Does exercise environment moderate the effects of Tai Chi on depression and anxiety? A systematic review and meta-analysis of indoor vs. outdoor practice settings.

BACKGROUND: Depression and anxiety are highly prevalent mental disorders that impose a substantial global health burden. As a traditional mind-body exercise, Tai Chi has demonstrated well-established non-pharmacological benefits for alleviating negative emotional symptoms. However, previous meta-analyses have primarily focused on intervention dosage (e.g., frequency and duration) or participant characteristics, while largely overlooking the potential influence of the physical exercise environment as a contextual ecological factor. This systematic review and meta-analysis aimed to evaluate the overall effects of Tai Chi on depression and anxiety and to determine whether indoor and outdoor practice settings moderate these mental health benefits.

METHODS: This systematic review and meta-analysis was conducted in accordance with the PRISMA guidelines. A comprehensive literature search was performed in CNKI, Web of Science, PubMed, the Cochrane Library, and Embase for studies published from database inception to June 2026. Randomized controlled trials (RCTs) investigating Tai Chi as the primary intervention and reporting outcomes related to depression and/or anxiety were included. Two reviewers independently screened studies, extracted data, and assessed the risk of bias using the RoB 2.0 tool. The certainty of evidence was evaluated using the GRADE approach. Standardized mean differences (SMDs) with 95% confidence intervals (CIs) were pooled using a random-effects model. Heterogeneity was assessed using Cochran's Q test and the I 2 statistic. Subgroup analyses and meta-regression were performed to examine the potential moderating effect of the exercise environment.

RESULTS: A total of 15 RCTs involving 847 participants were included. Tai Chi significantly reduced both depressive symptoms (SMD = -0.93, 95% CI: -1.25 to -0.61, I 2 = 75.1%) and anxiety symptoms (SMD = -0.93, 95% CI: -1.23 to -0.64, I 2 = 62.9%). Although univariate subgroup analyses descriptively showed larger effect sizes in outdoor settings than in indoor settings for both depression (SMD = -1.06 vs. -0.88) and anxiety (SMD = -1.08 vs. -0.90), outdoor subgroups comprised few studies (k = 4) with substantial heterogeneity (I 2 > 78%). Crucially, multivariable meta-regression analyses confirmed that the exercise environment was not a statistically significant independent moderator for either depression (p = 0.90) or anxiety (p = 0.21) after adjusting for age, intervention duration, and dosage parameters.

CONCLUSIONS: Tai Chi is an effective non-pharmacological intervention for alleviating depression and anxiety. However, current empirical evidence does not support an independent moderating effect of the exercise environment. The observed numerical differences between indoor and outdoor settings should be interpreted cautiously as preliminary and hypothesis-generating rather than confirmatory. Well-designed RCTs directly comparing standardized indoor vs. outdoor practice environments are warranted.