, are not known. Unlike depression, where the program variables associated with successful treatment have been reviewed systematically (30,34), such guidelines, other than those recommended for the general population (15) or similar to the general population (10) are nonexistent for people with schizophrenia. Such information would be of significant value to clinicians such as psychiatrists, psychologists, mental health nurses, and exercise physiologists who offer exercise advice to people with schizophrenia as part of a multidisciplinary treatment team and should be addressed.
Aim of This Review
Given the dearth of literature, the aim of this review was to describe the aerobic exercise program variables used in RCT that result in positive mental health outcomes for people with schizophrenia or schizoaffective disorder. This review differs from the Cochrane review (15), as we seek not to determine the effectiveness of exercise but, rather, to identify specifically the aerobic exercise program variables that resulted in positive mental health benefits for people with schizophrenia or schizoaffective disorder.
Methods
Search Strategy
We searched the following databases: PubMed, PsycINFO, PsycARTICLES, Psychological and Behavioral Sciences, SPORTDiscus, CINAHL, and Scopus. In addition, the authors’ personal bibliographic library was reviewed for pertinent articles. The reference lists of relevant articles were considered also. The PubMed search terms used were as follows: ((((schizophrenia[MeSH Major Topic]) OR (schizoaffective disorder[MeSH Terms])) AND ((exercise[MeSH Terms]) OR (aerobic exercises[MeSH Terms]))) AND ((Humans[Mesh]) AND (Randomized Controlled Trial[ptyp]) AND (adult[MeSH])))). Similar terms were used in all database searches. All references were imported into Endnote bibliographic software.
Inclusion Criteria
The review considered all RCT published from database inception until April 2013 fulfilling the following criteria.
Population: All adults aged 18 years and over with a diagnosis of schizophrenia or schizoaffective disorder as defined by the Diagnostic and Statistical Manual of Mental Disorders, 4th Edition (DSM-IV), or International Classification of Diseases and Related Health Problems, 10th Edition (ICD-10), or other validated criteria.
Intervention: an aerobic exercise program of any type and duration that meets the American College of Sports Medicine definition of aerobic exercise that is “regular, purposeful exercise that involves major muscle groups and is continuous and rhythmic in nature” (14).
Comparison group: any other intervention including pharmacotherapy, education, psychotherapy, other exercise intervention, or no intervention including wait list controls.
Outcome measures: validated psychological outcome measures of any type.
Exclusion Criteria
Any trial where a diagnosis was not made using DSM-IV or ICD-10 criteria or validated instruments was excluded. Trials investigating a mental illness other than schizophrenia or schizoaffective disorders such as depression, bipolar disorder, or posttraumatic stress disorder were excluded. Interventions that were not standard-accepted aerobic exercise interventions such as resistance training, yoga, tai chi, or stretching were excluded. Interventions that included aerobic exercise in addition to dietary modification to facilitate weight loss were excluded, as the specific effects of the exercise component could not be established. Cointerventions that included aerobic exercise and resistance training also were excluded.
Data Extraction and Study Quality Assessment
After removal of duplicate studies and scanning of titles and abstracts for studies that failed to meet the inclusion criteria, remaining studies were analyzed for the following data: exercise frequency (d·wk−1), exercise intensity (heart rate or perceived exertion scale), exercise session duration (number of minutes), type of exercise (walking, running, or other), duration of intervention (wk), delivery (group or individual), level of supervision (was it supervised and by whom), and adherence (number or percentage of completers).
All included trials were evaluated using the Physiotherapy Evidence Database (PEDro) scale. The PEDro scale is based on the Delphi list, which is a set of 11 criteria for quality assessment including study eligibility, use of randomization, allocation concealment, similarity of groups at baseline, blinding of the subjects, therapists, and outcome assessors, use of intention-to-treat analyses, reporting of both point estimates and measures of variability of the primary outcome, adequacy of follow-up, and use of between-group statistical comparisons. This instrument has been used previously in similar systematic reviews of exercise program variables (30,34) and demonstrates good interrater reliability (22). Since blinding participants and therapists or observers to an exercise intervention is not possible, the highest possible score using the PEDro scale is 8 of 10. The included studies were reviewed independently by both authors. Where any discrepancy in PEDro scores existed was resolved by personal discussion.
Results
Study Selection
Initial search results prior to quality assessment produced 434 articles (PubMed (131 articles), PsycINFO (37 articles), PsycARTICLES (2 articles), Psychological and Behavioural Sciences (14 articles), SPORTDiscus (4 articles), CINAHL (16 articles), and Scopus (230 articles)).
