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Exercise and Well-Being: A Review of Mental and Physical Health Benefits Associated With Physical Activity
Frank J Penedo; Jason R Dahn; Curr Opin Psychiatry. 2005; 18 (2): 189-193. ©2005 Lippincott Williams & Wilkins
Abstract and Introduction
Purpose of Review: This review highlights recent work evaluating the relationship between exercise, physical activity and physical and mental health. Both cross-sectional and longitudinal studies, as well as randomized clinical trials, are included. Special attention is given to physical conditions, including obesity, cancer, cardiovascular disease and sexual dysfunction. Furthermore, studies relating physical activity to depression and other mood states are reviewed. The studies include diverse ethnic populations, including men and women, as well as several age groups (e.g. adolescents, middle-aged and older adults).
Recent Findings: Results of the studies continue to support a growing literature suggesting that exercise, physical activity and physical-activity interventions have beneficial effects across several physical and mental-health outcomes. Generally, participants engaging in regular physical activity display more desirable health outcomes across a variety of physical conditions.
Similarly, participants in randomized clinical trials of physical-activity interventions show better health outcomes, including better general and health-related quality of life, better functional capacity and better mood states.
Summary: The studies have several implications for clinical practice and research. Most work suggests that exercise and physical activity are associated with better quality of life and health outcomes. Therefore, assessment and promotion of exercise and physical activity may be beneficial in achieving desired benefits across several populations. Several limitations were noted, particularly in research involving randomized clinical trials. These trials tend to involve limited sample sizes with short follow-up periods, thus limiting the clinical implications of the benefits associated with physical activity.
Recent reports suggest a worldwide epidemic in terms of obesity and a sedentary lifestyle, which are risk factors for multiple adverse health outcomes.
Studies have shown that physical inactivity doubles health risks and adds a disease burden to society comparable with smoking,[1] obesity and hypertension,[2] and such inactivity during middle age appears to shorten the life span.[3] Numerous studies have shown that physical activity has far-reaching benefits on health and disease, including reducing mortality rates.[4] Evidence supporting the physical and mental-health benefits of physical activity and exercise continues to accumulate at an accelerated rate. This review highlights
the very recent work (i.e. published within the last 12 months) evaluating the physical and mental-health benefits of exercise and physical activity. The review first presents literature documenting health benefits associated with physical activity, followed by studies reporting the relationship between physical activity and mental health.
Physical Health Benefits of Physical Activity
Several studies have shown that regular and moderate physical activity decreases the risk of coronary heart disease.[5,6] Recent evidence also shows that these benefits may extend beyond coronary heart disease. Among individuals with type 2 diabetes, decreases in systolic pressure associated with physical activity reduce risk for diabetes-related complication, diabetes-related death and myocardial infarction.[7] Additionally, there is some evidence that physical activity lowers risk factors associated with the development of type 2 diabetes mellitus,[8] in part through its impact on obesity. Furthermore, consequences of physical inactivity (e.g. obesity, diabetes) are related to both cancer incidence and mortality in various cancer (e.g. breast, endometrial)
populations.[9] Following are recently published studies, extending this work.
Regular physical activity can buffer the risks associated with being overweight or obese, independently of its effect on body weight. In a sample of 7867 adults, aged 51-61 years, followed over 4 years, being overweight or obese was associated with declines in physical health and development of a new physical difficulty (i.e. mobility difficulties).[10*] However, physical activity, as defined by regular light or vigorous exercise or household chores, reduced the risk of declining physical health independently of ability to achieve ideal body weight and other confounds (e.g. age, race, sex, socioeconomic status (SES), smoking, alcohol use). Therefore, while achieving ideal body weight remains a goal of many physical-activity interventions, it appears that engaging in exercise, even in the absence of significant weight reduction, may provide health benefits. Physical activity has been shown to reduce risks associated with type-2 diabetes and several studies have identified ethnic minorities at elevated risk. Ethnic-minority groups are more likely to report sub-optimal levels of physical activity. In a study assessing correlates of physical activity among African Americans with type-2 diabetes, researchers identified obesity, lower household income and the perception that one is more physically active than others as predictors of low physical activity.[11*] In a separate recent study evaluating 3075 ethnically diverse men and women aged 70-79 years, exercise, as defined by engaging in 20-30 minutes of moderate-intensity exercise on most days, was associated with better physical function (e.g. lower-extremity function, balance) independent of demographic and health-related factors.[12**] Findings suggest that engaging in some physical activities such as leisure activities may have some benefits but only participating in exercise leads to better physical functioning. Furthermore, physical-activity interventions targeting minority groups may need to be tailored to meet the specific needs of this population.
