Adding weights to a regular exercise routine has been shown to add muscle tone, decrease injury risk, and improve bone health. But its effects might also extend beyond the physical, as new evidence suggests that regular strength training may both ward off and fight symptoms of .

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That evidence comes from a meta-analysis, published earlier this month in JAMA , that examined the results of 33 randomized, controlled studies on depression and strength training — referred to as resistance exercise training in the paper. The studies included both males and females of varying ages, more than 2,000 participants in total.

When the results of the studies were aggregated, the researchers found that resistance training significantly reduced the incidence of depression. Regardless of whether participants had met a clinical cutoff for depression at the beginning of a study, the analysis showed, they were less likely to be depressed at the study’s conclusion if they had been assigned to a weight training group. The results were significant even when the researchers controlled for age, , or improvements in muscle mass — so even participants who saw few physical changes from strength training still tended to see improvements in mood.

The study didn’t attempt to examine exactly how resistance training helps depression, says lead author Brett Gordon, a doctoral student at the University of Limerick, but he pointed to several psychological and physiological factors that could be responsible for the link.

“Psychological mechanisms (could) include the expectancy of improved mental health following exercise, as well as social interaction and social support during exercise,” he says. He emphasized that more research was needed to confirm the exact mechanism.

Some past studies have suggested that forms of aerobic exercise like running, swimming, or biking may be as effective as conventional therapies in alleviating depression. The current study didn’t measure the efficacy of resistance training against that of , but Gordon says head-to-head studies comparing it to and other empirically validated treatments, like , are critical for a more complete understanding of its impact on depression.

A 2017 analysis, conducted by the same group of researchers, found that weight training was also an effective treatment for , and the current review adds to a growing body of evidence that exercise — in a variety of forms — is beneficial to mental health, experts say.

“This is a well-designed and conducted meta-analysis showing consistent evidence on the effects of resistance training on depressive symptoms,” says Felipe Barreto Schuch, who studies exercise and mental health at the Centro Universitário La Salle in Canoas, Brazil. Schuch, who was not involved in the study, points to a similar meta-analysis he led earlier this year, which concluded that various forms of physical activity were linked to decreased depression risk. “Therefore, both aerobic and anaerobic forms should be encouraged,” he says.

Gordon and his co-authors note that many of the studies included in their meta-analysis failed to report in-depth details of the intensity, duration, and type of strength training used by participants. Future trials would ideally quantify these factors in order to get a better sense of what “dose” of exercise is most effective for treating depression, Gordon says.

The World Health Organization (WHO) currently recommends that adults between the ages of 18 and 64 engage in 150 minutes of moderate-intensity or 75 minutes of high-intensity aerobic exercise each week. “At the moment, the best advice is to engage in any and all exercise types, and strive to achieve at least WHO physical activity guidelines,” Gordon says. For strength training, he suggests incorporating the American College of Sports Medicine’s guidelines, which for healthy adults includes working major muscle groups on two to three non-consecutive days each week.