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RESEARCH ARTICLE |
a Sticht Center on Aging, Department of Internal Medicine
b Department of Public Health Sciences, Wake Forest University School of Medicine, Winston-Salem, North Carolina
c Department of Health and Exercise Sciences, Wake Forest University, Winston-Salem, North Carolina
Brenda W. J. H. Penninx, Sticht Center on Aging, Wake Forest University School of Medicine, Medical Center Boulevard, Winston-Salem, NC 27157 E-mail: bpenninx{at}wfubmc.edu.
Decision Editor: Margie E. Lachman, PhD
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Abstract |
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THE many physical and physiological benefits of exercise for older persons have been well reported (King, Rejeski, and Buchner 1998
). However, benefits are not restricted to physical health alone but extend to the psychological domain of health as well. Longitudinal epidemiological studies have shown that a high level of physical activity reduces the risk of developing high depressive symptomatology over time (Farmer et al. 1988) and that this effect is not limited to individuals who have been active throughout their adult life. In short, physical activity seems to be an effective form of prevention for depressive symptomatology among older adults even when adopted later in life (Camacho, Roberts, Lazarus, Kaplan, and Cohen 1991). Physiological, biological, and psychological mechanisms have been suggested to explain the antidepressive effects of exercise (North, McCullagh, and Tran 1990).
Evidence for a beneficial effect of exercise on psychological health has been confirmed in several experimental studies, most of which have been conducted among clinically depressed persons. For example, Greist and colleagues 1979, McCann and Holmes 1984, and Martinsen, Medhus, and Sandvik 1985 have shown that clinically depressed persons randomized to an exercise program were more likely to improve their depression status than those not receiving an exercise program. Other experimental studies have shown that an exercise program appears to be at least as effective in reducing clinical depression as more conventional treatment regimens like antidepressant medication (Babyak et al. 2000; Blumenthal et al. 1999; McNeil, LeBlanc, and Joyner 1991) or psychotherapy (Freemont and Craighead 1987; Klein, Greist, and Gurman 1985). Also in older clinically depressed persons, evidence for an antidepressive effect of exercise is provided by controlled trials involving a resistance exercise program (Singh, Clements, and Fiatarone 1997) or an aerobic exercise program (Babyak et al. 2000; Blumenthal et al. 1999).
Whether exercise improves depressive symptomatology in a general older population has been less consistently demonstrated in trials; some have been positive (Blumenthal et al. 1991; Blumenthal, Williams, Needels, and Wallace 1982; Coyle and Santiago 1995; King, Taylor, and Haskell 1993; McMurdo and Rennie 1993; Williams and Lord 1997), whereas others have yielded null effects (Dustman et al. 1984; Emery and Gatz 1990; Jette et al. 1996; King, Taylor, Haskell, and DeBusk 1989; McMurdo and Burnett 1992; Pierce, Madden, Siegel, and Blumenthal 1993). Consequently, it has been suggested that the antidepressive effect of exercise is most likely due to normalizing depressed mood states in older participants who have high initial depression levels rather than to inducing improvements in all older participants (Craft and Landers 1998; King et al. 1993; Williams and Lord 1997). Because no earlier studies have directly compared the effect of exercise on mood among a sufficient number of older persons with initial high or low depression scores, it is rather unclear whether the antidepressive effect of exercise is general or specific to depressed persons.
Physical inactivity is very common among depressed persons (Penninx, Guralnik, Leveille, Ferrucci, and van Eijk 1999; Stephens 1988), partly because their attitudes toward exercise and exercise self-efficacy may be more negative. There is some evidence that compliance rates with a variety of treatment regimens are lower and dropout rates are higher among depressed older persons than among nondepressed peers (Blumenthal, Williams, Wallace, Williams, and Needels 1982; Shaw, Cronan, and Christie 1994). If this is true for exercise interventions as well, it would suggest that exercise programs may be less effective for improving physical function among persons with high depressive symptomatology than among persons with low depressive symptomatology.
Using data from the Fitness, Arthritis and Seniors Trial (FAST), a randomized exercise trial with a long duration (18 months) among older persons with knee osteoarthritis, the present study examined and compared whether exercise has equal benefit on outcomes representing emotional and physical health among older persons with initially high or low depressive symptomatology.