Several studies have evaluated the association among lifestyle factors such as physical activity, fruit and vegetable consumption and smoking, and health-related quality of life (HRQOL) in cancer survivors. In a study consisting of breast, colorectal and prostate cancer survivors, participants who engaged in recommended physical activity levels by the American Cancer Society [13] (i.e. 30 minutes of moderately intense exercise at least five or more days per week) reported significantly greater HRQOL. [14*] In contrast, adhering to fruit and vegetable recommendations was not related to HRQOL, suggesting that the benefits of physical activity may surpass modifications in diet. In metastatic disease, chemotherapeutic interventions are often associated with a series of side-effects, including fatigue and poor overall quality of life. A recent study evaluated women randomized to a seated exercise program using a home video three times per week while undergoing chemotherapy. Participation in the program was associated with a slower decline in general quality of life. Furthermore, individuals in the exercise program reported less increase in fatigue and less decline in physical well-being. [15*] Although relatively few randomized clinical trials have assessed the efficacy of physical-activity interventions in cancer survivors, a recent review [16**] suggests that these interventions can have both physical and mental-health benefits. In this study, the authors suggest that physical-activity interventions may be particularly beneficial in reducing the risk and disease burden conveyed by co-morbid conditions (e.g. obesity, cardiovascular disease (CVD)) among cancer patients by reducing fatigue, elevating mood, improving physical functioning and reducing physical-role limitations.
Cardiovascular Disease
Because risk factors associated with CVD may be modifiable via exercise and physical activity, most of the research in physical activity and disease outcomes has targeted this population. Wessel and colleagues [17**] evaluated 936 women undergoing coronary angiography for suspected myocardial ischemia. Higher physical fitness scores were significantly associated with less coronary artery disease (CAD) risk factors, less angiographic CAD and lower risk for adverse cardiovascular events. These relationships were independent of other risk factors, including obesity. Other work has evaluated use of cognitive-behavioral techniques in combination with exercise. A recent trial evaluated the effects of a cardiac rehabilitation program (CRP) versus a CRP plus a group-mediated cognitive-behavioral (GMCB) intervention (CRP + GMCB) among 147 older adults with heart disease or diagnosed 'at risk' for heart disease.[18*] The
CRP treatment condition consisted of 3 months of exercise training, following guidelines from the American Association of Cardiovascular and Pulmonary
Rehabilitation,[19] which involved exercise training performed 3 days per week with warm-up, aerobic, upper-extremity strength and cool-down phases lasting
50-60 minutes. Results showed that while men in both conditions showed significant improvements in HRQOL, women in the CRP + GMCB treatment
condition with low baseline levels of HRQOL showed greater improvements than women in the CRP-only condition. Findings propose that women may benefit from an enhanced intervention that uses cognitive-behavioral techniques designed to increase self-efficacy and social support. Some studies have focused on examining the relationship between physical activity and mortality and disease recurrence in CVD. In a study assessing 10-year mortality from all-causes CAD, CVD and cancer, in a sample of men and women, physical activity, as well as adherence to a Mediterranean diet, moderate alcohol use and non-smoking, were associated with more than a 50% lower rate of all-causes and cause-specific mortality.[20*] Other large-scale studies have provided support for the notion that exercise may reduce mortality and myocardial re-infarction incidence. In a separate study evaluating 2078 men and women with an acute myocardial infarction (AMI), individuals reporting regular exercise experienced less than 50% AMIs relative to participants who did not exercise regularly.[21*] This finding was statistically significant and independent of medical status or sociodemographic variables.
Arthritis, Sexual Dysfunction and Other Conditions
Arthritis is one of the most common and debilitating conditions experienced in later life. A recent study evaluated a 12-month community-based water exercise program in older (i.e. aged at least 60 years) sedentary men and women with knee-hip osteoarthritis.[22*] Researchers found that participants randomized to the water-exercise program showed significant improvements in physical function and reductions in the perception of pain, relative to control participants, at the completion of the 1-year intervention period. Furthermore, exercise participants displayed significantly better performance ascending and descending stairs and hip range of movements, suggesting that such interventions may be efficacious in improving overall physical function as well as other specific functional indices relevant to this population.
