Resistance Exercise Reduces Depressive Symptoms in Adults

by Christopher Moulton, PhD

Depression is one of the most common mood disorders in the US and worldwide. In 2016 an estimated 16.2 million adults, or 6.7% of US adults, suffered at least one major depressive episode,¹ while globally more than 300 million are afflicted.² Further, depression is comorbid with numerous chronic disease states including cardiovascular disease,³ type 2 diabetes,⁴ inflammatory bowel disease,⁵ and cognitive decline.⁶

Current frontline therapies such as psychotherapy and antidepressant medications present challenges related to treatment cost, compliance, and adverse effects;⁷ therefore, it is of interest to identify additional effective interventions that may be used as alternative or complementary treatments.

One such promising alternative is physical exercise, which may potentially increase the production or availability of neurotransmitters such as dopamine and serotonin, which are known to be diminished in depression.⁸ A meta-analysis of 8 clinical studies concluded that regular, deliberate physical activity should be included as a routine component in the management of depression in older adults based on a large effect size.⁹ However, this finding did not distinguish between aerobic exercise (intended to improve cardiorespiratory fitness) and resistance exercise (intended to improve muscular strength and function).

Numerous trials have been conducted to evaluate the independent benefit of resistance training on depression. These studies have varied widely with respect to design, enrollment criteria, intervention type, and other potentially important factors that could mediate a benefit. To date, there has not been a systematic evaluation of these trials in aggregate to estimate the effect of resistance training in adults with depressive symptoms.

Therefore, Gordon et al. conducted a meta-analysis of 33 clinical trials involving 1,877 participants.¹⁰ The investigators included studies that reported validated measures of depressive symptoms (e.g., Beck’s Depression Inventory) at baseline and post-intervention, and 4 factors were selected (total exercise volume, baseline mental health status, blinded allocation/assessment, and strength increase) as potential moderators of the effect of resistance exercise on depression. The typical resistance exercise program was 16 weeks in duration, and training sessions occurred on average 3x/week. The majority of the interventions were categorized as low- or moderate intensity, and the overall program adherence rate was 78%.

48 of the 54 identified effects were > 0, with a mean effect size (Δ = 0.66) indicating a moderate reduction in depressive symptoms that favored resistance exercise, and the analysis revealed a number needed to treat (NNT) of 4.¹⁰ Total exercise volume, mental health status, and strength increase were not related to the effect size, which measures the magnitude of a phenomenon. Effects were significantly smaller in studies where allocation and/or assessment was blinded (Δ = 0.56) than in studies where allocation and/or assessment was not blinded (Δ = 1.07).¹⁰ Blinded allocation may reflect a higher-quality, more controlled research design,¹¹ thereby potentially hewing closer to the “true effect” of the resistance exercise intervention.

Other analyses revealed that the effect size was greater among adults with symptoms at baseline that were indicative of mild-to-moderate depression (Δ = 0.90), which suggests that resistance exercise may be particularly effective in individuals with a greater degree of depressive symptoms.¹⁰

Clinicians wishing to implement effective complementary therapies for depression may consider prescribing resistance exercise, with appropriate attention given to program monitoring for compliance enhancement and behavioral skill training to facilitate long-term implementation into a patient’s lifestyle.¹²

Why is this Clinically Relevant?

• Depression and depressive symptoms are pervasive mental health burdens that are associated with numerous forms of chronic disease
• Practitioners need effective complementary strategies to address the challenges of depression in addition to standard clinical practices
• Prescription of controlled and well-monitored resistance training programs such as weight lifting, circuit training, and body weight exercise may be an effective alternative or adjuvant therapy for reducing the severity of depression and depressive symptoms

View the abstract

Citations

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