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Methods |
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). Participants were community-based adults with knee osteoarthritis who were recruited through local advertisements and mass mailings. Eligibility criteria were (a) 60 years of age or older; (b) pain in the knee(s) on most days of the month; (c) difficulty with at least one of the following due to knee pain: walking a quarter mile; climbing stairs; getting in and out of a car, bath, or bed; rising from a chair; or performing shopping, cleaning, or self-care activities; and (d) radiographic evidence of knee osteoarthritis. Exclusion criteria were (a) presence of a medical condition that precluded safe exercise participation (e.g., recent myocardial infarction or stroke, severe chronic obstructive pulmonary disease, congestive heart failure); (b) inflammatory arthritis; (c) regular exercise participation (more than one time per week for at least 20 min); or (d) inability to walk on a treadmill or to walk, unassisted, 128 m in 6 min. A total of 439 participants were enrolled and assigned to one of the three intervention arms (144 in the control condition, 146 in the resistance exercise program, and 149 in the aerobic exercise program). Baseline depression data were missing for 1 person, leaving 438 persons for the present study.
Interventions
Control condition (health education).
During the first 3 months, participants received monthly education sessions by a nurse on issues related to arthritis management. Later, participants were called bimonthly (Months 4 to 6) or monthly (Months 7 to 18) to maintain health updates and provide support.
Aerobic exercise program.
This program consisted of a 3-month facility-based walking program and a 15-month home-based walking program. The facility-based program took place at an indoor track under supervision of an exercise leader and was scheduled three times per week for 1 hr. Each session consisted of a 10-min warm-up and cool-down phase including flexibility stretches, and a 40-min period of walking at an intensity equivalent to 50%–70% of the heart rate reserve as determined from a screening exercise treadmill test. In Months 4 to 6, the exercise leader visited participants four times and called them six times to offer assistance and support in the development of a walking exercise program in their home environment. Most participants chose to walk on sidewalks along streets or in nearby parks, but some walked in a nearby facility such as a gymnasium or shopping mall. For the remainder of the exercise program, phone contacts were made every 3 weeks (Months 7 to 9) or monthly (Months 10 to 18). Attendance at the facility-based exercise sessions was registered by exercise leaders. In the home-based phase, participants maintained exercise logs in which they mentioned how many exercise sessions were conducted. To assess compliance, the percentage attendance was calculated by dividing the number of sessions completed by the number of sessions prescribed.
Resistance exercise program.
This program also consisted of a 3-month supervised facility-based program with three 1-hr sessions per week and a 15-month home-based program. Each session consisted of a 10-min warm-up and cool-down phase and a 40-min phase consisting of repetitions of various upper and lower body exercises using dumbbells and cuff weights. Weight was increased in a stepwise fashion as long as the participant could complete two sets of 10 repetitions. During the home-based phase, participants continued their exercises at home with dumbbells and cuff weights that were provided as part of the intervention. Weights were exchanged at the participant's request or after a determination was made to increase the weight during the face-to-face or telephone contacts with the exercise leader. These latter contacts occurred with the same frequency as in the aerobic exercise program. Like in the aerobic program, compliance was assessed as the percentage of attendance at exercise sessions.
Earlier papers on the FAST study have reported that the exercise interventions resulted in a lower score on a global disability questionnaire, improved physical performance and strength, improved aerobic capacity (for aerobic exercise only), decreased pain, and improved balance (Ettinger et al. 1997; Messier et al. 2000). A higher compliance with the exercise intervention resulted in more favorable outcomes for disability, physical performance, and pain (Ettinger et al. 1997). Depression data were not considered in these earlier articles.
Data Collection
Depression.
The presence of depressive symptoms was assessed using a short version of the Center for Epidemiologic Studies Depression (CES-D) scale (Radloff 1977) at baseline (before randomization) and in the assessments 3, 9, and 18 months postrandomization. The brief version of the CES-D asks about depressive feelings and behaviors experienced during the past week, with the original 0 (rarely or none) to 3 (most or all days) response format (Cronbach's 
= .74). The six items were chosen because of their ability to predict a clinical diagnosis of major depression in a community-based sample (Burnam, Wells, Leaske, and Landsverk 1988). In addition, the short-item version showed psychometric properties that compare favorably with the original 20-item format (Burnam et al. 1988). Data from two observational studies among older persons, the Longitudinal Aging Study Amsterdam (n = 3,107) and the Established Populations for Epidemiologic Studies of the Elderly (n = 2,812) yielded high correlations (.91 and .90, respectively) between the short CES-D version and the full CES-D. For assessing the effect of exercise intervention on depressive symptoms, we used the continuous CES-D score as the outcome. For comparing characteristics and intervention effects among persons with high and low depressive symptomatology, we dichotomized participants by using a baseline CES-D cutoff of 5, which is transformed from the commonly used cutoff of 16. Using data from the Longitudinal Aging Study Amsterdam, we found that the short CES-D version cutoff score of 5 had good criterion validity for major depression (sensitivity 86%, specificity 90%), similar to that of the full CES-D version cutoff (Beekman et al. 1997).