Some studies have assessed the extent to which physical activity is related to better health outcomes, such as erectile dysfunction. In a randomized trial of 110 obese men, aged 30-55 years, men who participated in an educational intervention received guidelines on how to achieve a reduction of 10% or more in their body weight by reducing caloric intake and increasing physical activity. Men randomized to the intervention reported significantly greater reductions in erectile dysfunction and such improvement was associated with increases in physical activity.[23*] Others have shown that after controlling for age, medical co-morbidity, fatigue and urinary/bowel functioning, greater levels of physical activity are associated with better sexual functioning among men treated for localized prostate cancer.[24*] These studies suggest that physical activity may have both direct (e.g. changes in vascular physiology) and indirect (e.g. enhancing mood) effects on erectile disfunction.
Other debilitating diseases such as chronic fatigue syndrome, lower-back pain and chronic obstructive pulmonary disease (COPD) have received limited
attention. In a study evaluating the effects of resistance training on functional outcomes in patients with COPD, researchers found that resistance training, in addition to aerobic exercise, improved several functional outcomes (e.g. walking distance, body strength).[25*] Participants were randomized into either resistance training and aerobic condition, or an aerobic-training-only control condition. Individuals participating in the combined intervention showed significant improvements in upper and lower body strength, and greater lean body mass and walking distance. These results suggest that aerobic-exercise programs enhanced with resistance training may derive greater benefits than aerobic exercise alone.
Low-back pain is a physical condition characterized by the need for pain medication and, in some cases, invasive medical procedures. In a study evaluating the efficacy of a 10-week aerobic-exercise program, participants randomized to the exercise condition showed significantly improved mood profiles. At 2.5 years post-intervention, participants in the exercise condition reported significantly lower numbers of pain-medication prescriptions and fewer physical-therapy referrals, as well as improvement in work functioning.[26*]
Mental-Health Benefits of Physical Activity
In addition to the direct physical-health benefits of physical activity, several studies suggest that engaging in physical activity or exercise programs can also benefit emotional well-being. Multiple studies indicate that physical activity improves mood and reduces symptoms of depression and anxiety.[27,28] Individuals diagnosed with major depression undergoing an aerobic-exercise intervention showed significant improvements in depression comparable to participants receiving psychotropic treatment.[29] Moreover, individuals in the aerobic exercise condition had significantly lower relapse rates than participants in the medication group. Other evidence suggests that consistent physical activity may prevent the onset of depression.[2] Furthermore, HRQOL appears to be improved through physical activity by enhancing the experience of well-being and increasing physical functioning in those with poor health.[4,30]
In this section, recent studies reporting the mental-health benefits of physical activity are discussed.
Among healthy older adults, resistance training has been associated with improved mood states. McLafferty and colleagues [31*] conducted a study examining the effects of a 24-week resistance training program with three weekly meetings. Following the program, participants reported significant improvements in total mood scores, as well as reductions in confusion, anger and tension. Similarly, physical activity has been reported as a correlate of positive mood among women. In a study evaluating predictors of mood among women who had recently started a walking program, in addition to social support, physical activity was significantly associated with greater positive mood.[32*]
Others have investigated the effects of less conventional physical-activity programs. West and colleagues [33**] evaluated whether alternative physical-activity programs, such as Hatha yoga and African dance, had an effect on psychological well-being. In this study, 69 participants were randomized to either an African dance, a Hatha yoga or a control classroom lecture condition. Results showed that participants randomized to the two physical-activity programs had significant reductions in perceived stress and negative affect.
While most prior work evaluating the effects of physical activity on mental health has focused on middle-aged and older populations, recent work has focused on adolescent groups. In a study with a sample consisting of over 4500 adolescents, naturally occurring increases in leisure-time physical activity (i.e. physical activity occurring outside of structured school-based programs) were significantly associated with fewer depressive symptoms over a 2-year period. [34*] The inverse relationship between physical activity and depressive symptoms was independent of possible confounding factors, including SES, gender and alcohol consumption. Collectively, these recent studies suggest that physical activities, including less conventional practices such as African dance, can exert positive mental-health benefits across several populations.