After removal of duplicates (88 articles), the remaining 346 articles were checked initially for suitability based on title and abstract. A further 319 articles were removed, leaving 27 articles for further analysis. The reasons for exclusion at this stage were as follows: not in English (17), no abstract available (3), not in an adult population (6), not an exercise intervention (173), not human trials (21), not an RCT (55), not people with schizophrenia (8), not a structured aerobic exercise intervention (22), and no psychological outcome (14). Full-text versions of the remaining 27 articles were obtained and further screened for exclusion.
Following the assessment of full-text articles, a further 24 articles were excluded for the following reasons: intervention included patients with conditions other than schizophrenia or schizoaffective disorder (7), intervention included both aerobic and resistance exercise as a combined intervention (4), intervention did not comply with the ACSM definition of aerobic exercise with respect to exercise type (5), intervention included a dietary component (5), intervention failed to include psychiatric outcomes (1), intervention included motivational interviewing in addition to exercise (1), and intervention included sports participation (1), leaving 3 articles with a total of 27 experimental group participants for final analysis. The selection process for included articles is shown in Figure 1.
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Figure 1: Flowchart of systematic review.
Study Quality
Study quality was assessed using the PEDro scale (22). Figure 2 shows the range of scores for included articles.
Figure 2: PEDro scores.
Diagnostic Criteria
Participants from all included studies were evaluated according to the criteria defined by DSM-IV (1,4) and ICD-10 (29). All studies included patients with a diagnosis of schizophrenia.
Study Outcomes
All studies reported positive changes in the outcomes for study participants included in the exercise group, which are summarized in Table 1.
Table 1: Changes in mental health outcome score from the included studies.
Program Variable Analysis
The program characteristics of the 3 included studies (1,4,29) are shown in Table 2. Exercise frequency was reported adequately in all studies (1,4,29). Exercise intensity was specified in all studies (1,4,29); however justification for the specified intensity was not reported in any study and differed between studies. Exercise duration was reported adequately in all studies (1,4,29). Exercise type was reported in two studies (4,29) but was not specified in one (1). Intervention duration was reported adequately in all studies (1,4,29). Two studies reported intervention delivery conducted on a group basis (1,4); however this was not reported in the remaining study (29). Only one study reported supervision of participants during exercise sessions (29); however the identity and qualifications of the supervisory staff are not reported. Only two studies reported adherence to the exercise intervention (4,29). Adverse events were not reported in any of the three included studies. No study reported control of usual daily activities or dietary intake, and no study reported using recovery strategies following exercise. In addition, prior exercise exposure, exercise preference, or injury history is not reported.
Table 2: Characteristics of included studies.
Discussion
The purpose of this review was to identify the exercise program variables that result in positive mental health outcomes for people with schizophrenia or schizoaffective disorder and provide recommendations for future research and clinical practice. This is the first ever review of this type, and three studies met our inclusion criteria.
All studies in the present review used an exercise frequency of 3 d·wk−1 (1,4,29). This is consistent with the guidelines for healthy adults (14), clinical populations (18), and people with depression (27,30,34).
This review highlights the poor reporting of the exercise intensity, and no study provided justification for the chosen exercise intensity. This is highly problematic, as it makes replication of successful studies impossible. Moreover in studies such as that of Acil et al. (1), the exercise intensity is described as not exceeding the age-predicted maximal heart rate (APMHR). In participants without medical screening or supervision, exercising to this level is contraindicated, and to date, the only study investigating the effect of high-intensity exercise in people with schizophrenia showed no improvement in symptoms (16). Similarly the study of Beebe et al. (4) reported exercising at a “target heart rate”; however the methods of determination and quantification of the target heart rate are not described, negating replication of this protocol. Finally the study of Pajonk et al. (29) reported an aerobic exercise protocol performed at a heart rate that elicits a blood lactate concentration of 1.5 to 2.0 mM. While this is likely to be of low-to-moderate effort, the rationale for this intensity is not provided. Thus the ability to determine the appropriate aerobic exercise intensity for people with schizophrenia or schizoaffective disorder cannot be determined from the current literature. Based on population health recommendations or the CPG of De Hert et al. (10), an exercise intensity of “moderate” defined as 3 to 6 Metabolic Equivalents (METs) or a heart rate of 55% to 70% maximal heart rate (28) may be used until future research demonstrates otherwise.