Physical function.
Three indicators of physical function were used: self-reported disability, 6-min walking speed, and knee pain. For these indicators, assessments were conducted before randomization and 3, 9, and 18 months postrandomization. These physical indicators are considered to be the main outcomes for the FAST study and have been used in earlier analyses (Ettinger et al. 1997).
A 23-item disability questionnaire assessed experienced difficulties with activities in five domains: mobility, transfer activities, upper extremity tasks, instrumental activities of daily living, and basic activities of daily living (Rejeski, Ettinger, Shumaker, James, et al. 1995). For each activity, participants were asked how much difficulty they had had over the past month doing this activity, with responses ranging from 1 (no difficulty) to 5 (unable to do). A composite disability score was created by averaging the scores on all 23 items. The internal reliability of the composite disability score was good (Cronbach's = .79). Walking speed was assessed during a 6-min test in which participants were asked to walk as far as they possibly could. The distance walked during a 6-min usual pace walk test was used to calculate the mean walking speed during these 6 min. The intensity of knee pain was measured by asking participants to rate the intensity of knee pain during the past week for six different activities of daily living on a Likert scale ranging from 1 (no pain) to 6 (excruciating pain). A summary pain intensity score was calculated by averaging the six scores for both ambulation and transfer activities (Rejeski, Ettinger, Shumaker, Heuser, et al. 1995).
Demographic and clinical variables.
Baseline demographics were age, gender, race, and education. Chronic comorbid conditions were considered to be present if participants had ever been told by a health professional that they had the following conditions: coronary heart disease (myocardial infarction, angioplasty, coronary artery bypass surgery, or angina), diabetes, or osteoarthritis in joints other than the knee (hands, spine, hips, or feet). Hypertension was defined as self-reported hypertension and concomitant use of antihypertensive medications or a blood pressure of 160/90mm Hg or more. Body mass index was calculated as measured weight in kilograms divided by the square of measured height in meters.
Statistical Analyses
Baseline characteristics and compliance to exercise were described and compared among participants with high and low depressive symptomatology. Differences in depression scores at 3, 9, and 18 months postrandomization across intervention groups were determined by repeated measures analysis of covariance, or ANCOVA (SAS PROC MIXED; Laird and Ware 1982) The advantage of this analysis is that it uses all available observations and adjusts results based on correlations between outcomes and predictor variables. If the probability of a follow-up observation being missing is dependent on either covariates included in the model or previously observed outcomes, then maximum-likelihood repeated measures ANCOVA can still provide unbiased parameter estimates. Analyses were adjusted for site, race, age, sex, education, and baseline depression score. This was done to correct for chance imbalances in prognostic factors between the groups and to reduce the variance estimate for between-group differences. Primary analyses were conducted by intention to treat using data of all randomized participants. Secondary analyses were conducted to examine the effect of compliance with exercise on depression score over time. Finally, separately for participants with initially high or low CES-D scores, repeated measures ANCOVAs were conducted to test the effects of exercise on disability score, walking speed, and pain score at 3, 9, and 18 months postrandomization. Because tests of Time of Follow-Up x Intervention Effect showed that the effect of the intervention was consistent over time for depression and all physical function outcomes, tests for between-group differences were averaged over the 3-, 9-, and 18-month follow-up. Adjusted least squares means obtained in the presence of such interactions are used in all figures to display trends across time.
