People who do resistance exercises like weight lifting may experience less anxiety than people who don't workout, a research review suggests.

Researchers analysed data from 16 previously published studies with a total of 922 participants who were randomly assigned to do resistance training or be inactive.

Resistance workouts were associated with a reduction in anxiety symptoms regardless of whether or not participants had a mental health disorder, though the effect was more pronounced in healthy people who didn't report any physical or psychological problems.

"The positive effects of exercise training on mental health are well established; however, the majority of this knowledge is based on studies involving aerobic based training," said lead study author Brett Gordon, a physical education and sports researcher at the University of Limerick in Ireland.

"RET (resistance exercise training) significantly reduced anxiety in both healthy participants and those with a physical or mental illness, and the effect size of these reductions is comparable to that of frontline treatments such as medication and psychotherapy," Gordon said by email. "RET is a low-cost behavior with minimal risk, and can be an effective tool to reduce anxiety for healthy and ill alike."

Because the analysis only focused on resistance training, the results can't show whether this type of activity might be better or worse than aerobic or other types of exercise for easing anxiety symptoms.

While the effects of resistance exercise on the brain are not as well understood as the impact of aerobic workouts, emerging research has also linked resistance training to less shrinkage of white matter in the brain, said Dianna Purvis Jaffin of the Brain Performance Institute at the University of Texas at Dallas.

White matter is composed of nerve fibers that connect neurons in different parts of the brain. Changes in white matter can occur with age, and are thought to be involved in cognitive and behavioral problems.

It's possible that exercise might help ease anxiety simply by distracting people from how they're feeling and giving them something else to focus on, Jaffin, who wasn't involved in the current study, said by email.

"Exercise generally requires some level of concentration on the activity and may serve as a distraction, and at least acutely (meaning - during that bout of exercise and a bit after) interrupt rumination and obsessive worrying," Jaffin said.

"Finally, since people with anxiety tend to have uncertainty about their future, they may obsessively worry and lack confidence," Jaffin added. "Exercise can improve self-efficacy, the belief that one can succeed in particular situations, which may make someone feel more empowered."

While the amount of exercise may influence the impact of workouts on mental health, there isn't enough evidence available yet to prescribe a specific amount of activity, said Steven Petruzzello, a body mechanics researcher at the University of Illinois Urbana-Champaign who wasn't involved in the study.

Absent this sort of prescription, choosing an enjoyable workout makes sense, Petruzzello said by email.

In the current analysis, people did resistance exercises on two to five days per week for an average of 11 weeks.

"The best advice at the present time is to 'just do it' - it being whatever the person finds enjoyable or at least tolerable," Petruzzello said. "For some that might mean going for a walk, for others it might entail more vigorous forms of activity."