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Physical Activity and Fatigue in Breast Cancer and Multiple Sclerosis: Psychosocial Mechanisms

From the Departments of Kinesiology and Community Health (E.M., S.M.W., R.W.M.), University of Illinois, Urbana, Illinois; Department of Medicine (L.Q.R.), Southern Illinois University School of Medicine, Springfield, Illinois; Faculty of Physical Education and Recreation (K.S.C.), University of Alberta, Edmonton, AB, Canada.

Address correspondence and reprint requests to Edward McAuley, Department of Kinesiology and Community Health, University of Illinois, 336 Freer Hall, Urbana, IL 61801. E-mail: emcauley{at}illinois.edu

Objective: To examine the role of self-efficacy and depression as potential pathways from physical activity to fatigue in two study samples: breast cancer survivors (BCS) (n = 192) and individuals with multiple sclerosis (MS) (n = 292).

Methods: We hypothesized that physical activity would be associated indirectly with fatigue through its influence on self-efficacy and depressive symptomatology. A cross-sectional path analysis (BCS) and a longitudinal panel model (MS) were conducted within a covariance modeling framework.

Results: Physical activity had a direct effect on self-efficacy and, in turn, self-efficacy had both a direct effect on fatigue and an indirect effect through depressive symptomatology in both samples. In the MS sample, physical activity also had a direct effect on fatigue. All model fit indices were excellent. These associations remained significant when controlling for demographics and health status indicators.

Conclusions: Our findings suggest support for at least one set of psychosocial pathways from physical activity to fatigue, an important concern in chronic disease. Subsequent work might replicate such associations in other diseased populations and attempt to determine whether model relations change with physical activity interventions, and the extent to which other known correlates of fatigue, such as impaired sleep and inflammation, can be incorporated into this model.

Key Words: breast cancer • multiple sclerosis • self-efficacy • physical activity • depression • fatigue

Abbreviations: MS = multiple sclerosis; BCS = breast cancer survivors; BMI = body mass index; CFI = Comparative Fit Index; SRMR = standardized root mean square residual; PDDS = patient determined disease steps; PA = physical activity; SE = self-efficacy; Dep = depressive mood.