Other studies have evaluated the extent to which physical activity can buffer age-related cognitive declines. Among 766 women aged 70-81 years, higher levels of physical activity were associated with better overall cognitive performance. Women in the highest physical-activity quintile of the sample displayed a 20% lower risk of developing cognitive impairment.[35**] This work is consistent with prior research suggesting that physically active older adults are less likely to develop normative age-related cognitive impairments. Studies evaluating the benefits of physical activity among specific subgroups that have been traditionally neglected are beginning to emerge. In a study among adults diagnosed with Down's syndrome, participation in a 12-week, 3-days-per-week exercise and health education program was associated with increased exercise self-efficacy, more positive expectations, fewer cognitive and emotional barriers and improved life satisfaction.[36**] Similarly, low-income Hispanic children in the 4th grade randomized to an aerobic-intensity physical-activity program improved cardiovascular fitness, reduced depression and increased self-esteem.[37*]
The majority of the US and world population continues to engage in sedentary lifestyles that are associated with multiple risk factors for negative health outcomes. A growing literature continues to support the notion that exercise and physical activity are associated with both physical and mental-health benefits across several diseases and diverse subpopulations. While most studies have documented benefits in cardiovascular disease, recent work has begun to focus on cancer survivors, as well as other chronic diseases that have received less attention in the literature. Although the evidence is strong, much work is needed to determine to what extent exercise and physical activity can ameliorate disease
processes and reduce morbidity and mortality. Many recent studies involved randomized clinical trials but were limited by several factors. First, most studies involving clinical trials assessing physical-activity interventions were limited in sample size. Secondly, although some studies assessed participants' 1-2-year post-intervention follow-ups, the majority were limited to results immediately following the intervention period.
Therefore, studies involving larger sample sizes with adequate follow-up time points may shed some light on whether such interventions may actually significantly impact on survival. A third limitation involves the highly variable exercise and physical-activity components in the studies reviewed. It remains a challenge to determine what is the right dosage of treatment to see actual gains associated with physical-activity interventions. Nonetheless, the findings reviewed are promising and generally support the case that engagement in exercise can improve physical and emotional well-being.
Papers of particular interest, published within the annual period of review, have been highlighted as:
* of special interest
** of outstanding interest
1. Pate R, Pratt M, Blair S, et al . Physical activity and public health: a recommendation from the Centers for Disease Control and Prevention and the American College of Sports Medicine. JAMA 1995; 273:402-406.
2. Paffenbarger R, Lee I, Leung R. Physical activity and personal characteristics associated with depression and suicide among American college
men. Acta Psychiatr Scand Suppl 1994; 377:16-22.
3. Paffenbarger R, Hyde R, Wing A, Hsied C. Physical activity, all-cause
mortality and longevity of college alumni. New Engl J Med 1986; 314:605-613.
4. Centers for Disease Control. Effects of physical activity on health and disease: a report from the Surgeon General [online] 2001;
http://www.cdc.gov/nccdphp/sgr/prerep.htm. [Accessed October 2004]
5. Allen J. Coronary risk factor modification in women after coronary artery bypass surgery. Nurs Res 1996; 45(5):260-265.
6. Blair SN. Physical activity, fitness and coronary heart disease. In:
Bouchard C, Shephard RJ, Stephens T, editors. Physical activity, fitness and
health: international proceedings and consensus statement. Champaign, IL:
Human Kinetics; 1994. pp. 579-590.
7. Adler A, Stratton I, Neil H, et al . Association of systolic blood pressure with macrovascular and microvascular complications of type 2 diabetes
(UKPDS 36): prospective observational study. BMJ 2000; 321:412-419.
8. Uusitupa M, Louheranta A, Lindström J, et al . The Finnish Diabetes Prevention Study. Br J Nutri 2000; 83(Suppl 1):S137-S142.
9. Magnusson C, Baron J, Persson I, et al . Body size in different
periods of life and breast cancer risk in post-menopausal women. Int J Cancer
1998; 76:29-34.
10. He X, Baker D. Body mass index, physical activity, and the risk of decline in overall health and physical functioning in late middle age. Am J Public Health 2004; 94(9):1567-1573. * This paper describes a prospective study with a large sample size documenting relationships among physical activity and health outcomes in middle-aged adults.