Exercise session duration was reported as 30 to 40 min in all studies (1,4,29). This is consistent with guidelines for healthy populations (14) and the most recent review of exercise program parameters for people with depression (34).
Differing types of aerobic exercise (treadmill walking and cycling) were utilized in two of the included studies (4,29); however exercise type was not reported in the remaining study (1). Given that all three studies demonstrated improvement in psychiatric outcomes, the choice of exercise type for people with schizophrenia or schizoaffective disorder may be unimportant. Other forms of aerobic exercise such as elliptical cross-trainers (33), outdoor walking (26), or participant’s preferred exercise (7) have been shown to be effective in programs for people with depression. Thus the choice of aerobic exercise for people with schizophrenia or schizoaffective disorder may be directed by availability of resources or access to funding rather than the “best” choice.
Study duration ranged from 10 to 16 wk, with a mean duration of 12.7 wk. Twelve weeks was the most commonly reported intervention duration in the recent review of exercise parameters for people with depression (34). No study investigated long-term outcomes, a limitation identified in the review of Bernard and Ninot (6). It is likely that, as with other chronic health conditions, a recommendation for ongoing exercise may be appropriate.
Group interventions were reported by two studies included in this review (1,4), with the final study not reporting the delivery method (29). No study reported using an individual delivery for exercise. Group-based exercise interventions may be beneficial for the development of peer support and socialization. Alternatively some people may prefer individualized exercise interventions due to the peer pressure, low self-efficacy, and perceived threat associated with a group environment. With the low number of studies included in the current review, the decision to provide a group or individual intervention may lay with funding or resources. It is likely more cost effective to offer a group-based exercise intervention; however the relative efficacy of group or individual exercise interventions has been not investigated yet.
In contrast to the review of exercise parameters for the treatment of depression where all included studies were supervised (34), supervision was reported in one study included in the present review (29); however the details of the supervision are not available. To date, the influence of exercise supervision on treatment outcomes for people with schizophrenia or schizoaffective disorder is unknown and should be investigated.
The mean adherence rate reported in the RCT included in this review is 64.5%; however only two studies reported adherence (4,29). From the data extracted from the three included studies, it is not possible to explore the relationships between exercise adherence and other program variables in significant detail. However from the available data, 30 min of treadmill walking 3 times weekly for 16 wk (4) results in similar adherence (67%) to a 12-wk program of 30-min cycling performed 3 times weekly (62%) (29). Whether this is a result of participant preference, prior exercise exposure, affect response to exercise, or other variables remains to be explored.
Recommendations from This Review
From the limited available evidence, it would seem that a program of aerobic exercise such as treadmill walking or cycling performed for 30 to 40 min per session and undertaken three times weekly for at least 12 wk will be effective at improving mental health outcomes for people with schizophrenia or schizoaffective disorder. The appropriate exercise intensity for people with schizophrenia or schizoaffective disorder remains unclear; however based on the guidelines for healthy people and the recommendations of De Hert et al. (10), an exercise intensity described as moderate is suggested. Exercise interventions delivered in a group format are effective; however the effectiveness of this format compared with that of individual or combined formats is unclear. Additionally while supervision of group exercise interventions is effective for people with schizophrenia or schizoaffective disorder, the true impact of this is equivocal.
To our knowledge, this is the first systematic review of the aerobic exercise program variables leading to improved mental health outcomes in people with schizophrenia or schizoaffective disorder. It is hoped that the findings from this review will lead future investigations and guide clinical practice in the prescription of aerobic exercise interventions for this vulnerable population.
Limitations
The present systematic review is not without limitation. We only included trials that included standard aerobic exercise interventions, which resulted in improved mental health outcomes in people with schizophrenia or schizoaffective disorder. The heterogeneous nature of intervention design including definition and assessment of exercise intensity and intervention delivery methodological concerns such as blinding of assessors make a meta-analytic approach impossible.
Future Recommendations
Systematic reviews on the application of exercise program variables in mental illnesses are limited by poor reporting of program variables in RCT. Therefore there is a need to develop and implement reporting standards, such that successful studies may be replicated. Collaboration with exercise physiologists who possess expertise in exercise intervention development and delivery may reduce the disparity in intervention design and allow future systematic reviews to include a meta-analytic approach. Finally as with depression and other mental illnesses, researchers may seek to determine the minimum clinically effective dose of aerobic exercise, which improves symptom severity and maximizes long-term adherence in people with schizophrenia.
The authors declare no conflict of interest and do not have any financial disclosures.
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