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Results |
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2 (2, N = 438) = .37, p = .83, or with baseline depressive symptomatology, 2 (1, N = 438) = .22, p = .63. Using the total study sample, Fig. 1 reports the results of repeated measures ANCOVAs, with depression as the outcome variable, time as the repeated measure, treatment group as the between-subjects factor, and adjustment for site, race, age, sex, education, and baseline depression score. This analysis examines whether follow-up depression scores differed significantly across the three assignment groups. Participants randomized to the aerobic exercise intervention group reported significantly lower depression scores over time (p < .001) than those in the control group. On average, the control group increased their depression score by 2% (from 2.74 to 2.80), whereas the aerobic exercise group reduced their score by 23% (from 2.74 to 2.12). Those in the resistance exercise group experienced a reduction of 6% (from 2.74 to 2.59), but their depression scores over time were not significantly different from those in the control group (p = .27).
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To examine whether a high compliance with the exercise program was associated with lower depressive feelings over time, we determined the average adjusted depression score by tertiles of exercise compliance using repeated measures ANCOVA adjusted for baseline depression score, disability, age, sex, race, education, and site. These analyses showed that, for both exercise programs, the highest compliance tertile had a lower average depression score than the lowest compliance tertile (Table 3 ). Persons who completed 79% or more of the resistance exercise sessions prescribed had a significantly lower adjusted depression score (M = 2.01, p = .004) than the controls (M = 2.80). For aerobic exercise, both the middle and the highest compliance tertiles had significantly lower depression scores during follow-up than the control group (ps = .009 and .01, respectively).
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Finally, the question arises as to whether the antidepressant effect found for aerobic exercise in our study can be partly explained by the fact that aerobic exercisers, when compared with controls, had lower disability, less pain, and an improved walking speed over time. To address this issue, we conducted additional, exploratory repeated measures ANCOVAs with time-dependent covariates for disability, pain, and walking speed. Analyses without time-dependent covariates revealed that the model-based estimate of the average follow-up depression score was 2.80 in the control group and 2.12 in the aerobic exercise group, t (864) = -3.40, p < .001. The time-dependent covariates for pain (p = .002) and disability (p = .003), but not the time-dependent covariate of walking speed (p = .91), were significant predictors of follow-up depression scores. When all time-dependent covariates were included in the analyses, the model-based estimate of the average follow-up depression score was 2.65 in the control group and 2.13 in the aerobic exercise group, t (861) = -2.48, p = .01. These analyses show that the difference in follow-up depression scores between the control group and the aerobic exercise group are somewhat smaller after considering change in pain and disability over time, but the difference between the groups remains statistically significant.
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Discussion |
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Overall, depression scores of persons with low initial depressive symptomatology appeared to increase over time. Part of this effect may be due to regression to the mean, because, in general, persons with low depression scores are likely to obtain higher scores over time. However, increasing depression over time may also be partly explained by an increasing progression of knee osteoarthritis in our sample. For example, this is illustrated by the fact that, although exercise participants were better off, physical disability scores over time tended to go up as well. Of particular interest is the finding that the depression scores in the aerobic exercise group did not show an increase over time (average 18-month change = 0%). Depression patterns among the persons with high initial depressive symptomatology were very different. Overall, persons in all three groups showed declining depression scores over time, with the most pronounced decline in the first 3 months. Again, this may be partly due to regression to the mean. A declining trend in depressive symptoms is in line with observational findings that about half of the older persons with high CES-D scores significantly improve depressive symptomatology over a short follow-up period (Beekman, Deeg, Smit, and van Tilburg 1995; Kennedy, Kelman, and Thomas 1991). After 3 months, depression scores went slightly up again but remained lower than the baseline depression scores. Depression patterns over time were similar in all three assignment groups, but participants in the aerobic exercise group had a significantly greater reduction in their depression scores (-40%) than participants in the control (-20%) and resistance exercise (-30%) groups.
It has been suggested that the antidepressive effect of exercise is due to normalizing depressed mood in persons who have high initial depression levels rather than inducing improvements in all persons (Craft and Landers 1998; King et al. 1993; Williams and Lord 1997). However, we found that in both persons with high and persons with low depressive symptomatology, the aerobic exercise group had significantly lower depression scores during follow-up than the control group. Thus, in line with the suggestion of North and colleagues 1990, the antidepressive effect of the aerobic exercise intervention is not limited to participants who have depressive symptomatology at baseline.