11. Pearte C, Gary T, Brancati F. Correlates of physical activity levels
in a sample of urban African Americans with type 2 diabetes. Ethn Dis 2004;
14(2):185-188. * This is one of the few available studies that evaluate an at-risk population for type 2 diabetes and obesity among a group traditionally excluded from such studies.
12. Brach J, Simonsick E, Kritchevsky S, et al . The association between physical function and lifestyle activity and exercise in the health, aging, and body composition study. JAGS 2004; 52:502-509. ** This is an excellent study, conducted among older adults and examining the effects of 20-30 minutes of moderate-intensity exercise. The study involves a reasonably large and diverse sample with physical-health outcomes.
13. American Cancer Society. Cancer Prevention and Early Detection: Cancer Facts and Figures. Atlanta, GA: American Cancer Society; 2002.
14. Blanchard C, Stein K, Baker F, et al . Association between current lifestyle behaviors and health-related quality of life in breast, colorectal and prostate cancer survivors. Psychol Health 2004; 19(1):1-13.
* This study is part of an emerging literature documenting the benefits of physical activity among the largest groups of cancer survivors and its effect on health-related quality of life.
15. Headley J, Ownby K, John L. The effect of seated exercise on fatigue
and quality of life in women with advanced breast cancer. Oncol Nurs Forum
2004; 31(5):977-983. * This is a study evaluating the effects of an exercise program on relevant health outcomes of women undergoing chemotherapy for advanced breast cancer.
16. Penedo F, Schneiderman N, Dahn J, Gonzalez JS. Physical activity interventions in the elderly: cancer and comorbidity. Cancer Invest 2004;
22(1):53-69. ** This is an excellent review of the efficacy of physical-activity interventions among older adults living with cancer and facing comorbidities.
The study includes a list of relevant published papers, as well as recommendations for future work with this population.
17. Wessel T, Arant C, Olson M, et al . Relationship of physical fitness vs body mass index with coronary artery disease and cardiovascular events in women. JAMA 2004; 292(10):1179-1187. ** This is an excellent study that relates higher physical activity to fewer adverse coronary artery events among women with CAD. These findings are independent of other risk factors, making a strong case for the efficacy of physical activity in reducing CAD risk.
18. Focht B, Brawley L, Rejeski W, Ambrosius W. Group-mediated activity counseling and traditional exercise therapy programs: effects on health-related quality of life among older adults in cardiac rehabilitation. Ann Behav Med 2004;
28(1):52-61. * This is one of the few studies that have tested and shown that adding a cognitive-behavioral approach to an exercise program produces added benefits to health-related quality of life, particularly among older women.
19. American Association of Cardiovascular and Pulmonary Rehabilitation:
Guidelines for Cardiac Rehabilitations and Secondary Prevention Programs.
3rd ed. Champaign, IL: Human Kinetics; 1999.
20. Knoops K, de Groot L, Kromhout D, et al . Mediterranean diet, lifestyle factors, and 10-year mortality in elderly European men and women: the
HALE project. JAMA 2004; 292(12):1433-1439. * This is a well-designed 10-year study, documenting the relationship between physical activity and other health behaviors on all-cause and specific mortality.
21. Blumenthal J, Babyak M, Carney R, et al . Exercise, depression, and mortality after myocardial infarction in the ENRICHD trial. Med Sci Sports
Exerc 2004; 36(5):746-755. * This is a study with a sample of over 2000 men and women, with findings suggesting that engagement in exercise is associated with a lower risk of acute myocardial infarction, independent of disease-related and sociodemographic factors.
22. Lin S, Davey R, Cochrane T. Community rehabilitation for older adults with osteoarthritis of the lower limb: a controlled clinical trial. Clin Rehabil 2004; 18(1):92-101. * This is a unique study that assesses the benefits of a community water-based exercise program in knee-hip osteoarthritis - a condition that is quite debilitating but has received limited attention in the physical-activity literature.
23. Esposito K, Giugliano F, Di Palo C, et al . Effect of lifestyle changes on erectile dysfunction in obese men: randomized controlled trial. JAMA 2004; 291(24):2978-2984. * This is one of the few available studies linking obesity and physical activity to erectile dysfunction among middle-aged obese men.
24. Dahn J, Penedo F, Molton I, et al . Physical activity and sexual functioning after radiation for prostate cancer: beneficial effects for external beam patients. Urology (in press). * A unique paper among cancer survivors that evaluates the relationship between physical activity levels and sexual functioning among men treated for localized prostate cancer.
