(Medscape) – Resistance exercise training (RET) significantly reduces depressive symptoms, new research shows.
Investigators analyzed trials that encompassed almost 2000 participants who engaged in RET and found that the intervention was associated with a significant reduction in depressive symptoms, regardless of how long the intervention or sessions lasted, how frequent they were, or how much exercise was prescribed.
These benefits accrued to both men and women and were present in participants with physical or mental illnesses and participants who did not experience an increase in strength.
“The available empirical evidence supports [the finding] that RET may be an effective alternative or adjuvant therapy for depressive symptoms,” lead author Brett Gordon, MSc, postgraduate researcher, Physical Education and Sports Sciences Department, University of Limerick, Ireland, told Medscape Medical News.
“The best advice is to exercise and/or to engage in recommended levels of physical activity, regardless of type,” he said.
The analysis was published online May 9 in JAMA Psychiatry.
Currently, frontline treatments for depression include medication and psychotherapy, but both can be expensive or of limited value, and the duration of efficacy can be short-lived, the authors write.
“Thus, there is a continued interest in alternative treatments for depression and continued need to compare potential alternative treatments with established treatments,” they write.
The authors call exercise interventions “promising treatments for depressive symptoms,” because they are “free from the adverse effects and high costs associated with antidepressant medications and psychotherapy.”
It has been established that exercise interventions are beneficial regarding a variety of depression-related outcomes. Beneficial effects include improvement in cardiovascular disease — the leading cause of death among people with major depressive disorder — and improvement in depressive symptoms among healthy as well as chronically ill adults.
RET interventions are “generally designed to increase strength, skeletal muscle mass, endurance, and/or power,” the authors write. Although the benefits of aerobic exercise training (AET) are well established, less is known regarding the associations of RET and depressive symptoms or how the two interventions compare with each other.
“Evidence of the improvement in depressive symptoms through exercise training to date has been based predominantly on findings from trials of aerobic exercise training — jogging, running, cycling,” Gordon explained.
“The effects of RET, or weightlifting and strength training, on depressive symptoms have remained relatively understudied and have not been summarized in a large-scale review,” he said.
To study currently available research findings regarding RET, the researchers conducted a systematic review and meta-analysis of 33 clinical trials that included a total of 1877 participants (947 particiapants in the RET groups, and 930 in control groups; mean age, 52 years [SD, 18 years]; 67% women).
To be included in the analysis, studies had to involve participants who were randomly assigned either to a group that received an RET intervention or to a nonactive control group. The studies also were required to include validated self-reports or clinician-rated measures of depressive symptoms, with participants assessed at baseline, at midintervention, and/or post intervention.
Depressive symptoms were the primary outcome in 18 RCTs (k = 37). The mean duration of prescribed RET programs was 16 weeks (range, 6 – 52 weeks).
The frequency of RET sessions ranged from 2 to 7 days per week. For most studies, RET sessions were conducted 3 days per week (20 RCTs; k = 30).
Of the 33 RCTs (k = 39), 25 evaluated participants with a physical or mental illness.
Adherence rates and attendance rates of participants were high. The mean adherence rate was 78% (SD, 18%) in studies that reported adherence. For studies that reported attendance, and mean attendance rates ranged from 87.5% to 94%.
The most frequently used measure of depressive symptoms was the Beck Depression Inventory (k = 21).
Of the 54 effects, 48 (89%) were scored >0, “indicating a reduction in depressive symptoms favoring RET”; 28 effects significantly favored RET.
RET was found to be associated with a significant reduction in depressive symptoms, with a “moderate-sized” mean effect ∆ of 0.66 (95% confidence interval [CI], 0.48 – 0.83; z = 7.35; P < .001).
However, the researchers also found significant heterogeneity (total Q = 216.92, df = 53; P < .001; I 2 = 76.0% [95% CI, 72.7% – 79.0%]), with sampling error accounting for 32.9% of observed variance.
Among the participants, the mean reduction in depressive symptoms resulted in a number needed to treat (NNT) of 4.
Although three effects larger than most were derived from a single study, the magnitude of these effects “appeared to be due partly to greater depressive symptoms in participants who were randomized to the intervention group, compared with controls,” the investigators write.
For this reason, the researchers recalculated the findings after removing this study from the analysis, and the effect remained “moderate and significant” (∆ = 0.53; 95% CI, 0.38-0.68; z = 7.00; P < .001).
The effects were significantly smaller when outcome allocation and/or assessment was blinded than when outcome allocation and/or assessment was not blinded (∆ = 0.56; 95% CI, 0.40 – 0.71 and ∆ = 1.07; 95% CI, 0.36 – 1.78, respectively).
Total volume of prescribed exercise, significant improvements in strength, and participants’ health status (β = -0.28; P = .09), β = 0.32; P = .09, and β = -0.23; P= .17, respectively) were not significantly related to effect size.
When the researchers compared the effects of RET with AET, they found a “small, non-significant mean effect favoring RET.
“The moderate-sized effect of RET on depressive symptoms found in our current quantitative review is consistent with previously reported effects of other forms of physical exercise on depressive symptoms,” said Gordon
He noted that “several potential social, cognitive, and neurobiological factors have been suggested to influence or help to explain how and why RET may reduce depressive symptoms” but that “this was not the focus of our current work.”
Nevertheless, “the larger percentage reduction found from RCTs of participants with elevated depressive symptoms, coupled with the significant difference based on initial severity of depressive symptoms, suggest that RET may be particularly helpful for reducing depressive symptoms in people with greater depressive symptoms,” the authors write.
Commenting on the study for Medscape Medical News, Gary Cooney, MBChB, MRCPsych, registrar in psychiatry, Gartnavel Royal Hospital, Glasgow, United Kingdom, who was not involved with the study, said the study “gives stronger evidence that perhaps has been previously demonstrated that resistance training can be helpful for depressive symptoms” — a finding he called “quite important.”
“There are certainly studies that find a positive effect on depression burden in other types of exercise, such as aerobic exercise, but I’m not sure I know a meta-analysis which shows such positive associations,” he said.
He said that he did not want to speculate as to what might be unique or special about RET, but acknowledged that this is “a question worth thinking about.”
He encouraged “routinely recommending exercise” to patients with depressive disorders because “there appears to be a growing body of evidence supporting exercise in the treatment of a range of mental health conditions.”
Gordon added, “It is clear that more research is needed regarding the specific mechanisms underlying exercise effects on depressive symptoms, particularly those that may be unique to RET.”
No source of funding for the study has been disclosed. The authors and Dr Cooney have disclosed no relevant financial relationships.
JAMA Psychiatry. Published online May 9, 2018. Abstract