For persons not clinically depressed, exercise trials have not always confirmed an antidepressant effect (Dustman et al. 1984; Emery and Gatz 1990; Jette et al. 1996; King et al. 1989; McMurdo and Burnett 1992; Pierce et al. 1993). However, some of these latter studies may have found null effects for nondepressed participants because their participants were relatively young and healthy and, consequently, not yet faced with the reality of declining function. Thus, our result of an antidepressive effect of aerobic exercise among nondepressed older persons with knee osteoarthritis may be unique to older adults who are prone to depressive symptoms that frequently accompany chronic diseases such as arthritis. Our results suggest that it is likely that exercise reduces depression in participants who are depressed and that exercise buffers nondepressed participants for events in life that may trigger depressive symptomatology.
Our findings add to the already existing debate in the literature about whether an aerobic exercise intervention is more effective than a resistance exercise intervention in improving mood. Only a few exercise studies have directly compared the psychological effects of aerobic and resistance exercise. Mutrie 1988 studied 24 participants with elevated depression scores and found that after 4 weeks the aerobic exercise group had a superior antidepressive effect compared with the resistance exercise group. Three other studies, however, were not able to find a difference between an aerobic and a nonaerobic exercise program (Doyne et al. 1987; Martinsen, Hoffart, and Solberg 1989; Sexton, Maero, and Dahl 1989). However, these previous studies are not comparable to our study as they all included young and healthy participants, the interventions were short and, therefore, probably had a high compliance, and the follow-up period was much shorter than the 18 months in our study. In our study, the absence of a favorable psychological effect in the resistance exercise group was consistent for both initially nondepressed and initially depressed persons. It is important to point out that we did find a favorable effect on mood among the persons most compliant with the resistance exercise program (upper tertile). This may suggest that, when performed regularly, resistance exercise may also have antidepressant effects among older persons. Future trials among the general older population should further explore whether aerobic exercise is really more effective for mood improvement than other modes of exercise.
Our time-dependent covariate analyses showed that the greater reduction in disability and pain over time among the aerobic exercisers may partly explain the antidepressant effect of aerobic exercise. However, after adjustment for changes in disability and pain over time, the aerobic group continued to have significantly lower depression scores than the control group. There have been several mechanisms offered as possible explanations for the effect that physical activity has on depression (North et al. 1990). These include but are not limited to increased aerobic capacity (Blumenthal et al. 1999), increases in circulating concentrations of brain amines and beta-endorphine (Ransford 1982), reduced activity of the hypothalamo-pituitary-adrenocortical axis (Pompe, Bernards, Meijman, and Heijnen 1999), increased feelings of mastery or self-efficacy (McAuley, Blissmer, Katula, Duncan, and Mihalko 2000), distraction, and a reduction in negative thought patterns (Hughes 1984). Because exercise was performed in a group setting, it is also possible that depression was affected in a positive manner by the social interaction between study participants. Because FAST was designed as an outcome trial and in-depth exploration of mediating mechanisms is not feasible, future studies should be designed to address this important topic.
We compared the physical benefits of exercise across initially depressed and initially nondepressed participants. Among both subgroups, aerobic and resistance exercise decreased disability scores, decreased pain scores, and improved walking speed (for aerobic exercise only). Even among the rather small subgroup of 98 depressed persons, various physical improvements associated with exercise were found to be statistically significant. This shows that depression does not moderate the efficacy on physical function. This equal efficacy may be explained by the fact that the 98 depressed persons in our study did not exhibit a lower compliance with or dropout rate from the exercise program.
Our study sample consisted of a selective group of older persons with knee osteoarthritis, and consequently, results may not be completely generalizable to the older population at large. In addition, our study did not include a psychiatric assessment of clinical depression, which makes it impossible to generalize our findings to clinically depressed older persons. Nevertheless, our findings illustrate that an exercise program, especially an aerobic one, may have significant beneficial emotional and physical effects among the general older population at large. Blumenthal and colleagues 1991 found that in older clinically depressed persons aerobic exercise is as effective in reducing depressive symptomatology as antidepressant medication. It is likely that other treatment options for depression, for example, medication or psychotherapy, do not have equal beneficial effects on physical function. Consequently, exercise may be a more complete treatment option for depression, as this not only improves emotional function but also has a positive influence on physical function. There exist strong reciprocal associations between depression and health decline in older persons (Penninx et al. 1998, Penninx et al. 1999). An exercise intervention could play an important role in preventing the process whereby physical and emotional dysfunction interact to cause a progressive downward spiral in the health of older persons.
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Acknowledgments |
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Received for publication October 10, 2000. Accepted for publication July 18, 2001.
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p < .10.