25. Panton L, Golden J, Broeder C, et al . The effects of resistance training on functional outcomes in patients with chronic obstructive pulmonary disease. Eur J App Physiol 2004; 91(4):443-449. * This study documents the benefits of resistance training among COPD patients, including improvements in body strength, lean body mass and walking distance.
26. Wallman K, Morton A, Goodman C, et al . Randomised controlled trial of graded exercise in chronic fatigue syndrome. Med J Aust 2004; 180(9):437-438.
* A study that documents benefits of exercise such as reductions in depression and improvements in cognitive function among CFS patients.
27. Ross C, Hayes D. Exercise and psychological well-being in the community. Am J Epidemiol 1988; 127:762-771.
28. Stephens T. Physical activity and mental health in the United States and Canada: evidence from four population surveys. Prev Med 1988; 17:35-47.
29. Babyak M, Blumenthal J, Herman S, et al . Exercise treatment for major depression: maintenance of therapeutic benefit at 10 months. Psychosom Med
2000; 62(5):633-638.
30. McAuley E, Rudolph D. Physical activity, aging, and psychological well-being. J Aging Phys Act 1995; 3:67-96.
31. McLafferty C, Wetzstein C, Hunter G. Resistance training is associated with improved mood in healthy older adults. Percept Mot Skills 2004; 93(3):947-957. * This study describes the effects of a 24-week resistance training program for older adults and documents program-associated improvements in total mood and reductions in confusion, anger and tension.
32. Janisse H, Nedd D, Escamilla S, Nies M. Physical activity, social support, and family structure as determinants of mood among European-American and African-American women. Women Health 2004; 39(1):101-116. * This is a study involving a diverse ethnic sample and documenting the benefits of a walking program on mood states among women.
33. West J, Otte C, Geher K, et al . Effects of Hatha yoga and African dance on perceived stress, affect, and salivary control. Ann Behav Med 2004;
28(1):114-118. ** This is an interesting study describing non-conventional exercise programs and their benefits in mental-health outcomes. Individuals in both programs displayed significant reductions in perceived stress and negative effect.
34. Motl R, Birbaum A, Kubik M, et al . Naturally occurring changes in physical activity are inversely related to depressive symptoms during early adolescence. Psychosom Med 2004; 66(3):336-342. * This is one of the few available studies documenting an inverse significant relationship between physical activity and depression in an adolescent sample.
35. Weuve J, Kang J, Manson J, et al . Physical activity, including walking, and cognitive function in older women. JAMA 2004; 292(12):1454-1461. ** This is a very good study, with a sample of 766 older women between the pages of 70 and 81 years. Findings suggest that women with the highest levels of physical activity had a significantly lowered risk of developing cognitive impairment.
36. Heller T, Hsieh K, Rimmer J. Attitudinal and psychosocial outcomes of a fitness and health education program on adults with Down syndrome. Am J
Ment Retard 2004; 109(2):175-185. ** This is a unique study among a population that has been largely neglected in the physical-activity literature. The study suggest that individuals with Down's syndrome can be engaged in structured exercise programs and that such programs may increase exercise self-efficacy, reduce cognitive and emotional barriers and improve life satisfaction.
37. Crews D, Lochbaum M, Landers D. Aerobic physical activity effects on psychological well-being in low-income Hispanic children. Percept Mot Skills
2004; 98(1):319-324. * This study documents the benefits of a physical-activity program, including improved cardiovascular fitness, reduced depression and improved self-esteem among 4th grade Hispanic children.
Abbreviation Notes
CAD = coronary artery disease; COPD = chronic obstructive pulmonary disease;
CRP = cardiac rehabilitation program; CVD = cardiovascular disease; GMCB =
group-mediated cognitive-behavioural; HRQOL = health-related quality of life.
Reprint Address
Correspondence to Frank J. Penedo, PhD, Department of Psychology, University of Miami, PO Box 248185, Coral Gables, FL 33124, USA Tel: +305 284 6711; fax: +305 284 9214; e-mail: _fpenedo@miami.edu_ (mailto:fpenedo@miami.edu)
Frank J Penedo, Jason R Dahn
A Department of Psychology and Sylvester Comprehensive Cancer Center,
University of Miami, Coral Gables
Miami Veteran's Affairs Medical Center, Miami, Florida, USA